Articles

Whales have been viewed as a source of CO2 because they respire tons of CO2 annually. However, their feces could possibly offset this impact, as they may be a great contributor to carbon export (removal from the atmosphere) to the depths of the ocean. Iron-rich whale feces stimulate the growth of phytoplankton, which leads to more CO2 drawn into the ocean through photosynthesis.

Lavery et al. conducted this study to find out whether the 12,000 sperm whales in the Southern Ocean are acting as a carbon sink. The authors wondered whether the whales help the ocean absorb more carbon from the atmosphere than the whales themselves release through respiration. They note that these animals consume prey outside of but defecate within the photic zone (the layer nearest to the ocean surface), raising nutrient availability in the layer of ocean where photosynthesis is possible. Whale feces are also in liquid form, which disperses and persists within this area.

Using existing data on whale populations, consumption patterns, and average rates of iron retention compared to what is expelled, the authors estimate that the South Ocean sperm whales contribute 36 tons of iron per year to the photic zone. After accounting for respiration rates, the authors conclude that whales do act as a net carbon sink by removing 2.4 X 105 metric tons of carbon from the atmosphere annually. Even under conservative scenarios (consumption of prey with lower iron concentrations), whales still help sequester more carbon than they respire.

These animals’ contribution to nutrient and carbon cycling in the ocean has previously been overlooked. Their feces not only enhance carbon sink in the ocean but also contribute to increasing numbers of prey. However, the reduction of sperm whales by commercial whaling has reduced krill populations and decreased allochthonous (originating externally) iron inputs to the Southern Ocean by 450 tons annually.

The reduction in sperm whale numbers owing to whaling has resulted in an extra 2 X 106 tonnes of carbon remaining in the atmosphere annually [Lavery 2010: 3].

In addition to sperm whales, there could be more organisms acting as carbon sinks in the ocean:

We have restricted our analysis to sperm whales; however, any organism that consumes prey outside the photic zone and defecates nutrient-rich waste that persists in the photic zone would stimulate new production and carbon export. Pygmy and dwarf sperm whales (Kogia spp.) and beaked whales (Family Ziphiidae) fulfill these criteria. The proportion of time baleen whales consume prey at depth is currently unknown, but fin whales (Balaenoptera physalus) dive to at least 470 m while feeding. Seals and sealions often consume prey at depth, but whether the[ir] waste is liquid (and buoyant) requires further investigation. [Lavery 2010: 4]

The ocean sequesters about 22% of global anthropogenic CO2 emissions. Marine vertebrates contribute to the ocean’s carbon sink capacity in various ways, such as by fertilizing coastal vegetated habitats, and (through the work of marine predators) protecting this vegetation from overgrazing. Additionally, fish sequester carbon in the deep sea when they sink to the bottom after their natural death, whereas fishing releases the carbon embodied in fish back into the atmosphere when the catch is processed and consumed. Large fish (tuna, mackerel, shark, and billfish) that die in the ocean particularly contribute to “blue carbon” because these species are more likely to sink than be eaten near the surface. Unlike the CO2 released by terrestrial animals after death, the embodied carbon in marine corpses remains in the deep ocean.

This study estimates the extent to which fisheries have obstructed blue carbon sequestration. Mariani et al. report that fishing prevented 21.8 ± 4.4 Mt C (million metric tons of carbon) between 1950 and 2014 from being sequestered in the deep ocean. Industrial fisheries (as opposed to smaller, artisanal fisheries) are responsible for 85% of this extraction.

The amount of blue carbon extracted from the ocean through the harvest of large fish increased by almost one order of magnitude in 65 years (from 0.13 Mt C in 1950 to 1.09 Mt C in 2015). Combining CO2 emissions from fishing fleet transport and that of the fish removal itself amounts to 20.4 MtCO2 emitted in 2014, which is equivalent to the annual emission of 4.5 million cars.

Moreover, the authors found that government subsidies are encouraging overfishing. Almost half of the blue carbon extracted from the world’s oceans comes from areas that would be economically unprofitable without subsidies.

Our findings thus show that government subsidies, through supporting large-scale exploitation of large-bodied fish that are economically unviable, exacerbate the depletion of a natural carbon sink [Mariani 2010: 2].

Limiting and managing all fisheries on the unprofitable areas of the oceans could reduce CO2 emissions, rebuild fish stocks, and promote carbon sequestration by increasing the populations of large-bodied fish and the eventual deadfall of their carcasses to the depths.

Billions of animals, including insects, mammals, fish, and birds, migrate through the planet every year, which uniquely influences the environment and the ecological communities along migration routes.

“The frequency of migrations and the immense number of individuals involved often mean that migrant inputs constitute “resource pulses,” defined as occasional, intense, brief episodes of increased resource availability that can profoundly alter demographic rates and abundances of interacting populations” [Bauer & Hoye 2014: 6]

Effect on nutrients, energy, and toxicants:

Migrants transport nutrients, energy, and other substances from one ecosystem to another, creating a net inflow of energy and nutrients into the destination ecosystem. For example, salmon increased the nitrogen and phosphorus in their spawning habitat by 190% and 390% when migrating from the ocean back to their natal lakes and streams. At the same time, migrants may also introduce and accumulate toxicants, such as heavy metals, to receiving communities.

Effect on propagule dispersal:

Migrants play an important role in dispersing propagules, such as seeds, suckers, or spores across the resident communities.

In light of the importance of dispersal for population structure, adaptive capabilities, and evolutionary trajectories in theoretical studies, such long-distance dispersal events may be highly important for the (re)colonization of unoccupied habitats, the recovery of lost populations, maintenance of gene flow, and gene mixing in metapopulations, even if they are relatively rare events [Bauer & Hoye 2014: 2].

Moreover, migrants could also disperse propagules within resident communities. For example, long-nosed bats are responsible for up to 100% of columnar cacti pollination when they migrate to western Mexico. It is important to note that the timing of migration is very important; the migrants can only serve as major pollinators when visiting the communities during peak flowering.

Effect on parasite dispersal:

Migrants may increase parasite dynamics by facilitating the long-distance dispersal of parasites (including zoonotic pathogens like Ebola that also affect humans) to resident species. A few key mechanisms are involved in migration-facilitated parasite dispersal. For example, migrating animals are likely exposed to a greater range of parasites than are resident species. Some migrant animals may have suppressed  immune responses due to the high investment of energy into migration, increasing their susceptibility to infection. In addition, while migrating, animals tend to aggregate in larger groups, thus enhancing transmission rates, compared to other times of the year when they are stationary.

However, the role of migrants in transmitting parasites is complicated. Studies of monarch butterflies have shown that they have a shorter flying distance when infected with parasites, andinfected Bewick’s swans delay their departure and travel shorter distances. These findings suggest that migrants may reduce infection risk through infection-induced delays.

Effect of migratory herbivores (plant-eating species):

Migrants may alter the nutrient cycling, productivity, the biomass of edible plants, and ground cover of dead plant material. The grazing intensity of migrant herbivores is decoupled from the timing of plant growth so plants can grow when they are left, which substantially increases the primary productivity compared to an ecosystem with the equivalent number of resident herbivores.

The outcome of the interaction between migrants and residents differs depending on the food resources. During periods of plenty of food residents could share the excess resources with the migrants. However, during the dry season when food is scarcer, synergistic negative effects may be created.

Effects of migratory predators:

Migratory predators can positively influence the communities through prey population control. For example, birds and bats may control the insect population, which reduces damage to crops. Seasonal outmigration may also reduce pressure on prey in the places left behind by migrants, allowing those populations to regrow.

Effects of migratory prey:

Migratory prey could be an important resource for resident predators. Some predators even time their reproduction to coincide with migratory prey to increase their reproductive rate.

Migratory prey may also provide resident prey with a temporal refuge from predation. However, an abundant number of migrants may harm residents by boosting the abundance of resident predators, which then switch to resident prey after the migratory prey departs.

Many ecosystems have evolved to depend upon the activities of both resident and transitory migrating animals, and understanding these relationships is critical to preserving and restoring ecosystem complexity and resiliency.

Across the globe, migration is an increasingly threatened phenomenon as a consequence of habitat destruction, creation of barriers, over-exploitation, and climate change. The loss of migrants and migratory behavior also entails the loss of their ecosystem services—the manifold transport and trophic effects outlined above. Management strategies must therefore be designed to conserve not only migratory species but also their ecosystem functions. Yet, the conservation of migrants poses exceptional scientific and societal challenges, as events at each stage of the migratory cycle affect behavior and demographic rates and ecological interactions at other stages [Bauer & Hoye 2014: 9].

This paper presents an analysis of microclimatic temperature effects of termite mounds in Zimbabwe and South Africa that provide important climatic “refuges” for other local organisms. The research compared the vegetation growing on the mounds with that on control plots in the surrounding savannah with respect to temperature differences. They found that more tall woody vegetation grows on termite mounds, compared to surrounding areas, creating shade that cools the mounds.

The authors observed that: “tall trees, being more prevalent on mounds, provide increased leafy, large-volume canopy and subcanopy vegetation, which in turn furnish more shade relative to the savanna matrix” [Joseph 2016: 7]. They found a 2°C temperature difference on the termite mounds compared to the surrounding area when the surrounding temperature was  34°C; the difference rose to 4°C at 40°C. Thus, these mound microhabitats maintained an even greater ambient temperature difference the warmer the ambient environment became.

Data were collected on 44 large termite mounds, each paired with off-mound savannah plots, in October 2015 (which was one of the hottest months on record in these areas) during the dry season. The mounds were more than 2 meters tall or more than 10 meters in diameter, and they were compared with an equivalently sized circular plot in the surrounding habitat. For each termite mound and control plot, the variables measured included: temperature, humidity, number of trees taller than 4 meters, tree canopy size, and amount of shade.

The median mean shade on mounds was 21% compared to 3% on the control plots, while the median maximum shade was 70% on mounds and only 10% on the surrounding plots, while humidity did not differ significantly. Such microclimates are likely to be important refugia for wildlife as droughts, fire events and higher ambient temperatures become more prevalent due to climate change.

Many large herbivores may have important roles in dryland ecosystems. Equids such as donkeys and horses, as well as elephants, have been reported to dig wells of a maximum depth of two meters, enhancing water availability for a variety of animals and plants. Noting that this subject has received limited research attention, the authors carried out a study for three summers at the Sonoran Desert of North America to survey changes in groundwater-fed streams and “equid well” water, and the associated effects on the ecosystem.

Effect on animals

They found that the equid wells “provided up to 74% of surface water by accessing the water table” at one of the four groundwater-fed streams they studied [Lundgren 2014: 1]. The wells were especially important at the intermittent stream (unsteady stream that occurs at irregular intervals), providing 100% of available surface water when all other water was lost.

The wells reduced the distance between neighboring water features significantly, thus reducing the distance that animals needed to travel to reach water. The water resources created by the equids also prevented some species from resorting to eating extra plant foods simply to extract its water content, as they are observed to do in the absence of available surface water. Using camera traps, the researchers observed 59 vertebrate species (limited to organisms weighing over 100g and excluding equids) at equid wells, 57 of which they recorded drinking. “Daily species richness was 64 and 51% higher on average at equid wells and background waters [other surface water, such as the streams], respectively, than at dry controls” [Lundgren 2014: 1].

Effects on vegetation

The presence of equid wells enhanced the growth of pioneer trees. The survey showed that the seeding density was higher in equid wells, which function as germination nurseries, than in the riverbank zone. Riverbanks were usually covered by herbs, which reduced the density of trees. Equid wells, on the other hand, provide a non-competitive environment for the small-seeded pioneer trees.

The feral donkeys that dug the equid wells are not native to this dryland ecosystem study site, and yet they proved to mitigate the effects of water reduction and high temperature on biodiversity and ecosystem function. Thus, the ecological roles once played by large native mammals that have since become extinct, can in some cases be filled by non-native substitutes (which are typically viewed as threats to conservation).

“The majority of the world’s 350,000 species of flowering plants rely on animal pollinators for reproduction” [Tremlett 2019: 2]. Of the many vertebrates performing this function, including birds, rodents, and reptiles, bats are thought to be the primary pollinators for about 1,000 species of plants across the tropics.

The authors of this study conducted this research in the municipality of Techaluta de Montenegro, Jalisco, Mexico, where they held exclusion experiments (alternately excluding different pollinator species) on Stenocereus queretaroensis, a type of cactus with edible fruit, to determine the efficiency of different pollinators. The experimental treatments allowed the authors to distinguish between nocturnal and diurnal (active in the daytime) pollinators, and between invertebrate and vertebrate pollinators.

Pollination carried out by birds and diurnal insects resulted in low seed sets, significantly lighter fruit weights, and lower sucrose concentrations compared to pollination carried out by bats.

This was the first research study to assess the impact of bat pollination on not only the quality of a high socio-economically important crop but also the yield of the crop.

We found that in the absence of pollination by nectarivorous bats, yield and quality (i.e. fruit weight, as size determines market value) of S. queretaroensis decreased significantly by 35% and 46% respectively. Hence, nectarivorous bats contribute substantially to the economic welfare of the rural production region [Tremlett 2019: 6].

However, despite its economic value, the significance of pollination by bats is not valued and appreciated. It is important to recognize the ecosystem services provided by bats, which might be crucial to sustaining rural livelihoods and well-being.

After having been wiped out by the 1920s, wolves were reintroduced to Yellowstone National Park in 1995-1996. This study assessed the importance of large carnivores to wild ungulates’ behavior and density, with secondary effects on plant communities, rivers and channels, and beaver communities. Focusing on the West and East Forks of Blacktail Deer Creek, the authors summarized the population trends of wolves, elk, and beaver; sampled the heights, recruitment, and browsing intensity of Geyer willow (a common local tall willow); measured dimensions of the channel, and ascertained beaver dam heights.

After the reintroduction of wolves, the Rocky Mountain elk population decreased from 17,000 in 1994 to about 4,000 to 5,000 in recent years. Browsing intensity therefore greatly decreased, leading to taller riparian willow stems, which is an important food web support and physical habitat for both terrestrial and aquatic wildlife species. The willow canopy cover over the water surface has also increased rapidly over the last two decades, which holds a significant role in supporting the aquatic biota:

Canopy cover can reduce the amount of solar radiation reaching a stream, especially important during summertime periods when solar angles are high, day lengths are long, and flows are normally low, thereby mediating potential increases in water temperature. Furthermore, invertebrates in the canopies of near‐channel willows provide food for fish and seasonal leaf‐fall represents an important carbon base for aquatic invertebrates which, in turn, provide ‘reciprocal flows of invertebrate prey’ to adjacent terrestrial consumers [Beschta & Ripple 2020: 8].

Another benefit of protecting the riparian vegetation from herbivores is the improvement of streambank stability. During the period of wolf absence, intensive elk herbivory caused streambank erosion and channel incision (river cuts downward into its bed, deepening the active channel and may lead to dissected landscape), resulting in less frequent overbank flow. The channel incision lowered water tables and reduced subsurface moisture in flood plain vegetation during summer.

The return of wolves started the process of riparian vegetation restoration, which in turn supported stream-dependent species such as beavers. The reduction of elk herbivory increased food sources and materials for beavers to construct dams, while also fostering the narrower and shallower channels preferred by beavers. Thus, along with the recovery of vegetation and channels, beavers have returned in 2018, creating active dams to further rehabilitate the ecosystem.

If beaver populations continue to increase over time, the ecological effects of these ‘ecosystem engineers’ may well have a significant role in restoring riparian vegetation, floodplains, and channel dimensions for at least portions of northern range streams [Beschta & Ripple 2020: 9].

Before the 1900s, wolves and other predators, such as bears and mountain lions, helped control the populations of herbivores in Yellowstone. However, the federal government exterminated these predators in a coordinated campaign. After the last wolf pack was killed, the elk numbers started increasing uncountably. The US Park Service subsequently attempted to control the elk population by shooting the animals or moving them out of the park.

When the park stopped killing elk in 1968, numbers shot up again from about 5,000 to close to 20,000. For the next several decades, elk cycled through population booms and collapses along with climate fluctuations; hard winters left the ground littered with hundreds of the carcasses of elk that had starved to death [Peterson 2020].

Wildlife officials, therefore, reintroduced wolves back to Yellowstone 25 years ago, which brought the elk population under control and ended their extreme population fluctuations due to climate variability. To study how the wolves maintained the balance, the scientists tracked the wolf packs and recorded details of elk kills by the wolves.

They found that the wolves killed cow elk during the years with normal amounts of rain and snow. During the dry years, when there is less vegetation and therefore less elk food, the wolves targeted bulls. The undernourished elk are generally easier to catch, so the wolves target bulls given their larger size. Sparing elk cows allows the elk to reproduce.

The wolves improve elk herd resilience by eliminating the weak and sick animals. Scientists believed the elk herds are now better prepared for climate change impact, such as the frequent droughts.

The result of reintroducing wolves to Yellowstone showed that wolves stabilize the elk population better than humans can. Now wolves may be reintroduced to other states which are home to a large number of elk.

This article considers the overlooked role of grasslands and large herbivores in carbon storage. The principal question the authors pose is: what is the impact of large wild and domestic herbivores on the ability of ecosystems to absorb and store carbon over the long term? Their answer is that the activity of species like cattle, bison, boars, elephants, and rhinoceros, can significantly enhance ecosystem retention of carbon.

Questioning the assumption that fast-growing aboveground vegetation, especially trees, is the primary nature-based terrestrial sink for carbon, the authors argue for a whole-ecosystem carbon storage perspective. One problem with focusing on carbon storage in aboveground vegetation rather than that in the soil, they note, is that vegetation is more transient and vulnerable to disturbances, such as fire, while soil carbon tends to be stable, at least under natural and well-managed grasslands. Furthermore, the authors argue that the conventional focus on aboveground carbon storage has led to the “simplistic” generalization that large herbivores can be expected to damage vegetative ecosystems, and therefore have a negative impact on ecosystem carbon storage.

Yet this view misses the overall ecological impact of large herbivores, such as contributing to the soil through their wastes, and their bioturbation (churning of the soil by animals) activity. On the surface, large animals trample, forage, wallow and dig; just below the surface, the burrowing and digging of tunnels by soil-dwelling mammals like gophers, moles, voles, and shrews further loosens the soil; still deeper, there is the casting, burrowing and mining by macrofauna like insects, worms and dung beetles. Together, the multi-levelled bioturbation of these different species facilitates the vertical mixing of the organic material, putting it into contact with mineral soil particles for longer-term storage. Large grazing herbivores participate in vertical soil mixing (along with the smaller animals at lower levels in the soil), and therefore play an essential role in the long-term buildup of mineral-associated organic matter.

In addition to disturbing and mixing the soil, and enriching it through their body wastes, large herbivores clear pyrogenic (combustible) material on the ground and low shrubbery, thus increasing fire resistance. Their grazing also increases fine root growth and root exudation, which leads to increased microbial biomass. In turn, “microbial residues and plant exudates are effective substrates for persistent soil organic matter formation in the mineral-associated organic matter” [Kristensen 2021: 4].

In their conclusion, the authors emphasize the ecological value of natural grasslands, and the importance of preserving them:

Understanding the role that large herbivores may play in enhancing ecosystem carbon persistence, by reducing the flammability of aboveground carbon and shifting carbon storage from vulnerable pools towards more persistent soil pools at the biome scale, is crucial to balancing the ecosystem services provided by semi-open herbivore-rich systems against potential services from alternative land-uses, such as afforestation [Kristensen 2021: 9].

Can large herbivores enhance ecosystem carbon persistence? Kristensen et al. 2021

This article considers the overlooked role of grasslands and large herbivores in carbon storage. The principal question the authors pose is: what is the impact of large wild and domestic herbivores on the ability of ecosystems to absorb and store carbon over the long term? Their answer is that the activity of species like cattle, bison, boars, elephants, and rhinoceros, can significantly enhance ecosystem retention of carbon.

Questioning the assumption that fast-growing aboveground vegetation, especially trees, is the primary nature-based terrestrial sink for carbon, the authors argue for a whole-ecosystem carbon storage perspective. One problem with focusing on carbon storage in aboveground vegetation rather than that in the soil, they note, is that vegetation is more transient and vulnerable to disturbances, such as fire, while soil carbon tends to be stable, at least under natural and well-managed grasslands. Furthermore, the authors argue that the conventional focus on aboveground carbon storage has led to the “simplistic” generalization that large herbivores can be expected to damage vegetative ecosystems, and therefore have a negative impact on ecosystem carbon storage.

Yet this view misses the overall ecological impact of large herbivores, such as contributing to the soil through their wastes, and their bioturbation (churning of the soil by animals) activity. On the surface, large animals trample, forage, wallow and dig; just below the surface, the burrowing and digging of tunnels by soil-dwelling mammals like gophers, moles, voles, and shrews further loosens the soil; still deeper, there is the casting, burrowing and mining by macrofauna like insects, worms and dung beetles. Together, the multi-levelled bioturbation of these different species facilitates the vertical mixing of the organic material, putting it into contact with mineral soil particles for longer-term storage. Large grazing herbivores participate in vertical soil mixing (along with the smaller animals at lower levels in the soil), and therefore play an essential role in the long-term buildup of mineral-associated organic matter.

In addition to disturbing and mixing the soil, and enriching it through their body wastes, large herbivores clear pyrogenic (combustible) material on the ground and low shrubbery, thus increasing fire resistance. Their grazing also increases fine root growth and root exudation, which leads to increased microbial biomass. In turn, “microbial residues and plant exudates are effective substrates for persistent soil organic matter formation in the mineral-associated organic matter” [Kristensen 2021: 4].

In their conclusion, the authors emphasize the ecological value of natural grasslands, and the importance of preserving them:

Understanding the role that large herbivores may play in enhancing ecosystem carbon persistence, by reducing the flammability of aboveground carbon and shifting carbon storage from vulnerable pools towards more persistent soil pools at the biome scale, is crucial to balancing the ecosystem services provided by semi-open herbivore-rich systems against potential services from alternative land-uses, such as afforestation [Kristensen 2021: 9].

25 years after returning to Yellowstone, wolves have helped stabilize the ecosystem, Peterson 2020

Before the 1900s, wolves and other predators, such as bears and mountain lions, helped control the populations of herbivores in Yellowstone. However, the federal government exterminated these predators in a coordinated campaign. After the last wolf pack was killed, the elk numbers started increasing uncountably. The US Park Service subsequently attempted to control the elk population by shooting the animals or moving them out of the park.

When the park stopped killing elk in 1968, numbers shot up again from about 5,000 to close to 20,000. For the next several decades, elk cycled through population booms and collapses along with climate fluctuations; hard winters left the ground littered with hundreds of the carcasses of elk that had starved to death [Peterson 2020].

Wildlife officials, therefore, reintroduced wolves back to Yellowstone 25 years ago, which brought the elk population under control and ended their extreme population fluctuations due to climate variability. To study how the wolves maintained the balance, the scientists tracked the wolf packs and recorded details of elk kills by the wolves.

They found that the wolves killed cow elk during the years with normal amounts of rain and snow. During the dry years, when there is less vegetation and therefore less elk food, the wolves targeted bulls. The undernourished elk are generally easier to catch, so the wolves target bulls given their larger size. Sparing elk cows allows the elk to reproduce.

The wolves improve elk herd resilience by eliminating the weak and sick animals. Scientists believed the elk herds are now better prepared for climate change impact, such as the frequent droughts.

The result of reintroducing wolves to Yellowstone showed that wolves stabilize the elk population better than humans can. Now wolves may be reintroduced to other states which are home to a large number of elk.

Can large carnivores change streams via a trophic cascade? Beschta & Ripple 2020

After having been wiped out by the 1920s, wolves were reintroduced to Yellowstone National Park in 1995-1996. This study assessed the importance of large carnivores to wild ungulates’ behavior and density, with secondary effects on plant communities, rivers and channels, and beaver communities. Focusing on the West and East Forks of Blacktail Deer Creek, the authors summarized the population trends of wolves, elk, and beaver; sampled the heights, recruitment, and browsing intensity of Geyer willow (a common local tall willow); measured dimensions of the channel, and ascertained beaver dam heights.

After the reintroduction of wolves, the Rocky Mountain elk population decreased from 17,000 in 1994 to about 4,000 to 5,000 in recent years. Browsing intensity therefore greatly decreased, leading to taller riparian willow stems, which is an important food web support and physical habitat for both terrestrial and aquatic wildlife species. The willow canopy cover over the water surface has also increased rapidly over the last two decades, which holds a significant role in supporting the aquatic biota:

Canopy cover can reduce the amount of solar radiation reaching a stream, especially important during summertime periods when solar angles are high, day lengths are long, and flows are normally low, thereby mediating potential increases in water temperature. Furthermore, invertebrates in the canopies of near‐channel willows provide food for fish and seasonal leaf‐fall represents an important carbon base for aquatic invertebrates which, in turn, provide ‘reciprocal flows of invertebrate prey’ to adjacent terrestrial consumers [Beschta & Ripple 2020: 8].

Another benefit of protecting the riparian vegetation from herbivores is the improvement of streambank stability. During the period of wolf absence, intensive elk herbivory caused streambank erosion and channel incision (river cuts downward into its bed, deepening the active channel and may lead to dissected landscape), resulting in less frequent overbank flow. The channel incision lowered water tables and reduced subsurface moisture in flood plain vegetation during summer.

The return of wolves started the process of riparian vegetation restoration, which in turn supported stream-dependent species such as beavers. The reduction of elk herbivory increased food sources and materials for beavers to construct dams, while also fostering the narrower and shallower channels preferred by beavers. Thus, along with the recovery of vegetation and channels, beavers have returned in 2018, creating active dams to further rehabilitate the ecosystem.

If beaver populations continue to increase over time, the ecological effects of these ‘ecosystem engineers’ may well have a significant role in restoring riparian vegetation, floodplains, and channel dimensions for at least portions of northern range streams [Beschta & Ripple 2020: 9].

Pollination by bats enhances both quality and yield of a major cash crop in Mexico, Tremlett et al. 2019

“The majority of the world’s 350,000 species of flowering plants rely on animal pollinators for reproduction” [Tremlett 2019: 2]. Of the many vertebrates performing this function, including birds, rodents, and reptiles, bats are thought to be the primary pollinators for about 1,000 species of plants across the tropics.

The authors of this study conducted this research in the municipality of Techaluta de Montenegro, Jalisco, Mexico, where they held exclusion experiments (alternately excluding different pollinator species) on Stenocereus queretaroensis, a type of cactus with edible fruit, to determine the efficiency of different pollinators. The experimental treatments allowed the authors to distinguish between nocturnal and diurnal (active in the daytime) pollinators, and between invertebrate and vertebrate pollinators.

Pollination carried out by birds and diurnal insects resulted in low seed sets, significantly lighter fruit weights, and lower sucrose concentrations compared to pollination carried out by bats.

This was the first research study to assess the impact of bat pollination on not only the quality of a high socio-economically important crop but also the yield of the crop.

We found that in the absence of pollination by nectarivorous bats, yield and quality (i.e. fruit weight, as size determines market value) of S. queretaroensis decreased significantly by 35% and 46% respectively. Hence, nectarivorous bats contribute substantially to the economic welfare of the rural production region [Tremlett 2019: 6].

However, despite its economic value, the significance of pollination by bats is not valued and appreciated. It is important to recognize the ecosystem services provided by bats, which might be crucial to sustaining rural livelihoods and well-being.

Equids engineer desert water availability, Lundgren et al. 2014

Many large herbivores may have important roles in dryland ecosystems. Equids such as donkeys and horses, as well as elephants, have been reported to dig wells of a maximum depth of two meters, enhancing water availability for a variety of animals and plants. Noting that this subject has received limited research attention, the authors carried out a study for three summers at the Sonoran Desert of North America to survey changes in groundwater-fed streams and “equid well” water, and the associated effects on the ecosystem.

Effect on animals

They found that the equid wells “provided up to 74% of surface water by accessing the water table” at one of the four groundwater-fed streams they studied [Lundgren 2014: 1]. The wells were especially important at the intermittent stream (unsteady stream that occurs at irregular intervals), providing 100% of available surface water when all other water was lost.

The wells reduced the distance between neighboring water features significantly, thus reducing the distance that animals needed to travel to reach water. The water resources created by the equids also prevented some species from resorting to eating extra plant foods simply to extract its water content, as they are observed to do in the absence of available surface water. Using camera traps, the researchers observed 59 vertebrate species (limited to organisms weighing over 100g and excluding equids) at equid wells, 57 of which they recorded drinking. “Daily species richness was 64 and 51% higher on average at equid wells and background waters [other surface water, such as the streams], respectively, than at dry controls” [Lundgren 2014: 1].

Effects on vegetation

The presence of equid wells enhanced the growth of pioneer trees. The survey showed that the seeding density was higher in equid wells, which function as germination nurseries, than in the riverbank zone. Riverbanks were usually covered by herbs, which reduced the density of trees. Equid wells, on the other hand, provide a non-competitive environment for the small-seeded pioneer trees.

The feral donkeys that dug the equid wells are not native to this dryland ecosystem study site, and yet they proved to mitigate the effects of water reduction and high temperature on biodiversity and ecosystem function. Thus, the ecological roles once played by large native mammals that have since become extinct, can in some cases be filled by non-native substitutes (which are typically viewed as threats to conservation).

Microclimates mitigate against hot temperatures in dryland ecosystems: termite mounds as an example, Joseph et al. 2016

This paper presents an analysis of microclimatic temperature effects of termite mounds in Zimbabwe and South Africa that provide important climatic “refuges” for other local organisms. The research compared the vegetation growing on the mounds with that on control plots in the surrounding savannah with respect to temperature differences. They found that more tall woody vegetation grows on termite mounds, compared to surrounding areas, creating shade that cools the mounds.

The authors observed that: “tall trees, being more prevalent on mounds, provide increased leafy, large-volume canopy and subcanopy vegetation, which in turn furnish more shade relative to the savanna matrix” [Joseph 2016: 7]. They found a 2°C temperature difference on the termite mounds compared to the surrounding area when the surrounding temperature was  34°C; the difference rose to 4°C at 40°C. Thus, these mound microhabitats maintained an even greater ambient temperature difference the warmer the ambient environment became.

Data were collected on 44 large termite mounds, each paired with off-mound savannah plots, in October 2015 (which was one of the hottest months on record in these areas) during the dry season. The mounds were more than 2 meters tall or more than 10 meters in diameter, and they were compared with an equivalently sized circular plot in the surrounding habitat. For each termite mound and control plot, the variables measured included: temperature, humidity, number of trees taller than 4 meters, tree canopy size, and amount of shade.

The median mean shade on mounds was 21% compared to 3% on the control plots, while the median maximum shade was 70% on mounds and only 10% on the surrounding plots, while humidity did not differ significantly. Such microclimates are likely to be important refugia for wildlife as droughts, fire events and higher ambient temperatures become more prevalent due to climate change.

Migratory animals couple biodiversity and ecosystem functioning worldwide, Bauer & Hoye 2014

Billions of animals, including insects, mammals, fish, and birds, migrate through the planet every year, which uniquely influences the environment and the ecological communities along migration routes.

“The frequency of migrations and the immense number of individuals involved often mean that migrant inputs constitute “resource pulses,” defined as occasional, intense, brief episodes of increased resource availability that can profoundly alter demographic rates and abundances of interacting populations” [Bauer & Hoye 2014: 6]

Effect on nutrients, energy, and toxicants:

Migrants transport nutrients, energy, and other substances from one ecosystem to another, creating a net inflow of energy and nutrients into the destination ecosystem. For example, salmon increased the nitrogen and phosphorus in their spawning habitat by 190% and 390% when migrating from the ocean back to their natal lakes and streams. At the same time, migrants may also introduce and accumulate toxicants, such as heavy metals, to receiving communities.

Effect on propagule dispersal:

Migrants play an important role in dispersing propagules, such as seeds, suckers, or spores across the resident communities.

In light of the importance of dispersal for population structure, adaptive capabilities, and evolutionary trajectories in theoretical studies, such long-distance dispersal events may be highly important for the (re)colonization of unoccupied habitats, the recovery of lost populations, maintenance of gene flow, and gene mixing in metapopulations, even if they are relatively rare events [Bauer & Hoye 2014: 2].

Moreover, migrants could also disperse propagules within resident communities. For example, long-nosed bats are responsible for up to 100% of columnar cacti pollination when they migrate to western Mexico. It is important to note that the timing of migration is very important; the migrants can only serve as major pollinators when visiting the communities during peak flowering.

Effect on parasite dispersal:

Migrants may increase parasite dynamics by facilitating the long-distance dispersal of parasites (including zoonotic pathogens like Ebola that also affect humans) to resident species. A few key mechanisms are involved in migration-facilitated parasite dispersal. For example, migrating animals are likely exposed to a greater range of parasites than are resident species. Some migrant animals may have suppressed  immune responses due to the high investment of energy into migration, increasing their susceptibility to infection. In addition, while migrating, animals tend to aggregate in larger groups, thus enhancing transmission rates, compared to other times of the year when they are stationary.

However, the role of migrants in transmitting parasites is complicated. Studies of monarch butterflies have shown that they have a shorter flying distance when infected with parasites, andinfected Bewick’s swans delay their departure and travel shorter distances. These findings suggest that migrants may reduce infection risk through infection-induced delays.

Effect of migratory herbivores (plant-eating species):

Migrants may alter the nutrient cycling, productivity, the biomass of edible plants, and ground cover of dead plant material. The grazing intensity of migrant herbivores is decoupled from the timing of plant growth so plants can grow when they are left, which substantially increases the primary productivity compared to an ecosystem with the equivalent number of resident herbivores.

The outcome of the interaction between migrants and residents differs depending on the food resources. During periods of plenty of food residents could share the excess resources with the migrants. However, during the dry season when food is scarcer, synergistic negative effects may be created.

Effects of migratory predators:

Migratory predators can positively influence the communities through prey population control. For example, birds and bats may control the insect population, which reduces damage to crops. Seasonal outmigration may also reduce pressure on prey in the places left behind by migrants, allowing those populations to regrow.

Effects of migratory prey:

Migratory prey could be an important resource for resident predators. Some predators even time their reproduction to coincide with migratory prey to increase their reproductive rate.

Migratory prey may also provide resident prey with a temporal refuge from predation. However, an abundant number of migrants may harm residents by boosting the abundance of resident predators, which then switch to resident prey after the migratory prey departs.

Many ecosystems have evolved to depend upon the activities of both resident and transitory migrating animals, and understanding these relationships is critical to preserving and restoring ecosystem complexity and resiliency.

Across the globe, migration is an increasingly threatened phenomenon as a consequence of habitat destruction, creation of barriers, over-exploitation, and climate change. The loss of migrants and migratory behavior also entails the loss of their ecosystem services—the manifold transport and trophic effects outlined above. Management strategies must therefore be designed to conserve not only migratory species but also their ecosystem functions. Yet, the conservation of migrants poses exceptional scientific and societal challenges, as events at each stage of the migratory cycle affect behavior and demographic rates and ecological interactions at other stages [Bauer & Hoye 2014: 9].

Let more big fish sink: Fisheries prevent blue carbon sequestration—half in unprofitable areas, Mariani et. al 2010

The ocean sequesters about 22% of global anthropogenic CO2 emissions. Marine vertebrates contribute to the ocean’s carbon sink capacity in various ways, such as by fertilizing coastal vegetated habitats, and (through the work of marine predators) protecting this vegetation from overgrazing. Additionally, fish sequester carbon in the deep sea when they sink to the bottom after their natural death, whereas fishing releases the carbon embodied in fish back into the atmosphere when the catch is processed and consumed. Large fish (tuna, mackerel, shark, and billfish) that die in the ocean particularly contribute to “blue carbon” because these species are more likely to sink than be eaten near the surface. Unlike the CO2 released by terrestrial animals after death, the embodied carbon in marine corpses remains in the deep ocean.

This study estimates the extent to which fisheries have obstructed blue carbon sequestration. Mariani et al. report that fishing prevented 21.8 ± 4.4 Mt C (million metric tons of carbon) between 1950 and 2014 from being sequestered in the deep ocean. Industrial fisheries (as opposed to smaller, artisanal fisheries) are responsible for 85% of this extraction.

The amount of blue carbon extracted from the ocean through the harvest of large fish increased by almost one order of magnitude in 65 years (from 0.13 Mt C in 1950 to 1.09 Mt C in 2015). Combining CO2 emissions from fishing fleet transport and that of the fish removal itself amounts to 20.4 MtCO2 emitted in 2014, which is equivalent to the annual emission of 4.5 million cars.

Moreover, the authors found that government subsidies are encouraging overfishing. Almost half of the blue carbon extracted from the world’s oceans comes from areas that would be economically unprofitable without subsidies.

Our findings thus show that government subsidies, through supporting large-scale exploitation of large-bodied fish that are economically unviable, exacerbate the depletion of a natural carbon sink [Mariani 2010: 2].

Limiting and managing all fisheries on the unprofitable areas of the oceans could reduce CO2 emissions, rebuild fish stocks, and promote carbon sequestration by increasing the populations of large-bodied fish and the eventual deadfall of their carcasses to the depths.

Iron defecation by sperm whales stimulates carbon export in the Southern Ocean, Lavery et. al 2010

Whales have been viewed as a source of CO2 because they respire tons of CO2 annually. However, their feces could possibly offset this impact, as they may be a great contributor to carbon export (removal from the atmosphere) to the depths of the ocean. Iron-rich whale feces stimulate the growth of phytoplankton, which leads to more CO2 drawn into the ocean through photosynthesis.

Lavery et al. conducted this study to find out whether the 12,000 sperm whales in the Southern Ocean are acting as a carbon sink. The authors wondered whether the whales help the ocean absorb more carbon from the atmosphere than the whales themselves release through respiration. They note that these animals consume prey outside of but defecate within the photic zone (the layer nearest to the ocean surface), raising nutrient availability in the layer of ocean where photosynthesis is possible. Whale feces are also in liquid form, which disperses and persists within this area.

Using existing data on whale populations, consumption patterns, and average rates of iron retention compared to what is expelled, the authors estimate that the South Ocean sperm whales contribute 36 tons of iron per year to the photic zone. After accounting for respiration rates, the authors conclude that whales do act as a net carbon sink by removing 2.4 X 105 metric tons of carbon from the atmosphere annually. Even under conservative scenarios (consumption of prey with lower iron concentrations), whales still help sequester more carbon than they respire.

These animals’ contribution to nutrient and carbon cycling in the ocean has previously been overlooked. Their feces not only enhance carbon sink in the ocean but also contribute to increasing numbers of prey. However, the reduction of sperm whales by commercial whaling has reduced krill populations and decreased allochthonous (originating externally) iron inputs to the Southern Ocean by 450 tons annually.

The reduction in sperm whale numbers owing to whaling has resulted in an extra 2 X 106 tonnes of carbon remaining in the atmosphere annually [Lavery 2010: 3].

In addition to sperm whales, there could be more organisms acting as carbon sinks in the ocean:

We have restricted our analysis to sperm whales; however, any organism that consumes prey outside the photic zone and defecates nutrient-rich waste that persists in the photic zone would stimulate new production and carbon export. Pygmy and dwarf sperm whales (Kogia spp.) and beaked whales (Family Ziphiidae) fulfill these criteria. The proportion of time baleen whales consume prey at depth is currently unknown, but fin whales (Balaenoptera physalus) dive to at least 470 m while feeding. Seals and sealions often consume prey at depth, but whether the[ir] waste is liquid (and buoyant) requires further investigation. [Lavery 2010: 4]

This article (also highlighted in Compendium v2n1) reviews research on the benefits of tree cover in relation to water and energy cycles.

Forests help produce rain. Vegetation releases water vapor through transpiration, increasing atmospheric moisture that is then transported by wind. In fact, “over most of the tropics, air that passes over forests for ten days typically produces at least twice as much rain as air that passes over sparse vegetation” [Ellison 2017: 53]. Forests also release biological particles, such as spores, bacteria and pollen into the atmosphere. Water condenses around these particles, forming raindrops.

In addition to the atmospheric moisture produced by forests that is transported by prevailing winds to generate downwind rain, forests also help transport moisture from the coasts to the interior of continents. According to the biotic pump theory [Makarieva & Gorshkov 2007], evapotranspiration over coastal forests creates low pressure zones that draw in atmospheric moisture from the ocean. This oceanic moisture eventually comes down as rain over land. Deforestation of coastal forests thus reduces this influx of moisture to land, while deforestation anywhere can decrease the reliability of rainfall downwind.

Through shading and evapotranspiration, forests cool the Earth’s surface in tropical and temperate climates. Due to a lower albedo compared to other land cover types at high latitudes, boreal forests potentially contribute to local warming. However, forests also increase cloud cover and thus albedo, higher in the atmosphere. In the absence of vegetation, such as in cities, solar energy remains in the environment in the form of heat, rather than driving evapotranspiration.

Using the sun’s energy, individual trees can transpire hundreds of liters of water per day. This represents a cooling power equivalent to 70 kWh for every 100 L of water transpired (enough to power two average household central air-conditioning units per day) [Ellison 2017: 54].

High-elevation forests have a unique potential to intercept fog and cloud droplets, which boosts tree growth, evapotranspiration, groundwater infiltration, and ultimately contributes up to 75% of catchment runoff. Tree cover can improve water infiltration due to increased organic matter to hold water and the presence of tree roots, which loosen and shade the soil and channel water into the ground. In areas where infiltration rates are greater than transpiration rates, the presence of trees increases groundwater recharge.

All of the aforementioned mechanisms distribute water naturally, hence reducing floods.

Local temperatures are affected not only by global climatic factors, but also by radiative (albedo) and non-radiative (evapotranspiration and convection) mechanisms related to local vegetation cover. Through evapotranspiration, solar energy is converted to latent heat and released from the planet’s surface, while convection refers to the turbulent mixing of air that dissipates sensible heat. The authors state that while albedo (reflectivity of land surface, which is often lower on forested land) is increasingly accounted for alongside greenhouse gases in climate models, the non-radiative mechanisms are not. However, the evapotranspiration and convection facilitated by vegetation have an important cooling effect and should therefore be included in models to avoid the risk of “promoting land sector policies that may be counter to the aims of mitigation or adaptation” [Bright 2017: 296].

The authors demonstrate that “non-radiative mechanisms dominate the local response in most regions for eight of nine common LCMC perturbations” [Bright 2017: 296]. Land cover and land management changes (LCMC) considered in the study include converting cropland or grassland to deciduous or evergreen forests. The authors found that gains in forest cover increased annual cooling in all but the northernmost latitudes, where the lower albedo of forests compared to grasslands had a warming effect that was stronger than the cooling effect of non-radiative mechanisms. In many regions, including much of Europe, the US, and the tropics, non-radiative cooling dominated albedo effects. “Over annual timescales, forest cover gains result in net cooling for many of the densely populated regions of the planet” [Bright 2017: 298].

Bright et al. conclude that “benchmarking the locally driven LCMC effect to that driven by global forcers (such as CO2) can provide an additional perspective by which to support the valuation of vegetated ecosystems and the local climate regulation services that they provide” [Bright 2017: 301].

This paper analyzes how land use and land cover change (LULCC) affects temperature and humidity. The authors examined the differential effects of forest versus deforested land on temperature and humidity by comparing different land-cover models. One model simulated the total potential vegetation (“PotVeg”) that would cover Earth in the absence of human interference, while the other was based on historical data of land use changes that occurred over a recent five-decade period (“AllHist”).

They found that deforested lands in mid-latitudes (North America, Eurasia) in the AllHist model are warmer and drier compared to the same lands covered in forest in the PotVeg model. Specifically, “conversion of mid-latitude natural forests to cropland and pastures is accompanied by an increase in the occurrence of hot-dry summers from once-in-a-decade to every 2–3 years” [Findell 2017: 1]. “Based on these simulations, the conversion of forests to cropland is coincident with much of the upper central US and central Europe experiencing extreme hot, dry summers” [Findell 2017: 6].

Turning lemons into lemonade, Sabajo et al. have used the great expansion of oil palm plantations and other crops in Indonesia to examine how such land-use change affects land surface temperature (LST). The authors observed a warming trend in the Jambi province of Sumatra of 1.05℃ and 1.56℃ in the morning and afternoon, respectively, between 2000 and 2015. The average morning (10:30 am) temperature increased by 0.07℃ per year; the midday afternoon (1:30 pm) temperature increased by 0.13℃ per year.

During roughly the same period (2000-2010), forest area decreased in Jambi by 17%, while oil palm and rubber plantations greatly expanded. Given that LST within the province’s remaining forests increased only .04C per year at 10:30 am, which the authors attribute mainly to global warming, they concluded that the overall higher province-wide daytime temperature increase was caused by the observed land cover change.

The team also compared temperatures between different land uses: forest, oil palm and rubber plantations, urban areas, and bare land. Despite having a higher albedo (reflectivity) than the forest areas, all converted (non-forest) lands were nonetheless warmer than forests, “suggesting that the albedo was not the dominant variable explaining the LST” [Sabajo 2017: 4629]. Evapotranspiration (ET) played a greater role. Non-vegetated surfaces (urban and bare) were the warmest.

The authors conclude: “The warming effect after forest conversion results from the reduced evaporative cooling, which was identified as the main determinant of regulating the surface temperature” [Sabajo 2017: 4631].

Deforestation has contributed to warming in the northern mid-latitudes of North America and Eurasia not only through a large contribution to global CO2 emissions, but also through biogeophysical effects. The latter refers to land-surface effects such as albedo and evapotranspiration, which vary according to the type of land cover. This study uses models to demonstrate that deforestation in the northern mid-latitudes has increased the intensity of hot days by about a third since pre-industrial times. Factoring in deforestation’s contribution to greenhouse gas emissions further increases deforestation’s heating effect.

Our best estimate suggests that the present-day contribution of deforestation to the TXx [yearly maximum temperature, or “hot days”] increase over this region still equals at least 50% once the warming entailed by the LCC [land cover change]-induced carbon emissions is considered [LeJeune 2018: 4].

“Extensive deforestation took place early in the industrial period over the northern mid-latitudes,” and then slowed down in the 20th Century [LeJeune 2018: 4]. By 1920, modeled increases of temperature “through biogeophysical effects had already reached 0.3°C (~75% of their present-day values) over the most deforested areas of North America and Eurasia. On average before 1920, local deforestation was responsible for most of the TXx [yearly maximum temperature] warming over these regions” [LeJeune 2018: 4]. Warming caused by greenhouse gases became more important during the 20th Century, “leading to a total warming of 1.3°C over North America and 1°C over Eurasia by the present-day” [LeJeune 2018: 4].

The amount of Earth’s green cover (measured as Leaf Area Index^[6]) has increased globally since 1980, especially in northern latitudes, where growing seasons have lengthened. This is due mainly to increasing CO2 concentration, but also to warmer temperatures and changing precipitation patterns, nitrogen deposition, and land-use change (such as afforestation in China). Higher ambient CO2 can stimulate photosynthesis and reduce water loss, but the extent of the CO2 fertilization depends on the availability of other key nutrients (nitrogen and phosphorus) and water. Warmer temperatures due to climate change have increased greening in northern latitudes by extending the growing season, but diminished greening in the tropics, where temperatures were already optimal.

Greater global green cover has observable feedbacks on climate and the carbon cycle. In addition to offsetting 28% of anthropogenic emissions since 1980, vegetation affects hydrological cycles and air-surface temperatures. Since the 1980s, increased global evapotranspiration (ET) is mainly attributable to increased global greening. Higher transpiration rates from vegetation can reduce or enhance groundwater storage locally, depending on how the atmospheric moisture generated through evapotranspiration is recycled into rain and where that rain falls. In the world’s great rainforests, vegetation preserves groundwater.

The enhanced precipitation over transpiring regions is particularly evident in moist forests like the Amazon or Congo, which are ‘closed’ atmospheric systems where 80% of the rainfall originates from upwind ET. Such an efficient atmospheric water recycling mitigates water loss from the soil, sustains inland vegetation and maintains mesic^[7] and humid ecosystems [Piao 2019: 9].

Vegetation affects land-surface temperature by way of ET (cooling effect) and albedo (warming or cooling effect, depending on how dark or light the surface is). While the relative strength of ET versus albedo varies by latitude, the net global effect of increasing vegetation cover is one of cooling the land surface.

While reforestation has been widely heralded as a means of sequestering carbon into the soil, there is growing evidence that it also serves to directly cool the land surface. But forests’ impacts on air temperature (measured over forests rather than within them) have been difficult to assess because of the confounding impacts of forest canopies on wind and temperature profiles near the surface. This study was implemented to create a new method for assessing to what degree forests also cool the air.

Most studies measure surface temperature, which “represents the aggregated temperature of solid canopy and soil elements,” and is measured at a midway point between the ground and the top of the canopy. Air temperature, on the other hand, is measured above the vegetation canopy (whether grasslands or forest). The study site, located in the Piedmont region near Durham North Carolina, consists of an old-field grassland, a pine forest, and an unevenly aged oak hickory forest, all within close proximity to each other. The study assessed temperatures at various heights in and above the grasslands and the two forests.

The authors found that surface temperatures are much lower in forests than in grassland; this difference often exceeds 5°C at midday during the growing season. Furthermore, the air is cooler over forests than over grasslands, though to a lesser degree than the surface temperature difference. The annual average air temperature difference of forests compared to grassland is 0.5°C to 1°C, while the difference reaches 2°C to 3°C during daytime growing season periods.

“Making the connection between land cover, surface temperature, and air temperature is becoming necessary for obtaining a complete picture of the climate mitigation and adaptation potential of managed land cover changes, including reforestation,” the authors conclude. “This energy balance perspective on the climate mitigation and adaptation potential of reforestation is especially relevant right now” given a recent global surge of interest in reforestation to sequester carbon [Novik & Katul 2020: 13].

Reforestation and afforestation (R&A) are well-established climate mitigation strategies in the wet tropics due to high carbon sequestration rates of forests/trees. However, at high latitudes (boreal regions), the low albedo of trees–compared to snow and other lighter land surfaces–leads to the absorption of energy, thus creating a warming effect that has a greater impact on temperature than the carbon capture accomplished by the limited vegetation productivity in boreal regions. This study explores the balance between albedo and carbon sequestration of forests at mid-latitudes, which has been less clear.

The authors found that forested areas have greater cloud cover than other types of land cover at midlatitudes, resulting in a higher albedo at the top of the atmosphere–where the clouds are–and leading to greater cooling. Specifically, they found “an association of forested lands with increased cloudiness… As a result, forests reflect extra solar radiation and thus reduce the radiative impacts of the lower surface albedo. This in turn implies a cooling effect of R&A at midlatitudes” [Cerasoli 2021: 1-2]. The increase in cloudiness is due to earlier afternoon cloud formation over forests compared to other vegetation types in wet regions.

Our results provide substantial evidence of remarkable benefits of R&A [reforestation and afforestation] around the 30° to 45° latitudinal range, due to the combined benefits of biomass gain and promotion of cloud formation over forests [Cerasoli 2021: 4].

Cloud cooling effects of afforestation and reforestation at midlatitudes, Cerasoli, Jin & Porporato 2021

Reforestation and afforestation (R&A) are well-established climate mitigation strategies in the wet tropics due to high carbon sequestration rates of forests/trees. However, at high latitudes (boreal regions), the low albedo of trees–compared to snow and other lighter land surfaces–leads to the absorption of energy, thus creating a warming effect that has a greater impact on temperature than the carbon capture accomplished by the limited vegetation productivity in boreal regions. This study explores the balance between albedo and carbon sequestration of forests at mid-latitudes, which has been less clear.

The authors found that forested areas have greater cloud cover than other types of land cover at midlatitudes, resulting in a higher albedo at the top of the atmosphere–where the clouds are–and leading to greater cooling. Specifically, they found “an association of forested lands with increased cloudiness… As a result, forests reflect extra solar radiation and thus reduce the radiative impacts of the lower surface albedo. This in turn implies a cooling effect of R&A at midlatitudes” [Cerasoli 2021: 1-2]. The increase in cloudiness is due to earlier afternoon cloud formation over forests compared to other vegetation types in wet regions.

Our results provide substantial evidence of remarkable benefits of R&A [reforestation and afforestation] around the 30° to 45° latitudinal range, due to the combined benefits of biomass gain and promotion of cloud formation over forests [Cerasoli 2021: 4].

The duality of reforestation impacts on surface and air temperature, Novick & Katul 2020

While reforestation has been widely heralded as a means of sequestering carbon into the soil, there is growing evidence that it also serves to directly cool the land surface. But forests’ impacts on air temperature (measured over forests rather than within them) have been difficult to assess because of the confounding impacts of forest canopies on wind and temperature profiles near the surface. This study was implemented to create a new method for assessing to what degree forests also cool the air.

Most studies measure surface temperature, which “represents the aggregated temperature of solid canopy and soil elements,” and is measured at a midway point between the ground and the top of the canopy. Air temperature, on the other hand, is measured above the vegetation canopy (whether grasslands or forest). The study site, located in the Piedmont region near Durham North Carolina, consists of an old-field grassland, a pine forest, and an unevenly aged oak hickory forest, all within close proximity to each other. The study assessed temperatures at various heights in and above the grasslands and the two forests.

The authors found that surface temperatures are much lower in forests than in grassland; this difference often exceeds 5°C at midday during the growing season. Furthermore, the air is cooler over forests than over grasslands, though to a lesser degree than the surface temperature difference. The annual average air temperature difference of forests compared to grassland is 0.5°C to 1°C, while the difference reaches 2°C to 3°C during daytime growing season periods.

“Making the connection between land cover, surface temperature, and air temperature is becoming necessary for obtaining a complete picture of the climate mitigation and adaptation potential of managed land cover changes, including reforestation,” the authors conclude. “This energy balance perspective on the climate mitigation and adaptation potential of reforestation is especially relevant right now” given a recent global surge of interest in reforestation to sequester carbon [Novik & Katul 2020: 13].

Characteristics, drivers and feedbacks of global greening, Piao et al. 2019

The amount of Earth’s green cover (measured as Leaf Area Index^[6]) has increased globally since 1980, especially in northern latitudes, where growing seasons have lengthened. This is due mainly to increasing CO2 concentration, but also to warmer temperatures and changing precipitation patterns, nitrogen deposition, and land-use change (such as afforestation in China). Higher ambient CO2 can stimulate photosynthesis and reduce water loss, but the extent of the CO2 fertilization depends on the availability of other key nutrients (nitrogen and phosphorus) and water. Warmer temperatures due to climate change have increased greening in northern latitudes by extending the growing season, but diminished greening in the tropics, where temperatures were already optimal.

Greater global green cover has observable feedbacks on climate and the carbon cycle. In addition to offsetting 28% of anthropogenic emissions since 1980, vegetation affects hydrological cycles and air-surface temperatures. Since the 1980s, increased global evapotranspiration (ET) is mainly attributable to increased global greening. Higher transpiration rates from vegetation can reduce or enhance groundwater storage locally, depending on how the atmospheric moisture generated through evapotranspiration is recycled into rain and where that rain falls. In the world’s great rainforests, vegetation preserves groundwater.

The enhanced precipitation over transpiring regions is particularly evident in moist forests like the Amazon or Congo, which are ‘closed’ atmospheric systems where 80% of the rainfall originates from upwind ET. Such an efficient atmospheric water recycling mitigates water loss from the soil, sustains inland vegetation and maintains mesic^[7] and humid ecosystems [Piao 2019: 9].

Vegetation affects land-surface temperature by way of ET (cooling effect) and albedo (warming or cooling effect, depending on how dark or light the surface is). While the relative strength of ET versus albedo varies by latitude, the net global effect of increasing vegetation cover is one of cooling the land surface.

Historical deforestation locally increased the intensity of hot days in northern mid-latitudes, Lejeune 2018

Deforestation has contributed to warming in the northern mid-latitudes of North America and Eurasia not only through a large contribution to global CO2 emissions, but also through biogeophysical effects. The latter refers to land-surface effects such as albedo and evapotranspiration, which vary according to the type of land cover. This study uses models to demonstrate that deforestation in the northern mid-latitudes has increased the intensity of hot days by about a third since pre-industrial times. Factoring in deforestation’s contribution to greenhouse gas emissions further increases deforestation’s heating effect.

Our best estimate suggests that the present-day contribution of deforestation to the TXx [yearly maximum temperature, or “hot days”] increase over this region still equals at least 50% once the warming entailed by the LCC [land cover change]-induced carbon emissions is considered [LeJeune 2018: 4].

“Extensive deforestation took place early in the industrial period over the northern mid-latitudes,” and then slowed down in the 20th Century [LeJeune 2018: 4]. By 1920, modeled increases of temperature “through biogeophysical effects had already reached 0.3°C (~75% of their present-day values) over the most deforested areas of North America and Eurasia. On average before 1920, local deforestation was responsible for most of the TXx [yearly maximum temperature] warming over these regions” [LeJeune 2018: 4]. Warming caused by greenhouse gases became more important during the 20th Century, “leading to a total warming of 1.3°C over North America and 1°C over Eurasia by the present-day” [LeJeune 2018: 4].

Expansion of oil palm and other cash crops causes an increase of the land surface temperature in the Jambi province in Indonesia, Sabajo 2017

Turning lemons into lemonade, Sabajo et al. have used the great expansion of oil palm plantations and other crops in Indonesia to examine how such land-use change affects land surface temperature (LST). The authors observed a warming trend in the Jambi province of Sumatra of 1.05℃ and 1.56℃ in the morning and afternoon, respectively, between 2000 and 2015. The average morning (10:30 am) temperature increased by 0.07℃ per year; the midday afternoon (1:30 pm) temperature increased by 0.13℃ per year.

During roughly the same period (2000-2010), forest area decreased in Jambi by 17%, while oil palm and rubber plantations greatly expanded. Given that LST within the province’s remaining forests increased only .04C per year at 10:30 am, which the authors attribute mainly to global warming, they concluded that the overall higher province-wide daytime temperature increase was caused by the observed land cover change.

The team also compared temperatures between different land uses: forest, oil palm and rubber plantations, urban areas, and bare land. Despite having a higher albedo (reflectivity) than the forest areas, all converted (non-forest) lands were nonetheless warmer than forests, “suggesting that the albedo was not the dominant variable explaining the LST” [Sabajo 2017: 4629]. Evapotranspiration (ET) played a greater role. Non-vegetated surfaces (urban and bare) were the warmest.

The authors conclude: “The warming effect after forest conversion results from the reduced evaporative cooling, which was identified as the main determinant of regulating the surface temperature” [Sabajo 2017: 4631].

The impact of anthropogenic land use and land cover change on regional climate extremes, Findell et al. 2017

This paper analyzes how land use and land cover change (LULCC) affects temperature and humidity. The authors examined the differential effects of forest versus deforested land on temperature and humidity by comparing different land-cover models. One model simulated the total potential vegetation (“PotVeg”) that would cover Earth in the absence of human interference, while the other was based on historical data of land use changes that occurred over a recent five-decade period (“AllHist”).

They found that deforested lands in mid-latitudes (North America, Eurasia) in the AllHist model are warmer and drier compared to the same lands covered in forest in the PotVeg model. Specifically, “conversion of mid-latitude natural forests to cropland and pastures is accompanied by an increase in the occurrence of hot-dry summers from once-in-a-decade to every 2–3 years” [Findell 2017: 1]. “Based on these simulations, the conversion of forests to cropland is coincident with much of the upper central US and central Europe experiencing extreme hot, dry summers” [Findell 2017: 6].

Local temperature response to land cover and management change driven by non-radiative processes, Bright et al. 2017

Local temperatures are affected not only by global climatic factors, but also by radiative (albedo) and non-radiative (evapotranspiration and convection) mechanisms related to local vegetation cover. Through evapotranspiration, solar energy is converted to latent heat and released from the planet’s surface, while convection refers to the turbulent mixing of air that dissipates sensible heat. The authors state that while albedo (reflectivity of land surface, which is often lower on forested land) is increasingly accounted for alongside greenhouse gases in climate models, the non-radiative mechanisms are not. However, the evapotranspiration and convection facilitated by vegetation have an important cooling effect and should therefore be included in models to avoid the risk of “promoting land sector policies that may be counter to the aims of mitigation or adaptation” [Bright 2017: 296].

The authors demonstrate that “non-radiative mechanisms dominate the local response in most regions for eight of nine common LCMC perturbations” [Bright 2017: 296]. Land cover and land management changes (LCMC) considered in the study include converting cropland or grassland to deciduous or evergreen forests. The authors found that gains in forest cover increased annual cooling in all but the northernmost latitudes, where the lower albedo of forests compared to grasslands had a warming effect that was stronger than the cooling effect of non-radiative mechanisms. In many regions, including much of Europe, the US, and the tropics, non-radiative cooling dominated albedo effects. “Over annual timescales, forest cover gains result in net cooling for many of the densely populated regions of the planet” [Bright 2017: 298].

Bright et al. conclude that “benchmarking the locally driven LCMC effect to that driven by global forcers (such as CO2) can provide an additional perspective by which to support the valuation of vegetated ecosystems and the local climate regulation services that they provide” [Bright 2017: 301].

Trees, forests and water: Cool insights for a hot world, Ellison et al. 2017

This article (also highlighted in Compendium v2n1) reviews research on the benefits of tree cover in relation to water and energy cycles.

Forests help produce rain. Vegetation releases water vapor through transpiration, increasing atmospheric moisture that is then transported by wind. In fact, “over most of the tropics, air that passes over forests for ten days typically produces at least twice as much rain as air that passes over sparse vegetation” [Ellison 2017: 53]. Forests also release biological particles, such as spores, bacteria and pollen into the atmosphere. Water condenses around these particles, forming raindrops.

In addition to the atmospheric moisture produced by forests that is transported by prevailing winds to generate downwind rain, forests also help transport moisture from the coasts to the interior of continents. According to the biotic pump theory [Makarieva & Gorshkov 2007], evapotranspiration over coastal forests creates low pressure zones that draw in atmospheric moisture from the ocean. This oceanic moisture eventually comes down as rain over land. Deforestation of coastal forests thus reduces this influx of moisture to land, while deforestation anywhere can decrease the reliability of rainfall downwind.

Through shading and evapotranspiration, forests cool the Earth’s surface in tropical and temperate climates. Due to a lower albedo compared to other land cover types at high latitudes, boreal forests potentially contribute to local warming. However, forests also increase cloud cover and thus albedo, higher in the atmosphere. In the absence of vegetation, such as in cities, solar energy remains in the environment in the form of heat, rather than driving evapotranspiration.

Using the sun’s energy, individual trees can transpire hundreds of liters of water per day. This represents a cooling power equivalent to 70 kWh for every 100 L of water transpired (enough to power two average household central air-conditioning units per day) [Ellison 2017: 54].

High-elevation forests have a unique potential to intercept fog and cloud droplets, which boosts tree growth, evapotranspiration, groundwater infiltration, and ultimately contributes up to 75% of catchment runoff. Tree cover can improve water infiltration due to increased organic matter to hold water and the presence of tree roots, which loosen and shade the soil and channel water into the ground. In areas where infiltration rates are greater than transpiration rates, the presence of trees increases groundwater recharge.

All of the aforementioned mechanisms distribute water naturally, hence reducing floods.

Earth is heating up: “Global surface temperature was 1.09°C higher in 2011– 2020 than 1850–1900,” according to the Intergovernmental Panel on Climate Change (IPCC)’s 6th Assessment Report.^[3] Yet the mercury is not rising uniformly around the world – the Arctic is warming faster than are the lower latitudes, and temperatures over land are higher than over the ocean. Local temperatures everywhere are also affected by the type of land cover, with paved areas being hotter than vegetated land.

In Phoenix, Arizona, the temperature topped 110°F during the summer of 2020 – not just once, but for 53 days.^[4] In the same year, Los Angeles experienced its hottest day ever: 122°F. Paris’ hottest day record was broken in 2019, and Buenos Aires’ second and third hottest days ever were in January 2022 (its hottest was in 1957). While climate change is to blame for the world’s increasing frequency of heatwaves, cities additionally experience the “urban heat island” (UHI) effect, which can add as much as 20°F compared to their rural surroundings.^[5]

To deal with heatwaves, the city of Phoenix established a new team to manage the public health effects of heat and find ways to reduce it. Part of the plan is doubling the city tree canopy to 25% coverage. Urban heat islands are created by a low ratio of vegetated surfaces relative to concrete, asphalt, and other unvegetated and impervious surfaces, which absorb sunlight as heat and radiate it back out. By contrast, plants use the sun’s energy to transpire water into the atmosphere, a process that cools rather than heats the surrounding air.

Many cities are planting trees to dampen scorching summer heat as public awareness of the relationship between vegetation and the UHI grows. Expanding public green space and tree canopy is a practical way for localities to adapt to the juggernaut of a changing climate because increased vegetation cover not only lowers local temperatures, but can also reduce the severity of flooding and drought by improving rainwater infiltration.

Just as increasing tree cover reduces temperatures in cities, reforestation has a cooling effect at regional and even global scales. The studies profiled below explore a variety of aspects of the relationship between vegetation types, especially forests, and temperature. All produced in the past ten years, these studies show that reforestation (establishing forest on previously forested land) and afforestation (foresting land that was not previously in forest) can lower temperatures, and that deforestation, conversely, has raised temperatures across vast areas.

For example, historical conversion of natural forests in the midlatitudes to cropland and pasture has more than tripled the occurrence of hot-dry summers in those areas [Findell 2017]. Clearing forests heats the land not only by releasing CO2, which contributes to the greenhouse effect, but also changes the albedo (reflectivity), surface roughness, and evapotranspiration (ET) rates of land surfaces. Land-cover changes affect the temperature through biophysical exchanges of water and energy between the land and the atmosphere.

By 1920, the biophysical effects of deforestation were the main cause of increasing temperatures in deforested parts of North America and Eurasia [LeJeune 2018]. Over the 20th Century, greenhouse gases started to play a bigger role in regional heating. Today, the combined effects of the biophysical changes and greenhouse gas emissions wrought by deforestation account for an estimated half of the temperature rise since pre-industrial times in deforested areas of the midlatitudes [LeJeune 2018].

Interestingly, the presence of forests affects surface temperatures differently depending on latitude, although globally, vegetation gain has a net cooling effect [Piao 2020]. In boreal regions, forestation is associated with a warming effect due to a lower albedo of forests compared to non-forest land. By contrast, deforestation warms the mid-latitudes and tropics – in spite of the lower surface albedo of forested land. The cooling effect of ET drives temperature regulation in the tropics, while both ET and cloud formation from forests cool the mid-latitudes.

The Jambi province of tropical Sumatra, Indonesia, warmed an average of 1.05°C between 2000 and 2015, a period that coincided with rapid deforestation [Sabajo 2017]. The forests that remained in Jambi during this period also warmed slightly, but much less so than the region as a whole. The authors suggest that the smaller temperature rise inside forests reflects global warming, while the greater regional warming is due to the combined effect of global warming and the biophysical effects of local deforestation.

Vegetation cover both affects and is affected by climate change. Piao et al. [2019] documented an increase in global greening since 1980, which they attribute in part to growth-inducing impacts of climate change. Warmer temperatures and the fertilization effects of higher CO2 concentration, but also nitrogen deposition and direct afforestation efforts, all have increased vegetation cover, though not evenly across the planet, and not necessarily where it would have the greatest cooling effect. For example, warmer temperatures increase vegetation in the northern latitudes by lengthening the growing season, but reduce vegetation in the tropics where historical temperatures are already optimal for plant growth.

In addition to modulating temperatures, forests also influence precipitation. Through ET – the very same mechanism responsible for cooling the land – forests recycle water back into the atmosphere. Globally, at least 40% of the rain that falls on land comes from evapotranspiration on land, while as much as 70% of rain originating over the Amazon is ET-fed [Ellison 2017]. In Europe, converting a limited proportion (not expected to impinge on food security) of agricultural lands would increase rainfall on the continent by an estimated 7.6%, an important augmentation given the growing frequency of drought there [Baker 2021].

The role that forests and other natural vegetation types play in mitigating global warming and softening the blow of climate extremes has not always been universally clear, but this is changing. The studies highlighted below, which illustrate the heat- and drought-limiting capacity of forests, are among a growing body of work pointing to the importance–and power–of natural climate solutions.

Summaries of articles showing the cooling effect of vegetation

Cloud cooling effects of afforestation and reforestation at midlatitudes, Cerasoli, Jin & Porporato 2021

Reforestation and afforestation (R&A) are well-established climate mitigation strategies in the wet tropics due to high carbon sequestration rates of forests/trees. However, at high latitudes (boreal regions), the low albedo of trees–compared to snow and other lighter land surfaces–leads to the absorption of energy, thus creating a warming effect that has a greater impact on temperature than the carbon capture accomplished by the limited vegetation productivity in boreal regions. This study explores the balance between albedo and carbon sequestration of forests at mid-latitudes, which has been less clear.

The authors found that forested areas have greater cloud cover than other types of land cover at midlatitudes, resulting in a higher albedo at the top of the atmosphere–where the clouds are–and leading to greater cooling. Specifically, they found “an association of forested lands with increased cloudiness… As a result, forests reflect extra solar radiation and thus reduce the radiative impacts of the lower surface albedo. This in turn implies a cooling effect of R&A at midlatitudes” [Cerasoli 2021: 1-2]. The increase in cloudiness is due to earlier afternoon cloud formation over forests compared to other vegetation types in wet regions.

Our results provide substantial evidence of remarkable benefits of R&A [reforestation and afforestation] around the 30° to 45° latitudinal range, due to the combined benefits of biomass gain and promotion of cloud formation over forests [Cerasoli 2021: 4].

The duality of reforestation impacts on surface and air temperature, Novick & Katul 2020

While reforestation has been widely heralded as a means of sequestering carbon into the soil, there is growing evidence that it also serves to directly cool the land surface. But forests’ impacts on air temperature (measured over forests rather than within them) have been difficult to assess because of the confounding impacts of forest canopies on wind and temperature profiles near the surface. This study was implemented to create a new method for assessing to what degree forests also cool the air.

Most studies measure surface temperature, which “represents the aggregated temperature of solid canopy and soil elements,” and is measured at a midway point between the ground and the top of the canopy. Air temperature, on the other hand, is measured above the vegetation canopy (whether grasslands or forest). The study site, located in the Piedmont region near Durham North Carolina, consists of an old-field grassland, a pine forest, and an unevenly aged oak hickory forest, all within close proximity to each other. The study assessed temperatures at various heights in and above the grasslands and the two forests.

The authors found that surface temperatures are much lower in forests than in grassland; this difference often exceeds 5°C at midday during the growing season. Furthermore, the air is cooler over forests than over grasslands, though to a lesser degree than the surface temperature difference. The annual average air temperature difference of forests compared to grassland is 0.5°C to 1°C, while the difference reaches 2°C to 3°C during daytime growing season periods.

“Making the connection between land cover, surface temperature, and air temperature is becoming necessary for obtaining a complete picture of the climate mitigation and adaptation potential of managed land cover changes, including reforestation,” the authors conclude. “This energy balance perspective on the climate mitigation and adaptation potential of reforestation is especially relevant right now” given a recent global surge of interest in reforestation to sequester carbon [Novik & Katul 2020: 13].

Characteristics, drivers and feedbacks of global greening, Piao et al. 2019

The amount of Earth’s green cover (measured as Leaf Area Index^[6]) has increased globally since 1980, especially in northern latitudes, where growing seasons have lengthened. This is due mainly to increasing CO2 concentration, but also to warmer temperatures and changing precipitation patterns, nitrogen deposition, and land-use change (such as afforestation in China). Higher ambient CO2 can stimulate photosynthesis and reduce water loss, but the extent of the CO2 fertilization depends on the availability of other key nutrients (nitrogen and phosphorus) and water. Warmer temperatures due to climate change have increased greening in northern latitudes by extending the growing season, but diminished greening in the tropics, where temperatures were already optimal.

Greater global green cover has observable feedbacks on climate and the carbon cycle. In addition to offsetting 28% of anthropogenic emissions since 1980, vegetation affects hydrological cycles and air-surface temperatures. Since the 1980s, increased global evapotranspiration (ET) is mainly attributable to increased global greening. Higher transpiration rates from vegetation can reduce or enhance groundwater storage locally, depending on how the atmospheric moisture generated through evapotranspiration is recycled into rain and where that rain falls. In the world’s great rainforests, vegetation preserves groundwater.

The enhanced precipitation over transpiring regions is particularly evident in moist forests like the Amazon or Congo, which are ‘closed’ atmospheric systems where 80% of the rainfall originates from upwind ET. Such an efficient atmospheric water recycling mitigates water loss from the soil, sustains inland vegetation and maintains mesic^[7] and humid ecosystems [Piao 2019: 9].

Vegetation affects land-surface temperature by way of ET (cooling effect) and albedo (warming or cooling effect, depending on how dark or light the surface is). While the relative strength of ET versus albedo varies by latitude, the net global effect of increasing vegetation cover is one of cooling the land surface.

Historical deforestation locally increased the intensity of hot days in northern mid-latitudes, Lejeune 2018

Deforestation has contributed to warming in the northern mid-latitudes of North America and Eurasia not only through a large contribution to global CO2 emissions, but also through biogeophysical effects. The latter refers to land-surface effects such as albedo and evapotranspiration, which vary according to the type of land cover. This study uses models to demonstrate that deforestation in the northern mid-latitudes has increased the intensity of hot days by about a third since pre-industrial times. Factoring in deforestation’s contribution to greenhouse gas emissions further increases deforestation’s heating effect.

Our best estimate suggests that the present-day contribution of deforestation to the TXx [yearly maximum temperature, or “hot days”] increase over this region still equals at least 50% once the warming entailed by the LCC [land cover change]-induced carbon emissions is considered [LeJeune 2018: 4].

“Extensive deforestation took place early in the industrial period over the northern mid-latitudes,” and then slowed down in the 20th Century [LeJeune 2018: 4]. By 1920, modeled increases of temperature “through biogeophysical effects had already reached 0.3°C (~75% of their present-day values) over the most deforested areas of North America and Eurasia. On average before 1920, local deforestation was responsible for most of the TXx [yearly maximum temperature] warming over these regions” [LeJeune 2018: 4]. Warming caused by greenhouse gases became more important during the 20th Century, “leading to a total warming of 1.3°C over North America and 1°C over Eurasia by the present-day” [LeJeune 2018: 4].

Expansion of oil palm and other cash crops causes an increase of the land surface temperature in the Jambi province in Indonesia, Sabajo 2017

Turning lemons into lemonade, Sabajo et al. have used the great expansion of oil palm plantations and other crops in Indonesia to examine how such land-use change affects land surface temperature (LST). The authors observed a warming trend in the Jambi province of Sumatra of 1.05℃ and 1.56℃ in the morning and afternoon, respectively, between 2000 and 2015. The average morning (10:30 am) temperature increased by 0.07℃ per year; the midday afternoon (1:30 pm) temperature increased by 0.13℃ per year.

During roughly the same period (2000-2010), forest area decreased in Jambi by 17%, while oil palm and rubber plantations greatly expanded. Given that LST within the province’s remaining forests increased only .04C per year at 10:30 am, which the authors attribute mainly to global warming, they concluded that the overall higher province-wide daytime temperature increase was caused by the observed land cover change.

The team also compared temperatures between different land uses: forest, oil palm and rubber plantations, urban areas, and bare land. Despite having a higher albedo (reflectivity) than the forest areas, all converted (non-forest) lands were nonetheless warmer than forests, “suggesting that the albedo was not the dominant variable explaining the LST” [Sabajo 2017: 4629]. Evapotranspiration (ET) played a greater role. Non-vegetated surfaces (urban and bare) were the warmest.

The authors conclude: “The warming effect after forest conversion results from the reduced evaporative cooling, which was identified as the main determinant of regulating the surface temperature” [Sabajo 2017: 4631].

The impact of anthropogenic land use and land cover change on regional climate extremes, Findell et al. 2017

This paper analyzes how land use and land cover change (LULCC) affects temperature and humidity. The authors examined the differential effects of forest versus deforested land on temperature and humidity by comparing different land-cover models. One model simulated the total potential vegetation (“PotVeg”) that would cover Earth in the absence of human interference, while the other was based on historical data of land use changes that occurred over a recent five-decade period (“AllHist”).

They found that deforested lands in mid-latitudes (North America, Eurasia) in the AllHist model are warmer and drier compared to the same lands covered in forest in the PotVeg model. Specifically, “conversion of mid-latitude natural forests to cropland and pastures is accompanied by an increase in the occurrence of hot-dry summers from once-in-a-decade to every 2–3 years” [Findell 2017: 1]. “Based on these simulations, the conversion of forests to cropland is coincident with much of the upper central US and central Europe experiencing extreme hot, dry summers” [Findell 2017: 6].

Local temperature response to land cover and management change driven by non-radiative processes, Bright et al. 2017

Local temperatures are affected not only by global climatic factors, but also by radiative (albedo) and non-radiative (evapotranspiration and convection) mechanisms related to local vegetation cover. Through evapotranspiration, solar energy is converted to latent heat and released from the planet’s surface, while convection refers to the turbulent mixing of air that dissipates sensible heat. The authors state that while albedo (reflectivity of land surface, which is often lower on forested land) is increasingly accounted for alongside greenhouse gases in climate models, the non-radiative mechanisms are not. However, the evapotranspiration and convection facilitated by vegetation have an important cooling effect and should therefore be included in models to avoid the risk of “promoting land sector policies that may be counter to the aims of mitigation or adaptation” [Bright 2017: 296].

The authors demonstrate that “non-radiative mechanisms dominate the local response in most regions for eight of nine common LCMC perturbations” [Bright 2017: 296]. Land cover and land management changes (LCMC) considered in the study include converting cropland or grassland to deciduous or evergreen forests. The authors found that gains in forest cover increased annual cooling in all but the northernmost latitudes, where the lower albedo of forests compared to grasslands had a warming effect that was stronger than the cooling effect of non-radiative mechanisms. In many regions, including much of Europe, the US, and the tropics, non-radiative cooling dominated albedo effects. “Over annual timescales, forest cover gains result in net cooling for many of the densely populated regions of the planet” [Bright 2017: 298].

Bright et al. conclude that “benchmarking the locally driven LCMC effect to that driven by global forcers (such as CO2) can provide an additional perspective by which to support the valuation of vegetated ecosystems and the local climate regulation services that they provide” [Bright 2017: 301].

Trees, forests and water: Cool insights for a hot world, Ellison et al. 2017

This article (also highlighted in Compendium v2n1) reviews research on the benefits of tree cover in relation to water and energy cycles.

Forests help produce rain. Vegetation releases water vapor through transpiration, increasing atmospheric moisture that is then transported by wind. In fact, “over most of the tropics, air that passes over forests for ten days typically produces at least twice as much rain as air that passes over sparse vegetation” [Ellison 2017: 53]. Forests also release biological particles, such as spores, bacteria and pollen into the atmosphere. Water condenses around these particles, forming raindrops.

In addition to the atmospheric moisture produced by forests that is transported by prevailing winds to generate downwind rain, forests also help transport moisture from the coasts to the interior of continents. According to the biotic pump theory [Makarieva & Gorshkov 2007], evapotranspiration over coastal forests creates low pressure zones that draw in atmospheric moisture from the ocean. This oceanic moisture eventually comes down as rain over land. Deforestation of coastal forests thus reduces this influx of moisture to land, while deforestation anywhere can decrease the reliability of rainfall downwind.

Through shading and evapotranspiration, forests cool the Earth’s surface in tropical and temperate climates. Due to a lower albedo compared to other land cover types at high latitudes, boreal forests potentially contribute to local warming. However, forests also increase cloud cover and thus albedo, higher in the atmosphere. In the absence of vegetation, such as in cities, solar energy remains in the environment in the form of heat, rather than driving evapotranspiration.

Using the sun’s energy, individual trees can transpire hundreds of liters of water per day. This represents a cooling power equivalent to 70 kWh for every 100 L of water transpired (enough to power two average household central air-conditioning units per day) [Ellison 2017: 54].

High-elevation forests have a unique potential to intercept fog and cloud droplets, which boosts tree growth, evapotranspiration, groundwater infiltration, and ultimately contributes up to 75% of catchment runoff. Tree cover can improve water infiltration due to increased organic matter to hold water and the presence of tree roots, which loosen and shade the soil and channel water into the ground. In areas where infiltration rates are greater than transpiration rates, the presence of trees increases groundwater recharge.

All of the aforementioned mechanisms distribute water naturally, hence reducing floods.

Jeannette Christine Armstrong is a Canadian author, educator, artist, and activist, who wrote this article about the traditional decision-making process in Okanagan, called “enowkinwixw,” which demonstrates a great practice of biophilia.

Okanagan, the Penticton Indian reservation in Canada where the author was born and raised, has a very fragile ecosystem. However, the author discovered that this community treats the land differently compared to other communities. They treasure natural resources and believe that the land is the people. They bear in mind that everything they have came from the land and that their every decision has a possibility to destroy the land. Therefore, they not only pay attention to the relationship among human beings but also how human relationships affect the land.

When the author was searching to understand how the community developed this form of interaction, the traditional decision-making process enowkinwixw caught her attention. The model is accomplished with four criteria:

This word demands four things from us: 1) that we solicit the most opposing views; 2) that we seek to understand those views using non-adversarial protocols; 3) that we each agree to be willing to make adjustments in our own interests to accommodate diverse needs expressed; and 4) that we collaboratively commit to support the outcomes [Armstrong 2020: 166].

Through this process, the minority voice is valued as it could point out the most important things that have been ignored. It is how the Okanagan could bring the minority into balance with the majority, minimize the conflicts and bring everyone to work together.

If we begin to think about the minority, about why there is a minority, why there is poverty, then we should be able to find creative ways to meet the needs of the minorities [Armstrong 2020 : 167].

The author believes that this is why the Okanagan community could add preservation of land into the decision-making process. By adopting enowkinwixw, the community respects every opinion from every perspective. Therefore, they train people to speak for different components that make up their existence, such as the children, the elders, and the water; while the author herself was appointed as a land speaker, who thinks and speaks for the land. In this way, the people realize that material things are not as important as the power of the land, which is what sustains them.

This mindset is meant to help the world achieve a harmonic relationship between people and nature.

A book review by Rachel West

As I read the first chapter, Wilson brought me far into the forests of the Amazon Basin to encounter canopy-dwelling birds and frogs found nowhere else on Earth; he showed me the life cycle of a tiny moth so specialized that the adult lives only in the fur of the 3-toed sloth, and held up fistfuls of forest soil teeming with tiny life to demonstrate that “the woods were a biological maelstrom of which only the surface could be scanned by the naked eye.”

With his astonishing eye for detail and his fluid prose, he fascinated me, he drew me in, he fed my curiosity…and then he reminded me: “Eliminate just one kind of tree out of hundreds in such a forest, and some of its pollinators, leaf eaters, and wood borers will disappear with it, then various of their parasites and key predators, and perhaps a species of bat or bird that depends on its fruit… and when will the reverberations end?”  

Throughout this book, Wilson brought me close to the beauty of living systems across the world. He taught me enough about them to make me curious, and then to make me care; and then, when he showed me how easily that entire system could be disrupted, he had my undivided attention. This kind of understanding and connection, Wilson argues—this human bond with other species—is an essential ingredient in motivating us to change our behaviors in order to slow the rate at which “the wildernesses of the world [are shriveling] into timber leases and threatened nature reserves.”

One of the challenges with building these connections and then acting upon them, Wilson suggests, is that we are programmed to operate in physiological, not ecological, time; that our minds “travel back and forth across hours, days, or at most a hundred years. The forests may all be cut, radiation slowly rise, and winters grow steadily colder, but if the effects are unlikely to become decisive for a few generations, very few people will be stirred to revolt.” But in recent times, our impact on ecosystems has been compressing “ecological time” to align with “physiological time,” and the results are becoming visible in the span of single generations; the massive Florida manatee die-off due to the destruction of their seagrass pastures is but one starkly visible example of the reverberation felt by the loss of a single species from an ecosystem.

In the chapter “The Conservation Ethic”, near the end of the book, Wilson explores the relationship between the human drive to perpetually expand—and the related desire for personal freedom, at least in Western cultures—and the necessity for conscious stewardship of the environment to ensure our ultimate survival—not only our physical survival, but our spiritual survival. He writes “The only way to make a conservation ethic work is to ground it in ultimately selfish reasoning.”  In other words, it is likely that wild species and places will be best understood and protected with respect to their perceived value, such as the vast array of plant compounds that have shown promise as anti-cancer compounds, or, as has been increasingly recognized in recent years, for the ability of wild places to improve the emotional and spiritual well-being of the people who spend time there.

This book is even more relevant now than it was when it was released in 1984, and thus has the potential to reach a broader audience today. More people may be ready to hear some of the truths held in this book because now, more than ever before, the human race is seeing, and feeling, the long-term effects of the way we have treated the planet.

(La Symbiose : Structures et Fonctions, Rôle Écologique et Évolutif)

Book review by Ehsan Kayal

What is symbiosis? How is it defined? What does it involve? And how did it come to be? These are some of the questions French Biologist Marc-André Sélosse explores in this book.

It is not simple to define “symbiosis,” which differs between the English and French languages. Sélosse focuses on the narrower French definition, which involves “long-term coexistence of two different organisms throughout their life with reciprocal benefits” [Sélosse 2000: 22]. In English, the term “symbiosis” refers not only to mutualism (reciprocal benefits), but also to parasitism or commensalism (one partner benefit without impacting the other partner). One important aspect of the study of mutualistic symbiosis is exploring reciprocal physiological exchanges that happen between symbionts (organisms involved in symbiosis). Such exchanges are facilitated by morphological changes in one, the other or both partners.

Sélosse offers readers a glimpse of the breadth of symbiotic relationships found in nature. For example, there are bacteria living inside worms around deep-sea vents in the ocean that use chemical energy seeping from the earth to create organic compounds that nourish their worm hosts. The author also highlights the case of lichen, which appears to be a single species, but is actually formed by a symbiosis between fungi and algae. Sélosse focuses especially on symbiosis involving mycorrhiza, which are the “symbiotic organs formed by a root and a fungus” [Sélosse 2000: 140], and on root nodules, the “symbiotic organs of legumes, often around roots, containing bacteria of the Rhizobiaceae family responsible for fixing nitrogen” [Sélosse 2000: 140].

Leguminous plant hosts provide their Rhizobia symbionts with carbon, while protecting these bacteria from harmful oxygen, in exchange for nitrogen. The efficiency of these symbiosis is such that the “rhizobiaceae-containing root nodules fix as much atmospheric nitrogen per year as the fertilizer industry” [Sélosse 2000: 54]. Similarly, plants with mycorrhizal associations supply their symbionts with carbon in exchange for water, phosphate and other nutrients furnished by the fungi. Studies have linked “an increasing diversity of mycorrhiza” with “increasing diversity of plants” [Sélosse 2000: 67].

Symbiosis can short-circuit the mineralization-immobilization cycle (conversion of inorganic compounds to organic compounds by micro-organisms or plants) by bringing together partners that thrive on each other’s by-products. This results in a “concentration of resources” [Sélosse 2000: 49] that allows organisms to conquer new ecological niches as exemplified by lichen and corals, but also playing a key role in the evolution of the soil that promotes vegetation successions [Sélosse 2000: 60]. For example, lichen is the first to colonize bare rock, where it produces citric acid and holds water, slowing altering the rock in the early stage of soil creation. Rhizobial symbioses then pitch in by fixing nitrogen, otherwise absent in a rocky substrate.

The book also flips some of the common understandings of organismal biology. For instance, many herbivores lack digestive enzymes to break down plant material. Rather, they feed on the population of microorganisms of their rumen, or the “pocket situated upstream of the stomach in ruminants that harbors a symbiotic microflora” [Sélosse 2000: 141]). The rumen is a large organ, whose volume can represent “8 to 15% of total body weight” [Sélosse 2000: 32]. That makes those microorganisms (protists, fungi and bacteria) the “true” herbivores, while the ruminants are secondary consumers.

The older traces of symbiosis predate the origin of the eukaryotic cell (cell with a nucleus enclosed within a nuclear envelope), where the mitochondrion (the energy-producing organelle of the cell) are descendants of a likely unique endosymbiotic event occurring some two billion years ago. In that event, an anaerobic archaean (third kingdom of life composed of unicellular organisms lacking a nucleus; the other two kingdoms are eukaryotes and bacteria) captured a facultative aerobic type of bacteria, which became mitochondria. Similarly, the acquisition by some eukaryotic cells of a chloroplast originating from cyanobacteria gave way to photosynthetic plants.

In some sense, “no organism lives alone, and each carries a symbiotic cortege without which one cannot understand neither the physiology nor the ecological success of the organism” [Sélosse 2000: 134].

Symbiosis: Structure and Functions, Ecological and Evolutionary Role, Sélosse 2000

(La Symbiose : Structures et Fonctions, Rôle Écologique et Évolutif)

Book review by Ehsan Kayal

What is symbiosis? How is it defined? What does it involve? And how did it come to be? These are some of the questions French Biologist Marc-André Sélosse explores in this book.

It is not simple to define “symbiosis,” which differs between the English and French languages. Sélosse focuses on the narrower French definition, which involves “long-term coexistence of two different organisms throughout their life with reciprocal benefits” [Sélosse 2000: 22]. In English, the term “symbiosis” refers not only to mutualism (reciprocal benefits), but also to parasitism or commensalism (one partner benefit without impacting the other partner). One important aspect of the study of mutualistic symbiosis is exploring reciprocal physiological exchanges that happen between symbionts (organisms involved in symbiosis). Such exchanges are facilitated by morphological changes in one, the other or both partners.

Sélosse offers readers a glimpse of the breadth of symbiotic relationships found in nature. For example, there are bacteria living inside worms around deep-sea vents in the ocean that use chemical energy seeping from the earth to create organic compounds that nourish their worm hosts. The author also highlights the case of lichen, which appears to be a single species, but is actually formed by a symbiosis between fungi and algae. Sélosse focuses especially on symbiosis involving mycorrhiza, which are the “symbiotic organs formed by a root and a fungus” [Sélosse 2000: 140], and on root nodules, the “symbiotic organs of legumes, often around roots, containing bacteria of the Rhizobiaceae family responsible for fixing nitrogen” [Sélosse 2000: 140].

Leguminous plant hosts provide their Rhizobia symbionts with carbon, while protecting these bacteria from harmful oxygen, in exchange for nitrogen. The efficiency of these symbiosis is such that the “rhizobiaceae-containing root nodules fix as much atmospheric nitrogen per year as the fertilizer industry” [Sélosse 2000: 54]. Similarly, plants with mycorrhizal associations supply their symbionts with carbon in exchange for water, phosphate and other nutrients furnished by the fungi. Studies have linked “an increasing diversity of mycorrhiza” with “increasing diversity of plants” [Sélosse 2000: 67].

Symbiosis can short-circuit the mineralization-immobilization cycle (conversion of inorganic compounds to organic compounds by micro-organisms or plants) by bringing together partners that thrive on each other’s by-products. This results in a “concentration of resources” [Sélosse 2000: 49] that allows organisms to conquer new ecological niches as exemplified by lichen and corals, but also playing a key role in the evolution of the soil that promotes vegetation successions [Sélosse 2000: 60]. For example, lichen is the first to colonize bare rock, where it produces citric acid and holds water, slowing altering the rock in the early stage of soil creation. Rhizobial symbioses then pitch in by fixing nitrogen, otherwise absent in a rocky substrate.

The book also flips some of the common understandings of organismal biology. For instance, many herbivores lack digestive enzymes to break down plant material. Rather, they feed on the population of microorganisms of their rumen, or the “pocket situated upstream of the stomach in ruminants that harbors a symbiotic microflora” [Sélosse 2000: 141]). The rumen is a large organ, whose volume can represent “8 to 15% of total body weight” [Sélosse 2000: 32]. That makes those microorganisms (protists, fungi and bacteria) the “true” herbivores, while the ruminants are secondary consumers.

The older traces of symbiosis predate the origin of the eukaryotic cell (cell with a nucleus enclosed within a nuclear envelope), where the mitochondrion (the energy-producing organelle of the cell) are descendants of a likely unique endosymbiotic event occurring some two billion years ago. In that event, an anaerobic archaean (third kingdom of life composed of unicellular organisms lacking a nucleus; the other two kingdoms are eukaryotes and bacteria) captured a facultative aerobic type of bacteria, which became mitochondria. Similarly, the acquisition by some eukaryotic cells of a chloroplast originating from cyanobacteria gave way to photosynthetic plants.

In some sense, “no organism lives alone, and each carries a symbiotic cortege without which one cannot understand neither the physiology nor the ecological success of the organism” [Sélosse 2000: 134].

Biophilia: the human bond with other species, Wilson 1984

A book review by Rachel West

As I read the first chapter, Wilson brought me far into the forests of the Amazon Basin to encounter canopy-dwelling birds and frogs found nowhere else on Earth; he showed me the life cycle of a tiny moth so specialized that the adult lives only in the fur of the 3-toed sloth, and held up fistfuls of forest soil teeming with tiny life to demonstrate that “the woods were a biological maelstrom of which only the surface could be scanned by the naked eye.”

With his astonishing eye for detail and his fluid prose, he fascinated me, he drew me in, he fed my curiosity…and then he reminded me: “Eliminate just one kind of tree out of hundreds in such a forest, and some of its pollinators, leaf eaters, and wood borers will disappear with it, then various of their parasites and key predators, and perhaps a species of bat or bird that depends on its fruit… and when will the reverberations end?”  

Throughout this book, Wilson brought me close to the beauty of living systems across the world. He taught me enough about them to make me curious, and then to make me care; and then, when he showed me how easily that entire system could be disrupted, he had my undivided attention. This kind of understanding and connection, Wilson argues—this human bond with other species—is an essential ingredient in motivating us to change our behaviors in order to slow the rate at which “the wildernesses of the world [are shriveling] into timber leases and threatened nature reserves.”

One of the challenges with building these connections and then acting upon them, Wilson suggests, is that we are programmed to operate in physiological, not ecological, time; that our minds “travel back and forth across hours, days, or at most a hundred years. The forests may all be cut, radiation slowly rise, and winters grow steadily colder, but if the effects are unlikely to become decisive for a few generations, very few people will be stirred to revolt.” But in recent times, our impact on ecosystems has been compressing “ecological time” to align with “physiological time,” and the results are becoming visible in the span of single generations; the massive Florida manatee die-off due to the destruction of their seagrass pastures is but one starkly visible example of the reverberation felt by the loss of a single species from an ecosystem.

In the chapter “The Conservation Ethic”, near the end of the book, Wilson explores the relationship between the human drive to perpetually expand—and the related desire for personal freedom, at least in Western cultures—and the necessity for conscious stewardship of the environment to ensure our ultimate survival—not only our physical survival, but our spiritual survival. He writes “The only way to make a conservation ethic work is to ground it in ultimately selfish reasoning.”  In other words, it is likely that wild species and places will be best understood and protected with respect to their perceived value, such as the vast array of plant compounds that have shown promise as anti-cancer compounds, or, as has been increasingly recognized in recent years, for the ability of wild places to improve the emotional and spiritual well-being of the people who spend time there.

This book is even more relevant now than it was when it was released in 1984, and thus has the potential to reach a broader audience today. More people may be ready to hear some of the truths held in this book because now, more than ever before, the human race is seeing, and feeling, the long-term effects of the way we have treated the planet.

An Okanagan Worldview of Society, Armstrong 2020

Jeannette Christine Armstrong is a Canadian author, educator, artist, and activist, who wrote this article about the traditional decision-making process in Okanagan, called “enowkinwixw,” which demonstrates a great practice of biophilia.

Okanagan, the Penticton Indian reservation in Canada where the author was born and raised, has a very fragile ecosystem. However, the author discovered that this community treats the land differently compared to other communities. They treasure natural resources and believe that the land is the people. They bear in mind that everything they have came from the land and that their every decision has a possibility to destroy the land. Therefore, they not only pay attention to the relationship among human beings but also how human relationships affect the land.

When the author was searching to understand how the community developed this form of interaction, the traditional decision-making process enowkinwixw caught her attention. The model is accomplished with four criteria:

This word demands four things from us: 1) that we solicit the most opposing views; 2) that we seek to understand those views using non-adversarial protocols; 3) that we each agree to be willing to make adjustments in our own interests to accommodate diverse needs expressed; and 4) that we collaboratively commit to support the outcomes [Armstrong 2020: 166].

Through this process, the minority voice is valued as it could point out the most important things that have been ignored. It is how the Okanagan could bring the minority into balance with the majority, minimize the conflicts and bring everyone to work together.

If we begin to think about the minority, about why there is a minority, why there is poverty, then we should be able to find creative ways to meet the needs of the minorities [Armstrong 2020 : 167].

The author believes that this is why the Okanagan community could add preservation of land into the decision-making process. By adopting enowkinwixw, the community respects every opinion from every perspective. Therefore, they train people to speak for different components that make up their existence, such as the children, the elders, and the water; while the author herself was appointed as a land speaker, who thinks and speaks for the land. In this way, the people realize that material things are not as important as the power of the land, which is what sustains them.

This mindset is meant to help the world achieve a harmonic relationship between people and nature.

Anthropogenic environmental change and global dispersal of a wide variety of species outside their native ranges has expanded the range of “cosmopolitan,” non-native species and shrunk the range of regional and endemic species. “This replacement of specific native forms by generalist non-natives in space and time has mixed the taxonomic composition of once disparate biotas, an occurrence termed ‘biotic homogenization’” [Olden 2004: 18].

The authors explore the effect of this “global erosion of regional distinctiveness” [Olden 2004: 18] at three levels: Genetic homogenization reduces genetic variability within species or among populations of species, while taxonomic homogenization reduces distinctiveness among communities. Functional homogenization refers to a reduction of functional traits within an ecosystem. The identity of species making up a community, along with their respective functional traits, determines “ecosystem functions (such as nutrient retention or energy flow)” [Olden 2004: 20], so that narrowing species compositions risks diminishing ecosystem function.

A decrease in functional diversity might reduce overall community and ecosystem functioning, stability and resistance to environmental change by simply narrowing the available range of species-specific responses. Consider a severe drought that strongly affects a subset of species in a community that has (or lacks) a particular suite of functional traits. Historical communities, with much greater breadth in functional space, should exhibit higher resistance or resilience when compared with homogenized communities [Olden 2004: 20].

Genetic homogenization occurs when two distinct locally adapted populations of the same species interbreed. It also occurs when a single variety (such as captive fish bred in a central location) are released in many places to replenish dwindling native stocks. While such mixing has the potential to increase species diversity, this outcome is not assured.

Intraspecific hybridization can homogenize the unique characteristics of geographically distinct populations, as well as compromise the fitness of individuals by disrupting local adaptations [Olden 2004: 19].

This article emphasizes the importance of species interactions as drivers of ecosystem function.

The classic conservation approach is to set aside national parks or to target specific species for protection, based on their rarity or endangered status. However, these approaches can have trade-offs for non-target species, while also potentially failing to protect ecosystem function. The authors, therefore, suggest that species interactions based on their functional significance should be the main focus on conservation efforts.

We propose that a shift in focus from species to interaction networks is necessary to achieve pressing conservation management and restoration ecology goals of conserving biodiversity, ecosystem processes and ultimately landscape-scale delivery of ecosystem services [Harvey 2017: 371].

Species depend on many other species in their communities, either directly or indirectly. An example of indirect dependence is the Phengaris arion butterfly’s need for European rabbits. The butterfly uses ant nests made in the open areas supplied by rabbit grazing for development of its larvae. Thus, no rabbits means no ants, which means no Phengaris arion.

Focusing on species interactions is more meaningful even than measuring species richness (the number of different species), because interactions can disappear – even if both species are present – if either group’s abundance has significantly dropped. The authors offer the example of 59 regionally extinct lepidoptera (butterfly and moth) species of central Europe. Eight of these extinctions were associated with the loss of particular host plant species, which actually occurred after the lepidoptera went extinct.

Focusing on species interactions is more meaningful even than measuring species richness (the number of different species), because interactions can disappear – even if both species are present – if either group’s abundance has significantly dropped.

Thus, strong declines of host plants can have cascading extinction effects on higher trophic levels before the plants actually go extinct, illustrating that interactions can be lost before any actual decline in species richness (plants persisted at low abundance). This illustrates that preserving keystone interactions, rather than species, can be a proactive way to maintain ecosystem integrity in the face of global change instead of allocating resources to already endangered species [Harvey 2017: 372].

There is interdependence among species even between neighboring ecosystems. For example, a manta ray species in the Palmyra Atoll south of Hawaii depends on two species of native trees to maintain its ocean plankton diet. When these trees were replaced with cultivated coconut palms, marine-foraging birds no longer nested on that shore, depriving the coastal waters of the nitrogen runoff from their guano, which had been feeding the plankton population.

The authors recommend that “the main lever to restore or conserve ecological network structure and stability is the management of spatial configuration” [Harvey 2017: 377]. Reflecting on the Palmyra Atoll, for example, it’s clear that a marine conservation plan would be incomplete without considering the nutrient flow from the tree-bird interactions on land.

Bio4Climate has been studying the Miyawaki Method of reforestation over the past several months. This 50-year-old technique involves densely planting native forest species from shrub to canopy layer to create tiny, fast-growing urban ecosystems^[3]. Members of our staff have joined local efforts to establish Miyawaki “mini-forests” in Cambridge, MA, in Los Angeles, CA, and one in France.

The attractiveness of the Miyawaki Method should be understood in the context of a growing global zest for tree planting, such as the World Economic Forum’s 1 Trillion Trees campaign and the Bonn Initiative. In fact, tree planting initiatives can have various goals – including timber production and carbon capture, both of which favor fast-growing, often non-native trees, or erosion control or improving ground permeability. When ecosystem restoration is the explicit goal, however, reforestation aims to reestablish the full complement of ecosystem functions and wildlife habitat inherent in native ecosystems.

Not only the Miyawaki Method, but many eco-restoration initiatives favor the use of native plants over exotic species. Indigenous plants are preferred because they are typically well-adapted to local environmental conditions. Additionally, native plants interact in important ways with other local species, such as by serving as food sources for herbivores, and thus transferring energy up the food chain. Many insects, for example, are specialists and can use only certain species in their diets. When these particular plant species are replaced by non-natives or otherwise lost locally, the insects that depend on them also disappear.

Several studies by Tallamy and his colleagues [Burghardt 2008, Burghardt 2010, Narango 2017, Tallamy 2020] working in eastern US illustrate the critical role of native plants for local moths and butterflies (also called “lepidopterans”), and thus also for the birds that depend on these insects. In 2010, Burghardt, et al. reported on a two-year experiment showing that lepidopteran richness (number of species) and abundance were lower on non-native compared to native plants.

The authors explain that insect herbivores are adapted to the self-defensive toxins produced by plants for only certain plant species, which makes them especially vulnerable when those species are replaced by non-natives. This is particularly true for specialists, which make up the majority of insect herbivore species: “Most species are specialists that use only a few of the myriad plant lineages available to them for growth and reproduction. … Specialists have followed an evolutionary path that has enabled them to circumvent particular plant defenses by developing highly specific behavioral and physiological adaptations that defuse such defenses” [Burghardt 2010: 2]. The authors add, however, that “even the most generalized insect herbivores use only a small fraction of the plants in their environments” [Burghardt 2010: 2].

As expected, specialist lepidopteran species fared worse on non-natives than did the generalists, which can eat a greater variety of foods and survive in wider habitat ranges, although both groups suffered. Non-native plants (Norway maple, for example) that were similar to native ones (red maple) were more commonly used by lepidopterans, than were non-natives with no related native counterpart. The authors explain that “insect herbivores adapted to the chemical challenges [toxic plant defenses] of particular native hosts may be able to adopt a novel plant species as a host if its phytochemistry is sufficiently similar to the original hosts” [Burghardt 2010: 10]. Only 7% of specialist species used non-natives with no similar native counterpart as hosts, while less than half of generalists did.

A Washington DC study [Narango 2017] showed that both lepidoptera and their bird predators prospered in the presence of native plants:

Native plants were more likely to host a higher biomass of caterpillars compared to non-native plants, and chickadees strongly preferred to forage in native plants that supported the most caterpillars. In addition, chickadees were less likely to breed in yards as the dominance of non-native plants increased [Narango 2017: 42].

A related study [Burghardt 2008] showed greater diversity and abundance of both lepidoptera and birds (including birds dependent on insects to feed their young) in suburban yards with native plants only, compared to yards with a mix of native and non-native plants. Interestingly, all yards in the study had similar levels of overall plant diversity, suggesting that it is native biodiversity rather than biodiversity per se that counts, at least for butterflies, moths and birds.

These studies illustrate the dependence of herbivorous insects on particular co-evolved plants, and how the food web is affected when that relationship is interrupted. A related line of inquiry is whether plants themselves depend on other plants with which they share a common history. The answer to this is less clear. Thorpe et al. [2011] point out that the effects of plant-plant interactions on evolution have received less attention from researchers:

Research on plant-consumer, plant-pollinator and plant-disperser interactions has been central to understanding the complex mutualistic and co-dependent interactions among species that structure communities. However, with some notable exceptions, interactions among plants have not been emphasized as processes that contribute to selection and evolution [Thorpe 2011: 730].

Thorpe et al. [2011] highlight studies suggesting that plants, like insects, are adapted to the toxins produced by plants with which they co-evolved. Several North American experiments show that exotic European plants strongly inhibit the growth of native plants, while not negatively affecting European members of the same genus as the inhibited native plants. “Biogeographical differences in the effects of allelopathic chemicals circumstantially suggest they have roles as drivers of evolution” [Thorpe 2011: 735], state the authors. They add, however, that invasive species exert selection pressure fairly quickly on the communities they enter, resulting in adaptation that is passed on to the next generations.

In addition, plants are able to divvy up limited resources through “niche complementarity,” which is “the idea that different species or functional groups occupy niches different enough from each other to more fully utilize resources or space, increasing and stabilizing productivity, and making it more difficult for other species to enter the community” [Thorpe 2011: 733]. The authors cite a 1976 study that “found that resource partitioning, as estimated from spatial overlap among root systems, was higher in stable prairie communities with a long community history than in early successional old-field communities composed of species without a common history” [Thorpe 2011: 733].

The question of whether plant interactions drive evolution is related to an ongoing debate about the nature of a plant community. Two competing schools of thought regarding the nature of a stand of plants growing together geographically are represented by two early 20th Century botanists. H.A. Gleason observed “that species are ‘individualistically’ distributed along omnipresent environmental gradients and thus cannot form bounded communities” [van der Maarel 2013: 2]. In this view, species distribution is driven by each species’ particular tolerance to various environmental conditions, and “that the level of interactions and interdependence is relatively low, or at least nonspecific” [Barbour 1987: 158].

Barbour et al. explain that E. Clements, by contrast, compared a plant community with an integral organism, where the whole is greater than the sum of its parts, and whose component species are interdependent in the sense that they are bound together by multiple positive (and neutral) interactions. Both camps have observed that particular plant species grow together reliably in identifiable groups, forming a vegetation type (like an oak-beech forest, for example).

Fossil records indicate that some of these groups (or very closely related precursors) have lived together for thousands or even millions of years. During that time, it is possible that an intricate balance has been fashioned. Community members share incoming solar radiation, soil water, and nutrients to produce a constant biomass; they recycle nutrients from the soil to living tissue and back again; and they alternate with each other in time and space [Barbour 1987: 155].

Do plant species grow together in definable communities simply because they share the same environmental needs or are they also somewhat interdependent members of a specific community? The jury seems still to be out on this question. Regarding the larger ecological community (including animals), Steen et al. [2017] propose the concept of an “evolutionary community,” which emphasizes interdependence among specific groups of species.

What processes cause a group of species to cohere into a community? We argue that the parts of Evolutionary Communities are bound together by interspecific interactions in a shared biotic and abiotic environment, which promote co-evolution and community structure and dynamics. For example, longleaf pine trees are conduits for lightning strikes that ignite a highly flammable understory, often including dropped longleaf pine needles. The resulting ground fires are necessary for reproduction of other species and maintain habitat suitable for others (e.g., gopher tortoises). Gopher tortoises, through the process of burrow creation, provide structure important to other species. The establishment of one or more of the species listed above facilitated the persistence of additional species [Steen 2017: 1025].

These authors add that the Evolutionary Community concept can “help us understand what many conservation and restoration efforts are trying to accomplish” [Steen 2017: 1031],

stress that interspecies interdependence is a key concept for conservation, and call for the latter to focus less on species and more on interactions among species.

We propose that a shift in focus from species to interaction networks is necessary to achieve pressing conservation management and restoration ecology goals of conserving biodiversity, ecosystem processes and ultimately landscape-scale delivery of ecosystem services [Harvey 2017: 371].

All of these studies shed some light on the role of native species in the Miyawaki Method and other eco-restoration approaches. Is it possible, though, that non-native species could replace certain native species in a way that fulfills the ecological role of the replaced natives? In some contexts, it seems that communities of non-local species can thrive. Jones [2013] cites a perhaps not-terribly representational study of the vegetation on an island stranded between Africa and Brazil. This study documents “a highly functional cloud forest on Ascension Island in the south Atlantic made up of species with no history of coevolution, having been introduced from various continents. Thus, plants do not necessarily need to have co-evolved together either locally or nonlocally to display desirable community-level interactions” [Jones 2013: 1114].

By contrast, numerous studies document local ecological decline resulting from the establishment of non-native species. Jones [2013] supports the premise that local species are generally the best choice for eco-restoration, but he notes that in the context of environmental change, it may sometimes be possible that local species are no longer the best adapted.

Globally, 13,168 plant species (3.9% of known vascular plants) have become naturalized outside their native range due to human activity [van Kleunen 2015]. The anthropogenically expanding distribution of generalist species is shrinking the range of regional, endemic, often specialist species. This process, referred to as biotic homogenization, results in a “global erosion of regional distinctiveness” [Olden 2004: 18].

At the genetic level, homogenization threatens to diminish the local adaptations of native species through mixing of populations; at the ecosystem level, functional homogenization “might reduce overall community and ecosystem functioning, stability and resistance to environmental change by simply narrowing the available range of species-specific responses” [Olden 2004: 20]. Thus, there are local, regional, and global consequences of biotic homogenization.

With respect to the role of native species in eco-restoration, the Society for Ecological Restoration [SER 2019] distinguishes between restoration and “rehabilitation.”

Rehabilitation activities are well suited to a broad range of land and water management sectors where substantial native ecosystem recovery is not possible or desirable due to competing and legitimate human needs. … rehabilitation projects achieving some improvements in ecological conditions can later be targeted for ecological restoration. For instance, where revegetation of a degraded rangeland, or post-mine site, with a mix of native and nonnative plant species and native microsymbionts has resulted in improved soil function, restoration plans can be developed that include harvesting nonnative species and replacing them with native species as well as taking other actions to assist the system to recovering to the condition it would have been in if degradation had not occurred. In some cases where soil has been stabilized with nonnative species, native species can be added (or helped to recover spontaneously) and nonnative species removed to ultimately assist the recovery of a native ecosystem [SER 2019: 52].

In summary, it seems that while plant species can potentially adapt to growing with plants from outside their native range, this can sometimes take time, limiting growth of species or communities at least in the short term. By contrast, many native herbivore species are likely to become locally extinct rather than adapt to non-native plants when the latter displace natives. The loss of insects blocks the flow of energy from plants up the food chain, negatively affecting ecosystem function. While native plants are a more perfect ecosystem puzzle piece, non-native species certainly have important roles to play – at least in ecosystem “rehabilitation” as noted above and potentially to substitute for extinct natives of the same genus or functional group. Additional novel species groupings can be expected as climate change drives some species to migrate to more suitable latitudes.  

Native plants article summaries

The following articles lay out a few key ecological concepts and terms that may be helpful to become familiar with for the growing number of biodiversity-conscious people and organizations that are beginning to plant more native plants on their land.

Native plants, native ecosystems, and native landscapes: an ecological definition of “native” will promote effective conservation and restoration, Wilson, Hibbs & Alverson 1991 

Produced by the Native Plant Society of Oregon, this article argues that, while the use of native species is an accepted tenet of conservation, the term “native” is not necessarily well understood; they attempt to clarify the term.

“Any definition of a native species, native ecosystem, or native landscape requires an historical benchmark” [Wilson 1991: 16]. Over the past 20,000 years, “vegetation in the Willamette Valley has changed dramatically with changing climate. Vegetation in a single place has probably varied from boreal parkland, to conifer forest, to oak savanna, to prairie. Each climatic phase supported a different flora” [Wilson 1991: 16]. Each of these vegetation types was native to a particular place, according to particular climatic conditions that changed overtime. The vegetation that developed in the past 10,000 years – the current Holocene period of climate stability – is thus the relevant reference.

“For the Pacific Northwest, the period that ended with Euro-American settlement is a natural historical benchmark. This period lasted long enough to have a significant impact on the vegetation of the region. The climates of much earlier times were different enough to limit their usefulness in defining today’s ecosystems” [Wilson 1991: 16]. Thus, “any species that had occurred in a particular ecological habitat [of the Pacific Northwest] before Euro-American settlement is a species native to that habitat” [Wilson 1991: 17].

A native ecosystem, then, is one dominated by native plants, animals and microorganisms that occurred together before the time of Euro-American settlement. Key species – for example, the dominant photosynthesizing plants, the top carnivores, the important decomposers, the nitrogen-fixers – must be present for a native ecosystem to persist and function on its own. To artificially maintain a conserved or restored ecosystem without all of its crucial components is both difficult and expensive. The species of native ecosystem must also occur together in nature. For example, landscaping with an artificial mixture of native species like vine maple, blue bunch wheatgrass, and Jeffrey pine does not produce a native ecosystem. These species are native to different areas within Oregon, but they would not naturally grow together in the same ecosystem. Restoration of native ecosystems must also account for proper structure and appearance. For example, a red fescue lawn does not have the structural complexity and species diversity exhibited by native bunchgrass prairies [Wilson 1991: 17].

Key species – for example, the dominant photosynthesizing plants, the top carnivores, the important decomposers, the nitrogen-fixers – must be present for a native ecosystem to persist and function on its own. To artificially maintain a conserved or restored ecosystem without all of its crucial components is both difficult and expensive [Wilson 1991: 17].

The community as an ecological unit, Barbour, Burk & Pitts 1987

This article provides an overview of types of plant communities and the process of succession in those communities.

In each type of habitat, certain species group together as a community. Fossil records indicate that some of these groups (or very closely related precursors) have lived together for thousands or even millions of years. During that time, it is possible that an intricate balance has been fashioned. Community members share incoming solar radiation, soil water, and nutrients to produce a constant biomass; they recycle nutrients from the soil to living tissue and back again; and they alternate with each other in time and space. Synecologists attempt to determine what is involved in this balance between all the species of a community and their environment [Barbour 1987: 155].

Community concepts and attributes

A plant community is an identifiable stand of plants growing together in a certain spot. Clusters of species, called associations, are often found growing together in several different places within a larger region. “An association is a particular type of community, which has been described sufficiently and repeatedly in several locations such that we can conclude that it has: (a) a relatively consistent floristic composition, (b) a uniform physiognomy [appearance], and (c) a distribution that is characteristic of a particular habitat” [Barbour 1987: 156].

There are opposing views about why particular plant species are often found growing together in a plant community. The continuum view posits that species distribution is driven individualistically by each species’ particular tolerance to various environmental conditions. By contrast, the association view suggests that a plant community is an integrated whole, whose component species are interdependent.

Whatever the reasons that particular species tend to grow together in stands, however, such stands “exhibit collective or emergent attributes beyond those of the individual populations” [Barbour 1987: 159]. Examples of such community attributes include its vertical structure, canopy cover, species composition and diversity, biomass, productivity, stability, and nutrient cycling, for example.

Succession

Ecological succession is an important concept that helps explain the particular assemblage of plants growing in a given location.

“Plant succession is a directional, cumulative change in the species that occupy a given area through time” [Barbour 1987: 230]. This does not refer to cyclical changes that occur over seasons, nor to changes occurring in response to climate shifts over extremely long time spans like thousands or millions of years. Rather, succession is when the composition of plants at a particular site changes over a period of decades to centuries.

Succession begins when pioneer species colonize bare ground. These first arrivals tend to be opportunists that grow fast, reproduce quickly, and do not live long. The early successional plants start to improve the habitat conditions for other, more competitive plants to then take over, displacing the pioneers. “One of the driving forces behind succession is the effect plants may have on their habitat. Plants cast shade, add to the litter, dampen temperature oscillations, and increase the humidity, and their roots change the soil structure and chemistry. … Both the environment and the community change, and this metamorphosis is due to the activities of the organisms themselves.” [Barbour 1987: 233]

Overtime, slower-growing, larger, longer-living plant species outcompete the earlier successional species, eventually forming a climax community, which is not subsequently replaced by any other community. “Succession often leads to communities with greater and greater complexity and biomass and to habitats that are progressively more and more mesic (moist)” [Barbour 1987: 233]. Such changes result in climax communities tending to be self-sustaining due to efficient nutrient cycling and internal moderation of external fluctuations in temperature and humidity.

The particular plant composition of a climax community depends on the regional climate, as well as local soil conditions and topography, meaning that several climax communities can exist in a given landscape.

Typically, many plant communities coexist in a complex mosaic pattern. That is, one climax community does not cover an entire region. … In [some] cases, the mosaic reflects topographic differences, such as south-facing versus north-facing slopes, basins with poor drainage and fine-textured soil versus upland slopes with good drainage and coarser soil, or different distances from a stress such as salt spray. In such cases, the communities within the mosaic do not bear a successional relationship to one another; they constitute a toposequence. Each community in a toposequence may, in fact, be a climax community [Barbour 1987: 238].

Understanding ecological succession can help us to predict the future vegetation of a site by observing its current vegetation. “It is often possible to estimate a community’s future composition by extrapolation from changes measured in a short time, by comparing other communities that have plants of different ages, or by noting differences between overstory plants and understory seedlings” [Barbour 1987: 231] In some cases, the understory seedlings will later become the canopy, provided the localized conditions support this succession.

Vegetation Ecology: Historical Notes and Outline, van der Maarel & Franklin 2013

These authors define the concept of a plant community through discussion of its evolution. They start by defining the term ‘vegetation’ in a way that may surprise some readers because it excludes plants growing in certain situations. To be considered vegetation, plants need to emerge spontaneously.

Vegetation, the central object of study in vegetation ecology, can be loosely defined as a system of largely spontaneously growing plants. Not all growing plants form vegetation, for instance, a sown corn field or a flower bed in a garden do not. But the weeds surrounding such plants do form vegetation. A pine plantation will become vegetation after some years of spontaneous growth of the pine trees and the subsequent development of an understory [van der Maarel 2013: 1].

Two competing schools of thought regarding the nature of a stand of plants growing together geographically are represented by two early 20th Century botanists. H.A. Gleason observed “that species are ‘individualistically’ distributed along omnipresent environmental gradients and thus cannot form bounded communities” [van der Maarel 2013: 2]. By contrast, E. Clements compared plant community with an integral organism, where the whole was greater than the sum of its parts. During the same time period, the Braun-Blanquet approach was developed, which “paid much attention to the relations of plant communities with the environment and the interactions within communities, which is now incorporated in the concept of ecosystem” [van der Maarel 2013: 2].

The authors state that while individual plant species are distributed according to abiotic environmental conditions, the fact of being co-located with particular sets of other species in a particular environment results in interspecies interactions, which are in fact ecosystem processes (emergent properties).

In conclusion, a plant community is generally recognized as a relatively uniform piece of vegetation in a uniform environment, with a recognizable floristic composition and structure, that is relatively distinct from the surrounding vegetation. Even if the populations of the participating species are usually distributed individualistically in the landscape, they may well interact within the community and build up an integrated unit with emergent properties. At the same time, plant communities can be convenient units for conveying information about vegetation and its environment [van der Maarel 2013: 4].

Vegetation types and their broad-scale distribution, Box & Fujiwara 2013

A vegetation type, or plant community, is identifiable by its distinct appearance compared to other landscape types within a landscape. For example, a grassland and a wetland differ in appearance from each other and from a forest, while a wetland-forest is yet another visibly different vegetation type. Plant species are recognizable by their form, which is related to how the plant functions. For example, in dry environments, plant leaves are more compact with harder surfaces to limit water loss, while plants in wetter environments have larger, “softer” leaves that release water readily when pores open to take in CO2. Such leaves have more surface area for photosynthesis, resulting in faster growth.

This form-function relationship explains why vegetation types differ around the globe. Plant species are adapted to particular climatic conditions according to their proximity to the equator or a coastline, for example, or their elevation.

The geographic regularity of vegetation distribution arises, of course, from the geographic regularity of Earth’s main climatic regions, driven by the global circulation pattern of the Earth’s atmosphere [Box 2013: 466].

Predictive modeling of the potential natural vegetation pattern in northeastern China, Liu et al. 2009

This study uses the concept of Potential Natural Vegetation (PNV), developed in the mid-1900s by German botanist Reinhold Tüxen. Described by the authors as “one of the most successful novelties in vegetation science over the last decades” [Liu 2009: 1313], PNV can be defined as a projection of the natural vegetation that would exist in a given area in the absence of human interference.

“By showing the relationships between environmental variables and vegetation types, maps of the PNV are an important instrument in the study and planning of the environment, and act as decision-support tools for the solutions to environmental issues” [Liu 2009: 1313]. Such maps are informed by studying remnant natural (old growth) vegetation in the area and site observations of the area to be mapped.

Computer modeling can be used to predict “the geographic distribution of vegetation composition across a landscape from mapped environmental variables, such as climate, soils, and geology. When a predictive vegetation modeling is calibrated using observation of vegetation composition taken from mature or ‘climax’ vegetation stands, then potential natural vegetation is portrayed in a predictive map” [Liu 209: 1314].

Focusing on northeastern China, the study identified 16 vegetation types in the region, along with the environmental factors influencing their distribution. Climatic factors included: mean annual temperature, mean temperature of the coldest month, relative humidity, and potential evapotranspiration rate. Topographical factors were elevation and slope.

“Generally, as the elevation increases, the change of temperature and moisture leads to the obvious differentiation phenomenon in vegetation vertical zones. Slope is related to the hydrology (overland and subsurface flow velocity and runoff rate) and potential soil moisture and soil development of a habitat” [Liu 2009: 1315].

They compared the map created by their model to existing vegetation maps of the region. “Visual comparison of the predicted PNV distributions with their actual equivalents indicates a good agreement” [Liu 2009: 1317]. Some modeled vegetation types did not agree with existing maps, however, meaning that “some more important environmental factors may have been missing in the model” [Liu 2009: 1318]. The authors also state that calibrating their model with additional field data on what is currently growing, collected from throughout the region, would improve the model’s accuracy.

The article concludes by stating that a ‘vegetation-environment’ model can help to determine PNV under not only current, but also predicted future environmental conditions.

Conceptualizing communities as natural entities: a philosophical argument with basic and applied implications, Steen et al. 2017

Ecological restoration aims to recreate lost or degraded ecological communities. However, “community” has been a difficult concept to define – should the definition stress dominant species, species interactions, or a subset of strongly interacting species? These authors propose defining community on the basis of co-evolutionary relationships among species.

We propose that an Evolutionary Community is conceptualized as a unique grouping of species, which occur in a given geographic area and are connected by interspecific and abiotic interactions that have evolved over time [Steen 2017: 1021].

By treating communities “as entities that have formed over evolutionary time; this [Evolutionary Community] concept allows for a philosophical platform to help us understand what many conservation and restoration efforts are trying to accomplish” [Steen 2017: 1031]. That is, it offers a way to conceptualize the end goal of a restoration project. A particular evolutionary community could be recreated by assembling the constituent species, resulting in the ecological interactions among the species resuming as before.

What processes cause a group of species to cohere into a community? We argue that the parts of Evolutionary Communities are bound together by interspecific interactions in a shared biotic and abiotic environment, which promote co-evolution and community structure and dynamics. For example, longleaf pine trees are conduits for lightning strikes that ignite a highly flammable understory, often including dropped longleaf pine needles. The resulting ground fires are necessary for reproduction of other species and maintain habitat suitable for others (e.g., gopher tortoises). Gopher tortoises, through the process of burrow creation, provide structure important to other species. The establishment of one or more of the species listed above facilitated the persistence of additional species [Steen 2017: 1025].

Likewise, the demise of one species will negatively affect, or even cause the demise of, other species that depend on it. Thus, the reason to preserve or recreate an integral community is to support the interdependent component species, each of which in turn support the community as a whole.

Bridging ecology and conservation: from ecological networks to ecosystem function, Harvey et al. 2017

This article emphasizes the importance of species interactions as drivers of ecosystem function.

The classic conservation approach is to set aside national parks or to target specific species for protection, based on their rarity or endangered status. However, these approaches can have trade-offs for non-target species, while also potentially failing to protect ecosystem function. The authors, therefore, suggest that species interactions based on their functional significance should be the main focus on conservation efforts.

We propose that a shift in focus from species to interaction networks is necessary to achieve pressing conservation management and restoration ecology goals of conserving biodiversity, ecosystem processes and ultimately landscape-scale delivery of ecosystem services [Harvey 2017: 371].

Species depend on many other species in their communities, either directly or indirectly. An example of indirect dependence is the Phengaris arion butterfly’s need for European rabbits. The butterfly uses ant nests made in the open areas supplied by rabbit grazing for development of its larvae. Thus, no rabbits means no ants, which means no Phengaris arion.

Focusing on species interactions is more meaningful even than measuring species richness (the number of different species), because interactions can disappear – even if both species are present – if either group’s abundance has significantly dropped. The authors offer the example of 59 regionally extinct lepidoptera (butterfly and moth) species of central Europe. Eight of these extinctions were associated with the loss of particular host plant species, which actually occurred after the lepidoptera went extinct.

Focusing on species interactions is more meaningful even than measuring species richness (the number of different species), because interactions can disappear – even if both species are present – if either group’s abundance has significantly dropped.

Thus, strong declines of host plants can have cascading extinction effects on higher trophic levels before the plants actually go extinct, illustrating that interactions can be lost before any actual decline in species richness (plants persisted at low abundance). This illustrates that preserving keystone interactions, rather than species, can be a proactive way to maintain ecosystem integrity in the face of global change instead of allocating resources to already endangered species [Harvey 2017: 372].

There is interdependence among species even between neighboring ecosystems. For example, a manta ray species in the Palmyra Atoll south of Hawaii depends on two species of native trees to maintain its ocean plankton diet. When these trees were replaced with cultivated coconut palms, marine-foraging birds no longer nested on that shore, depriving the coastal waters of the nitrogen runoff from their guano, which had been feeding the plankton population.

The authors recommend that “the main lever to restore or conserve ecological network structure and stability is the management of spatial configuration” [Harvey 2017: 377]. Reflecting on the Palmyra Atoll, for example, it’s clear that a marine conservation plan would be incomplete without considering the nutrient flow from the tree-bird interactions on land.

Interactions among plants and evolution, Thorpe et al. 2011

This review explores the question of whether plant-plant interactions drive evolutionary changes. “If such evolution is common, plant communities are not random assemblages of species.” The topic is under-studied compared to plant interactions with other groups.

Research on plant–consumer, plant–pollinator and plant–disperser interactions has been central to understanding the complex mutualistic and co-dependent interactions among species that structure communities. However, with some notable exceptions, interactions among plants have not been emphasized as processes that contribute to selection and evolution [Thorpe 2011: 730].

“The simplest interactions among plants are direct interactions, such as facilitation, resource competition and allelopathy” [Thorpe 2011: 731]. Facilitation is when one plant protects an adjacent plant, such as from drought and heat by providing shade, for example, or from browsing by being thorny or toxic to herbivores and surrounding the facilitated plant. Allelopathy refers to plants’ release of toxic substances that suppress the growth of another organism, including other plants. In natural communities, any given plant may be interacting with several different plants at the same time.

In natural communities, any given plant may be interacting with several different plants at the same time.

Competition for sunlight, water, and nutrients drives niche differentiation, or the carving out by species of particular spaces or timing within an ecosystem to obtain a share of limited resources. “The exceptionally rich body of ecological literature on the niche is based in part on the idea that competition can drive the evolution of niche differentiation, thus allowing species to coexist” [Thorpe 2011: 732].

Thorpe et al. refer to an example from a 1976 article by Parrish & Bazzaz , who “found that resource partitioning, as estimated from spatial overlap among root systems, was higher in stable prairie communities with a long community history than in early successional old-field communities composed of species without a common history” [Thorpe 2011: 731]. In other words, plants with a long coexistence history more efficiently divvy up resources than do species lacking a common community history.

The primary hypothesis for positive diversity–ecosystem function relationships has been niche ‘complementarity’, the idea that different species or functional groups occupy niches different enough from each other to more fully utilize resources or space, increasing and stabilizing productivity, and making it more difficult for other species to enter the community [Thorpe 2011: 733].

The authors are somewhat inconclusive, however, about what drives niche complementarity (resource partitioning).

We do not yet know whether complementarity is produced by interactions causing evolutionary shifts in niche space (and thus coexistence and more complete resource use) or by sorting of the existing species pool [Thorpe 2011: 733].

Plants can also adapt to one another’s allelopathic substances over time, a fact that contributes to the argument that plant-plant interactions produce evolutionary changes. “Recent experiments raise the possibility that some invaders may exude allelochemicals that are relatively ineffective against neighbors in natural communities, but highly inhibitory to plants in invaded communities” [Thorpe 2011: 734].

Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities, Burghardt et al. 2010

This research evaluates the impact of the invasion of non-native plants in the distribution of lepidopteran (butterfly, skipper, and moth) communities. The authors assert that although the introduction of non-native plants has not resulted in a “global extinction”, they have had a considerable impact on how ecosystems function—they often result in significant bottom-up reductions of energy available in local food webs.

The experiment established four gardens near mature woodlots containing most, if not all, of the native species planted within the treatment. The richness and abundance were then compared for lepidopteran communities found on native versus corresponding non-native congener^[4] species of 13 woody plant genera. For example, the genus Acer (maple) was selected for this study because the native and non-native maples were widespread in that area. In separate plots, the researchers also compared native plants and unrelated (non-congeneric) non-native plants for lepidopteran richness and abundance.

The study found that lepidopterans suffer from the replacement of native plants by non-natives, especially when those non-natives are unrelated to any native plant species. The authors explain that “insect herbivores adapted to the chemical challenges [toxic plant defenses] of particular native hosts may be able to adopt a novel plant species as a host if its phytochemistry is sufficiently similar to the original hosts” [Burghardt 2010: 10]. Over the two-year study, lepidopteran abundance and richness were depressed both on congener and (unrelated) non-congener non-native plants, but especially on the latter.

The study found that lepidopterans suffer from the replacement of native plants by non-natives, especially when those non-natives are unrelated to any native plant species.

Specialist lepidopteran species, which require specific diet and habitat conditions to survive, fared worse on non-natives than did generalists, which can eat a variety of foods and survive in many different habitats. The authors note, for example, that “geographically novel congeners were acceptable hosts to less than half of the generalists and only one fourth of the specialists that we found on native congeners in 2009” [Burghardt 2010: 11]. Only 7% of specialist species used non-congener non-natives as hosts.

The authors argue that the loss of lepidopteran diversity and abundance due to the displacement of native plant species with non-natives can ripple up the food chain, reducing diversity at higher trophic levels. Reduced diversity leads to lower ecosystem productivity and stability, thus disrupting the whole system.

The authors argue that the loss of lepidopteran diversity and abundance due to the displacement of native plant species with non-natives can ripple up the food chain, reducing diversity at higher trophic levels. Reduced diversity leads to lower ecosystem productivity and stability, thus disrupting the whole system.

Because insect herbivores are near the hub of most terrestrial food webs, comprising essential food stuffs for an incredible diversity of insect predators and parasitoids, spiders, amphibians, lizards, rodents, bats, birds, and even higher predators such as foxes and bears, it is particularly important to understand changes wrought by non-native plants on this critical taxon [Burghardt 2010: 13].

Impact of Native Plants on Bird and Butterfly Biodiversity in Suburban Landscapes, Burghardt, Tallamy & Shriver 2008

In this study, the insect and bird populations of six pairs of suburban yards were measured. Each pair contained one conventionally landscaped yard containing native canopy trees and a mixture of native and non-native shrubs, grasses and understory trees; and one yard with native species only (canopy, understory, shrub and grasses). The level of plant diversity was comparable between each of the pair; only the proportion of native species differed. The authors found that:

Avian abundance, diversity, richness, and biomass (particularly bird species of conservation concern) were all greater on native properties. Native nesting birds that are mostly dependent on insect populations to feed their young were more abundant on native properties. Lepidoptera [butterfly and moth species] abundance and diversity were also higher on native properties, suggesting that food availability might account for the differences detected in the bird communities between native and conventionally landscaped sites [Burghardt 2008: 223].

These results support the authors’ hypothesis based on an understanding of the co-evolutionary roots of species interactions.

Theory backed by decades of empirical evidence predicts that up to 90% of all species of insect herbivores can successfully reproduce only on plant lineages with which they have shared an evolutionary history [Burghardt 2008: 220].

Native plants improve breeding and foraging habitat for an insectivorous bird, Narango, Tallamy & Marra 2017

This study examined whether non-native plants in residential Washington DC limited the presence of the Carolina chickadee, a local breeding insectivore.

We predicted that areas with more native plants would support more chickadees, and chickadees would forage more often in the most insect-producing native plants [Narango 2017: 43].

The authors had also considered the possibility that non-native plants could promote increases in other food items (e.g. non-native arthropods), keeping overall prey biomass similar between native and non-native plants. What they found, though, affirmed their prediction: native plants produce more caterpillars, which in turn support more chickadees. In fact, the birds avoided foraging in non-native plants, including non-native species of the same tree genera: the chickadees preferred maples native to the eastern US compared to European-origin maples.

Native plants produce more caterpillars, which in turn support more chickadees.

Native plants were more likely to host a higher biomass of caterpillars compared to non-native plants, and chickadees strongly preferred to forage in native plants that supported the most caterpillars. In addition, chickadees were less likely to breed in yards as the dominance of non-native plants increased [Narango 2017: 42].

Also unique to our study is that we measured the probability of caterpillar occurrence between congeneric species (e.g. native vs. non-native Acer [maple]). This is particularly important considering the popularity and invasive qualities of congeneric species in this region such as Acer platanoides and Quercus acutissima. Although non-native congeners support more caterpillars in comparison to plants unrelated to any native species, congeners had a 47% (CI: 34%–59%) lower probability of having caterpillars compared to native species [Narango 2017: 47].

The authors state that local insects are adapted to local plants, presumably due to their shared co-evolutionary history.

This occurs in part because herbivorous insects have adapted to circumvent the phytochemical defenses of particular plant lineages, resulting in a radiation of specialized plant-insect associations. During urban conversion, native plants are replaced by non-native species with novel chemical, physical, and phenological features for which native herbivorous arthropods have few physiological or behavioral adaptations [Narango 2017: 42].

Do non-native plants contribute to insect declines? Tallamy, Narango & Mitchell 2020

The widespread distribution of plants outside of their native range due to human activity is a significant yet underrecognized cause of global insect decline, according to this article. To illuminate the issue, the authors: “examine the evidence for and against the hypothesis that long term changes in the species composition of plant assemblages have contributed to local and global declines in the abundance and diversity of the insect communities dependent upon those assemblages” [Tallamy 2020: 2].

To be sure, insect conservationists have long noted the importance of habitat containing appropriate native host plants, but the widespread replacement of native host plants with non-native species has yet to penetrate the growing literature on insect declines in any meaningful way [Tallamy 2020: 1].

It is not simply the absence of native plants harms plant-eating insects, however, but also the presence of non-natives. While some insects feed successfully on non-native plants, this is the minority. Most either avoid non-native plants, or do use them and are killed or malnourished by doing so. For example,

Swallowworts (Vincetoxicum spp.) are confamilials of milkweeds (Asclepias spp.) and have become invasive in parts of the northeastern United States. Similar phytochemistry between swallowworts and milkweeds can lead monarch butterflies (Danaus plexxipus) and milkweed beetles (Chrysochus auratus) to fatally mistake these chemically protected plants as hosts. The degree to which Vincetoxicum act as ecological traps for these taxa is likely to become more pronounced as the plants become dominant and displace milkweeds in the landscape [Tallamy 2020: 3].

Species that share a particular environment over hundreds or thousands of years evolve in relation to one another. For plant-eating insects, adapting to certain plants meant developing “traits to detect and tolerate plant defenses over time” [Tallamy 2020: 2]. Most herbivorous insects adapted to only a particular set of plants, specializing in feeding on those plant hosts.

The diet of most insects is constrained to a single plant family in any one habitat or location, with dietary specialization even narrower both in many temperate lineages and hyper-diverse tropical lineages. In fact, diet specialization increases with decreasing latitudes, concurrent with theories of increased plant and animal diversity in the tropics [Tallamy 2020: 2].

When native plants are displaced in the landscape by non-native species, phytophagous [plant-eating] insects typically do not recognize the novel host for feeding or oviposition [egg laying], or may be unable to overcome novel plant defenses. The concurrent loss of native plant hosts and dominance of non-native plants can lead to local extirpation of phytophagous insects and thus to changes in the composition and structure of local food webs [Tallamy 2020: 2].

The most likely successful substitute for a native plant is a non-native plant in the same genus or family.

Non-native congeners [members of the same genus] or confamilials [members of the same family] that are similar in foliar chemistry and nutrition, phenology, and morphology, may occasionally serve as novel hosts for herbivorous insects and support higher diversity and abundance than non-native, non-congeners. However, novel use of congeners may increase larval mortality, extend development or pupation time, reduce biomass, and reduce fitness compared to that of native hosts [Tallamy 2020: 3].

The narrower the native plant diet an insect species has, the less likely to tolerate novel, non-native food sources. However, there are more species of specialist insects than of generalists, meaning a larger proportion of susceptible species. Adaptability to exotic host plants also depends on an insects’ feeding habits.

Insects with chewing (mandibulate) mouthparts are typically more susceptible to defensive secondary metabolites contained in leaf vacuoles than are insects with sucking (haustelate) mouthparts that tap into poorly defended xylem or phloem fluids. Thus, sucking insects find novel non-native plants to be acceptable hosts more often than do chewing species [Tallamy 2020: 4].

Considering that there are more than 4.5 times as many mandibulate insect herbivores as haustelate species, there is reason for concern when non-native plants replace native hosts; the largest guild of insect herbivores is also the most vulnerable to non-native plants and the most valuable to insectivores [Tallamy 2020: 5].

“The dispersal and spread of invasive plants has been driven by global trade networks and colonialism” [Tallamy 2020: 6] and, more specifically, from agroforestry, forestry, agriculture, and horticulture.

Although plants have always distributed themselves around the globe, the increased temporal and spatial mobility of humans has resulted in an extraordinary increase in the rate of plant movements and most species’ introductions have happened in the last 200 years. Habitat is rapidly being converted from coevolved native ecosystems into novel assemblages of plants and animals, making the conversion of native plant communities into plant assemblages dominated by non-native species one of the most ubiquitous threats to biodiversity today. The introduction of non-native plants has completely transformed the composition of present-day plant communities in both natural and human-dominated ecosystems around the globe and the magnitude of introductions is staggering. An estimated 13,168 plant species (about 3.9% of global vascular flora) have been introduced and naturalized beyond their native ranges as a result of human activity [Tallamy 2020: 6].

Global exchange and accumulation of non-native species, van Kleunen et al. 2015

The ecological, economic, and social damage of human-mediated dispersal of species into new regions, where they possess the ability to naturalize (become self-sustaining their new homeland), is one of the defining features of the Anthropocene Epoch. Globally, human activity has led to the naturalization of nearly 13,168 plant species (equal in size to the native European flora). The results from this research provide a baseline for monitoring global changes in biodiversity while highlighting the immediate action that has to be taken to comprehend and determine the spread of alien species on an international scale.

The ecological, economic, and social damage of human-mediated dispersal of species into new regions, where they possess the ability to naturalize (become self-sustaining their new homeland), is one of the defining features of the Anthropocene Epoch.

At least 3.9% of all currently known vascular plant species have become naturalized outside their natural ranges as a result of human activity. With the continued practice of international traffic and trade and globalization, the likelihood of more and more species being introduced and getting naturalized outside their native range is high.

To assess the accumulation of naturalized species in each continent as well as which continents have been the major donors of alien naturalized plant species globally, the researchers used a novel database, Global Naturalized Alien Flora (GloNAF), in addition to the data on the origin of naturalized species and estimates of the number of native species per continent. They found that when not taking into account the differences in total area, North America has accumulated the highest number of naturalized species (n=5,958). However, when considering the difference in total area, Australasia (a region comprising Australia, New Zealand, and neighboring islands) was found to have more extra-continental species than North America.

One possible explanation is that Australia’s long biogeographical isolation and drying climate have resulted in a native flora that is phylogenetically distinct, but not well-adapted to exploit the novel habitats created by European settlers [van Kleunen 2015: 101].

The major donors of alien species are Europe and temperate Asia, while North America is also a significant donor.

Ecological and evolutionary consequences of biotic homogenization, Olden et al. 2004

Anthropogenic environmental change and global dispersal of a wide variety of species outside their native ranges has expanded the range of “cosmopolitan,” non-native species and shrunk the range of regional and endemic species. “This replacement of specific native forms by generalist non-natives in space and time has mixed the taxonomic composition of once disparate biotas, an occurrence termed ‘biotic homogenization’” [Olden 2004: 18].

The authors explore the effect of this “global erosion of regional distinctiveness” [Olden 2004: 18] at three levels: Genetic homogenization reduces genetic variability within species or among populations of species, while taxonomic homogenization reduces distinctiveness among communities. Functional homogenization refers to a reduction of functional traits within an ecosystem. The identity of species making up a community, along with their respective functional traits, determines “ecosystem functions (such as nutrient retention or energy flow)” [Olden 2004: 20], so that narrowing species compositions risks diminishing ecosystem function.

A decrease in functional diversity might reduce overall community and ecosystem functioning, stability and resistance to environmental change by simply narrowing the available range of species-specific responses. Consider a severe drought that strongly affects a subset of species in a community that has (or lacks) a particular suite of functional traits. Historical communities, with much greater breadth in functional space, should exhibit higher resistance or resilience when compared with homogenized communities [Olden 2004: 20].

Genetic homogenization occurs when two distinct locally adapted populations of the same species interbreed. It also occurs when a single variety (such as captive fish bred in a central location) are released in many places to replenish dwindling native stocks. While such mixing has the potential to increase species diversity, this outcome is not assured.

Intraspecific hybridization can homogenize the unique characteristics of geographically distinct populations, as well as compromise the fitness of individuals by disrupting local adaptations [Olden 2004: 19].

Linking Restoration and Ecological Succession, Walker, Walker & Hobbs (eds) 2007

This book draws lessons from ecological succession theory to inform ecological restoration, stating that: “restoration is fundamentally the management of succession” [Walker 2007: vi]. The latter is the natural process by which plants first colonize “new” land (post landslide, glacial retreat or volcanic eruption, for example) or degraded land, and over time develop into mature ecosystems through a series of changing plant communities. Ecological restoration is a human-led initiative to restore functioning ecosystems, or at least vegetation, on land degraded through human activity. The ultimate goal of restoration is to “establish a self-sufficient ecosystem that requires minimal or no continuing human inputs in order to provide a continuing supply of goods and services” [Hobbs 2007: 177].

Effective ecosystem restoration requires ecological knowledge. Likewise, the outcomes of such projects demonstrate our comprehension, or lack thereof, of ecological concepts: “Restoration is the acid test of our ability to understand not only how ecosystems are assembled and held together but also how they change over time” [Walker 2007: vi]. The authors contend, however, that restoration projects are more often guided by engineering, horticulture, and agronomy than by ecology. Aiming to clarify the ways in which ecological succession theory can and should inform restoration, this book poses the question: “What is the minimum amount of biophysical and successional information needed to restore a specific landscape or area” [Walker 2007b: 2]?

Succession comprises many ecological processes that underpin all ecological restoration and ecological restoration is a manipulation of these processes to achieve its goals. This means it is essential to understand how succession operates, and when and how to manipulate it [Prach 2007: 121].

Restoration can explicitly embrace a hands-off approach, where land is simply left to repair itself through natural ecological succession. On the other hand, understanding the successional process allows manipulation of various stages to speed up the process. For example, in the first stage of primary succession “winds deposit dust, pollen, seeds, and insects crucial to reducing infertility” [del Moral 2007: 23], on bare, inhospitable ground. Tough pioneer plants are able to establish then create shade, trap sediment, and deposit organic matter when they die, creating slightly better conditions for the next wave of colonizing plants. To mimic this first stage of site “amelioration”, the site can be physically manipulated by reshaping the ground for improved drainage or adding organic matter, for example.

Biological manipulation involves sowing or planting local/native varieties of later successional species that may not be otherwise present in the area due to human transformation of the broader landscape. While earlier successional species tend to have small, easily transported seeds, the later successional species (such as large canopy trees) that are often the target of restoration efforts often have large, less mobile seeds. Thus, if those plants are not present in the immediate environment as seed stock, they may never establish in the restored site without human assistance.

Near-Natural Silviculture: Sustainable Approach for Urban Re-naturalization Assessment Based on 10 Years Recovering Dynamics and Eco-Benefits in Shanghai, Guo et. al 2015

As one of China’s major cities, Shanghai’s natural sub-ecosystem^[5] has suffered drastic damage due to human activities and urbanization. Although urban re-naturalization has gained attention from city leaders, urban tree planting has largely consisted of two methods with limited ecological potential. One favors fast-growing monocultures to produce timber products and other benefits, while the other approach is to plant non-native species for decorative purposes. The authors believe the restoration progress of the natural sub-ecosystem could be further improved by adopting the “near-natural” method based on the concepts of potential natural vegetation^[6] and ecological succession.

The near-natural forest uses all native species and aims to create a complex structure with high biodiversity, high biomass and multiplayer canopies. It was adopted successfully in many countries, but the authors thought long-term studies of these forests were lacking. Therefore, they conducted a 10-year study at a near-natural forest established in 2000 in Pudong New Area of Shanghai to investigate the effectiveness of the forest in providing ecological benefits.

Results showed that the near-natural forest had higher sustainability value than artificial (“even-aged, managed”) forest in Shanghai based on its ecological and economic benefits. The high tree density and multiple vertical structures of the forest improved the air quality and soil fertility and decreased the concentrations of air bacteria and dust. It also had a much lower planting and maintenance cost than artificial traditional methods. Although the near-natural forest could not transcend the benefits of the natural forest, the study successfully proved its important role in urban re-naturalization by bridging the difference between the artificial and natural forests.

Results showed that the near-natural forest had higher sustainability value than artificial (“even-aged, managed”) forest in Shanghai based on its ecological and economic benefits

Over the course of the study, authors discovered a potential limitation of the approach, at least in its application in Shanghai. They observed high evergreen seedlings mortality, attributable to over-exposure to sunlight. Therefore, in subsequent plantings in 2003 and 2004, the authors modified the approach to optimize it to local conditions:

The key to the new method is to create a mixed deciduous–evergreen community by simultaneously planting shade-tolerant evergreen broad-leaved species and light-demanding deciduous broad-leaved species, but using smaller individuals for the former and larger individuals for the latter to form a multilayer vegetation structure. The shade-tolerant evergreen species benefit from the rapid growth of the light-demanding deciduous species, which offer shade and nutrients in the form of litter layer-based fertilizer, improving the soil for the evergreen species [Guo 2015: 5].

Overall, they suggest that the near-natural forest is a very sustainable method to be applied in Shanghai.

Tree planting is not a simple science, Holl & Brancalion 2020

Well-planned tree-planting projects are an important component of global efforts to improve ecological and human well-being. But tree planting becomes problematic when it is promoted as a simple, silver bullet solution and overshadows other actions that have greater potential for addressing the drivers of specific environmental problems, such as taking bold and rapid steps to reduce deforestation and greenhouse gas emissions [Holl 2020: 580].

Some of the pitfalls to avoid in tree planting initiatives, according to the authors, include:

• Use of non-native species, which does not result in a true forest and can result in ground water depletion in arid environments.
• Planting trees in historic grasslands and savannas, harming those native ecosystems and species.
• Abandoning trees after they are planted, which can result in high mortality due to insufficient water for developing saplings, being shaded out by faster growing herbaceous plants, grazing, or being re-cleared.
• Planting trees in agricultural land, which risks pushing crop production into native forest land, which is then deforested.

The authors insist that reforestation takes careful planning, stakeholder engagement, clear goal-setting, and long-term monitoring and adaptive management of planted tree stands to ensure their survival. Above all, existing mature, native forests should be preserved.

The authors insist that reforestation takes careful planning, stakeholder engagement, clear goal-setting, and long-term monitoring and adaptive management of planted tree stands to ensure their survival. Above all, existing mature, native forests should be preserved.

The first priority to increase the overall number of trees on the planet must be to reduce the current rapid rate of forest clearing and degradation in many areas of the world. The immediate response of the G7 nations to the 2019 Amazon fires was to offer funding to reforest these areas, rather than to address the core issues of enforcing laws, protecting lands of indigenous people, and providing incentives to landowners to maintain forest cover. The simplistic assumption that tree planting can immediately compensate for clearing intact forest is not uncommon. Nonetheless, a large body of literature shows that even the best-planned restoration projects rarely fully recover the biodiversity of intact forest, owing to a lack of sources of forest-dependent flora and fauna in deforested landscapes, as well as degraded abiotic conditions resulting from anthropogenic activities [Holl 2020: 581].

“The tamarin is unable to do anything to save its own species. And we, human beings, are the ones who are destroying their environment,” says conservationist Gabriela Rezende. “So, when I got the opportunity to see this animal in the wild, I felt partly responsible for its future.”

Rezende works with the Institute for Ecological Research in the Brazilian state of Sao Paolo to create ecological corridors connecting the forest fragments where the world’s only 1,800 black lion tamarin live in isolated populations. Since 1984, the institute has worked to protect this small primate species, which had reached a low point of 100 individuals and was listed as “critically endangered.” In addition to research and forest restoration, the institute also does environmental education with the local communities. This includes collaboration on nine tree nurseries administered by local people as small businesses that also provide school kids the chance to learn about local forest species that will be planted in corridors.

Leveraging a state policy requiring 20% of privately owned property to be in nature reserves, Rezende worked with landowners to identify patches to be restored that would physically connect forest fragments. Once corridors are complete, the total amount of land in connected habitat will be 111,000 acres. Rezende estimates the black lion tamarin population could increase 30% once it’s able to use the whole forest corridor. The restoration project will benefit other species too, including anteaters, tapirs (a pig-like animal with a short trunk), pumas, and ocelots (another wild cat species).

The Belize government approved a plan in February 2018 to create a 110-square-kilometer biological corridor connecting two nature reserves in the northeast of the country. This outcome resulted from collaboration among NGOs, the government and private property owners. The latter agreed to conserve (to not deforest or otherwise degrade) the parts of their land that would become part of the wildlife corridor. In exchange, the government would not collect taxes on this land. This corridor, which was initiated in the context of the larger Mesoamerican Biological Corridor project, is meant to protect jaguars, cougars and tapirs, among other wildlife.

One of the world’s largest corridor projects is the Mesoamerican Biological Corridor (MBC). Initiated in the 1990s, the MBC aims to connect protected areas between southeastern Mexico and Panama [Meyer 2019: 2].

The ecological functionality of the MBC has not been much assessed, in part because direct approaches to measuring connectivity are costly and challenging. In this study, researchers used a simpler, indirect approach to measure forest connectivity through Panama for nine mammals. Using camera traps (cameras that are automatically triggered by a change in some activity in the vicinity, like the presence of an animal), they documented the presence (or absence) of these mammals in 28 forest sites along the Atlantic coast. The corridor was presumed to be functioning for animals whose presence was established across the entire length of the monitored range.

The species monitored in this study are forest specialists, including ungulates, carnivores and an insectivore, all of which are threatened by habitat loss and hunting, some more than others. Of the 43% of land in Panama that is forested, 44% is protected, mostly along the Atlantic coast. Steady economic development threatens remaining ecosystems with investments in large infrastructure projects, real estate, mining, tourism, and energy.

Large mammals are an indicator species for the success of conservation efforts. This is because:

Large mammals are generally at a higher risk of extinction in disturbed landscapes than other taxa because their large home ranges and low population densities at broad spatial scales mean their populations are more likely to be fragmented and because they are heavily hunted [Meyer 2019: 3].

The researchers found that even the four most prevalent species in the study are susceptible to population fragmentation by any further habitat loss.

We found that there was little connectivity for white-lipped peccary [a pig-like animal] and white-tailed deer and that, although 4 of the species (collared peccary, red brocket deer, puma, and ocelot [a wild cat]) occurred in most of the sites, a small decrease in connectivity of 20% would disrupt their continuous distributions across Panama. White-lipped peccary, giant anteater, white-tailed deer, jaguar, and tapir [a pig-like animal with a short trunk] had lower probability of occurring in all the sites and were therefore even more at risk of connectivity loss, as evidenced by >1 connectivity gap. This indicates the MBC may not function for the majority of species, especially considering we did not account for potential effects of hunting, which would make connectivity even more challenging [Meyer 2019: 8].

Citing imminent development projects, such as a new road that will pass through the forested northern coast and associated large hotel projects, the authors predict that ongoing loss of connectivity is likely. Moreover, the deteriorating condition of the corridor in Panama bodes poorly for the MBC overall.

The disruption of connectivity between tropical forests in Central America, and hence the possible separation of mammal populations, is an indicator of the overall functioning of the MBC for wildlife [Meyer 2019: 11].

Written by an anthropologist working in Central American conservation efforts for more than 10 years, this article describes the Mesoamerican Biological Corridor (MBC) project as having succumbed to a neoliberal agenda. Although originally spearheaded by Central American environmentalists, the notion of cross-border environmental collaboration was adopted by the World Bank and large international conservation organizations working in Central America in the 1990s. In the hands of these international giants, the biological corridor initiative became a bureaucratic, top-down project, deaf to the voices of local communities.

With all this new bureaucracy, a broad and unfocused agenda, and the challenges of high-level political coordination, the MBC quickly lost its potential to inject a stronger environmental justice component into regional biodiversity conservation programs.

Indeed, the MBC that emerged from the World Bank’s incubator was decidedly more business-oriented than initial proposals for Central American environmental coordination at the 1992 Earth Summit [Grandia 2007: 486].

In this context, the MBC’s conservation efforts have focused more on securing land for protected parks and less on community-based initiatives. The author suggests that in addition to land protection, the MBC should engage farmers in capacity building for eco-agriculture with a view toward achieving landscape-wide ecological connectivity.

The corridor approach might also draw greater attention to the agrarian contexts outside of parks, which may be just as ecologically important as what happens inside parks. By bringing agricultural systems into conservation debates, corridors may present new opportunities for supporting fair-trade projects and other small-scale agroforestry systems compatible with conservation. In other words, corridors could offer a method for moving beyond protectionism to embrace a mosaic vision for conservation that includes local people more explicitly. Corridor planning frameworks also could provide more democratic conservation forums [Grandia 2007: 484].

At the end of the 1980s, as a period of severe conflict in Central America was winding down, most countries in the isthmus signed the Charter Agreement for the Protection of the Environment, which established a sustainable development commission. At the same time, the “Central American Protected Areas System (SICAP) created approximately 11.5 million hectares of protected areas throughout the region” [Dettman 2006: 18].

This paved the way for international attention and investment in what became the Mesoamerican Biological Corridor (MBC). The original intention was to promote biodiversity and economic development in tandem through investment in local projects. However, in the 2000s, the international coordinators of the MBC shifted the focus from biodiversity protection (although the establishment of ecological corridors remains an objective) to a greater emphasis on economic development. This author explains that the institution’s decision-making process is overly top-down, and would benefit from input from local people who are implementing projects on the ground.

The concept of sustainable development presumes that human economic systems and overall wellbeing depend on functioning ecosystems. Therefore, ecological rhythms should not be transgressed to the point that they fail to provide the vital services needed today and in future generations.

According to this model, economic development becomes a necessary but insufficient condition for society to progress [Beauvais & Matagne 1999: 6, translated].

Costa Rica holds at least 5% of the world’s species, in spite of making up 0.03% of its land surface. As an isthmus, Costa Rica is influenced by weather patterns from two oceans, as well as a north-south migration route. In addition to this, its mountainous terrain creates a heterogenous mosaic of habitats and niches. However, the country has been severely deforested. Forest covered 66% of land surface in 1940, and only 25% by 1987; the loss of forest led to extreme erosion.

As presented in this article, an ecological corridor consists of at least two protected ecosystem patches that are connected by a protected vegetated strip of at least a few kilometers in width, and the whole area surrounded by a buffer zone. Multiple units of two connected patches could in turn be connected, stretching into a corridor that the whole length of the country. A green Costa Rican corridor could connect to green corridors in adjacent countries, ultimately recreating the entire isthmic corridor that once existed.

However, the tone of this article is not optimistic about conservation, citing several political obstacles to conservation and ecosystem restoration. According to the authors, a combination of neocolonialist pressure, poverty, corruption, and capitalistic interests allow for trees to be cut even in protected areas and prevent the establishment of new protected areas and corridors.

The fate of biodiversity within protected areas is therefore inextricably linked to the broader landscape context, including how the surrounding agricultural matrix is designed and managed [Harvey 2007: 8].

Rather than discussing ecological corridors per se, this article emphasizes the importance of a whole-landscape approach to biodiversity conservation. Pointing out that protected nature reserves are weakened when isolated, these authors focus on the role of the entire surrounding agricultural matrix for restoring connectivity.

In contrast to the prevailing trend of managing protected areas and productive lands separately, we propose integrated landscape management in which conservation and production units within the agricultural matrix are managed jointly for long-term sustainability. We do not advocate agricultural intensification to spare further forest conversion because this approach is unlikely to have the intended outcome, for reasons discussed. Instead, conservation efforts should be based on the recognition that how agriculture is conducted and how different land uses are distributed spatially and temporally determine the region’s biodiversity. Lasting conservation will therefore require alliances among conservation biologists, farmers, and land managers to actively plan the future of Mesoamerican landscapes [Harvey 2007: 9].

The sections of the agricultural matrix the authors prioritize for biodiversity conservation include areas near riparian and other key ecological corridors, and they recommend leveraging support for the Mesoamerican Biological Corridor to spur regional action. Priority conservation areas are also more likely to encompass landscapes with a high diversity of indigenous and traditional cropping systems than those dedicated to industrial agriculture because “the chances of reconciling farming and biodiversity conservation there [agro-industrial systems] are slim” [Harvey 2007: 10].

The authors argue that, in contrast to large-scale, export-oriented industrial production, small-holder and indigenous agricultural systems are more compatible with biodiversity conservation, increased food production and rural income. The authors propose economic and regulatory instruments and greater regional collaboration to enhance native tree cover on farms, promote traditional, ecologically based farming practices, and to protect remaining intact habitat and restore degraded lands. The overarching vision is to accomplish conservation and agricultural production objectives for the region in mutually reinforcing ways.

The fate of biodiversity within protected areas is therefore inextricably linked to the broader landscape context, including how the surrounding agricultural matrix is designed and managed [Harvey 2007: 8].

In spite of its obvious benefits, agriculture, which covers one third of the Earth’s land surface, damages biodiversity and ecosystem services. In some regions, land degradation and depletion of water resources from irrigation have been so great that historical levels of food production in these regions risk decline. Some areas of previously productive farmland will likely need to be retired from use. Within this context, maintaining and enhancing natural corridors and promoting semi-natural, multifunctional landscapes can significantly contribute to recovering biodiversity and mitigating air and water pollution.

Using California’s San Joaquin Valley (SJV) as a case study, this paper illustrates a pragmatic approach to incorporating ecological corridors into working landscapes. The authors offer a new analytical approach that simultaneously incorporates resource-constrained (water, in this case) land-use change (LUC) modeling within the planning and optimization process. The goals are to simultaneously:

• Meet water-use-reduction policy goals for the area under study within the next two decades
• Identify lands for retirement that are (1) likely to be retired anyways and (2) offer high-value habitat for native species and biodiversity.

Over the past century, SJV has been transformed into one of the largest agricultural economies in the world. However, this economic success has been costly to the SJV in several ways, including:

• Damaged infrastructure: high rates of groundwater extraction in the SJV have led to groundwater overdraft and unreplenished aquifers, resulting in large-scale land subsidence. Most of the subbasins in the SJV are categorized as critically overdrawn, and some regions have sunk over 8 meters since the early 20th century; this land subsidence further imperils water availability and quality by impacting water storage and delivery infrastructure.
• Decreased human health, as a result of impaired air and water quality, leading to chronic health problems
• Threats to wildlife and biodiversity; for example, some species have lost up to 98% of their habitat range, and over 35 native species are listed as threatened or endangered

“In response to these challenges, and amid significant drought-driven fallowing, California passed the Sustainable Groundwater Management Act (SGMA), which … obligates locally governed groundwater subbasins to develop plans that will achieve sustainable groundwater use over the next two decades” [Bryant 2020: 2]. To meet these requirements, many subbasins will meet with severe groundwater pumping restrictions. If these areas are not able to coordinate their pumping activities and augment water supplies, the SGMA may require a reduction in cultivation area through fallowing or permanent retirement.

Given the likely retirement of 86,000 ha of irrigated agricultural land, the authors explore spatial optimization of retired land for conservation efforts. They find that a key strategy is the identification of areas that were destined for retirement from cropping which could be shifted to restoration and habitat enhancement, as well as possibly shifting some areas destined for retirement that have “low habitat value” with regards to wildlife for areas with “high habitat value.” Priority restoration areas identified in this analysis include many that are contiguous and located near designated wildlife areas.

Importantly, the analysis presented here is “explicitly organized to help inform engagement between conservation actors and agricultural land managers about how habitat goals can be achieved in ways that benefit communities in the SJV” [Bryant 2020: 3]. The potential positive futures indicated by such analysis can be used to identify opportunities for collaboration between the conservation and agricultural communities, with a goal of guiding land use change toward achieving multiple benefits, such as recovery of imperiled natural communities, resilient agricultural production, and improved public health outcomes.

While it poses a great challenge, the impending transformation in the SJV also presents an opportunity to proactively shape the landscape in ways that not only ensure agricultural and water sustainability, but also achieve many other socio-ecological goals, such as biodiversity protection and improved human health. However, given that achievement of many of these objectives is determined by where things happen on the landscape (rather than simply the aggregate amounts of cultivation, retirement, or restoration), stakeholders need a systematic way to integrate these objectives to inform multi-benefit spatial planning [Bryant 2020: 4].

Produced by a regional consortium on the environment in Brittany, France, this report describes the ecological value of woody strips encircling agricultural fields and enmeshing the countryside, their decline, and ways to incentivize their protection.

Brittany is a heavily agricultural region that also features a long stretch of coastline where urban development and expansion is ongoing. Due to mechanization and enlargement of farm fields, average parcel size has increased since the 1950s, shrinking the extent of woody hedgerow (“bocage”) between fields. Between 1996 and 2008, the total length of hedgerow decreased 12%. This change is concerning because Brittany is already one of the most fragmented and least wooded parts of France.

The report explains the value of the bocage is its provisioning of habitat, connectivity between habitats, biodiversity, erosion control, groundwater recharge, and flood mitigation. Half the population of Brittany lives in areas susceptible to flooding. Furthermore, at least five endangered animal species depend on the habitat created by the bocage. Protection of this woody network is key to remedying both problems, while also providing direct benefits to farmers, such as habitat for pest predators.

The form and shape of the bocage varies throughout the region, but can include grasses, bushes and/or trees, forming one or more layers of vegetation; and heterogenous landscape features such as berms, ditches, logs, and rocks/boulders, which create microhabitats.

The network of hedge and berms, accompanied by fields, ponds and wetlands, constitutes an important natural environment because of its heterogeneity and potential for complex exchanges. It has the particularity of being able to reach a myriad of increasingly isolated natural spaces in the heart of a changing agricultural countryside subject to ongoing urbanization. Similar to a forest edge environment, the richness of the bocage can be explained by the diversity of habitats it adjoins [OEB 2018: 8, translated].

Regulatory and incentive programs payments have sought to encourage farmers to preserve their hedgerows. However, the authors suggest that a stronger economic valuation of these linear woods is needed to protect and expand them. They suggest strategies for stimulating the market for firewood and other products harvested from sustainably managed hedgerow, where biodiversity protection is an explicit aim and co-benefit.

Americas Context

This article reviews the historical development of two pieces of environmental legislation in France – the use of the “mitigation hierarchy” to assess and limit environmental impact in project development and the promotion of ecological corridors. Theoretically, these two laws overlap when urban development projects in proximity to areas of ecological significance use the mitigation hierarchy (avoid, reduce, compensate) to ensure these zones are protected within the scope of the project.

• 1976: “Protection of Nature” law in France introduced the mitigation hierarchy, aiming to avoid or reduce harm to the environment, or to compensate if harm is unavoidable.
• 1992: Concept of “biodiversity” entered public discourse internationally, following the Earth Summit in Rio, Brazil.
• 1996: France ratified European ecological corridor strategy.
• 1999-2000: Concept of “sustainable development” emerged in France.
• 2004: National strategy for protecting biodiversity adopted.
• 2007: “Grenelle de l’Environnement” meeting created the “Trame Verte et Bleue” (TVB) policy (green and blue infrastructure, encompassing ecological corridors)
• 2016: Biodiversity law enacted, creating national agency and regional committees on biodiversity

In spite of this policy evolution, commitment to ecological corridors has yet to move from a “TVB papier” to a “TVB de projets et d’action.” In other words, much discussion and mapping efforts have not yet resulted in the development of the imagined ecological corridor network. The authors speculate as to why this is so, explaining that the resources and coordination needed for enforcement are lacking. Even though “the creation, preservation and restoration of ecological connectivity” has been integrated into urban planning code, such considerations are often sidelined. Furthermore, definitions are vague: the objective of the TVB is the “good condition” of ecological continuity, but “good condition” is not defined. Lastly, taking action in defense of ecological continuity requires pro-active collaboration among levels of government from local to regional to national.

The authors propose better integration of these to policy tools. For example, the TVB designates certain non-protected areas throughout the country that are ecologically functional and serve a role in the eco-corridor network as key areas to “preserve.” With better communication between this TVB framework, the mitigation hierarchy could be applied at the level of “avoiding” harm to places designated as preservation priorities, but lacking formal “protected” status. In projects where harm is unavoidable, the mitigation hierarchy could be applied at the level of “reducing” harm to maximize the percentage of remaining green space as well as the permeability to wildlife of the built structures (such as passageways through fences). The “compensation” level of the mitigation hierarchy could be applied in the context of regenerating ecosystem function to areas designated in the TVB schema as needing ecosystem restoration.

The authors note that advocates for the TVB are clustered at the national level and within research institutions, while the people responsible for urban planning decisions are local and are not necessarily well versed in the scientific framework for the TVB. Local actors tend to focus on priorities other than ecological continuity. One measure to address this, according to the authors, would be the training of local “relays” to transmit knowledge of ecological principles vis a vis the TVB to local urban planners.

Spurred to action by the European Union and a vision for a pan-European ecological network, France encoded the idea of the “trames vertes et bleues” into law in 2009. The national government worked with all the regional governments to develop maps showing areas with the highest levels of biodiversity. This includes protected areas, stretches of coastline, riparian zones, woods, and other undeveloped areas, whether public or private. The maps also show ecological corridors – both those in good condition needing to be preserved, and those that are highly degraded and requiring restoration.

The regional maps are meant to be integrated into urban planning at the level of city and county (department). Rather than being a regulatory tool, the maps are an information source allowing urban development to proceed in a way that limits impact on biodiversity. The ecological corridor initiative is designed as an invitation and encouragement to local governments, organizations, businesses and individuals to collaborate and to act in favor of biodiversity.

The preservation and restoration of ecosystem connectivity entails acting everywhere possible: in rural environments, in aquatic ecosystems and in urban areas [MTES 2017, translation].

While not an ecological corridor per se, the Natura 2000 network is the largest coordinated network of conservation areas in the world. Covering 17.9% of Europe’s land area and nearly 10% of the continent’s marine areas, the network includes 27,852 sites with an area of 1,358,125 km2. The terrestrial portion of the Natura 2000 network is mostly covered by forests and transitional shrublands. It also includes grasslands and wetlands, as well as pastures, cropland and a small amount of artificial surface (developed/built land).

Member States need to ensure that sufficient protection and appropriate measures are implemented in Natura 2000 sites for habitats and species of community interest and that they form a functional network [EEA 2020: 109].

However, the sites are not strictly protected by virtue of being part of the network. In fact, the sites include a variety of land uses.

Within the network, arable land and permanent crops have increased, while grasslands and forests have decreased. … Pastures and mosaic farmland (with approximately 18 %) and inland wetlands and water bodies (with approximately 10 %) have been extensively transformed into arable land and permanent crops both inside and outside the network. Recent research has shown, however, that high nature value (HNV) farmland inside Natura 2000 sites is less likely to be converted into artificial surfaces than such farmland outside the network and is more likely to maintain its pattern of mosaic farming [EEA 2020: 113].

This assessment of the network’s effectiveness found that “species and habitats are more likely to have a good conservation status if they are well covered by the Natura 2000 network” [EEA 2020: 121]. However, limited monitoring inside and outside the network prevents a more detailed analysis of Natura 2000’s effectiveness. Furthermore, due to a limited implementation of conservation measures, the network’s potential has not yet been fully “unlocked,” according to the report.

To improve Natura 2000’s potential, the authors recommend, among other measures, improving connectivity between protected areas. Noting that sites chosen for inclusion in the network are often motivated by economic rather than ecological interests.

Incoherent planning and site selection approaches between and within Member States has led to insufficient functional connectivity and spatial connectedness between neighboring countries and habitats and gaps in coherence within Member States. This highlights the need to increase connections between protected areas and the level of protection beyond the site [EEA 2020: 122].

Also recommended is increasing stakeholder participation, such as through citizen science monitoring initiatives, and better integration of biodiversity protections into other policy domains.

The resulting low awareness of the diverse benefits produced by the Natura 2000 network is often compounded by a long-standing conflict between economic or political interests and conservation goals. There is thus an urgent need to increase coherence between biodiversity policy and other policy areas, such as in the fields of agriculture and economic and rural development, and create a more integrated approach to address potential conflicts and trade-offs between various interests while fostering synergies [EEA 2020: 124].

The report’s summary conclusion recommends increasing marine and terrestrial conservation areas in the Natura 2000 network to 30% each, strictly protecting these areas, and improving connectivity among them.

Conceptually the inverse of wildlife corridors, fences aim to disconnect. They are built to separate people across national borders, livestock from predators, to delineate property lines, and even to protect wildlife conservation reserves. Globally, fences are ubiquitous, more prevalent even than roads, and proliferating. Yet their ecological impact is relatively unstudied.

Fences are often framed as a management tool rather than a globally significant ecological feature, and they are a notable omission from efforts to map global infrastructure, including the human footprint [McInturff 2020: 971].

This analysis reviews 446 studies starting from 1948 on various types of fencing to assess impacts; however, most of the studies focus on the effect of fencing on particular species (specifically, those the fencing is meant to protect), rather than on multiple species, communities or ecosystems.

Conservation and restoration fences, for example, have support within the literature for their beneficial effects for wildlife and sensitive plant species for which they are built, making such species “winners” in the fencing game. On the other hand, there is a critical lack of information on species that are not the targets for which fences are built, and our review shows that only 10.8% (48 of 446) of studies focus on nontarget species [McInturff 2020: 975].

While fences aiming to protect particular species usually achieve that goal, they inevitably hurt other species.

… often the clearest winners because of fencing are the species that humans value most, whereas losers are inevitable but may remain invisible [McInturff 2020: 975].

Broadly speaking, fences favor generalists and disturbance specialists, many of which are invasive, as well as small and small-ranged, nonmigratory species. Fences therefore heavily restrict what makes a species a winner [McInturff 2020: 975].

The deleterious effects of fences include: impeding migration, reducing gene flow between populations, restructuring community composition and obstructing interspecies interactions, such as between predators and prey. These community-level changes can have ripple effects in the ecosystem. For example, livestock fences effectively excluding dingoes in Australia led to this large predator’s eradication. “Without dingoes, researchers have tracked a continental-scale mesopredator [mid-level predator] release that has altered biodiversity and habitats over enormous areas of Australia” [McInturff 2020: 979].

While fences limit certain interspecies interactions, they concentrate others:

Even where conservation or restoration fences seemingly protect whole habitats, research still points to differential outcomes for constituent species. In addition, pathogens and parasites may spread more rapidly where species interactions are concentrated within reserves. In central Kenya, for example, smaller fenced reserves produced higher gastrointestinal parasite infection rates among impala [McInturff 2020: 977].

The authors recommend a greater research focus on the cumulative ecological effects of fencing, policy that limits fence building and encourages fence removal or fence design that is more wildlife-friendly. They caution that fencing is among the major drivers of anthropogenic change.

As fencing continues to rapidly proliferate, there is potential for a dangerous future in which fences simultaneously alter ecological processes at multiple scales, likely producing more losers than winners, and potentially resulting in ecosystem state shift or collapse [McInturff 2020: 977].

Livestock fences effectively excluding dingoes in Australia led to this large predator’s eradication. “Without dingoes, researchers have tracked a continental-scale mesopredator [a mid-level predator] release that has altered biodiversity and habitats over enormous areas of Australia” [McInturff 2020: 979].

European Context

‘Road verges’ are strips of land on either side of roads and highways that are on average 3-4m wide, but can be as narrow as a few centimeters or many meters wide. “Road verges are commonly grassland habitats, but can be shrubland, forest or artificial arrangements of trees and horticultural plants, and we use the term also to include bare earth and freshwater bodies (e.g. ditches)” [Phillips 2019: 489]. They can also be barren ground or ditch. Not all road verges are managed; when management does occur, it is typically geared toward safety – clearing vegetation to enhance visibility.

There is currently an estimated 36 million linear kilometers of road network in the world, the length of which is expected to increase by 70% by 2050; thus, the total area of road verges will increase as well. “Road and road verge construction will displace habitats and cause many negative ecological and social impacts” [Phillips 2019: 494]. However, there is potential to mitigate that impact by maximizing the ecological value of road verges. Currently, “there may well be 270,000 km2 of road verge globally (0.2% of land), which is similar to the total area of the United Kingdom” [Phillips 2019: 492], with this surface area expected to grow.

While roads run like a network of veins across landscapes, causing widespread negative ecological impacts to adjacent areas, road verges form a parallel network and have the potential both partially to mitigate negative impacts of roads and to deliver environmental benefits [Phillips 2019: 490].

Where roads cut through natural habitat, the road verges will represent a net loss of biodiversity. By contrast, verges can increase biodiversity in highly degraded environments such as cities or industrial farmland. Furthermore, because of the growing urban population, the importance of natural and semi-natural environments will be increasingly important. Road verges designed to maximize ecological value thus have an important role to play in the health and wellbeing of urban residents.

Road verges might increase connectivity in highly modified urban and agricultural landscapes if road verges of suitable size, habitat quality and continuity are created alongside roads, at least for species that are highly mobile or able to persist in narrow, linear habitats [Phillips 2019: 495].

While roads often act as barriers to wildlife and ecological connectivity, ecological corridor design could benefit by taking into account the potential benefits of road verges.

If road verges were integrated into such [ecological corridor design] projects, they might play an important future role in increasing connectivity between natural and semi-natural habitats, particularly across otherwise habitat-poor, human-dominated landscapes where roads often occur [Phillips 2019: 495].

Road verges designed to maximize ecological value thus have an important role to play in the health and wellbeing of urban residents.

Habitat fragmentation, a frequent consequence of habitat loss, is a primary threat to populations and species because isolated subpopulations are expected to experience reduced population viability and ultimately greater risk of extinction. Colonization and gene flow between habitat patches, however, can mitigate these effects [Gilbert-Norton 2010: 661].

This meta-analysis, consisting of 78 experiments from 35 studies, asked the question: Do ecological corridors increase movement between habitat patches, and how does that differ among taxa? The study’s results answer the first part of the research question affirmatively: “There was approximately 50% more movement between habitat patches connected by a corridor than between isolated habitat patches” [Gilbert-Norton 2010: 665].

Furthermore, corridors increase movement for all taxa. “Most corridors are created for terrestrial vertebrates, including birds, although our data suggest that invertebrates and plants also benefit from corridors” [Gilbert-Norton 2010: 665]. This study found that corridors work equally well for all taxa except birds, for whom the corridors were used less; however, birds still favored corridors compared to surrounding matrix.

While three quarters of the experiments showed corridors to be more effective for movement compared to the matrix landscape, 23% of experiments showed corridors were less effective. The authors suggest several explanations for this result. It’s possible that the “matrix habitat has been misclassified as nonhabitat for a study organism” [Gilbert-Norton 2010: 665], that the habitat quality of the corridor is not particularly high, or that the corridor is difficult to locate, given its small size compared to surrounding landscape. Furthermore, use of corridors varies by species.

That almost a quarter of the studies showed organisms used matrix habitat rather than corridors to move between habitat patches furthers the idea that although corridors may be used by many species, they are unlikely to be used by all species, and whether corridors are relevant for land managers may depend on the species of interest [Gilbert-Norton 2010: 665].

The authors also observed that organisms showed greater use of natural corridors (those existing prior to the study) compared to those created and maintained for the study. The real-world applicability of this, as the authors note, is that “it may be better to protect natural landscape features that function as corridors rather than attempting to create corridors” [Gilbert-Norton 2010: 667]. This highlights the importance of protecting natural or semi-natural lands from development.

In contrast to the Gao et al. [2017] article (above), this study maps out an ecological network spanning the entire nation of China. Most such ecological corridor analysis has previously focused at the local and regional levels, according to the authors. They note that in addition to protecting biodiversity, ecological corridors (ECs) purify air, regulate climate, and “realize the movement of material, energy, and information in the ecosystem” [Liang 2018: 23].

This study identifies a couple of dozen high priority areas for conservation based on the existing diversity and quality of the landscape. These high priority areas encompassed seven ecotones (broadleaf forest, coniferous forest, shrub, herbaceous plant, sparse vegetation, wetland, water body), while built up areas such as cities were low priorities. The authors mapped these conservation priority zones against existing formally protected areas (which cover 15% of the country), finding only 19% overlap and, thus, revealing extensive conservation gaps.

The majority of China’s nature reserves were established without a clear planning framework, and couldn’t maximize efficiency of conservation targets. … important zones for species migration are not considered as conservation goals in the current nature reserve system [Liang 2018: 26].

The ecological corridors were identified by examining the pathways with the least amount of potential resistance (such as built infrastructure) to animals moving along them. The shortest routes were not necessarily chosen given the need to bypass urban areas. The map created through this study offers useful information for national conservation planning.

From a long-term conservation perspective, in view of the rapid habitat loss and biodiversity reduction, the ecological network represents a valuable tool to protect the biotope^[5] and their ecological functions in China. In this regard, our results show the importance and need to develop a national protection network maintaining connectivity among them in order to achieve high cost efficiency [Liang 2018: 27].

Changzhou is a city near the Yangtze River delta on the east coast of China that has undergone extensive urban development. “From 2006 to 2014, the built-up area in the city increased by 25.68%” [Gao 2017: 2]. This study is part of an effort to boost biodiversity and ecosystem services in the city, which, at the time of the study, had a few protected patches but no corridors connecting them.

The authors identified potential corridors by comparing three different methods for assessing the level of resistance wildlife would face in moving across the landscape from one habitat patch to another. Corridors were identified by mapping out the paths of least resistance. Potential corridors consisted mainly of riparian greenspaces, followed by forest and farmland, and included between 3.45% and 16% built-up space, depending on the method used. Corridor width was assumed to be 30m. Connection of the most important protected patches should be prioritized in corridor construction.

The International Union for Conservation of Nature (IUCN), which created these guidelines, is an international environmental network founded in 1948 that provides conservation data, assessment and analysis to governments, NGOs and private entities. IUCN also manages the Red List of Threatened Species. This connectivity guideline is part of a series of best practices for protected area land managers.

Providing a definition and context for the importance of connectivity, the authors state:

‘Ecological connectivity’ is the unimpeded movement of species and the flow of natural processes that sustain life on Earth. This is not an overstatement. Without connectivity, ecosystems cannot function properly, and without well-functioning ecosystems, biodiversity and other fundamentals of life are at risk [Hilty 2020: xii].

Moreover,

Most global, regional and national targets for biodiversity conservation, climate change and environmental sustainability cannot be met unless ecological connectivity conservation is addressed [Hilty 2020: 48].

In short, ecological connectivity undergirds the conditions for life on Earth. The authors explain that the concept of connectivity reflects an evolution in conservation science. Previously, nature conservation consisted primarily of setting aside areas of undisturbed or minimally disturbed land. While protected areas remain the foundation of nature conservation, “they are no longer considered sufficient in many places. It is now understood that active measures must also be taken to maintain, enhance or restore ecological connectivity among and between protected areas and OECMs^[4] [Hilty 2020: 2].”

Hence,

These Guidelines have been drafted to help clarify and standardize a shift in conservation practice from a narrow focus on individual protected areas to considering them as essential parts of large landscape conservation networks. This is done through creating ‘ecological networks for conservation’ that are specifically designed, implemented and managed to ensure that ecological connectivity is maintained and enhanced where it is present, or restored where it has been lost. Unless systems of protected areas and OECMs retain all essential ecosystem processes, they are not sufficient [Hilty 2020: 3].

The guidelines emphasize the importance of clearly defining one or more ecological objectives for establishing a corridor, such as to facilitate gene dispersal, migration, or adaptation to climate change for particular or multiple species. Clearly defined objectives allow for a corridor to be created in a way that leads to successful outcomes vis a vis the objectives. Primary objectives should relate directly to ecological connectivity, while complementary social or economic objectives (ecosystem services, such as flood and erosion control, enhancing crop pollination, for example) may also be included.

The toolbox for connectivity conservation includes various types of formal and informal recognition, national legislation, local and regional zoning regulations, conservation easements, conservancy design and transportation planning [Hilty 2020: 48].

The importance of connectivity is increasingly recognized in international treaties, and in national and sub-national planning and policy initiatives.

Until recently, connectivity legislation was rare at the national or even sub-national level. Now, countries such as Bhutan, Costa Rica and Tanzania, and sub-national jurisdictions such as California and New Mexico (USA), have enacted corridor legislation. Additionally, site-specific legislation has been enacted in some countries. For example, the South Korea Act on the Protection of the Baekdu Daegan Mountain System, 2003 (Act no. 7038), which came into effect in 2005, designates an area of 263,427 ha. Of this, 86% is made up of 183 existing protected areas and 14% consists of new buffer and core areas that create a biodiversity corridor along the main mountain range of the Korean Peninsula [Hilty 2020: 45].

However, mostly countries have not yet effectively integrated connectivity into policy and planning. Partly this is due to the complexity of establishing ecological corridors.

Connectivity conservation requires innovative implementation approaches to conserve lands and water within the conservation matrix – across patterns of resource use, jurisdictions, cultures and geographies [Hilty 2020: 48].

These guidelines are meant as a toolbox to help local, regional, national and international entities navigate that complexity.

‘Ecological connectivity’ is the unimpeded movement of species and the flow of natural processes that sustain life on Earth. This is not an overstatement. Without connectivity, ecosystems cannot function properly, and without well-functioning ecosystems, biodiversity and other fundamentals of life are at risk [Hilty 2020: xii].

Currently, 15.1% of land on Earth is conservation protected. This article maps out an additional 35.3% of land needing near-term protection, along with ecological corridor routes connecting these areas. Half of the planet’s land is needed to serve as a Global Safety Net to biodiversity loss and stabilize the global climate.

While the parallel crises of biodiversity loss and climate change have generally been approached separately, a key solution for two of the most pressing challenges of our time is the same: conserve enough nature and in the right places [Dinerstein 2020: 1].

The “right places” were identified by mapping areas with rare or endangered species, biodiversity hotspots^[3], and places with distinct species assemblages. Onto this, the authors mapped areas where wild large mammals are still able to range widely and freely, a phenomenon that has become rare globally given the extent of anthropogenic land conversion, and areas of remaining intact wilderness.

The study also maps out a system of wildlife corridors to connect conservation areas. Only half of currently protected areas are connected. “Connecting all current terrestrial protected areas via potential wildlife and climate corridors (using 2.5 km as an average corridor width) adds 5,705,206 km2 or 4.3% of the terrestrial realm” [Dinerstein 2020: 4]. Assuming the additional lands identified in this study for conservation are formally protected, the amount of land needed for connectivity would be significantly reduced.

While large conservation protections require national leadership to achieve, the need to establish connectivity presents a role for local and regional actors to restore degraded lands in their midst.

The connectivity analysis offers a template to build from and engage local and regional entities in designing programs centered on restoring connectivity. This effort could merge with global habitat restoration and native tree-planting initiatives now under way [Dinerstein 2020: 7].

Focusing restoration efforts on degraded lands that can serve as wildlife corridors could help achieve other objectives, such as the Bonn Challenge. Similarly, massive tree-planting programs, if designed using native species and planted to restore corridors, riparian and coastal vegetation, and upper watersheds, could contribute to stabilizing climate and restoring connectivity [Dinerstein 2020: 7].

At the national level, countries could use the Global Safety Net framework to map out their own corresponding national safety nets. The 20 countries with the greatest role to play in establishing the Global Safety Net include: Russia, Brazil, Indonesia, the United States, Costa Rica, Peru, and Namibia.

Investments needed for the establishment and management of additional protected areas and restoration of degraded lands, while substantial, are small compared with enormous fossil fuel subsidies. The estimated $4.7 trillion per year in fossil fuel subsidies are expected to decline as the Paris Climate Agreement is implemented, making government resources available for restoring, rather than destroying, our global climate system [Dinerstein 2020: 7].

The authors emphasize that the conservation goals of the Global Safety Net are achievable, especially if indigenous people’s land rights are honored. One third of land identified for a Global Safety Net is managed by indigenous communities in a way that preserves biodiversity and regulates Earth’s atmosphere.

A “Global Safety Net” to reverse biodiversity loss and stabilize Earth’s climate, Dinerstein et al. 2020

Currently, 15.1% of land on Earth is conservation protected. This article maps out an additional 35.3% of land needing near-term protection, along with ecological corridor routes connecting these areas. Half of the planet’s land is needed to serve as a Global Safety Net to biodiversity loss and stabilize the global climate.

While the parallel crises of biodiversity loss and climate change have generally been approached separately, a key solution for two of the most pressing challenges of our time is the same: conserve enough nature and in the right places [Dinerstein 2020: 1].

The “right places” were identified by mapping areas with rare or endangered species, biodiversity hotspots^[3], and places with distinct species assemblages. Onto this, the authors mapped areas where wild large mammals are still able to range widely and freely, a phenomenon that has become rare globally given the extent of anthropogenic land conversion, and areas of remaining intact wilderness.

The study also maps out a system of wildlife corridors to connect conservation areas. Only half of currently protected areas are connected. “Connecting all current terrestrial protected areas via potential wildlife and climate corridors (using 2.5 km as an average corridor width) adds 5,705,206 km2 or 4.3% of the terrestrial realm” [Dinerstein 2020: 4]. Assuming the additional lands identified in this study for conservation are formally protected, the amount of land needed for connectivity would be significantly reduced.

While large conservation protections require national leadership to achieve, the need to establish connectivity presents a role for local and regional actors to restore degraded lands in their midst.

The connectivity analysis offers a template to build from and engage local and regional entities in designing programs centered on restoring connectivity. This effort could merge with global habitat restoration and native tree-planting initiatives now under way [Dinerstein 2020: 7].

Focusing restoration efforts on degraded lands that can serve as wildlife corridors could help achieve other objectives, such as the Bonn Challenge. Similarly, massive tree-planting programs, if designed using native species and planted to restore corridors, riparian and coastal vegetation, and upper watersheds, could contribute to stabilizing climate and restoring connectivity [Dinerstein 2020: 7].

At the national level, countries could use the Global Safety Net framework to map out their own corresponding national safety nets. The 20 countries with the greatest role to play in establishing the Global Safety Net include: Russia, Brazil, Indonesia, the United States, Costa Rica, Peru, and Namibia.

Investments needed for the establishment and management of additional protected areas and restoration of degraded lands, while substantial, are small compared with enormous fossil fuel subsidies. The estimated $4.7 trillion per year in fossil fuel subsidies are expected to decline as the Paris Climate Agreement is implemented, making government resources available for restoring, rather than destroying, our global climate system [Dinerstein 2020: 7].

The authors emphasize that the conservation goals of the Global Safety Net are achievable, especially if indigenous people’s land rights are honored. One third of land identified for a Global Safety Net is managed by indigenous communities in a way that preserves biodiversity and regulates Earth’s atmosphere.

Guidelines for conserving connectivity through ecological networks and corridors, Hilty et al. 2020

The International Union for Conservation of Nature (IUCN), which created these guidelines, is an international environmental network founded in 1948 that provides conservation data, assessment and analysis to governments, NGOs and private entities. IUCN also manages the Red List of Threatened Species. This connectivity guideline is part of a series of best practices for protected area land managers.

Providing a definition and context for the importance of connectivity, the authors state:

‘Ecological connectivity’ is the unimpeded movement of species and the flow of natural processes that sustain life on Earth. This is not an overstatement. Without connectivity, ecosystems cannot function properly, and without well-functioning ecosystems, biodiversity and other fundamentals of life are at risk [Hilty 2020: xii].

Moreover,

Most global, regional and national targets for biodiversity conservation, climate change and environmental sustainability cannot be met unless ecological connectivity conservation is addressed [Hilty 2020: 48].

In short, ecological connectivity undergirds the conditions for life on Earth. The authors explain that the concept of connectivity reflects an evolution in conservation science. Previously, nature conservation consisted primarily of setting aside areas of undisturbed or minimally disturbed land. While protected areas remain the foundation of nature conservation, “they are no longer considered sufficient in many places. It is now understood that active measures must also be taken to maintain, enhance or restore ecological connectivity among and between protected areas and OECMs^[4] [Hilty 2020: 2].”

Hence,

These Guidelines have been drafted to help clarify and standardize a shift in conservation practice from a narrow focus on individual protected areas to considering them as essential parts of large landscape conservation networks. This is done through creating ‘ecological networks for conservation’ that are specifically designed, implemented and managed to ensure that ecological connectivity is maintained and enhanced where it is present, or restored where it has been lost. Unless systems of protected areas and OECMs retain all essential ecosystem processes, they are not sufficient [Hilty 2020: 3].

The guidelines emphasize the importance of clearly defining one or more ecological objectives for establishing a corridor, such as to facilitate gene dispersal, migration, or adaptation to climate change for particular or multiple species. Clearly defined objectives allow for a corridor to be created in a way that leads to successful outcomes vis a vis the objectives. Primary objectives should relate directly to ecological connectivity, while complementary social or economic objectives (ecosystem services, such as flood and erosion control, enhancing crop pollination, for example) may also be included.

The toolbox for connectivity conservation includes various types of formal and informal recognition, national legislation, local and regional zoning regulations, conservation easements, conservancy design and transportation planning [Hilty 2020: 48].

The importance of connectivity is increasingly recognized in international treaties, and in national and sub-national planning and policy initiatives.

Until recently, connectivity legislation was rare at the national or even sub-national level. Now, countries such as Bhutan, Costa Rica and Tanzania, and sub-national jurisdictions such as California and New Mexico (USA), have enacted corridor legislation. Additionally, site-specific legislation has been enacted in some countries. For example, the South Korea Act on the Protection of the Baekdu Daegan Mountain System, 2003 (Act no. 7038), which came into effect in 2005, designates an area of 263,427 ha. Of this, 86% is made up of 183 existing protected areas and 14% consists of new buffer and core areas that create a biodiversity corridor along the main mountain range of the Korean Peninsula [Hilty 2020: 45].

However, mostly countries have not yet effectively integrated connectivity into policy and planning. Partly this is due to the complexity of establishing ecological corridors.

Connectivity conservation requires innovative implementation approaches to conserve lands and water within the conservation matrix – across patterns of resource use, jurisdictions, cultures and geographies [Hilty 2020: 48].

These guidelines are meant as a toolbox to help local, regional, national and international entities navigate that complexity.

‘Ecological connectivity’ is the unimpeded movement of species and the flow of natural processes that sustain life on Earth. This is not an overstatement. Without connectivity, ecosystems cannot function properly, and without well-functioning ecosystems, biodiversity and other fundamentals of life are at risk [Hilty 2020: xii].

Constructing ecological networks based on habitat quality assessment: a case study of Changzhou, China, Gao et al. 2017

Changzhou is a city near the Yangtze River delta on the east coast of China that has undergone extensive urban development. “From 2006 to 2014, the built-up area in the city increased by 25.68%” [Gao 2017: 2]. This study is part of an effort to boost biodiversity and ecosystem services in the city, which, at the time of the study, had a few protected patches but no corridors connecting them.

The authors identified potential corridors by comparing three different methods for assessing the level of resistance wildlife would face in moving across the landscape from one habitat patch to another. Corridors were identified by mapping out the paths of least resistance. Potential corridors consisted mainly of riparian greenspaces, followed by forest and farmland, and included between 3.45% and 16% built-up space, depending on the method used. Corridor width was assumed to be 30m. Connection of the most important protected patches should be prioritized in corridor construction.

Integrating priority areas and ecological corridors into national network for conservation planning in China, Liang et al. 2018

In contrast to the Gao et al. [2017] article (above), this study maps out an ecological network spanning the entire nation of China. Most such ecological corridor analysis has previously focused at the local and regional levels, according to the authors. They note that in addition to protecting biodiversity, ecological corridors (ECs) purify air, regulate climate, and “realize the movement of material, energy, and information in the ecosystem” [Liang 2018: 23].

This study identifies a couple of dozen high priority areas for conservation based on the existing diversity and quality of the landscape. These high priority areas encompassed seven ecotones (broadleaf forest, coniferous forest, shrub, herbaceous plant, sparse vegetation, wetland, water body), while built up areas such as cities were low priorities. The authors mapped these conservation priority zones against existing formally protected areas (which cover 15% of the country), finding only 19% overlap and, thus, revealing extensive conservation gaps.

The majority of China’s nature reserves were established without a clear planning framework, and couldn’t maximize efficiency of conservation targets. … important zones for species migration are not considered as conservation goals in the current nature reserve system [Liang 2018: 26].

The ecological corridors were identified by examining the pathways with the least amount of potential resistance (such as built infrastructure) to animals moving along them. The shortest routes were not necessarily chosen given the need to bypass urban areas. The map created through this study offers useful information for national conservation planning.

From a long-term conservation perspective, in view of the rapid habitat loss and biodiversity reduction, the ecological network represents a valuable tool to protect the biotope^[5] and their ecological functions in China. In this regard, our results show the importance and need to develop a national protection network maintaining connectivity among them in order to achieve high cost efficiency [Liang 2018: 27].

A meta-analytic review of corridor effectiveness, Gilbert-Norton et al. 2010

Habitat fragmentation, a frequent consequence of habitat loss, is a primary threat to populations and species because isolated subpopulations are expected to experience reduced population viability and ultimately greater risk of extinction. Colonization and gene flow between habitat patches, however, can mitigate these effects [Gilbert-Norton 2010: 661].

This meta-analysis, consisting of 78 experiments from 35 studies, asked the question: Do ecological corridors increase movement between habitat patches, and how does that differ among taxa? The study’s results answer the first part of the research question affirmatively: “There was approximately 50% more movement between habitat patches connected by a corridor than between isolated habitat patches” [Gilbert-Norton 2010: 665].

Furthermore, corridors increase movement for all taxa. “Most corridors are created for terrestrial vertebrates, including birds, although our data suggest that invertebrates and plants also benefit from corridors” [Gilbert-Norton 2010: 665]. This study found that corridors work equally well for all taxa except birds, for whom the corridors were used less; however, birds still favored corridors compared to surrounding matrix.

While three quarters of the experiments showed corridors to be more effective for movement compared to the matrix landscape, 23% of experiments showed corridors were less effective. The authors suggest several explanations for this result. It’s possible that the “matrix habitat has been misclassified as nonhabitat for a study organism” [Gilbert-Norton 2010: 665], that the habitat quality of the corridor is not particularly high, or that the corridor is difficult to locate, given its small size compared to surrounding landscape. Furthermore, use of corridors varies by species.

That almost a quarter of the studies showed organisms used matrix habitat rather than corridors to move between habitat patches furthers the idea that although corridors may be used by many species, they are unlikely to be used by all species, and whether corridors are relevant for land managers may depend on the species of interest [Gilbert-Norton 2010: 665].

The authors also observed that organisms showed greater use of natural corridors (those existing prior to the study) compared to those created and maintained for the study. The real-world applicability of this, as the authors note, is that “it may be better to protect natural landscape features that function as corridors rather than attempting to create corridors” [Gilbert-Norton 2010: 667]. This highlights the importance of protecting natural or semi-natural lands from development.

Characterizing multispecies connectivity across a transfrontier conservation landscape, Brennan et al. 2020

Connectivity conservation pays attention to landscape connectivity to support animal species’ movements, keep ecological processes intact, and promote biodiversity. While the strategy of conserving connected, non-fragmented areas and respecting animals’ movement patterns is sound, in practice these plans are usually designed around a single species and its needs.

Brennan et al. looked at the limitations of a single-species focus, and evaluated the movement patterns of multiple species. They created connectivity maps for six large mammal species in the Kavango-Zambezi (KAZA) transfrontier conservation area straddling Angola, Zambia, Zimbabwe, Botswana, and Namibia, and assessed how each individual species’ connectivity maps correlated with that of the others.

This then allowed the authors to identify good ‘surrogate species for connectivity’ – that is, species whose connectivity maps were good representations of other species’ movements through the same area. They also took a look at different types of barriers to animal movements and determined that fences were the greatest obstacle to movement, while roads, rivers, and human-settled areas also deterred movement. Finally, they identified connectivity hotspots on the landscape, which are like bottlenecks through which multiple species pass due to barriers elsewhere. These connectivity hotspots are thus essential places to focus conservation efforts.

The researchers found the hyena and African wild dog to be the most apt surrogate species for connectivity, in spite of a popular practice of using elephants to determine the geographic targets of conservation efforts.

In our examination of connectivity across the landscape, female elephants were found to be only weakly correlated with the five other species in our study. Spotted hyena and African wild dog, in contrast, were strongly correlated with the greatest number of species. They also appeared to be complementary surrogates (i.e. they were correlated with different species), in which case combining their connectivity models could further extend the relevancy of connectivity conservation plans to other species. Thus, as both species are also charismatic, wide-ranging species of conservation concern, they may represent good umbrella species for connectivity in the KAZA region [Brennan 2020: 1707].

They went on to say that “while elephants may not be good surrogate species for connectivity across entire landscapes, they may still be effective as a surrogate at local scales where they can help protect local movement pathways or stepping-stone habitats for other species” [Brennan 2020: 1707].

Their conclusion is not that we should stop paying attention to elephants, which serve important ecological functions and are an iconic and culturally significant animal. Rather, we should look for gaps that may arise if we only conserve areas based on elephant movements, and put these techniques of comparing and combining different species’ movement patterns to use. Noting that animal movements and ecological dynamics play out at different scales, from entire landscapes and transnational parks to smaller corridors, they emphasized the importance of looking at connectivity for multiple species at multiple scales. They urged researchers and policy makers to take a more holistic multi-species approach to connectivity conservation.

Salvaging bycatch data for conservation: unexpected benefits of restored grasslands to amphibians in wetland buffer zones and ecological corridors, Mester et al. 2020

This study considers the effect of grassland restoration on amphibian populations in a 760-acre nature reserve – the Egyek-Pusztakócs Marsh System (EPMS) – established on former farmland in Hungary. The study shows that grassland restoration increased habitat range and quality for amphibians, extended hydrological supply, and limited genetic erosion among previously isolated populations. It also illustrates the role of smaller-scale ecological corridors.

Grassland restoration … creates corridors that maintain connectivity among the amphibian (sub)populations in the EPMS but it may also increase the permeability of the landscape to establish and maintain connections to other nearby metapopulations. Grassland restoration can thus also have an effect of minimizing genetic erosion of populations induced by isolation, which is one of the major causes of global amphibian decline [Mester 2020: 7].

Restoration can benefit amphibians by increasing the area of grasslands available for a variety of life activities such as foraging, burrowing, dispersal/ migration, or hiding from predators, aestivation and hibernation in the non-breeding period and by ensuring functional connectivity between wetlands both in the breeding and non-breeding periods [Mester 2020: 9].

Ecosystem service provision by road verges, Phillips et al. 2019

‘Road verges’ are strips of land on either side of roads and highways that are on average 3-4m wide, but can be as narrow as a few centimeters or many meters wide. “Road verges are commonly grassland habitats, but can be shrubland, forest or artificial arrangements of trees and horticultural plants, and we use the term also to include bare earth and freshwater bodies (e.g. ditches)” [Phillips 2019: 489]. They can also be barren ground or ditch. Not all road verges are managed; when management does occur, it is typically geared toward safety – clearing vegetation to enhance visibility.

There is currently an estimated 36 million linear kilometers of road network in the world, the length of which is expected to increase by 70% by 2050; thus, the total area of road verges will increase as well. “Road and road verge construction will displace habitats and cause many negative ecological and social impacts” [Phillips 2019: 494]. However, there is potential to mitigate that impact by maximizing the ecological value of road verges. Currently, “there may well be 270,000 km2 of road verge globally (0.2% of land), which is similar to the total area of the United Kingdom” [Phillips 2019: 492], with this surface area expected to grow.

While roads run like a network of veins across landscapes, causing widespread negative ecological impacts to adjacent areas, road verges form a parallel network and have the potential both partially to mitigate negative impacts of roads and to deliver environmental benefits [Phillips 2019: 490].

Where roads cut through natural habitat, the road verges will represent a net loss of biodiversity. By contrast, verges can increase biodiversity in highly degraded environments such as cities or industrial farmland. Furthermore, because of the growing urban population, the importance of natural and semi-natural environments will be increasingly important. Road verges designed to maximize ecological value thus have an important role to play in the health and wellbeing of urban residents.

Road verges might increase connectivity in highly modified urban and agricultural landscapes if road verges of suitable size, habitat quality and continuity are created alongside roads, at least for species that are highly mobile or able to persist in narrow, linear habitats [Phillips 2019: 495].

While roads often act as barriers to wildlife and ecological connectivity, ecological corridor design could benefit by taking into account the potential benefits of road verges.

If road verges were integrated into such [ecological corridor design] projects, they might play an important future role in increasing connectivity between natural and semi-natural habitats, particularly across otherwise habitat-poor, human-dominated landscapes where roads often occur [Phillips 2019: 495].

Road verges designed to maximize ecological value thus have an important role to play in the health and wellbeing of urban residents.

Fence ecology: frameworks for understanding the ecological effects of fences, McInturff et al. 2020

Conceptually the inverse of wildlife corridors, fences aim to disconnect. They are built to separate people across national borders, livestock from predators, to delineate property lines, and even to protect wildlife conservation reserves. Globally, fences are ubiquitous, more prevalent even than roads, and proliferating. Yet their ecological impact is relatively unstudied.

Fences are often framed as a management tool rather than a globally significant ecological feature, and they are a notable omission from efforts to map global infrastructure, including the human footprint [McInturff 2020: 971].

This analysis reviews 446 studies starting from 1948 on various types of fencing to assess impacts; however, most of the studies focus on the effect of fencing on particular species (specifically, those the fencing is meant to protect), rather than on multiple species, communities or ecosystems.

Conservation and restoration fences, for example, have support within the literature for their beneficial effects for wildlife and sensitive plant species for which they are built, making such species “winners” in the fencing game. On the other hand, there is a critical lack of information on species that are not the targets for which fences are built, and our review shows that only 10.8% (48 of 446) of studies focus on nontarget species [McInturff 2020: 975].

While fences aiming to protect particular species usually achieve that goal, they inevitably hurt other species.

… often the clearest winners because of fencing are the species that humans value most, whereas losers are inevitable but may remain invisible [McInturff 2020: 975].

Broadly speaking, fences favor generalists and disturbance specialists, many of which are invasive, as well as small and small-ranged, nonmigratory species. Fences therefore heavily restrict what makes a species a winner [McInturff 2020: 975].

The deleterious effects of fences include: impeding migration, reducing gene flow between populations, restructuring community composition and obstructing interspecies interactions, such as between predators and prey. These community-level changes can have ripple effects in the ecosystem. For example, livestock fences effectively excluding dingoes in Australia led to this large predator’s eradication. “Without dingoes, researchers have tracked a continental-scale mesopredator [mid-level predator] release that has altered biodiversity and habitats over enormous areas of Australia” [McInturff 2020: 979].

While fences limit certain interspecies interactions, they concentrate others:

Even where conservation or restoration fences seemingly protect whole habitats, research still points to differential outcomes for constituent species. In addition, pathogens and parasites may spread more rapidly where species interactions are concentrated within reserves. In central Kenya, for example, smaller fenced reserves produced higher gastrointestinal parasite infection rates among impala [McInturff 2020: 977].

The authors recommend a greater research focus on the cumulative ecological effects of fencing, policy that limits fence building and encourages fence removal or fence design that is more wildlife-friendly. They caution that fencing is among the major drivers of anthropogenic change.

As fencing continues to rapidly proliferate, there is potential for a dangerous future in which fences simultaneously alter ecological processes at multiple scales, likely producing more losers than winners, and potentially resulting in ecosystem state shift or collapse [McInturff 2020: 977].

Livestock fences effectively excluding dingoes in Australia led to this large predator’s eradication. “Without dingoes, researchers have tracked a continental-scale mesopredator [a mid-level predator] release that has altered biodiversity and habitats over enormous areas of Australia” [McInturff 2020: 979].

European Context

Status of the Natura 2000 network (from State of Nature in the EU report), EEA (European Environmental Agency) 2020

While not an ecological corridor per se, the Natura 2000 network is the largest coordinated network of conservation areas in the world. Covering 17.9% of Europe’s land area and nearly 10% of the continent’s marine areas, the network includes 27,852 sites with an area of 1,358,125 km2. The terrestrial portion of the Natura 2000 network is mostly covered by forests and transitional shrublands. It also includes grasslands and wetlands, as well as pastures, cropland and a small amount of artificial surface (developed/built land).

Member States need to ensure that sufficient protection and appropriate measures are implemented in Natura 2000 sites for habitats and species of community interest and that they form a functional network [EEA 2020: 109].

However, the sites are not strictly protected by virtue of being part of the network. In fact, the sites include a variety of land uses.

Within the network, arable land and permanent crops have increased, while grasslands and forests have decreased. … Pastures and mosaic farmland (with approximately 18 %) and inland wetlands and water bodies (with approximately 10 %) have been extensively transformed into arable land and permanent crops both inside and outside the network. Recent research has shown, however, that high nature value (HNV) farmland inside Natura 2000 sites is less likely to be converted into artificial surfaces than such farmland outside the network and is more likely to maintain its pattern of mosaic farming [EEA 2020: 113].

This assessment of the network’s effectiveness found that “species and habitats are more likely to have a good conservation status if they are well covered by the Natura 2000 network” [EEA 2020: 121]. However, limited monitoring inside and outside the network prevents a more detailed analysis of Natura 2000’s effectiveness. Furthermore, due to a limited implementation of conservation measures, the network’s potential has not yet been fully “unlocked,” according to the report.

To improve Natura 2000’s potential, the authors recommend, among other measures, improving connectivity between protected areas. Noting that sites chosen for inclusion in the network are often motivated by economic rather than ecological interests.

Incoherent planning and site selection approaches between and within Member States has led to insufficient functional connectivity and spatial connectedness between neighboring countries and habitats and gaps in coherence within Member States. This highlights the need to increase connections between protected areas and the level of protection beyond the site [EEA 2020: 122].

Also recommended is increasing stakeholder participation, such as through citizen science monitoring initiatives, and better integration of biodiversity protections into other policy domains.

The resulting low awareness of the diverse benefits produced by the Natura 2000 network is often compounded by a long-standing conflict between economic or political interests and conservation goals. There is thus an urgent need to increase coherence between biodiversity policy and other policy areas, such as in the fields of agriculture and economic and rural development, and create a more integrated approach to address potential conflicts and trade-offs between various interests while fostering synergies [EEA 2020: 124].

The report’s summary conclusion recommends increasing marine and terrestrial conservation areas in the Natura 2000 network to 30% each, strictly protecting these areas, and improving connectivity among them.

Blue and green corridors [Les trames vertes et bleues] in France, Ministry of Ecological Transition 2017

Spurred to action by the European Union and a vision for a pan-European ecological network, France encoded the idea of the “trames vertes et bleues” into law in 2009. The national government worked with all the regional governments to develop maps showing areas with the highest levels of biodiversity. This includes protected areas, stretches of coastline, riparian zones, woods, and other undeveloped areas, whether public or private. The maps also show ecological corridors – both those in good condition needing to be preserved, and those that are highly degraded and requiring restoration.

The regional maps are meant to be integrated into urban planning at the level of city and county (department). Rather than being a regulatory tool, the maps are an information source allowing urban development to proceed in a way that limits impact on biodiversity. The ecological corridor initiative is designed as an invitation and encouragement to local governments, organizations, businesses and individuals to collaborate and to act in favor of biodiversity.

The preservation and restoration of ecosystem connectivity entails acting everywhere possible: in rural environments, in aquatic ecosystems and in urban areas [MTES 2017, translation].

Articulating the politics of green and blue infrastructure and the mitigation hierarchy for effective biodiversity preservation in France [Articuler la politique Trame verte et bleue et la séquence Éviter-réduire-compenser: complémentarités et limites pour une préservation efficace de la biodiversité en France], Chaurand & Bigard 2019

This article reviews the historical development of two pieces of environmental legislation in France – the use of the “mitigation hierarchy” to assess and limit environmental impact in project development and the promotion of ecological corridors. Theoretically, these two laws overlap when urban development projects in proximity to areas of ecological significance use the mitigation hierarchy (avoid, reduce, compensate) to ensure these zones are protected within the scope of the project.

• 1976: “Protection of Nature” law in France introduced the mitigation hierarchy, aiming to avoid or reduce harm to the environment, or to compensate if harm is unavoidable.
• 1992: Concept of “biodiversity” entered public discourse internationally, following the Earth Summit in Rio, Brazil.
• 1996: France ratified European ecological corridor strategy.
• 1999-2000: Concept of “sustainable development” emerged in France.
• 2004: National strategy for protecting biodiversity adopted.
• 2007: “Grenelle de l’Environnement” meeting created the “Trame Verte et Bleue” (TVB) policy (green and blue infrastructure, encompassing ecological corridors)
• 2016: Biodiversity law enacted, creating national agency and regional committees on biodiversity

In spite of this policy evolution, commitment to ecological corridors has yet to move from a “TVB papier” to a “TVB de projets et d’action.” In other words, much discussion and mapping efforts have not yet resulted in the development of the imagined ecological corridor network. The authors speculate as to why this is so, explaining that the resources and coordination needed for enforcement are lacking. Even though “the creation, preservation and restoration of ecological connectivity” has been integrated into urban planning code, such considerations are often sidelined. Furthermore, definitions are vague: the objective of the TVB is the “good condition” of ecological continuity, but “good condition” is not defined. Lastly, taking action in defense of ecological continuity requires pro-active collaboration among levels of government from local to regional to national.

The authors propose better integration of these to policy tools. For example, the TVB designates certain non-protected areas throughout the country that are ecologically functional and serve a role in the eco-corridor network as key areas to “preserve.” With better communication between this TVB framework, the mitigation hierarchy could be applied at the level of “avoiding” harm to places designated as preservation priorities, but lacking formal “protected” status. In projects where harm is unavoidable, the mitigation hierarchy could be applied at the level of “reducing” harm to maximize the percentage of remaining green space as well as the permeability to wildlife of the built structures (such as passageways through fences). The “compensation” level of the mitigation hierarchy could be applied in the context of regenerating ecosystem function to areas designated in the TVB schema as needing ecosystem restoration.

The authors note that advocates for the TVB are clustered at the national level and within research institutions, while the people responsible for urban planning decisions are local and are not necessarily well versed in the scientific framework for the TVB. Local actors tend to focus on priorities other than ecological continuity. One measure to address this, according to the authors, would be the training of local “relays” to transmit knowledge of ecological principles vis a vis the TVB to local urban planners.

Woods and hedgerows of Brittany countryside [Le bocage Bretagne], OEB (L’Observatoire de l’Environnement en Bretagne) 2018

Produced by a regional consortium on the environment in Brittany, France, this report describes the ecological value of woody strips encircling agricultural fields and enmeshing the countryside, their decline, and ways to incentivize their protection.

Brittany is a heavily agricultural region that also features a long stretch of coastline where urban development and expansion is ongoing. Due to mechanization and enlargement of farm fields, average parcel size has increased since the 1950s, shrinking the extent of woody hedgerow (“bocage”) between fields. Between 1996 and 2008, the total length of hedgerow decreased 12%. This change is concerning because Brittany is already one of the most fragmented and least wooded parts of France.

The report explains the value of the bocage is its provisioning of habitat, connectivity between habitats, biodiversity, erosion control, groundwater recharge, and flood mitigation. Half the population of Brittany lives in areas susceptible to flooding. Furthermore, at least five endangered animal species depend on the habitat created by the bocage. Protection of this woody network is key to remedying both problems, while also providing direct benefits to farmers, such as habitat for pest predators.

The form and shape of the bocage varies throughout the region, but can include grasses, bushes and/or trees, forming one or more layers of vegetation; and heterogenous landscape features such as berms, ditches, logs, and rocks/boulders, which create microhabitats.

The network of hedge and berms, accompanied by fields, ponds and wetlands, constitutes an important natural environment because of its heterogeneity and potential for complex exchanges. It has the particularity of being able to reach a myriad of increasingly isolated natural spaces in the heart of a changing agricultural countryside subject to ongoing urbanization. Similar to a forest edge environment, the richness of the bocage can be explained by the diversity of habitats it adjoins [OEB 2018: 8, translated].

Regulatory and incentive programs payments have sought to encourage farmers to preserve their hedgerows. However, the authors suggest that a stronger economic valuation of these linear woods is needed to protect and expand them. They suggest strategies for stimulating the market for firewood and other products harvested from sustainably managed hedgerow, where biodiversity protection is an explicit aim and co-benefit.

Americas Context

Shaping land use change (LUC) and ecosystem restoration in a water-stressed agricultural landscape to achieve multiple benefits, Bryant et al. 2020

In spite of its obvious benefits, agriculture, which covers one third of the Earth’s land surface, damages biodiversity and ecosystem services. In some regions, land degradation and depletion of water resources from irrigation have been so great that historical levels of food production in these regions risk decline. Some areas of previously productive farmland will likely need to be retired from use. Within this context, maintaining and enhancing natural corridors and promoting semi-natural, multifunctional landscapes can significantly contribute to recovering biodiversity and mitigating air and water pollution.

Using California’s San Joaquin Valley (SJV) as a case study, this paper illustrates a pragmatic approach to incorporating ecological corridors into working landscapes. The authors offer a new analytical approach that simultaneously incorporates resource-constrained (water, in this case) land-use change (LUC) modeling within the planning and optimization process. The goals are to simultaneously:

• Meet water-use-reduction policy goals for the area under study within the next two decades
• Identify lands for retirement that are (1) likely to be retired anyways and (2) offer high-value habitat for native species and biodiversity.

Over the past century, SJV has been transformed into one of the largest agricultural economies in the world. However, this economic success has been costly to the SJV in several ways, including:

• Damaged infrastructure: high rates of groundwater extraction in the SJV have led to groundwater overdraft and unreplenished aquifers, resulting in large-scale land subsidence. Most of the subbasins in the SJV are categorized as critically overdrawn, and some regions have sunk over 8 meters since the early 20th century; this land subsidence further imperils water availability and quality by impacting water storage and delivery infrastructure.
• Decreased human health, as a result of impaired air and water quality, leading to chronic health problems
• Threats to wildlife and biodiversity; for example, some species have lost up to 98% of their habitat range, and over 35 native species are listed as threatened or endangered

“In response to these challenges, and amid significant drought-driven fallowing, California passed the Sustainable Groundwater Management Act (SGMA), which … obligates locally governed groundwater subbasins to develop plans that will achieve sustainable groundwater use over the next two decades” [Bryant 2020: 2]. To meet these requirements, many subbasins will meet with severe groundwater pumping restrictions. If these areas are not able to coordinate their pumping activities and augment water supplies, the SGMA may require a reduction in cultivation area through fallowing or permanent retirement.

Given the likely retirement of 86,000 ha of irrigated agricultural land, the authors explore spatial optimization of retired land for conservation efforts. They find that a key strategy is the identification of areas that were destined for retirement from cropping which could be shifted to restoration and habitat enhancement, as well as possibly shifting some areas destined for retirement that have “low habitat value” with regards to wildlife for areas with “high habitat value.” Priority restoration areas identified in this analysis include many that are contiguous and located near designated wildlife areas.

Importantly, the analysis presented here is “explicitly organized to help inform engagement between conservation actors and agricultural land managers about how habitat goals can be achieved in ways that benefit communities in the SJV” [Bryant 2020: 3]. The potential positive futures indicated by such analysis can be used to identify opportunities for collaboration between the conservation and agricultural communities, with a goal of guiding land use change toward achieving multiple benefits, such as recovery of imperiled natural communities, resilient agricultural production, and improved public health outcomes.

While it poses a great challenge, the impending transformation in the SJV also presents an opportunity to proactively shape the landscape in ways that not only ensure agricultural and water sustainability, but also achieve many other socio-ecological goals, such as biodiversity protection and improved human health. However, given that achievement of many of these objectives is determined by where things happen on the landscape (rather than simply the aggregate amounts of cultivation, retirement, or restoration), stakeholders need a systematic way to integrate these objectives to inform multi-benefit spatial planning [Bryant 2020: 4].

Integrating Agricultural Landscapes with Biodiversity Conservation in the Mesoamerican Hotspot, Harvey et al. 2007

The fate of biodiversity within protected areas is therefore inextricably linked to the broader landscape context, including how the surrounding agricultural matrix is designed and managed [Harvey 2007: 8].

Rather than discussing ecological corridors per se, this article emphasizes the importance of a whole-landscape approach to biodiversity conservation. Pointing out that protected nature reserves are weakened when isolated, these authors focus on the role of the entire surrounding agricultural matrix for restoring connectivity.

In contrast to the prevailing trend of managing protected areas and productive lands separately, we propose integrated landscape management in which conservation and production units within the agricultural matrix are managed jointly for long-term sustainability. We do not advocate agricultural intensification to spare further forest conversion because this approach is unlikely to have the intended outcome, for reasons discussed. Instead, conservation efforts should be based on the recognition that how agriculture is conducted and how different land uses are distributed spatially and temporally determine the region’s biodiversity. Lasting conservation will therefore require alliances among conservation biologists, farmers, and land managers to actively plan the future of Mesoamerican landscapes [Harvey 2007: 9].

The sections of the agricultural matrix the authors prioritize for biodiversity conservation include areas near riparian and other key ecological corridors, and they recommend leveraging support for the Mesoamerican Biological Corridor to spur regional action. Priority conservation areas are also more likely to encompass landscapes with a high diversity of indigenous and traditional cropping systems than those dedicated to industrial agriculture because “the chances of reconciling farming and biodiversity conservation there [agro-industrial systems] are slim” [Harvey 2007: 10].

The authors argue that, in contrast to large-scale, export-oriented industrial production, small-holder and indigenous agricultural systems are more compatible with biodiversity conservation, increased food production and rural income. The authors propose economic and regulatory instruments and greater regional collaboration to enhance native tree cover on farms, promote traditional, ecologically based farming practices, and to protect remaining intact habitat and restore degraded lands. The overarching vision is to accomplish conservation and agricultural production objectives for the region in mutually reinforcing ways.

The fate of biodiversity within protected areas is therefore inextricably linked to the broader landscape context, including how the surrounding agricultural matrix is designed and managed [Harvey 2007: 8].

The concept of green corridor and sustainable development in Costa Rica, Beauvais & Matagne 1999

The concept of sustainable development presumes that human economic systems and overall wellbeing depend on functioning ecosystems. Therefore, ecological rhythms should not be transgressed to the point that they fail to provide the vital services needed today and in future generations.

According to this model, economic development becomes a necessary but insufficient condition for society to progress [Beauvais & Matagne 1999: 6, translated].

Costa Rica holds at least 5% of the world’s species, in spite of making up 0.03% of its land surface. As an isthmus, Costa Rica is influenced by weather patterns from two oceans, as well as a north-south migration route. In addition to this, its mountainous terrain creates a heterogenous mosaic of habitats and niches. However, the country has been severely deforested. Forest covered 66% of land surface in 1940, and only 25% by 1987; the loss of forest led to extreme erosion.

As presented in this article, an ecological corridor consists of at least two protected ecosystem patches that are connected by a protected vegetated strip of at least a few kilometers in width, and the whole area surrounded by a buffer zone. Multiple units of two connected patches could in turn be connected, stretching into a corridor that the whole length of the country. A green Costa Rican corridor could connect to green corridors in adjacent countries, ultimately recreating the entire isthmic corridor that once existed.

However, the tone of this article is not optimistic about conservation, citing several political obstacles to conservation and ecosystem restoration. According to the authors, a combination of neocolonialist pressure, poverty, corruption, and capitalistic interests allow for trees to be cut even in protected areas and prevent the establishment of new protected areas and corridors.

The Mesoamerican Biological Corridor in Panama and Costa Rica, Dettman 2006

At the end of the 1980s, as a period of severe conflict in Central America was winding down, most countries in the isthmus signed the Charter Agreement for the Protection of the Environment, which established a sustainable development commission. At the same time, the “Central American Protected Areas System (SICAP) created approximately 11.5 million hectares of protected areas throughout the region” [Dettman 2006: 18].

This paved the way for international attention and investment in what became the Mesoamerican Biological Corridor (MBC). The original intention was to promote biodiversity and economic development in tandem through investment in local projects. However, in the 2000s, the international coordinators of the MBC shifted the focus from biodiversity protection (although the establishment of ecological corridors remains an objective) to a greater emphasis on economic development. This author explains that the institution’s decision-making process is overly top-down, and would benefit from input from local people who are implementing projects on the ground.

Between Bolivar and Bureaucracy: The Mesoamerican Biological Corridor, Liza Grandia 2007

Written by an anthropologist working in Central American conservation efforts for more than 10 years, this article describes the Mesoamerican Biological Corridor (MBC) project as having succumbed to a neoliberal agenda. Although originally spearheaded by Central American environmentalists, the notion of cross-border environmental collaboration was adopted by the World Bank and large international conservation organizations working in Central America in the 1990s. In the hands of these international giants, the biological corridor initiative became a bureaucratic, top-down project, deaf to the voices of local communities.

With all this new bureaucracy, a broad and unfocused agenda, and the challenges of high-level political coordination, the MBC quickly lost its potential to inject a stronger environmental justice component into regional biodiversity conservation programs.

Indeed, the MBC that emerged from the World Bank’s incubator was decidedly more business-oriented than initial proposals for Central American environmental coordination at the 1992 Earth Summit [Grandia 2007: 486].

In this context, the MBC’s conservation efforts have focused more on securing land for protected parks and less on community-based initiatives. The author suggests that in addition to land protection, the MBC should engage farmers in capacity building for eco-agriculture with a view toward achieving landscape-wide ecological connectivity.

The corridor approach might also draw greater attention to the agrarian contexts outside of parks, which may be just as ecologically important as what happens inside parks. By bringing agricultural systems into conservation debates, corridors may present new opportunities for supporting fair-trade projects and other small-scale agroforestry systems compatible with conservation. In other words, corridors could offer a method for moving beyond protectionism to embrace a mosaic vision for conservation that includes local people more explicitly. Corridor planning frameworks also could provide more democratic conservation forums [Grandia 2007: 484].

Effectiveness of Panama as an intercontinental land bridge for large mammals, Meyer et al. 2019

One of the world’s largest corridor projects is the Mesoamerican Biological Corridor (MBC). Initiated in the 1990s, the MBC aims to connect protected areas between southeastern Mexico and Panama [Meyer 2019: 2].

The ecological functionality of the MBC has not been much assessed, in part because direct approaches to measuring connectivity are costly and challenging. In this study, researchers used a simpler, indirect approach to measure forest connectivity through Panama for nine mammals. Using camera traps (cameras that are automatically triggered by a change in some activity in the vicinity, like the presence of an animal), they documented the presence (or absence) of these mammals in 28 forest sites along the Atlantic coast. The corridor was presumed to be functioning for animals whose presence was established across the entire length of the monitored range.

The species monitored in this study are forest specialists, including ungulates, carnivores and an insectivore, all of which are threatened by habitat loss and hunting, some more than others. Of the 43% of land in Panama that is forested, 44% is protected, mostly along the Atlantic coast. Steady economic development threatens remaining ecosystems with investments in large infrastructure projects, real estate, mining, tourism, and energy.

Large mammals are an indicator species for the success of conservation efforts. This is because:

Large mammals are generally at a higher risk of extinction in disturbed landscapes than other taxa because their large home ranges and low population densities at broad spatial scales mean their populations are more likely to be fragmented and because they are heavily hunted [Meyer 2019: 3].

The researchers found that even the four most prevalent species in the study are susceptible to population fragmentation by any further habitat loss.

We found that there was little connectivity for white-lipped peccary [a pig-like animal] and white-tailed deer and that, although 4 of the species (collared peccary, red brocket deer, puma, and ocelot [a wild cat]) occurred in most of the sites, a small decrease in connectivity of 20% would disrupt their continuous distributions across Panama. White-lipped peccary, giant anteater, white-tailed deer, jaguar, and tapir [a pig-like animal with a short trunk] had lower probability of occurring in all the sites and were therefore even more at risk of connectivity loss, as evidenced by >1 connectivity gap. This indicates the MBC may not function for the majority of species, especially considering we did not account for potential effects of hunting, which would make connectivity even more challenging [Meyer 2019: 8].

Citing imminent development projects, such as a new road that will pass through the forested northern coast and associated large hotel projects, the authors predict that ongoing loss of connectivity is likely. Moreover, the deteriorating condition of the corridor in Panama bodes poorly for the MBC overall.

The disruption of connectivity between tropical forests in Central America, and hence the possible separation of mammal populations, is an indicator of the overall functioning of the MBC for wildlife [Meyer 2019: 11].

Belize creates one of Central America’s largest biological corridors, Dasgupta 2018

The Belize government approved a plan in February 2018 to create a 110-square-kilometer biological corridor connecting two nature reserves in the northeast of the country. This outcome resulted from collaboration among NGOs, the government and private property owners. The latter agreed to conserve (to not deforest or otherwise degrade) the parts of their land that would become part of the wildlife corridor. In exchange, the government would not collect taxes on this land. This corridor, which was initiated in the context of the larger Mesoamerican Biological Corridor project, is meant to protect jaguars, cougars and tapirs, among other wildlife.

The woman building the forest corridors saving Brazil’s black lion tamarin, Zanon 2020

“The tamarin is unable to do anything to save its own species. And we, human beings, are the ones who are destroying their environment,” says conservationist Gabriela Rezende. “So, when I got the opportunity to see this animal in the wild, I felt partly responsible for its future.”

Rezende works with the Institute for Ecological Research in the Brazilian state of Sao Paolo to create ecological corridors connecting the forest fragments where the world’s only 1,800 black lion tamarin live in isolated populations. Since 1984, the institute has worked to protect this small primate species, which had reached a low point of 100 individuals and was listed as “critically endangered.” In addition to research and forest restoration, the institute also does environmental education with the local communities. This includes collaboration on nine tree nurseries administered by local people as small businesses that also provide school kids the chance to learn about local forest species that will be planted in corridors.

Leveraging a state policy requiring 20% of privately owned property to be in nature reserves, Rezende worked with landowners to identify patches to be restored that would physically connect forest fragments. Once corridors are complete, the total amount of land in connected habitat will be 111,000 acres. Rezende estimates the black lion tamarin population could increase 30% once it’s able to use the whole forest corridor. The restoration project will benefit other species too, including anteaters, tapirs (a pig-like animal with a short trunk), pumas, and ocelots (another wild cat species).

Establishing ecological corridors is a way to mitigate the effects of habitat loss and fragmentation. Ecological corridors are linear landscape elements connecting otherwise isolated habitat patches within a larger matrix of environmentally degraded lands (urban or agricultural, for example). The corridors facilitate gene dispersal and migration, while also expanding habitat range for species constrained by patch size. They can take the form of riparian (river) ecosystems, hedge networks, forest edges, or grassy bands.

Ecological (wildlife/biological) corridors are based on the concept of connectivity, which is essential to ecosystem functioning, and thus to the persistence of life on earth. When connectivity is disrupted, so are “ecological processes such as gene flow, pollination, [and] wildlife dispersal” [Estreguil 2013: 5]. Dinerstein et al. [2020] recommend establishing a global safety net against the intertwined threats of climate change and biodiversity loss. For this, they suggest the protection of 50% of land surface as intact, interconnected ecosystems.

The field of conservation has recently integrated the idea of connectivity, thus moving beyond efforts to simply set aside protected patches. Beginning in the 1990s, the study of ecological corridors has investigated their effect on biodiversity, their traction in the realm of public policy, and strategies for mapping corridors. Most studies show that ecological corridors are indeed effective in protecting species, although some species benefit more than others, depending on corridor design. Achieving political salience for such initiatives, however, appears to be as difficult as for any other conservation project.

Nevertheless, the mapping and development of ecological corridors is a way to enter into conversation with multiple stakeholders about conservation and the potential for collaboration. While establishing large protected areas often falls under the jurisdiction of national governments, restoring strips of land to connect these areas is well suited to the work of communities, local planners and public and private land managers. Within a regional, national or international context, establishing a network of connected ecosystems calls for coordination at multiple levels of government.

In 2009, the French government encoded the idea of ecological corridors into law, thus initiating a process for mapping out degraded areas and those with higher levels of ecosystem intactness. In collaboration with local and national actors, each regional government engaged in a process of mapping out land, whether public or private, where ecosystems are in relatively good condition and should be preserved, and where land is in poor condition and should be restored. The maps also include potential ecological corridor routes.

The combining of the regional maps into a whole country map thus creates a coherent ecological framework for land protection and restoration efforts. It is a tool to help local and regional planners prioritize conservation efforts in the places likely to best protect wildlife and ecosystem processes. While urban planning documents are expected to take these maps into account, the manner and extent to which ecological concerns are weighted in urban planning decisions is subject to local interpretation. Thus, the maps can serve as a tool for those motivated to protect the environment, yet they remain easily sidelined by the less motivated.

In their 2019 assessment of French ecological corridor efforts, Chaurand & Bigard suggest that part of the reason corridor development has not been more readily adopted at the local level is that much of the knowledge and enthusiasm for the idea exists at the national level among researchers and program leaders. To remedy this, they recommend investing in a system to relay information between local and national actors.

Similarly, critiques of the MesoAmerican Biological Corridor (MBC) have noted the shortcomings of a top-heavy approach [Dettman 2006, Grandia 2007, Harvey 2007, Beauvais & Matagne 1999]. Funded by the World Bank and led largely by international conservation organizations, development of this ecological corridor appears not to have effectively partnered with nor sought adequate input from local communities.

Consequently, the MBC has met with limited success in terms of biodiversity conservation. Connectivity for nine mammals in the Panama portion of the MBC is already severely fractured and predicted to decline further with planned road construction and other development projects on the horizon. In light of these findings, the authors of a Panama study [Meyer 2019] are not particularly optimistic about the condition of ecological connectivity in the MBC overall.

On a brighter note, Belize has recently approved a plan under the rubric of the MBC to establish a 110 km2 ecological corridor, which will be one of Central America’s largest. This was the outcome of collaboration between landowners, government and NGOs. South of the MBC, another ecological corridor is being developed in Brazil [Zanon 2020]. Thanks to the work of a local NGO that combines conservation with local community education, additional corridors will create a total of 44,920 ha2 of connected habitat. This is expected to increase the population of the threatened target species (black lion tamarin) by 30%.

These two examples notwithstanding, it is ironic that ecological corridors (designed to mitigate the effects of habitat destruction) are subject to the same pressures and obstacles as the problem they aim to remedy. Difficulty stems from the multiplicity of economic interests in land and a mosaic of ownership titles across a given landscape. Furthermore, the ecological concept of connectivity is not necessarily understood by the general public or policy makers, resulting in its low ranking as policy priority.

The ecological concept of connectivity is not necessarily understood by the general public or policy makers, resulting in its low ranking as policy priority.

The European Natura 2000 network, which helped spur France’s ecological corridor mapping initiative, is a continent-wide network of natural or semi-natural areas. However, the vast majority of these sites (86%) are unconnected to one another [Estreguil 2013], a fact which severely limits their value to wildlife. In spite of covering 18% of the land area of Europe, the nearly 28,000 sites in the network are isolated islands of nature within a generally hostile surrounding landscape.

There is the need to acknowledge nature as a system rather than individual parts. The establishment of N2K [Natura 2000] network (i.e. the sum of the individual sites) should be distinguished from the establishment of the overall ecological coherence of the network [Estreguil 2013: 5].

Furthermore, the areas themselves are not formally protected and can theoretically be developed; however, they are less likely to be developed by virtue of being a Natura 2000 site. A 2018 EEA assessment suggested that to “unlock” the potential of this ecological network, biodiversity policy should be thoroughly integrated by member states with economic development and other public policy domains, and that greater stakeholder engagement should be sought such as through citizen science biodiversity monitoring initiatives.

The enormous potential of ecological corridors fully depends on concerted efforts to communicate the meaning and importance of connectivity to stakeholders at every level of government and within the general public.

There is the need to acknowledge nature as a system rather than individual parts [Estreguil 2013: 5].

Ecological corridor article summaries

A “Global Safety Net” to reverse biodiversity loss and stabilize Earth’s climate, Dinerstein et al. 2020

Currently, 15.1% of land on Earth is conservation protected. This article maps out an additional 35.3% of land needing near-term protection, along with ecological corridor routes connecting these areas. Half of the planet’s land is needed to serve as a Global Safety Net to biodiversity loss and stabilize the global climate.

While the parallel crises of biodiversity loss and climate change have generally been approached separately, a key solution for two of the most pressing challenges of our time is the same: conserve enough nature and in the right places [Dinerstein 2020: 1].

The “right places” were identified by mapping areas with rare or endangered species, biodiversity hotspots^[3], and places with distinct species assemblages. Onto this, the authors mapped areas where wild large mammals are still able to range widely and freely, a phenomenon that has become rare globally given the extent of anthropogenic land conversion, and areas of remaining intact wilderness.

The study also maps out a system of wildlife corridors to connect conservation areas. Only half of currently protected areas are connected. “Connecting all current terrestrial protected areas via potential wildlife and climate corridors (using 2.5 km as an average corridor width) adds 5,705,206 km2 or 4.3% of the terrestrial realm” [Dinerstein 2020: 4]. Assuming the additional lands identified in this study for conservation are formally protected, the amount of land needed for connectivity would be significantly reduced.

While large conservation protections require national leadership to achieve, the need to establish connectivity presents a role for local and regional actors to restore degraded lands in their midst.

The connectivity analysis offers a template to build from and engage local and regional entities in designing programs centered on restoring connectivity. This effort could merge with global habitat restoration and native tree-planting initiatives now under way [Dinerstein 2020: 7].

Focusing restoration efforts on degraded lands that can serve as wildlife corridors could help achieve other objectives, such as the Bonn Challenge. Similarly, massive tree-planting programs, if designed using native species and planted to restore corridors, riparian and coastal vegetation, and upper watersheds, could contribute to stabilizing climate and restoring connectivity [Dinerstein 2020: 7].

At the national level, countries could use the Global Safety Net framework to map out their own corresponding national safety nets. The 20 countries with the greatest role to play in establishing the Global Safety Net include: Russia, Brazil, Indonesia, the United States, Costa Rica, Peru, and Namibia.

Investments needed for the establishment and management of additional protected areas and restoration of degraded lands, while substantial, are small compared with enormous fossil fuel subsidies. The estimated $4.7 trillion per year in fossil fuel subsidies are expected to decline as the Paris Climate Agreement is implemented, making government resources available for restoring, rather than destroying, our global climate system [Dinerstein 2020: 7].

The authors emphasize that the conservation goals of the Global Safety Net are achievable, especially if indigenous people’s land rights are honored. One third of land identified for a Global Safety Net is managed by indigenous communities in a way that preserves biodiversity and regulates Earth’s atmosphere.

Guidelines for conserving connectivity through ecological networks and corridors, Hilty et al. 2020

The International Union for Conservation of Nature (IUCN), which created these guidelines, is an international environmental network founded in 1948 that provides conservation data, assessment and analysis to governments, NGOs and private entities. IUCN also manages the Red List of Threatened Species. This connectivity guideline is part of a series of best practices for protected area land managers.

Providing a definition and context for the importance of connectivity, the authors state:

‘Ecological connectivity’ is the unimpeded movement of species and the flow of natural processes that sustain life on Earth. This is not an overstatement. Without connectivity, ecosystems cannot function properly, and without well-functioning ecosystems, biodiversity and other fundamentals of life are at risk [Hilty 2020: xii].

Moreover,

Most global, regional and national targets for biodiversity conservation, climate change and environmental sustainability cannot be met unless ecological connectivity conservation is addressed [Hilty 2020: 48].

In short, ecological connectivity undergirds the conditions for life on Earth. The authors explain that the concept of connectivity reflects an evolution in conservation science. Previously, nature conservation consisted primarily of setting aside areas of undisturbed or minimally disturbed land. While protected areas remain the foundation of nature conservation, “they are no longer considered sufficient in many places. It is now understood that active measures must also be taken to maintain, enhance or restore ecological connectivity among and between protected areas and OECMs^[4] [Hilty 2020: 2].”

Hence,

These Guidelines have been drafted to help clarify and standardize a shift in conservation practice from a narrow focus on individual protected areas to considering them as essential parts of large landscape conservation networks. This is done through creating ‘ecological networks for conservation’ that are specifically designed, implemented and managed to ensure that ecological connectivity is maintained and enhanced where it is present, or restored where it has been lost. Unless systems of protected areas and OECMs retain all essential ecosystem processes, they are not sufficient [Hilty 2020: 3].

The guidelines emphasize the importance of clearly defining one or more ecological objectives for establishing a corridor, such as to facilitate gene dispersal, migration, or adaptation to climate change for particular or multiple species. Clearly defined objectives allow for a corridor to be created in a way that leads to successful outcomes vis a vis the objectives. Primary objectives should relate directly to ecological connectivity, while complementary social or economic objectives (ecosystem services, such as flood and erosion control, enhancing crop pollination, for example) may also be included.

The toolbox for connectivity conservation includes various types of formal and informal recognition, national legislation, local and regional zoning regulations, conservation easements, conservancy design and transportation planning [Hilty 2020: 48].

The importance of connectivity is increasingly recognized in international treaties, and in national and sub-national planning and policy initiatives.

Until recently, connectivity legislation was rare at the national or even sub-national level. Now, countries such as Bhutan, Costa Rica and Tanzania, and sub-national jurisdictions such as California and New Mexico (USA), have enacted corridor legislation. Additionally, site-specific legislation has been enacted in some countries. For example, the South Korea Act on the Protection of the Baekdu Daegan Mountain System, 2003 (Act no. 7038), which came into effect in 2005, designates an area of 263,427 ha. Of this, 86% is made up of 183 existing protected areas and 14% consists of new buffer and core areas that create a biodiversity corridor along the main mountain range of the Korean Peninsula [Hilty 2020: 45].

However, mostly countries have not yet effectively integrated connectivity into policy and planning. Partly this is due to the complexity of establishing ecological corridors.

Connectivity conservation requires innovative implementation approaches to conserve lands and water within the conservation matrix – across patterns of resource use, jurisdictions, cultures and geographies [Hilty 2020: 48].

These guidelines are meant as a toolbox to help local, regional, national and international entities navigate that complexity.

‘Ecological connectivity’ is the unimpeded movement of species and the flow of natural processes that sustain life on Earth. This is not an overstatement. Without connectivity, ecosystems cannot function properly, and without well-functioning ecosystems, biodiversity and other fundamentals of life are at risk [Hilty 2020: xii].

Constructing ecological networks based on habitat quality assessment: a case study of Changzhou, China, Gao et al. 2017

Changzhou is a city near the Yangtze River delta on the east coast of China that has undergone extensive urban development. “From 2006 to 2014, the built-up area in the city increased by 25.68%” [Gao 2017: 2]. This study is part of an effort to boost biodiversity and ecosystem services in the city, which, at the time of the study, had a few protected patches but no corridors connecting them.

The authors identified potential corridors by comparing three different methods for assessing the level of resistance wildlife would face in moving across the landscape from one habitat patch to another. Corridors were identified by mapping out the paths of least resistance. Potential corridors consisted mainly of riparian greenspaces, followed by forest and farmland, and included between 3.45% and 16% built-up space, depending on the method used. Corridor width was assumed to be 30m. Connection of the most important protected patches should be prioritized in corridor construction.

Integrating priority areas and ecological corridors into national network for conservation planning in China, Liang et al. 2018

In contrast to the Gao et al. [2017] article (above), this study maps out an ecological network spanning the entire nation of China. Most such ecological corridor analysis has previously focused at the local and regional levels, according to the authors. They note that in addition to protecting biodiversity, ecological corridors (ECs) purify air, regulate climate, and “realize the movement of material, energy, and information in the ecosystem” [Liang 2018: 23].

This study identifies a couple of dozen high priority areas for conservation based on the existing diversity and quality of the landscape. These high priority areas encompassed seven ecotones (broadleaf forest, coniferous forest, shrub, herbaceous plant, sparse vegetation, wetland, water body), while built up areas such as cities were low priorities. The authors mapped these conservation priority zones against existing formally protected areas (which cover 15% of the country), finding only 19% overlap and, thus, revealing extensive conservation gaps.

The majority of China’s nature reserves were established without a clear planning framework, and couldn’t maximize efficiency of conservation targets. … important zones for species migration are not considered as conservation goals in the current nature reserve system [Liang 2018: 26].

The ecological corridors were identified by examining the pathways with the least amount of potential resistance (such as built infrastructure) to animals moving along them. The shortest routes were not necessarily chosen given the need to bypass urban areas. The map created through this study offers useful information for national conservation planning.

From a long-term conservation perspective, in view of the rapid habitat loss and biodiversity reduction, the ecological network represents a valuable tool to protect the biotope^[5] and their ecological functions in China. In this regard, our results show the importance and need to develop a national protection network maintaining connectivity among them in order to achieve high cost efficiency [Liang 2018: 27].

A meta-analytic review of corridor effectiveness, Gilbert-Norton et al. 2010

Habitat fragmentation, a frequent consequence of habitat loss, is a primary threat to populations and species because isolated subpopulations are expected to experience reduced population viability and ultimately greater risk of extinction. Colonization and gene flow between habitat patches, however, can mitigate these effects [Gilbert-Norton 2010: 661].

This meta-analysis, consisting of 78 experiments from 35 studies, asked the question: Do ecological corridors increase movement between habitat patches, and how does that differ among taxa? The study’s results answer the first part of the research question affirmatively: “There was approximately 50% more movement between habitat patches connected by a corridor than between isolated habitat patches” [Gilbert-Norton 2010: 665].

Furthermore, corridors increase movement for all taxa. “Most corridors are created for terrestrial vertebrates, including birds, although our data suggest that invertebrates and plants also benefit from corridors” [Gilbert-Norton 2010: 665]. This study found that corridors work equally well for all taxa except birds, for whom the corridors were used less; however, birds still favored corridors compared to surrounding matrix.

While three quarters of the experiments showed corridors to be more effective for movement compared to the matrix landscape, 23% of experiments showed corridors were less effective. The authors suggest several explanations for this result. It’s possible that the “matrix habitat has been misclassified as nonhabitat for a study organism” [Gilbert-Norton 2010: 665], that the habitat quality of the corridor is not particularly high, or that the corridor is difficult to locate, given its small size compared to surrounding landscape. Furthermore, use of corridors varies by species.

That almost a quarter of the studies showed organisms used matrix habitat rather than corridors to move between habitat patches furthers the idea that although corridors may be used by many species, they are unlikely to be used by all species, and whether corridors are relevant for land managers may depend on the species of interest [Gilbert-Norton 2010: 665].

The authors also observed that organisms showed greater use of natural corridors (those existing prior to the study) compared to those created and maintained for the study. The real-world applicability of this, as the authors note, is that “it may be better to protect natural landscape features that function as corridors rather than attempting to create corridors” [Gilbert-Norton 2010: 667]. This highlights the importance of protecting natural or semi-natural lands from development.

Characterizing multispecies connectivity across a transfrontier conservation landscape, Brennan et al. 2020

Connectivity conservation pays attention to landscape connectivity to support animal species’ movements, keep ecological processes intact, and promote biodiversity. While the strategy of conserving connected, non-fragmented areas and respecting animals’ movement patterns is sound, in practice these plans are usually designed around a single species and its needs.

Brennan et al. looked at the limitations of a single-species focus, and evaluated the movement patterns of multiple species. They created connectivity maps for six large mammal species in the Kavango-Zambezi (KAZA) transfrontier conservation area straddling Angola, Zambia, Zimbabwe, Botswana, and Namibia, and assessed how each individual species’ connectivity maps correlated with that of the others.

This then allowed the authors to identify good ‘surrogate species for connectivity’ – that is, species whose connectivity maps were good representations of other species’ movements through the same area. They also took a look at different types of barriers to animal movements and determined that fences were the greatest obstacle to movement, while roads, rivers, and human-settled areas also deterred movement. Finally, they identified connectivity hotspots on the landscape, which are like bottlenecks through which multiple species pass due to barriers elsewhere. These connectivity hotspots are thus essential places to focus conservation efforts.

The researchers found the hyena and African wild dog to be the most apt surrogate species for connectivity, in spite of a popular practice of using elephants to determine the geographic targets of conservation efforts.

In our examination of connectivity across the landscape, female elephants were found to be only weakly correlated with the five other species in our study. Spotted hyena and African wild dog, in contrast, were strongly correlated with the greatest number of species. They also appeared to be complementary surrogates (i.e. they were correlated with different species), in which case combining their connectivity models could further extend the relevancy of connectivity conservation plans to other species. Thus, as both species are also charismatic, wide-ranging species of conservation concern, they may represent good umbrella species for connectivity in the KAZA region [Brennan 2020: 1707].

They went on to say that “while elephants may not be good surrogate species for connectivity across entire landscapes, they may still be effective as a surrogate at local scales where they can help protect local movement pathways or stepping-stone habitats for other species” [Brennan 2020: 1707].

Their conclusion is not that we should stop paying attention to elephants, which serve important ecological functions and are an iconic and culturally significant animal. Rather, we should look for gaps that may arise if we only conserve areas based on elephant movements, and put these techniques of comparing and combining different species’ movement patterns to use. Noting that animal movements and ecological dynamics play out at different scales, from entire landscapes and transnational parks to smaller corridors, they emphasized the importance of looking at connectivity for multiple species at multiple scales. They urged researchers and policy makers to take a more holistic multi-species approach to connectivity conservation.

Salvaging bycatch data for conservation: unexpected benefits of restored grasslands to amphibians in wetland buffer zones and ecological corridors, Mester et al. 2020

This study considers the effect of grassland restoration on amphibian populations in a 760-acre nature reserve – the Egyek-Pusztakócs Marsh System (EPMS) – established on former farmland in Hungary. The study shows that grassland restoration increased habitat range and quality for amphibians, extended hydrological supply, and limited genetic erosion among previously isolated populations. It also illustrates the role of smaller-scale ecological corridors.

Grassland restoration … creates corridors that maintain connectivity among the amphibian (sub)populations in the EPMS but it may also increase the permeability of the landscape to establish and maintain connections to other nearby metapopulations. Grassland restoration can thus also have an effect of minimizing genetic erosion of populations induced by isolation, which is one of the major causes of global amphibian decline [Mester 2020: 7].

Restoration can benefit amphibians by increasing the area of grasslands available for a variety of life activities such as foraging, burrowing, dispersal/ migration, or hiding from predators, aestivation and hibernation in the non-breeding period and by ensuring functional connectivity between wetlands both in the breeding and non-breeding periods [Mester 2020: 9].

Ecosystem service provision by road verges, Phillips et al. 2019

‘Road verges’ are strips of land on either side of roads and highways that are on average 3-4m wide, but can be as narrow as a few centimeters or many meters wide. “Road verges are commonly grassland habitats, but can be shrubland, forest or artificial arrangements of trees and horticultural plants, and we use the term also to include bare earth and freshwater bodies (e.g. ditches)” [Phillips 2019: 489]. They can also be barren ground or ditch. Not all road verges are managed; when management does occur, it is typically geared toward safety – clearing vegetation to enhance visibility.

There is currently an estimated 36 million linear kilometers of road network in the world, the length of which is expected to increase by 70% by 2050; thus, the total area of road verges will increase as well. “Road and road verge construction will displace habitats and cause many negative ecological and social impacts” [Phillips 2019: 494]. However, there is potential to mitigate that impact by maximizing the ecological value of road verges. Currently, “there may well be 270,000 km2 of road verge globally (0.2% of land), which is similar to the total area of the United Kingdom” [Phillips 2019: 492], with this surface area expected to grow.

While roads run like a network of veins across landscapes, causing widespread negative ecological impacts to adjacent areas, road verges form a parallel network and have the potential both partially to mitigate negative impacts of roads and to deliver environmental benefits [Phillips 2019: 490].

Where roads cut through natural habitat, the road verges will represent a net loss of biodiversity. By contrast, verges can increase biodiversity in highly degraded environments such as cities or industrial farmland. Furthermore, because of the growing urban population, the importance of natural and semi-natural environments will be increasingly important. Road verges designed to maximize ecological value thus have an important role to play in the health and wellbeing of urban residents.

Road verges might increase connectivity in highly modified urban and agricultural landscapes if road verges of suitable size, habitat quality and continuity are created alongside roads, at least for species that are highly mobile or able to persist in narrow, linear habitats [Phillips 2019: 495].

While roads often act as barriers to wildlife and ecological connectivity, ecological corridor design could benefit by taking into account the potential benefits of road verges.

If road verges were integrated into such [ecological corridor design] projects, they might play an important future role in increasing connectivity between natural and semi-natural habitats, particularly across otherwise habitat-poor, human-dominated landscapes where roads often occur [Phillips 2019: 495].

Road verges designed to maximize ecological value thus have an important role to play in the health and wellbeing of urban residents.

Fence ecology: frameworks for understanding the ecological effects of fences, McInturff et al. 2020

Conceptually the inverse of wildlife corridors, fences aim to disconnect. They are built to separate people across national borders, livestock from predators, to delineate property lines, and even to protect wildlife conservation reserves. Globally, fences are ubiquitous, more prevalent even than roads, and proliferating. Yet their ecological impact is relatively unstudied.

Fences are often framed as a management tool rather than a globally significant ecological feature, and they are a notable omission from efforts to map global infrastructure, including the human footprint [McInturff 2020: 971].

This analysis reviews 446 studies starting from 1948 on various types of fencing to assess impacts; however, most of the studies focus on the effect of fencing on particular species (specifically, those the fencing is meant to protect), rather than on multiple species, communities or ecosystems.

Conservation and restoration fences, for example, have support within the literature for their beneficial effects for wildlife and sensitive plant species for which they are built, making such species “winners” in the fencing game. On the other hand, there is a critical lack of information on species that are not the targets for which fences are built, and our review shows that only 10.8% (48 of 446) of studies focus on nontarget species [McInturff 2020: 975].

While fences aiming to protect particular species usually achieve that goal, they inevitably hurt other species.

… often the clearest winners because of fencing are the species that humans value most, whereas losers are inevitable but may remain invisible [McInturff 2020: 975].

Broadly speaking, fences favor generalists and disturbance specialists, many of which are invasive, as well as small and small-ranged, nonmigratory species. Fences therefore heavily restrict what makes a species a winner [McInturff 2020: 975].

The deleterious effects of fences include: impeding migration, reducing gene flow between populations, restructuring community composition and obstructing interspecies interactions, such as between predators and prey. These community-level changes can have ripple effects in the ecosystem. For example, livestock fences effectively excluding dingoes in Australia led to this large predator’s eradication. “Without dingoes, researchers have tracked a continental-scale mesopredator [mid-level predator] release that has altered biodiversity and habitats over enormous areas of Australia” [McInturff 2020: 979].

While fences limit certain interspecies interactions, they concentrate others:

Even where conservation or restoration fences seemingly protect whole habitats, research still points to differential outcomes for constituent species. In addition, pathogens and parasites may spread more rapidly where species interactions are concentrated within reserves. In central Kenya, for example, smaller fenced reserves produced higher gastrointestinal parasite infection rates among impala [McInturff 2020: 977].

The authors recommend a greater research focus on the cumulative ecological effects of fencing, policy that limits fence building and encourages fence removal or fence design that is more wildlife-friendly. They caution that fencing is among the major drivers of anthropogenic change.

As fencing continues to rapidly proliferate, there is potential for a dangerous future in which fences simultaneously alter ecological processes at multiple scales, likely producing more losers than winners, and potentially resulting in ecosystem state shift or collapse [McInturff 2020: 977].

Livestock fences effectively excluding dingoes in Australia led to this large predator’s eradication. “Without dingoes, researchers have tracked a continental-scale mesopredator [a mid-level predator] release that has altered biodiversity and habitats over enormous areas of Australia” [McInturff 2020: 979].

European Context

Status of the Natura 2000 network (from State of Nature in the EU report), EEA (European Environmental Agency) 2020

While not an ecological corridor per se, the Natura 2000 network is the largest coordinated network of conservation areas in the world. Covering 17.9% of Europe’s land area and nearly 10% of the continent’s marine areas, the network includes 27,852 sites with an area of 1,358,125 km2. The terrestrial portion of the Natura 2000 network is mostly covered by forests and transitional shrublands. It also includes grasslands and wetlands, as well as pastures, cropland and a small amount of artificial surface (developed/built land).

Member States need to ensure that sufficient protection and appropriate measures are implemented in Natura 2000 sites for habitats and species of community interest and that they form a functional network [EEA 2020: 109].

However, the sites are not strictly protected by virtue of being part of the network. In fact, the sites include a variety of land uses.

Within the network, arable land and permanent crops have increased, while grasslands and forests have decreased. … Pastures and mosaic farmland (with approximately 18 %) and inland wetlands and water bodies (with approximately 10 %) have been extensively transformed into arable land and permanent crops both inside and outside the network. Recent research has shown, however, that high nature value (HNV) farmland inside Natura 2000 sites is less likely to be converted into artificial surfaces than such farmland outside the network and is more likely to maintain its pattern of mosaic farming [EEA 2020: 113].

This assessment of the network’s effectiveness found that “species and habitats are more likely to have a good conservation status if they are well covered by the Natura 2000 network” [EEA 2020: 121]. However, limited monitoring inside and outside the network prevents a more detailed analysis of Natura 2000’s effectiveness. Furthermore, due to a limited implementation of conservation measures, the network’s potential has not yet been fully “unlocked,” according to the report.

To improve Natura 2000’s potential, the authors recommend, among other measures, improving connectivity between protected areas. Noting that sites chosen for inclusion in the network are often motivated by economic rather than ecological interests.

Incoherent planning and site selection approaches between and within Member States has led to insufficient functional connectivity and spatial connectedness between neighboring countries and habitats and gaps in coherence within Member States. This highlights the need to increase connections between protected areas and the level of protection beyond the site [EEA 2020: 122].

Also recommended is increasing stakeholder participation, such as through citizen science monitoring initiatives, and better integration of biodiversity protections into other policy domains.

The resulting low awareness of the diverse benefits produced by the Natura 2000 network is often compounded by a long-standing conflict between economic or political interests and conservation goals. There is thus an urgent need to increase coherence between biodiversity policy and other policy areas, such as in the fields of agriculture and economic and rural development, and create a more integrated approach to address potential conflicts and trade-offs between various interests while fostering synergies [EEA 2020: 124].

The report’s summary conclusion recommends increasing marine and terrestrial conservation areas in the Natura 2000 network to 30% each, strictly protecting these areas, and improving connectivity among them.

Blue and green corridors [Les trames vertes et bleues] in France, Ministry of Ecological Transition 2017

Spurred to action by the European Union and a vision for a pan-European ecological network, France encoded the idea of the “trames vertes et bleues” into law in 2009. The national government worked with all the regional governments to develop maps showing areas with the highest levels of biodiversity. This includes protected areas, stretches of coastline, riparian zones, woods, and other undeveloped areas, whether public or private. The maps also show ecological corridors – both those in good condition needing to be preserved, and those that are highly degraded and requiring restoration.

The regional maps are meant to be integrated into urban planning at the level of city and county (department). Rather than being a regulatory tool, the maps are an information source allowing urban development to proceed in a way that limits impact on biodiversity. The ecological corridor initiative is designed as an invitation and encouragement to local governments, organizations, businesses and individuals to collaborate and to act in favor of biodiversity.

The preservation and restoration of ecosystem connectivity entails acting everywhere possible: in rural environments, in aquatic ecosystems and in urban areas [MTES 2017, translation].

Articulating the politics of green and blue infrastructure and the mitigation hierarchy for effective biodiversity preservation in France [Articuler la politique Trame verte et bleue et la séquence Éviter-réduire-compenser: complémentarités et limites pour une préservation efficace de la biodiversité en France], Chaurand & Bigard 2019

This article reviews the historical development of two pieces of environmental legislation in France – the use of the “mitigation hierarchy” to assess and limit environmental impact in project development and the promotion of ecological corridors. Theoretically, these two laws overlap when urban development projects in proximity to areas of ecological significance use the mitigation hierarchy (avoid, reduce, compensate) to ensure these zones are protected within the scope of the project.

• 1976: “Protection of Nature” law in France introduced the mitigation hierarchy, aiming to avoid or reduce harm to the environment, or to compensate if harm is unavoidable.
• 1992: Concept of “biodiversity” entered public discourse internationally, following the Earth Summit in Rio, Brazil.
• 1996: France ratified European ecological corridor strategy.
• 1999-2000: Concept of “sustainable development” emerged in France.
• 2004: National strategy for protecting biodiversity adopted.
• 2007: “Grenelle de l’Environnement” meeting created the “Trame Verte et Bleue” (TVB) policy (green and blue infrastructure, encompassing ecological corridors)
• 2016: Biodiversity law enacted, creating national agency and regional committees on biodiversity

In spite of this policy evolution, commitment to ecological corridors has yet to move from a “TVB papier” to a “TVB de projets et d’action.” In other words, much discussion and mapping efforts have not yet resulted in the development of the imagined ecological corridor network. The authors speculate as to why this is so, explaining that the resources and coordination needed for enforcement are lacking. Even though “the creation, preservation and restoration of ecological connectivity” has been integrated into urban planning code, such considerations are often sidelined. Furthermore, definitions are vague: the objective of the TVB is the “good condition” of ecological continuity, but “good condition” is not defined. Lastly, taking action in defense of ecological continuity requires pro-active collaboration among levels of government from local to regional to national.

The authors propose better integration of these to policy tools. For example, the TVB designates certain non-protected areas throughout the country that are ecologically functional and serve a role in the eco-corridor network as key areas to “preserve.” With better communication between this TVB framework, the mitigation hierarchy could be applied at the level of “avoiding” harm to places designated as preservation priorities, but lacking formal “protected” status. In projects where harm is unavoidable, the mitigation hierarchy could be applied at the level of “reducing” harm to maximize the percentage of remaining green space as well as the permeability to wildlife of the built structures (such as passageways through fences). The “compensation” level of the mitigation hierarchy could be applied in the context of regenerating ecosystem function to areas designated in the TVB schema as needing ecosystem restoration.

The authors note that advocates for the TVB are clustered at the national level and within research institutions, while the people responsible for urban planning decisions are local and are not necessarily well versed in the scientific framework for the TVB. Local actors tend to focus on priorities other than ecological continuity. One measure to address this, according to the authors, would be the training of local “relays” to transmit knowledge of ecological principles vis a vis the TVB to local urban planners.

Woods and hedgerows of Brittany countryside [Le bocage Bretagne], OEB (L’Observatoire de l’Environnement en Bretagne) 2018

Produced by a regional consortium on the environment in Brittany, France, this report describes the ecological value of woody strips encircling agricultural fields and enmeshing the countryside, their decline, and ways to incentivize their protection.

Brittany is a heavily agricultural region that also features a long stretch of coastline where urban development and expansion is ongoing. Due to mechanization and enlargement of farm fields, average parcel size has increased since the 1950s, shrinking the extent of woody hedgerow (“bocage”) between fields. Between 1996 and 2008, the total length of hedgerow decreased 12%. This change is concerning because Brittany is already one of the most fragmented and least wooded parts of France.

The report explains the value of the bocage is its provisioning of habitat, connectivity between habitats, biodiversity, erosion control, groundwater recharge, and flood mitigation. Half the population of Brittany lives in areas susceptible to flooding. Furthermore, at least five endangered animal species depend on the habitat created by the bocage. Protection of this woody network is key to remedying both problems, while also providing direct benefits to farmers, such as habitat for pest predators.

The form and shape of the bocage varies throughout the region, but can include grasses, bushes and/or trees, forming one or more layers of vegetation; and heterogenous landscape features such as berms, ditches, logs, and rocks/boulders, which create microhabitats.

The network of hedge and berms, accompanied by fields, ponds and wetlands, constitutes an important natural environment because of its heterogeneity and potential for complex exchanges. It has the particularity of being able to reach a myriad of increasingly isolated natural spaces in the heart of a changing agricultural countryside subject to ongoing urbanization. Similar to a forest edge environment, the richness of the bocage can be explained by the diversity of habitats it adjoins [OEB 2018: 8, translated].

Regulatory and incentive programs payments have sought to encourage farmers to preserve their hedgerows. However, the authors suggest that a stronger economic valuation of these linear woods is needed to protect and expand them. They suggest strategies for stimulating the market for firewood and other products harvested from sustainably managed hedgerow, where biodiversity protection is an explicit aim and co-benefit.

Americas Context

Shaping land use change (LUC) and ecosystem restoration in a water-stressed agricultural landscape to achieve multiple benefits, Bryant et al. 2020

In spite of its obvious benefits, agriculture, which covers one third of the Earth’s land surface, damages biodiversity and ecosystem services. In some regions, land degradation and depletion of water resources from irrigation have been so great that historical levels of food production in these regions risk decline. Some areas of previously productive farmland will likely need to be retired from use. Within this context, maintaining and enhancing natural corridors and promoting semi-natural, multifunctional landscapes can significantly contribute to recovering biodiversity and mitigating air and water pollution.

Using California’s San Joaquin Valley (SJV) as a case study, this paper illustrates a pragmatic approach to incorporating ecological corridors into working landscapes. The authors offer a new analytical approach that simultaneously incorporates resource-constrained (water, in this case) land-use change (LUC) modeling within the planning and optimization process. The goals are to simultaneously:

• Meet water-use-reduction policy goals for the area under study within the next two decades
• Identify lands for retirement that are (1) likely to be retired anyways and (2) offer high-value habitat for native species and biodiversity.

Over the past century, SJV has been transformed into one of the largest agricultural economies in the world. However, this economic success has been costly to the SJV in several ways, including:

• Damaged infrastructure: high rates of groundwater extraction in the SJV have led to groundwater overdraft and unreplenished aquifers, resulting in large-scale land subsidence. Most of the subbasins in the SJV are categorized as critically overdrawn, and some regions have sunk over 8 meters since the early 20th century; this land subsidence further imperils water availability and quality by impacting water storage and delivery infrastructure.
• Decreased human health, as a result of impaired air and water quality, leading to chronic health problems
• Threats to wildlife and biodiversity; for example, some species have lost up to 98% of their habitat range, and over 35 native species are listed as threatened or endangered

“In response to these challenges, and amid significant drought-driven fallowing, California passed the Sustainable Groundwater Management Act (SGMA), which … obligates locally governed groundwater subbasins to develop plans that will achieve sustainable groundwater use over the next two decades” [Bryant 2020: 2]. To meet these requirements, many subbasins will meet with severe groundwater pumping restrictions. If these areas are not able to coordinate their pumping activities and augment water supplies, the SGMA may require a reduction in cultivation area through fallowing or permanent retirement.

Given the likely retirement of 86,000 ha of irrigated agricultural land, the authors explore spatial optimization of retired land for conservation efforts. They find that a key strategy is the identification of areas that were destined for retirement from cropping which could be shifted to restoration and habitat enhancement, as well as possibly shifting some areas destined for retirement that have “low habitat value” with regards to wildlife for areas with “high habitat value.” Priority restoration areas identified in this analysis include many that are contiguous and located near designated wildlife areas.

Importantly, the analysis presented here is “explicitly organized to help inform engagement between conservation actors and agricultural land managers about how habitat goals can be achieved in ways that benefit communities in the SJV” [Bryant 2020: 3]. The potential positive futures indicated by such analysis can be used to identify opportunities for collaboration between the conservation and agricultural communities, with a goal of guiding land use change toward achieving multiple benefits, such as recovery of imperiled natural communities, resilient agricultural production, and improved public health outcomes.

While it poses a great challenge, the impending transformation in the SJV also presents an opportunity to proactively shape the landscape in ways that not only ensure agricultural and water sustainability, but also achieve many other socio-ecological goals, such as biodiversity protection and improved human health. However, given that achievement of many of these objectives is determined by where things happen on the landscape (rather than simply the aggregate amounts of cultivation, retirement, or restoration), stakeholders need a systematic way to integrate these objectives to inform multi-benefit spatial planning [Bryant 2020: 4].

Integrating Agricultural Landscapes with Biodiversity Conservation in the Mesoamerican Hotspot, Harvey et al. 2007

The fate of biodiversity within protected areas is therefore inextricably linked to the broader landscape context, including how the surrounding agricultural matrix is designed and managed [Harvey 2007: 8].

Rather than discussing ecological corridors per se, this article emphasizes the importance of a whole-landscape approach to biodiversity conservation. Pointing out that protected nature reserves are weakened when isolated, these authors focus on the role of the entire surrounding agricultural matrix for restoring connectivity.

In contrast to the prevailing trend of managing protected areas and productive lands separately, we propose integrated landscape management in which conservation and production units within the agricultural matrix are managed jointly for long-term sustainability. We do not advocate agricultural intensification to spare further forest conversion because this approach is unlikely to have the intended outcome, for reasons discussed. Instead, conservation efforts should be based on the recognition that how agriculture is conducted and how different land uses are distributed spatially and temporally determine the region’s biodiversity. Lasting conservation will therefore require alliances among conservation biologists, farmers, and land managers to actively plan the future of Mesoamerican landscapes [Harvey 2007: 9].

The sections of the agricultural matrix the authors prioritize for biodiversity conservation include areas near riparian and other key ecological corridors, and they recommend leveraging support for the Mesoamerican Biological Corridor to spur regional action. Priority conservation areas are also more likely to encompass landscapes with a high diversity of indigenous and traditional cropping systems than those dedicated to industrial agriculture because “the chances of reconciling farming and biodiversity conservation there [agro-industrial systems] are slim” [Harvey 2007: 10].

The authors argue that, in contrast to large-scale, export-oriented industrial production, small-holder and indigenous agricultural systems are more compatible with biodiversity conservation, increased food production and rural income. The authors propose economic and regulatory instruments and greater regional collaboration to enhance native tree cover on farms, promote traditional, ecologically based farming practices, and to protect remaining intact habitat and restore degraded lands. The overarching vision is to accomplish conservation and agricultural production objectives for the region in mutually reinforcing ways.

The fate of biodiversity within protected areas is therefore inextricably linked to the broader landscape context, including how the surrounding agricultural matrix is designed and managed [Harvey 2007: 8].

The concept of green corridor and sustainable development in Costa Rica, Beauvais & Matagne 1999

The concept of sustainable development presumes that human economic systems and overall wellbeing depend on functioning ecosystems. Therefore, ecological rhythms should not be transgressed to the point that they fail to provide the vital services needed today and in future generations.

According to this model, economic development becomes a necessary but insufficient condition for society to progress [Beauvais & Matagne 1999: 6, translated].

Costa Rica holds at least 5% of the world’s species, in spite of making up 0.03% of its land surface. As an isthmus, Costa Rica is influenced by weather patterns from two oceans, as well as a north-south migration route. In addition to this, its mountainous terrain creates a heterogenous mosaic of habitats and niches. However, the country has been severely deforested. Forest covered 66% of land surface in 1940, and only 25% by 1987; the loss of forest led to extreme erosion.

As presented in this article, an ecological corridor consists of at least two protected ecosystem patches that are connected by a protected vegetated strip of at least a few kilometers in width, and the whole area surrounded by a buffer zone. Multiple units of two connected patches could in turn be connected, stretching into a corridor that the whole length of the country. A green Costa Rican corridor could connect to green corridors in adjacent countries, ultimately recreating the entire isthmic corridor that once existed.

However, the tone of this article is not optimistic about conservation, citing several political obstacles to conservation and ecosystem restoration. According to the authors, a combination of neocolonialist pressure, poverty, corruption, and capitalistic interests allow for trees to be cut even in protected areas and prevent the establishment of new protected areas and corridors.

The Mesoamerican Biological Corridor in Panama and Costa Rica, Dettman 2006

At the end of the 1980s, as a period of severe conflict in Central America was winding down, most countries in the isthmus signed the Charter Agreement for the Protection of the Environment, which established a sustainable development commission. At the same time, the “Central American Protected Areas System (SICAP) created approximately 11.5 million hectares of protected areas throughout the region” [Dettman 2006: 18].

This paved the way for international attention and investment in what became the Mesoamerican Biological Corridor (MBC). The original intention was to promote biodiversity and economic development in tandem through investment in local projects. However, in the 2000s, the international coordinators of the MBC shifted the focus from biodiversity protection (although the establishment of ecological corridors remains an objective) to a greater emphasis on economic development. This author explains that the institution’s decision-making process is overly top-down, and would benefit from input from local people who are implementing projects on the ground.

Between Bolivar and Bureaucracy: The Mesoamerican Biological Corridor, Liza Grandia 2007

Written by an anthropologist working in Central American conservation efforts for more than 10 years, this article describes the Mesoamerican Biological Corridor (MBC) project as having succumbed to a neoliberal agenda. Although originally spearheaded by Central American environmentalists, the notion of cross-border environmental collaboration was adopted by the World Bank and large international conservation organizations working in Central America in the 1990s. In the hands of these international giants, the biological corridor initiative became a bureaucratic, top-down project, deaf to the voices of local communities.

With all this new bureaucracy, a broad and unfocused agenda, and the challenges of high-level political coordination, the MBC quickly lost its potential to inject a stronger environmental justice component into regional biodiversity conservation programs.

Indeed, the MBC that emerged from the World Bank’s incubator was decidedly more business-oriented than initial proposals for Central American environmental coordination at the 1992 Earth Summit [Grandia 2007: 486].

In this context, the MBC’s conservation efforts have focused more on securing land for protected parks and less on community-based initiatives. The author suggests that in addition to land protection, the MBC should engage farmers in capacity building for eco-agriculture with a view toward achieving landscape-wide ecological connectivity.

The corridor approach might also draw greater attention to the agrarian contexts outside of parks, which may be just as ecologically important as what happens inside parks. By bringing agricultural systems into conservation debates, corridors may present new opportunities for supporting fair-trade projects and other small-scale agroforestry systems compatible with conservation. In other words, corridors could offer a method for moving beyond protectionism to embrace a mosaic vision for conservation that includes local people more explicitly. Corridor planning frameworks also could provide more democratic conservation forums [Grandia 2007: 484].

Effectiveness of Panama as an intercontinental land bridge for large mammals, Meyer et al. 2019

One of the world’s largest corridor projects is the Mesoamerican Biological Corridor (MBC). Initiated in the 1990s, the MBC aims to connect protected areas between southeastern Mexico and Panama [Meyer 2019: 2].

The ecological functionality of the MBC has not been much assessed, in part because direct approaches to measuring connectivity are costly and challenging. In this study, researchers used a simpler, indirect approach to measure forest connectivity through Panama for nine mammals. Using camera traps (cameras that are automatically triggered by a change in some activity in the vicinity, like the presence of an animal), they documented the presence (or absence) of these mammals in 28 forest sites along the Atlantic coast. The corridor was presumed to be functioning for animals whose presence was established across the entire length of the monitored range.

The species monitored in this study are forest specialists, including ungulates, carnivores and an insectivore, all of which are threatened by habitat loss and hunting, some more than others. Of the 43% of land in Panama that is forested, 44% is protected, mostly along the Atlantic coast. Steady economic development threatens remaining ecosystems with investments in large infrastructure projects, real estate, mining, tourism, and energy.

Large mammals are an indicator species for the success of conservation efforts. This is because:

Large mammals are generally at a higher risk of extinction in disturbed landscapes than other taxa because their large home ranges and low population densities at broad spatial scales mean their populations are more likely to be fragmented and because they are heavily hunted [Meyer 2019: 3].

The researchers found that even the four most prevalent species in the study are susceptible to population fragmentation by any further habitat loss.

We found that there was little connectivity for white-lipped peccary [a pig-like animal] and white-tailed deer and that, although 4 of the species (collared peccary, red brocket deer, puma, and ocelot [a wild cat]) occurred in most of the sites, a small decrease in connectivity of 20% would disrupt their continuous distributions across Panama. White-lipped peccary, giant anteater, white-tailed deer, jaguar, and tapir [a pig-like animal with a short trunk] had lower probability of occurring in all the sites and were therefore even more at risk of connectivity loss, as evidenced by >1 connectivity gap. This indicates the MBC may not function for the majority of species, especially considering we did not account for potential effects of hunting, which would make connectivity even more challenging [Meyer 2019: 8].

Citing imminent development projects, such as a new road that will pass through the forested northern coast and associated large hotel projects, the authors predict that ongoing loss of connectivity is likely. Moreover, the deteriorating condition of the corridor in Panama bodes poorly for the MBC overall.

The disruption of connectivity between tropical forests in Central America, and hence the possible separation of mammal populations, is an indicator of the overall functioning of the MBC for wildlife [Meyer 2019: 11].

Belize creates one of Central America’s largest biological corridors, Dasgupta 2018

The Belize government approved a plan in February 2018 to create a 110-square-kilometer biological corridor connecting two nature reserves in the northeast of the country. This outcome resulted from collaboration among NGOs, the government and private property owners. The latter agreed to conserve (to not deforest or otherwise degrade) the parts of their land that would become part of the wildlife corridor. In exchange, the government would not collect taxes on this land. This corridor, which was initiated in the context of the larger Mesoamerican Biological Corridor project, is meant to protect jaguars, cougars and tapirs, among other wildlife.

The woman building the forest corridors saving Brazil’s black lion tamarin, Zanon 2020

“The tamarin is unable to do anything to save its own species. And we, human beings, are the ones who are destroying their environment,” says conservationist Gabriela Rezende. “So, when I got the opportunity to see this animal in the wild, I felt partly responsible for its future.”

Rezende works with the Institute for Ecological Research in the Brazilian state of Sao Paolo to create ecological corridors connecting the forest fragments where the world’s only 1,800 black lion tamarin live in isolated populations. Since 1984, the institute has worked to protect this small primate species, which had reached a low point of 100 individuals and was listed as “critically endangered.” In addition to research and forest restoration, the institute also does environmental education with the local communities. This includes collaboration on nine tree nurseries administered by local people as small businesses that also provide school kids the chance to learn about local forest species that will be planted in corridors.

Leveraging a state policy requiring 20% of privately owned property to be in nature reserves, Rezende worked with landowners to identify patches to be restored that would physically connect forest fragments. Once corridors are complete, the total amount of land in connected habitat will be 111,000 acres. Rezende estimates the black lion tamarin population could increase 30% once it’s able to use the whole forest corridor. The restoration project will benefit other species too, including anteaters, tapirs (a pig-like animal with a short trunk), pumas, and ocelots (another wild cat species).

A well-watered mulberry tree has been credited with averting the danger of destructive wildfires from destroying Brett Hawkins’ home during 2020’s unprecedented fire season in Australia. When massive fires raged through the bush through the summer, many homes were completely engulfed. However, Hawkins attested that when he returned to his home after evacuating,

‘I could see straight away the house was intact — the roof was intact, but everything else around it was burnt, with the exception of the mulberry tree.’ He described the stark scene greeting him upon arriving back home, ‘It was apocalyptic,’ Mr. Hawkins said. ‘There was not a tree left, ash on the ground and smouldering embers everywhere.’ But among the blackened trees, Mr. Hawkins found his mudbrick house and mulberry tree in full leaf [Aubrey 2020].

In the season’s drought, he had been rationing water, but sparing some to keep his tree hydrated and healthy, which may have been a contributing factor in its resistance. According to the article, “Mr. Hawkins believed that by heavily watering the tree, combined with luck regarding which direction the fires came, the full heat of the bushfires was shifted.” [Aubrey 2020]

Another important feature is the mulberry’s lack of dried leaves and brush at its base that might pose a danger of igniting. Other species, like eucalyptus, with oily leaves that could dry out, or pine trees whose long branches catch dry leaves, are less ideal.

A tree expert from the Fenner School of Environment at the Australian National University analyzed some of the possible factors leading to the survival of this mulberry tree and what it might teach those wishing to fortify the fire resilience of their homes and properties. “While there does not seem to be a clear answer on what to plant to ‘fire-proof’ your house, Professor Brack said a well-watered tree, with a clear trunk and no loose, dry leaves or branches is a good start” [Aubrey 2020].

Nader et al. survey herbicides, prescribed fire, mechanized treatments, hand cutting, and grazing animals as fire management techniques. Managing vegetation involves “changing the plant community to decrease the flame height when fire occurs,” favoring native species that may be more resilient to fire, and altering the landscape to create fuel breaks, which are patches across which it is hard for fire to jump [Nader 2007: 18].

Focusing their analysis on grazing and the contexts in which it is most useful, the authors note that there are many site and animal specific factors to take into account for successful implementation.

[Grazing] is a complex, dynamic tool with many plant and animal variables, and it requires sufficient knowledge of the critical control points to reach treatment objectives. Those control points involve the species of livestock grazed (cattle, sheep, goats, or a combination); the animals’ previous grazing experience (which can affect their preferences for certain plants); time of year as it relates to plant physiology (animal consumption is directed by the seasonal nutrient content); animal concentration or stocking density during grazing; grazing duration; plant secondary compounds; and animal physiological state [Nader 2007: 19].

Grazing has the advantage of keeping nutrients in the ecosystem, unlike mechanical methods that harvest vegetation to be sold as biomass chips (like wood chips). This means that when animals digest vegetation and excrete on the landscape, they participate in the local nutrient cycle. Animals also trample soil, which can crush fine fuel and mix it into the soil, where it cannot contribute to ignition, which reduces one contributing factor to persistent and destructive blazes.  Animals do more than just remove extra vegetation – they can have many beneficial interactions within a given ecosystem.

Any grazing plan designed for fuel reduction needs to consider the grazing impacts on parameters other than just simply reduction. The effects of the grazing management should be studied for their impact on water quality, compaction, riparian vegetation, disease interaction with wildlife (bluetongue, pasturella), and weed transmission. The positive aspects of grazing over other treatments also should be weighed, including recycling of nutrients into the products of food and fiber [Nader 2007: 22].

By introducing grazing animals into a landscape or agricultural system, managers can affect biodiversity in complex ways. The authors mention that “Hadar et al. reported that light grazing increased plant diversity on treated sites. Thus, when proposing a stocking rate for treatment consumption, the environmental impact needs to be considered” [Nader 2007: 22].

Nader et al. conclude that “grazing is best used when addressing vegetation with stems of smaller diameters that make up the 1- and 10-hour fuels. These two fuel classes are important because they can greatly impact the rate of spread of a fire, as well as flame height” [Nader 2007: 19]. While they call for further research to validate anecdotal accounts supporting grazing and understand its best practice, they maintain that “prescribed grazing has the potential to be an ecologically and economically sustainable management tool for reduction of fuel loads” [Nader 2007: 20].

This study examines the positive effects of beaver damming on the resistance of landscapes to wildfire damage. The authors find that in riparian corridors (areas along rivers), the presence of beavers and their dams can create refuges that withstand blazes that consume surrounding vegetation.

Beavers play an important role in wetland habitats and are known as ecosystem engineers for the way they can shape landscapes with their activities. Beaver dams slow down water moving across a landscape, holding it in place for longer and allowing water to infiltrate into the soil, which raises water tables.

The combination of building flow obstructions (dams), accumulating water (ponds), and spreading that water out in the landscape (channels) gives beavers the unique potential to modulate environmental extremes such as flood and drought. When it comes to water, beavers slow it, spread it, and store it.

Due to the fact that beaver channels and dams spread water out in the landscape and store it broadly in adjacent soils, the vegetation near beaver ponds doesn’t experience as much reduced water availability during drought. Drought-stricken vegetation burns more easily than lush, green vegetation, so it follows that the vegetation around beaver ponds would be more difficult to burn than vegetation around undammed creeks [Fairfax and Whittle 2020: 1].

Fairfax and Whittle observed the effects of beaver dams on preventing fire spread to the areas where they had built dams, examples of which are shown in satellite imagery below.

The authors quantify the effects of beaver activity in fireproofing areas by examining the Normalized Difference Vegetation Index (NDVI) observed in satellite imagery before, during, and after wildfire years in the American West. They found that while vegetation is able to reestablish itself a year after fire damage regardless of beaver activity due to its own resilience to fire, areas in beaver dammed zones maintained vegetation even during wildfires, demonstrating actual resistance to blazes, not just the ability to recover after damage. They note how vital this is for those ecosystems and the life within them.         

These ribbons of fire-resistant riparian corridor may be particularly important for species that are unable to physically escape wildfire. They can provide temporary habitat for fish, amphibians, reptiles, small mammals, wild and domestic ungulates, and birds that are unable to outrun/outfly the spread of flames. While we found that beaver activity does play a significant role in maintaining vegetation greenness during wildfires, it does not appear to play a significant role in the ability for a riparian corridor to rebound in the year following fire. Riparian vegetation NDVI rebounded in the year following the fire regardless of proximity to beaver activity. Thus, we would describe beaver activity as creating refugia during wildfire, but not necessarily changing the long-term landscape outcomes [Fairfax and Whittle 2020: 7].

The survival of wildlife is crucial to these ecosystems, and beaver activity uniquely contributes to the creation of refuge areas that resist burning and can provide shelter for animals during these destructive events. The authors conclude,

As it stands today, wetland habitat is very limited and beavers can create and maintain wetland habitat that persists through flood, drought, and, as we have shown in this study, fire. This has immediate relevance to scientists and practitioners across North America and Eurasia, particularly in places with increasing wildfire risk and existing or planned beaver populations. Perhaps instead of relying solely on human engineering and management to create and maintain fire-resistant landscape patches, we could benefit from beavers’ ecosystem engineering to achieve the same goals at a lower cost [Fairfax and Whittle 2020: 7].

It has long been suspected that the increasing abundance of invasive grass species may contribute to wildfires in the United States by adding abundant new fuels to ecosystems, increasing the range of conditions that lead to fire ignition, and enabling the development of larger, hotter fires. The new fire regimes (patterns of fire duration, intensity, and spread) that emerge can in turn destabilize wildlife and lead to local extinctions while expanding favorable habitat for the invasive species, for many of these grasses recover quickly after fires, providing renewed fuel and potentially increasing the frequency of fires.

The authors of this paper provide a comprehensive analysis on the impact of 12 non-native grasses on the occurrence (whether a fire occurred in a particular place), frequency (how many times a place burned), and size of wildfires. The research was conducted across 29 US ecoregions, including deserts, temperate forests, wetlands, woodlands, river valleys, shrublands, and coastal plains. Data were collected and combined from fire records and records of invasive grasses, and results from “invaded” regions and nearby “uninvaded” regions were compared. The authors also considered human activities and ecological factors related to fire.

One of the most notorious impacts of nonnative, invasive grasses is the alteration of fire regimes. Yet, most evidence of these impacts comes from local-scale studies, making it unclear whether they have broader implications for national and regional fire management. Our analysis of 12 invasive grasses documents regional-scale alteration of fire regimes for 8 species, which are already increasing fire occurrence by up to 230% and fire frequency by up to 150%. These impacts were demonstrated across US ecoregions and vegetation types, suggesting that many ecosystems are vulnerable to a novel grass-fire cycle. Managing existing grass invasions and preventing future introductions presents a key opportunity to remediate the ecological and economic consequences of invasive species and fire [Fusco 2019: 23594]

The results of this analysis showed that 8 of the 12 invasive grass species examined were associated with significantly higher fire occurrence and fire frequency, and that fire occurrence more than doubled for two of these species. Three of the species did not impact fire occurrence, and a decrease in fires was associated with one species (a wetlands grass species). The impact on fire size was variable, with two species associated with larger fires, three species associated with smaller fires.

Individually, climate change is expected to increase the potential for fire occurrence by 150% by the end of the century based on projected changes in temperature and precipitation. Here we show that 8 invasive grass species are already associated with increased rates of fire occurrence by 27 to 230%, and 6 invasive grass species are associated with increased mean fire frequency by 24 to 150%, compounding current and future fire risk across the United States. [Fusco et al. 2019: 23595]

The authors suggest that fire and invasive species managers work together to create integrated management plans; otherwise, the convergence of human activities, climate change, and invasive species will continue to promote wildfires across the United States.

Indigenous groups across the world have developed ecological knowledge linked to the places they inhabit, including prescribed fire practices used to maintain healthy ecosystems. Mistry et al. examine the challenges Indigenous communities in South America face in managing the landscape through fire and preserving such knowledge across generations in sometimes hostile political climates. However, there is growing recognition that Indigenous people have a vital role to play in combating climate change and supporting biodiversity and healthy ecosystems.

Emerging research shows the fundamental role of Indigenous land-use practices for controlling deforestation and reducing CO2 emissions—analysis of satellite imagery suggests that Indigenous lands have reduced rates of deforestation and habitat conversion, and lower greenhouse gas (GHG) emissions, compared with surrounding areas [Mistry 2016: 1].

While indigenous groups’ use of prescribed fire early in the dry season to prevent destructive out-of-control fires is gaining broad recognition, that hasn’t necessarily translated into greater respect or autonomy for those communities. Instead, Indigenous people may be given auxiliary roles in fire management, or have their knowledge utilized but implemented by non-local organizations in structures that fail to benefit or empower the local communities themselves. While this may still achieve desired wildfire management results, it weakens intergenerational knowledge transfer and undermines the social and spiritual role of prescribed fire within communities.

Mistry et al. argue that “Indigenous fire management is effective in that it is an emergent property of a linked social-ecological system where Indigenous knowledge and culture, and associated livelihoods, are intimately interconnected with landscape management practices” [Mistry 2016: 4]. Precisely because prescribed fire matters to Indigenous communities as something more than a tool in the toolkit of managing wildfires, it is effective when carried out by those communities in reducing risk of destructive wildfires and supporting healthy and biodiverse ecosystems.

Importantly, the numerous uses of fire mean that burning is a relatively constant activity, particularly during the dry season, generally at low levels, thereby helping to prevent the build-up of flammable fuel and incidents of large-scale uncontrollable wildfires. Experimental studies of fire behaviour suggest that this patch mosaic burning not only reduces the occurrence of dangerous fires, but also increases spatial and temporal vegetation heterogeneity and biodiversity [Mistry 2016: 4].

These authors distinguish between Indigenous relationships to ecosystems and market-based approaches to ecosystem services valuation, which attempt to incentivize conservation through payment. While the goal of the market-based approach is to monitor and preserve functioning ecosystems, “their ideological foundations within a neoliberal agenda that promotes ‘selling nature to save it’ is in stark contradiction with Indigenous ontologies based on human–nonhuman–spiritual relationships” [Mistry 2016: 2].

Within Indigenous communities, fire plays a role in social bonding, intergenerational knowledge transfer, and agricultural practices. Mistry et al. argue that

savanna and forest ecosystems are being protected within Indigenous lands not because they are being ‘managed’ in a direct and active way, but as the indirect outcome of a healthy social–ecological system, i.e. the outcome of practices that maintain social and ecological integrity, or what can be termed ‘community owned solutions [Mistry 2016: 4].

But challenges, including loss of fire knowledge by younger generations within Indigenous groups because of outside pressures and encroachment, pose a threat to these fire management practices. For example, in Venezuela and Brazil,

young Wapishana and Makushi and some community leaders were more critical about the use of fire as they had more regular contact with state natural resource management officials and environmental organizations that promoted antifire discourses. As with the Krahô, changing Indigenous values to focus on fire prevention and suppression could have the effect of making the problem worse [Mistry 2016: 4].

That is, when prescribed burning is taken out of its original context and represented to younger generations of Indigenous people and land stewards as simply a well-incentivized tool, the Indigenous communities themselves are diminished, along with the robustness of their ecological knowledge that gets passed forward.

In spite of lingering antagonistic views in Brazil and Venezuela toward indigenous fire management, attitudes are changing.

Not only is there a move away from categorizing all fire as ‘bad’; there is also a recognition that Indigenous fire knowledge is a valid form of knowledge that could inform policy-making [Mistry et al. 2016: 6].

Mistry et al. suggest the best way to achieve both ecological and communal health might be through power-sharing arrangements. By empowering Indigenous communities, national governments could in turn work toward their fire management and biodiversity conservation goals. This might require evaluating ecological health in ways beyond just quantitative metrics, which reduce these complex systems down to a set of standardized numbers, as well as the recognition that the well-being of these ecosystems is tied to the Indigenous communities that inhabit them, according to the authors:

There needs to be enabling policies that focus on legitimizing and strengthening Indigenous fire management as a community owned solution. Critically, as community owned fire management is intricately linked with Indigenous survival strategies, so too must firefighting and prescribed burning be grounded in local social–ecological systems. We believe it is necessary to define long-term actions to support the integrated functioning and survival of Indigenous communities as a whole, rather than focusing on isolated issues (e.g. carbon retention) or benefits for some individuals (e.g. hiring Indigenous firefighters) [Mistry 2016: 8].

This systems approach may well be the key to successful long-term fire management. The authors offer this challenge:

What we want to do is not promote one over the other, but encourage decision-makers to engage with, and appreciate, Indigenous perspectives and worldviews on fire management. Community owned solutions acknowledge collectivity, spirituality, process orientation and locality, whereas many expert-led fire management interventions often result in promoting individualism, ethnocentrism, rationality, efficiency, commercialism and globalization. The question we raise is this: can the ‘community owned solutions’ approach be the mechanism through which Indigenous perspectives can be represented within fire management [Mistry et al. 2016: 8]?

Wildfire is a challenge that threatens human settlement at an increasing scale, but planning and development does not always address this threat. In fact, policy around land use is in large part responsible for the destruction of homes and property and the threat to human life that occurs in wildland-urban interfaces (WUIs). While there is much literature on how to suppress fires, mitigate their damage, or manage for less destructive fire seasons, a more far-reaching strategy would be to stop building in fire prone areas. Land use decisions can be improved to lessen the risk of infrastructure loss and foster healthy ecosystem function.

Land use planning is an alternative that represents a further shift in thinking, beyond the preparation of communities to withstand an inevitable fire, to preventing new residential structures from being exposed to fire in the first place. The reason homes are vulnerable to fires at the wildland-urban interface is a function of its very definition: “where homes meet or intermingle with wildland vegetation”. In other words, the location and pattern of homes influence their fire risk, and past land-use decision-making has allowed homes to be constructed in highly flammable areas. [Syphard 2013: 1-2]

In many areas, including in California, we have come to expect fire, but have not necessarily learned to live with it. The authors of this study analyzed what types of human development carried out in the next several years might contribute to or avert the risk of fire damage. They examined the South Coast Ecoregion of San Diego County, which they describe as:

topographically diverse with high levels of biodiversity, and urban development has been the primary cause of natural habitat loss and species extinction. Owing to the Mediterranean climate, with mild, wet winters and long summer droughts, the native shrublands dominating the landscape are extremely fire-prone [Syphard et al. 2013: 2].

This study acknowledges the responsibility humans have in shaping the landscape and its biodiversity, and in contributing to fire activity by building into wild areas and expanding WUI. They sought to understand how patterns of development and housing density might influence future fire spread and intensity. They found that

structures in areas with low- to intermediate- housing density were most likely to burn, potentially due to intermingling with wildland vegetation or difficulty of firefighter access. Fire frequency also tends to be highest at low to intermediate housing density, at least in regions where humans are the primary cause of ignitions [Syphard 2013: 2].

Though it is impossible to reverse the effects of policies that have shaped the fire landscape we have today, understanding the way human behavior contributes to our own risk of harm from wildfire can help us plan intelligently going forward. The authors conclude that

With projections of substantial global change in climate and human development, we recommend that land use planning should be considered as an important component to fire risk management, potentially to become as successful as the prevention of building on flood plains. History has shown us that preventing fires is impossible in areas where large wildfires are a natural ecological process. As Roger Kennedy put it, “the problem isn’t fires; the problem is people in the wrong places [Syphard 2013: 10-11].

In this podcast interview, Dr. Chad Hanson, an ecologist and fire researcher, shares his perspective on the 2018 wildfires in the American West and some myths that have circulated about fire management in their wake.

First, there is a perception that wildfires in forested regions are so devastating that they reverse the ‘carbon sink’ effect of forests, releasing the carbon of the burned biomass back into the atmosphere. Forests still sequester large amounts of carbon, even if they experience wildfires, because most of the forest remains intact even through blazes. Models that fault wildfires for turning forests into net carbon emitters rest on the assumption that all of the carbon that would usually be stored in a forest is combusted during a fire, but this is far from the reality, in which just a small fraction of a forest’s biomass is consumed. As Hanson says,

In fact, even in the most intensely burned patches where a fire kills all the trees (which in reality, even in the biggest fires, it’s only a small portion, a minor portion of the overall fire)… But even in those areas, only about two or three percent of the above ground biomass is actually consumed, in other words, ends up as carbon. The trees are still standing there [Hanson 2018].

Second, the intensity of fires has not been universally increasing in recent years. We are experiencing a lot of geographically large fires, but these are not necessarily high intensity fires. The percentage of high intensity fire today is similar to historical precedent, and overall, there is much less fire in our landscapes now than in Earth’s geological history. Further, even in the highest intensity fires, forests are never decimated past the point of no return. Trees and vegetation are reestablished after fires, and the ash left behind is dense with nutrients, promoting new growth. Even dead trees, which have long been thought to be responsible for contributing to high intensity fires, are actually not shown to drive fire intensity, according to Hanson.

This series of myths – that forest fires are raging with high intensities, that they burn up so much biomass as to make forests ineffective sources of carbon sequestration, and that the only way to manage forests to avoid these outcomes is to thin out the trees – hinder our understanding of forest management and allow false and harmful solutions to propagate. As a result of these perceptions, proponents of logging have pushed to expand logging operations, purportedly as a fire management strategy. However, according to Hanson, logging is actually linked to greater fire intensity. He explains that small materials, like twigs, are more flammable than trunks.

Tree trunks are not combustible. They really just don’t burn. Again, outer bark can burn, but the trees themselves don’t burn. What logging does is it removes noncombustible material essentially from the forest and leaves behind very combustible kindling, like slash debris – the branches and small twigs and things like that that are not possible to get up off the forest floor after the tree trunks are removed and that’s very combustible.

The other thing that logging does is that it reduces the cooling shade of the forest canopy. By removing a lot of trees, you have more sunlight reaching the forest floor, and what that does is it creates hotter and drier conditions and that means everything on the forest floor gets more dried out, more potentially combustible, and logging also spreads invasive weeds like cheatgrass, which is very, very flammable. Cheatgrass loves a lot of sunlight and so you get a lot of that after intensive logging.

And the last [problem with logging] is a little bit more technical, but basically when you have a lot more trees, it cuts down on the wind speeds that drive fires. It has a buffering effect in a sense. And when a lot of the trees are removed, that buffering effect is reduced or eliminated and fire spreads through those forests faster [Hanson 2018].

This three-fold effect of logging makes forests more vulnerable, and it is important to dispel the concept that removing trees is the best way to keep people safe from fires. Hanson criticizes the opportunism of using these fire myths to advance an agenda of logging. He cautions that when fire science and policy emerge from the U.S. Forest Service, which manages national forests and gains a good deal of revenue from logging, there is a perverse incentive to keep practicing logging as fire management. He calls for clearer and more public communication from scientists to dispel fire myths and share recent findings that have been shifting so much of what we know about fire science.

Hanson says that the best strategy to ensure the protection of homes from wildfire is to focus on the homes themselves. This can be done by using fire resistant building materials, fire-proofing roofs, erecting rain gutter guards to prevent the accumulation of small fuels like pine needles, pruning the vegetation in a 100-foot radius of a house, and removing small shrubs and branches of mature trees, while leaving those trees standing. Fire management interventions at this level are shown to be far more effective at preventing damage than attempts to control the fuel load of fires within forests.

Hanson points out the need to decouple fires that occur in remote forest ecosystems and those that rage through human settlements and urban communities, because thinning out vegetation in attempts to suppress the former do not actually protect against the latter. In fact, thinning forests undermines the ecological processes that fire serves in forest systems. When discussing fires that have devastated homes and lives, he says

I mean, where’s the forest in Malibu? There’s no forest. These are chaparral ecosystems, most of the fires that are burned homes and lives have been lost are not in forest. In fact, they’re mostly nowhere near forests. They’re in grasslands, chaparral shrub habitat, oak woodlands. But the areas that are in forest, where we’ve had tragic loss of homes and lives, these are mostly areas where we’ve had intensive logging, and it’s like I mentioned earlier, you know, more logging is typically associated with more intense fire at a faster rate of spread. [Hanson 2018]

He advocates for a greater focus on fire prevention around homes and communities themselves, in what is known as ‘defensible space.’ He points out that such measures are a great source of jobs, as well as an effective intervention curbing the destructiveness of fires. With a shift in focus from forest thinning to fire-proofing, and better understanding and communication of fire science, we can let go of some of the fire myths that have been dictating policy and failing to meet public needs.

More logging is typically associated with more intense fire at a faster rate of spread [Hanson 2018].

Our burning planet: why we must learn to live with fire, Pyne 2020

Steven J. Pyne is an emeritus professor at Arizona State University and the author of several books on fire history and policy. He wrote this opinion piece as a protest against the prevention and suppression of wildfires in our land management process. He argues that revising our perception of fire and accepting its presence in ecosystems is critical to our ongoing relationship with our planet.

He describes “a paradox at the core of Earth’s unraveling firescapes,” that “we have too many bad fires — fires that kill people, burn towns, and trash valued landscapes. We have too few good ones — fires that enhance ecological integrity and hold fires within their historic ranges” [Pyne 2020]. Operating under a paradigm of total fire suppression leads us astray in managing landscapes, while we so readily accept fire in the form of fossil fuel combustion in so much of our lives. Pyne sees these behaviors as evidence that our relationship with fire is out of whack.

He stresses the importance of distinguishing between burning in living ecosystems and burning the fossils of life from past ages.

The critical contrast lies in a deeper dialectic than burned and unburned landscapes. It is a dialectic between burning living biomass and burning fossil biomass. We are taking stuff out of the geologic past, burning it in the present with all kinds of little understood consequences, and passing the effluent into the geologic future.

…

Fires in living landscapes come with ecological checks and balances. Fires in lithic landscapes have no boundaries save those humans impose on themselves [Pyne 2020].

Pyne associates three paradoxes with our current fire policies. First, abandoning a traditional lore of “light burning” has removed good fires and left us with only bad and harmful ones. When controlled burns are not practiced regularly to manage landscapes, vegetation can build up and fuel the intensity and spread of uncontrolled blazes that spark.

Second and surprisingly: “The Earth does not have more fire today than before fossil fuels emerged as a primary source of energy: It has significantly less” [Pyne 2020]. That is, the amount of land burned in fires has actually decreased, while the presence of intense “feral flames” has increased. The decrease in the scope of fire is largely due to the move away from fire’s use in agriculture and its replacement with modern techniques, including machinery powered by combustion. As Pyne describes,

Farmers had relied on fire to fertilize, fumigate, and alter microclimates. Fire did all this in one catalytic process that self-propagated. But with the transition to fossil biomass, modern agriculture found surrogates with artificial fertilizers, pesticides, and herbicides, and it now had the fossil-fuel-powered machines to distribute them. Production became more efficient; transport, more dense. As agriculture joins a modern economy, working flames recede [Pyne 2020].

What we are left with is intense, destructive wildfire, rather than helpful working fire. Pyne points out that we now only see one half of fire’s possibilities, since the working fire shaping landscapes and agricultural systems is notably absent. He says: “Landscape fire fades; what fire persists tends to be outbreaks of feral fire. We see those oft-disastrous flames. We don’t see the lost fires or the sublimated fires in machines that removed them” [Pyne 2020].

The third paradox is that as we reduce our use of fossil fuels going forward (as one sort of fire), we will have a greater need “to manage fire in living landscapes.” So Pyne calls for us “to reinstate the right kind of fire, and … adapt to fire’s presence and let it do the work for us.” He pushes for the recognition that transitioning away from our reliance on fossil fuel burning is an important but incomplete step in balancing ecosystem health. Fires in living systems have an important role to play, and according to Pyne, “the need is not just to reduce fuels to help contain wildfires; those missing fires did biological work for which no single surrogate exists” [Pyne 2020]. He asserts that we will need to reintroduce fire as a staple tool on our landscapes.

Fires in living systems have an important role to play, and according to Pyne, “the need is not just to reduce fuels to help contain wildfires; those missing fires did biological work for which no single surrogate exists.” He asserts that we will need to reintroduce fire as a staple tool on our landscapes.

Pyne concludes with a call for the overhaul of our conceptual and policy treatment of fire.

Anthropogenic fire needs more room to maneuver – more geographic space, more legal space, more political space, more conceptual space. … Equally, society needs to rethink liability law to reduce the risks incurred by fire officers doing a necessary job …; adapt air quality regulations …; and tweak National Environmental Policy Act review processes … [to] accommodate the realities of restored fire at a landscape scale. … Communities in the fire equivalents of floodplains need hardening [Pyne 2020].

He proposes that fire restoration jobs can replace those lost from forestry and fire suppression. He admits that our understanding of fire biology requires more research, and that our greatest need is for “a working fire culture … that ensures fire’s proper place in the landscape” by renewing “our ancient alliance” with fire and making it “an indispensable friend.”

Fire Myths, Hanson 2018

In this podcast interview, Dr. Chad Hanson, an ecologist and fire researcher, shares his perspective on the 2018 wildfires in the American West and some myths that have circulated about fire management in their wake.

First, there is a perception that wildfires in forested regions are so devastating that they reverse the ‘carbon sink’ effect of forests, releasing the carbon of the burned biomass back into the atmosphere. Forests still sequester large amounts of carbon, even if they experience wildfires, because most of the forest remains intact even through blazes. Models that fault wildfires for turning forests into net carbon emitters rest on the assumption that all of the carbon that would usually be stored in a forest is combusted during a fire, but this is far from the reality, in which just a small fraction of a forest’s biomass is consumed. As Hanson says,

In fact, even in the most intensely burned patches where a fire kills all the trees (which in reality, even in the biggest fires, it’s only a small portion, a minor portion of the overall fire)… But even in those areas, only about two or three percent of the above ground biomass is actually consumed, in other words, ends up as carbon. The trees are still standing there [Hanson 2018].

Second, the intensity of fires has not been universally increasing in recent years. We are experiencing a lot of geographically large fires, but these are not necessarily high intensity fires. The percentage of high intensity fire today is similar to historical precedent, and overall, there is much less fire in our landscapes now than in Earth’s geological history. Further, even in the highest intensity fires, forests are never decimated past the point of no return. Trees and vegetation are reestablished after fires, and the ash left behind is dense with nutrients, promoting new growth. Even dead trees, which have long been thought to be responsible for contributing to high intensity fires, are actually not shown to drive fire intensity, according to Hanson.

This series of myths – that forest fires are raging with high intensities, that they burn up so much biomass as to make forests ineffective sources of carbon sequestration, and that the only way to manage forests to avoid these outcomes is to thin out the trees – hinder our understanding of forest management and allow false and harmful solutions to propagate. As a result of these perceptions, proponents of logging have pushed to expand logging operations, purportedly as a fire management strategy. However, according to Hanson, logging is actually linked to greater fire intensity. He explains that small materials, like twigs, are more flammable than trunks.

Tree trunks are not combustible. They really just don’t burn. Again, outer bark can burn, but the trees themselves don’t burn. What logging does is it removes noncombustible material essentially from the forest and leaves behind very combustible kindling, like slash debris – the branches and small twigs and things like that that are not possible to get up off the forest floor after the tree trunks are removed and that’s very combustible.

The other thing that logging does is that it reduces the cooling shade of the forest canopy. By removing a lot of trees, you have more sunlight reaching the forest floor, and what that does is it creates hotter and drier conditions and that means everything on the forest floor gets more dried out, more potentially combustible, and logging also spreads invasive weeds like cheatgrass, which is very, very flammable. Cheatgrass loves a lot of sunlight and so you get a lot of that after intensive logging.

And the last [problem with logging] is a little bit more technical, but basically when you have a lot more trees, it cuts down on the wind speeds that drive fires. It has a buffering effect in a sense. And when a lot of the trees are removed, that buffering effect is reduced or eliminated and fire spreads through those forests faster [Hanson 2018].

This three-fold effect of logging makes forests more vulnerable, and it is important to dispel the concept that removing trees is the best way to keep people safe from fires. Hanson criticizes the opportunism of using these fire myths to advance an agenda of logging. He cautions that when fire science and policy emerge from the U.S. Forest Service, which manages national forests and gains a good deal of revenue from logging, there is a perverse incentive to keep practicing logging as fire management. He calls for clearer and more public communication from scientists to dispel fire myths and share recent findings that have been shifting so much of what we know about fire science.

Hanson says that the best strategy to ensure the protection of homes from wildfire is to focus on the homes themselves. This can be done by using fire resistant building materials, fire-proofing roofs, erecting rain gutter guards to prevent the accumulation of small fuels like pine needles, pruning the vegetation in a 100-foot radius of a house, and removing small shrubs and branches of mature trees, while leaving those trees standing. Fire management interventions at this level are shown to be far more effective at preventing damage than attempts to control the fuel load of fires within forests.

Hanson points out the need to decouple fires that occur in remote forest ecosystems and those that rage through human settlements and urban communities, because thinning out vegetation in attempts to suppress the former do not actually protect against the latter. In fact, thinning forests undermines the ecological processes that fire serves in forest systems. When discussing fires that have devastated homes and lives, he says

I mean, where’s the forest in Malibu? There’s no forest. These are chaparral ecosystems, most of the fires that are burned homes and lives have been lost are not in forest. In fact, they’re mostly nowhere near forests. They’re in grasslands, chaparral shrub habitat, oak woodlands. But the areas that are in forest, where we’ve had tragic loss of homes and lives, these are mostly areas where we’ve had intensive logging, and it’s like I mentioned earlier, you know, more logging is typically associated with more intense fire at a faster rate of spread. [Hanson 2018]

He advocates for a greater focus on fire prevention around homes and communities themselves, in what is known as ‘defensible space.’ He points out that such measures are a great source of jobs, as well as an effective intervention curbing the destructiveness of fires. With a shift in focus from forest thinning to fire-proofing, and better understanding and communication of fire science, we can let go of some of the fire myths that have been dictating policy and failing to meet public needs.

More logging is typically associated with more intense fire at a faster rate of spread [Hanson 2018].

Land use planning and wildfire: development policies influence future probability of housing loss, Syphard et al. 2013

Wildfire is a challenge that threatens human settlement at an increasing scale, but planning and development does not always address this threat. In fact, policy around land use is in large part responsible for the destruction of homes and property and the threat to human life that occurs in wildland-urban interfaces (WUIs). While there is much literature on how to suppress fires, mitigate their damage, or manage for less destructive fire seasons, a more far-reaching strategy would be to stop building in fire prone areas. Land use decisions can be improved to lessen the risk of infrastructure loss and foster healthy ecosystem function.

Land use planning is an alternative that represents a further shift in thinking, beyond the preparation of communities to withstand an inevitable fire, to preventing new residential structures from being exposed to fire in the first place. The reason homes are vulnerable to fires at the wildland-urban interface is a function of its very definition: “where homes meet or intermingle with wildland vegetation”. In other words, the location and pattern of homes influence their fire risk, and past land-use decision-making has allowed homes to be constructed in highly flammable areas. [Syphard 2013: 1-2]

In many areas, including in California, we have come to expect fire, but have not necessarily learned to live with it. The authors of this study analyzed what types of human development carried out in the next several years might contribute to or avert the risk of fire damage. They examined the South Coast Ecoregion of San Diego County, which they describe as:

topographically diverse with high levels of biodiversity, and urban development has been the primary cause of natural habitat loss and species extinction. Owing to the Mediterranean climate, with mild, wet winters and long summer droughts, the native shrublands dominating the landscape are extremely fire-prone [Syphard et al. 2013: 2].

This study acknowledges the responsibility humans have in shaping the landscape and its biodiversity, and in contributing to fire activity by building into wild areas and expanding WUI. They sought to understand how patterns of development and housing density might influence future fire spread and intensity. They found that

structures in areas with low- to intermediate- housing density were most likely to burn, potentially due to intermingling with wildland vegetation or difficulty of firefighter access. Fire frequency also tends to be highest at low to intermediate housing density, at least in regions where humans are the primary cause of ignitions [Syphard 2013: 2].

Though it is impossible to reverse the effects of policies that have shaped the fire landscape we have today, understanding the way human behavior contributes to our own risk of harm from wildfire can help us plan intelligently going forward. The authors conclude that

With projections of substantial global change in climate and human development, we recommend that land use planning should be considered as an important component to fire risk management, potentially to become as successful as the prevention of building on flood plains. History has shown us that preventing fires is impossible in areas where large wildfires are a natural ecological process. As Roger Kennedy put it, “the problem isn’t fires; the problem is people in the wrong places [Syphard 2013: 10-11].

Community owned solutions for fire management in tropical ecosystems: case studies from Indigenous communities of South America, Mistry et al. 2016

Indigenous groups across the world have developed ecological knowledge linked to the places they inhabit, including prescribed fire practices used to maintain healthy ecosystems. Mistry et al. examine the challenges Indigenous communities in South America face in managing the landscape through fire and preserving such knowledge across generations in sometimes hostile political climates. However, there is growing recognition that Indigenous people have a vital role to play in combating climate change and supporting biodiversity and healthy ecosystems.

Emerging research shows the fundamental role of Indigenous land-use practices for controlling deforestation and reducing CO2 emissions—analysis of satellite imagery suggests that Indigenous lands have reduced rates of deforestation and habitat conversion, and lower greenhouse gas (GHG) emissions, compared with surrounding areas [Mistry 2016: 1].

While indigenous groups’ use of prescribed fire early in the dry season to prevent destructive out-of-control fires is gaining broad recognition, that hasn’t necessarily translated into greater respect or autonomy for those communities. Instead, Indigenous people may be given auxiliary roles in fire management, or have their knowledge utilized but implemented by non-local organizations in structures that fail to benefit or empower the local communities themselves. While this may still achieve desired wildfire management results, it weakens intergenerational knowledge transfer and undermines the social and spiritual role of prescribed fire within communities.

Mistry et al. argue that “Indigenous fire management is effective in that it is an emergent property of a linked social-ecological system where Indigenous knowledge and culture, and associated livelihoods, are intimately interconnected with landscape management practices” [Mistry 2016: 4]. Precisely because prescribed fire matters to Indigenous communities as something more than a tool in the toolkit of managing wildfires, it is effective when carried out by those communities in reducing risk of destructive wildfires and supporting healthy and biodiverse ecosystems.

Importantly, the numerous uses of fire mean that burning is a relatively constant activity, particularly during the dry season, generally at low levels, thereby helping to prevent the build-up of flammable fuel and incidents of large-scale uncontrollable wildfires. Experimental studies of fire behaviour suggest that this patch mosaic burning not only reduces the occurrence of dangerous fires, but also increases spatial and temporal vegetation heterogeneity and biodiversity [Mistry 2016: 4].

These authors distinguish between Indigenous relationships to ecosystems and market-based approaches to ecosystem services valuation, which attempt to incentivize conservation through payment. While the goal of the market-based approach is to monitor and preserve functioning ecosystems, “their ideological foundations within a neoliberal agenda that promotes ‘selling nature to save it’ is in stark contradiction with Indigenous ontologies based on human–nonhuman–spiritual relationships” [Mistry 2016: 2].

Within Indigenous communities, fire plays a role in social bonding, intergenerational knowledge transfer, and agricultural practices. Mistry et al. argue that

savanna and forest ecosystems are being protected within Indigenous lands not because they are being ‘managed’ in a direct and active way, but as the indirect outcome of a healthy social–ecological system, i.e. the outcome of practices that maintain social and ecological integrity, or what can be termed ‘community owned solutions [Mistry 2016: 4].

But challenges, including loss of fire knowledge by younger generations within Indigenous groups because of outside pressures and encroachment, pose a threat to these fire management practices. For example, in Venezuela and Brazil,

young Wapishana and Makushi and some community leaders were more critical about the use of fire as they had more regular contact with state natural resource management officials and environmental organizations that promoted antifire discourses. As with the Krahô, changing Indigenous values to focus on fire prevention and suppression could have the effect of making the problem worse [Mistry 2016: 4].

That is, when prescribed burning is taken out of its original context and represented to younger generations of Indigenous people and land stewards as simply a well-incentivized tool, the Indigenous communities themselves are diminished, along with the robustness of their ecological knowledge that gets passed forward.

In spite of lingering antagonistic views in Brazil and Venezuela toward indigenous fire management, attitudes are changing.

Not only is there a move away from categorizing all fire as ‘bad’; there is also a recognition that Indigenous fire knowledge is a valid form of knowledge that could inform policy-making [Mistry et al. 2016: 6].

Mistry et al. suggest the best way to achieve both ecological and communal health might be through power-sharing arrangements. By empowering Indigenous communities, national governments could in turn work toward their fire management and biodiversity conservation goals. This might require evaluating ecological health in ways beyond just quantitative metrics, which reduce these complex systems down to a set of standardized numbers, as well as the recognition that the well-being of these ecosystems is tied to the Indigenous communities that inhabit them, according to the authors:

There needs to be enabling policies that focus on legitimizing and strengthening Indigenous fire management as a community owned solution. Critically, as community owned fire management is intricately linked with Indigenous survival strategies, so too must firefighting and prescribed burning be grounded in local social–ecological systems. We believe it is necessary to define long-term actions to support the integrated functioning and survival of Indigenous communities as a whole, rather than focusing on isolated issues (e.g. carbon retention) or benefits for some individuals (e.g. hiring Indigenous firefighters) [Mistry 2016: 8].

This systems approach may well be the key to successful long-term fire management. The authors offer this challenge:

What we want to do is not promote one over the other, but encourage decision-makers to engage with, and appreciate, Indigenous perspectives and worldviews on fire management. Community owned solutions acknowledge collectivity, spirituality, process orientation and locality, whereas many expert-led fire management interventions often result in promoting individualism, ethnocentrism, rationality, efficiency, commercialism and globalization. The question we raise is this: can the ‘community owned solutions’ approach be the mechanism through which Indigenous perspectives can be represented within fire management [Mistry et al. 2016: 8]?

Invasive grasses increase fire occurrence and frequency across US ecoregions, Fusco et al. 2019

It has long been suspected that the increasing abundance of invasive grass species may contribute to wildfires in the United States by adding abundant new fuels to ecosystems, increasing the range of conditions that lead to fire ignition, and enabling the development of larger, hotter fires. The new fire regimes (patterns of fire duration, intensity, and spread) that emerge can in turn destabilize wildlife and lead to local extinctions while expanding favorable habitat for the invasive species, for many of these grasses recover quickly after fires, providing renewed fuel and potentially increasing the frequency of fires.

The authors of this paper provide a comprehensive analysis on the impact of 12 non-native grasses on the occurrence (whether a fire occurred in a particular place), frequency (how many times a place burned), and size of wildfires. The research was conducted across 29 US ecoregions, including deserts, temperate forests, wetlands, woodlands, river valleys, shrublands, and coastal plains. Data were collected and combined from fire records and records of invasive grasses, and results from “invaded” regions and nearby “uninvaded” regions were compared. The authors also considered human activities and ecological factors related to fire.

One of the most notorious impacts of nonnative, invasive grasses is the alteration of fire regimes. Yet, most evidence of these impacts comes from local-scale studies, making it unclear whether they have broader implications for national and regional fire management. Our analysis of 12 invasive grasses documents regional-scale alteration of fire regimes for 8 species, which are already increasing fire occurrence by up to 230% and fire frequency by up to 150%. These impacts were demonstrated across US ecoregions and vegetation types, suggesting that many ecosystems are vulnerable to a novel grass-fire cycle. Managing existing grass invasions and preventing future introductions presents a key opportunity to remediate the ecological and economic consequences of invasive species and fire [Fusco 2019: 23594]

The results of this analysis showed that 8 of the 12 invasive grass species examined were associated with significantly higher fire occurrence and fire frequency, and that fire occurrence more than doubled for two of these species. Three of the species did not impact fire occurrence, and a decrease in fires was associated with one species (a wetlands grass species). The impact on fire size was variable, with two species associated with larger fires, three species associated with smaller fires.

Individually, climate change is expected to increase the potential for fire occurrence by 150% by the end of the century based on projected changes in temperature and precipitation. Here we show that 8 invasive grass species are already associated with increased rates of fire occurrence by 27 to 230%, and 6 invasive grass species are associated with increased mean fire frequency by 24 to 150%, compounding current and future fire risk across the United States. [Fusco et al. 2019: 23595]

The authors suggest that fire and invasive species managers work together to create integrated management plans; otherwise, the convergence of human activities, climate change, and invasive species will continue to promote wildfires across the United States.

Smokey the Beaver: beaver‐dammed riparian corridors stay green during wildfire throughout the western USA, Fairfax and Whittle 2020

This study examines the positive effects of beaver damming on the resistance of landscapes to wildfire damage. The authors find that in riparian corridors (areas along rivers), the presence of beavers and their dams can create refuges that withstand blazes that consume surrounding vegetation.

Beavers play an important role in wetland habitats and are known as ecosystem engineers for the way they can shape landscapes with their activities. Beaver dams slow down water moving across a landscape, holding it in place for longer and allowing water to infiltrate into the soil, which raises water tables.

The combination of building flow obstructions (dams), accumulating water (ponds), and spreading that water out in the landscape (channels) gives beavers the unique potential to modulate environmental extremes such as flood and drought. When it comes to water, beavers slow it, spread it, and store it.

Due to the fact that beaver channels and dams spread water out in the landscape and store it broadly in adjacent soils, the vegetation near beaver ponds doesn’t experience as much reduced water availability during drought. Drought-stricken vegetation burns more easily than lush, green vegetation, so it follows that the vegetation around beaver ponds would be more difficult to burn than vegetation around undammed creeks [Fairfax and Whittle 2020: 1].

Fairfax and Whittle observed the effects of beaver dams on preventing fire spread to the areas where they had built dams, examples of which are shown in satellite imagery below.

The authors quantify the effects of beaver activity in fireproofing areas by examining the Normalized Difference Vegetation Index (NDVI) observed in satellite imagery before, during, and after wildfire years in the American West. They found that while vegetation is able to reestablish itself a year after fire damage regardless of beaver activity due to its own resilience to fire, areas in beaver dammed zones maintained vegetation even during wildfires, demonstrating actual resistance to blazes, not just the ability to recover after damage. They note how vital this is for those ecosystems and the life within them.         

These ribbons of fire-resistant riparian corridor may be particularly important for species that are unable to physically escape wildfire. They can provide temporary habitat for fish, amphibians, reptiles, small mammals, wild and domestic ungulates, and birds that are unable to outrun/outfly the spread of flames. While we found that beaver activity does play a significant role in maintaining vegetation greenness during wildfires, it does not appear to play a significant role in the ability for a riparian corridor to rebound in the year following fire. Riparian vegetation NDVI rebounded in the year following the fire regardless of proximity to beaver activity. Thus, we would describe beaver activity as creating refugia during wildfire, but not necessarily changing the long-term landscape outcomes [Fairfax and Whittle 2020: 7].

The survival of wildlife is crucial to these ecosystems, and beaver activity uniquely contributes to the creation of refuge areas that resist burning and can provide shelter for animals during these destructive events. The authors conclude,

As it stands today, wetland habitat is very limited and beavers can create and maintain wetland habitat that persists through flood, drought, and, as we have shown in this study, fire. This has immediate relevance to scientists and practitioners across North America and Eurasia, particularly in places with increasing wildfire risk and existing or planned beaver populations. Perhaps instead of relying solely on human engineering and management to create and maintain fire-resistant landscape patches, we could benefit from beavers’ ecosystem engineering to achieve the same goals at a lower cost [Fairfax and Whittle 2020: 7].

Planned Herbivory in the Management of Wildfire Fuels, Nader et al. 2007

Nader et al. survey herbicides, prescribed fire, mechanized treatments, hand cutting, and grazing animals as fire management techniques. Managing vegetation involves “changing the plant community to decrease the flame height when fire occurs,” favoring native species that may be more resilient to fire, and altering the landscape to create fuel breaks, which are patches across which it is hard for fire to jump [Nader 2007: 18].

Focusing their analysis on grazing and the contexts in which it is most useful, the authors note that there are many site and animal specific factors to take into account for successful implementation.

[Grazing] is a complex, dynamic tool with many plant and animal variables, and it requires sufficient knowledge of the critical control points to reach treatment objectives. Those control points involve the species of livestock grazed (cattle, sheep, goats, or a combination); the animals’ previous grazing experience (which can affect their preferences for certain plants); time of year as it relates to plant physiology (animal consumption is directed by the seasonal nutrient content); animal concentration or stocking density during grazing; grazing duration; plant secondary compounds; and animal physiological state [Nader 2007: 19].

Grazing has the advantage of keeping nutrients in the ecosystem, unlike mechanical methods that harvest vegetation to be sold as biomass chips (like wood chips). This means that when animals digest vegetation and excrete on the landscape, they participate in the local nutrient cycle. Animals also trample soil, which can crush fine fuel and mix it into the soil, where it cannot contribute to ignition, which reduces one contributing factor to persistent and destructive blazes.  Animals do more than just remove extra vegetation – they can have many beneficial interactions within a given ecosystem.

Any grazing plan designed for fuel reduction needs to consider the grazing impacts on parameters other than just simply reduction. The effects of the grazing management should be studied for their impact on water quality, compaction, riparian vegetation, disease interaction with wildlife (bluetongue, pasturella), and weed transmission. The positive aspects of grazing over other treatments also should be weighed, including recycling of nutrients into the products of food and fiber [Nader 2007: 22].

By introducing grazing animals into a landscape or agricultural system, managers can affect biodiversity in complex ways. The authors mention that “Hadar et al. reported that light grazing increased plant diversity on treated sites. Thus, when proposing a stocking rate for treatment consumption, the environmental impact needs to be considered” [Nader 2007: 22].

Nader et al. conclude that “grazing is best used when addressing vegetation with stems of smaller diameters that make up the 1- and 10-hour fuels. These two fuel classes are important because they can greatly impact the rate of spread of a fire, as well as flame height” [Nader 2007: 19]. While they call for further research to validate anecdotal accounts supporting grazing and understand its best practice, they maintain that “prescribed grazing has the potential to be an ecologically and economically sustainable management tool for reduction of fuel loads” [Nader 2007: 20].

Landscape rehydration ‘better than dams’ in improving farm production, reducing fire risk, Major 2020

A project in Queensland, Australia has met with success in its efforts to rehydrate the landscape on the farmland property of Worona Station, improving biodiversity, water retention, and resistance to erosion and fire. Worona Station had been degraded and faced serious erosion issues, so Chris Le Feuvre, the owner, partnered with consultancy groups of NQ Dry Tropics and the Mulloon Institute in a project to rehydrate his land.

The project team has used a combination of planned grazing and small, low-tech dams to combat erosion problems. The grazing technique involves:

Splitting paddocks into small sizes and using large mobs of cattle grazing on rotation … grazing pasture more intensively while giving it longer to rest, [thereby] increasing carrying capacity.

Grazing in this way (which is evocative of Allan Savory’s Holistic Planned Grazing methodology) has resulted in increased pasture species diversity and boosted plant growth, allowing the Le Feuvre to double his herd size. Planned grazing has also reduced sediment runoff from the property. Sam Skeat, a grazing officer with NQ Dry Tropics, attests to the importance of grazing.

The plug-and-pond technique — also known as leaky weirs — involves small dam-like structures to lift the bed level of the water, which is then run onto the floodplain to grow pasture and recharge aquifers. While weirs have been strategically constructed, Mr. Skeat said grazing management was the most important tool to improve water retention in a landscape. ‘If you can use cattle as a tool to regenerate the grassland, you’ll get more infiltration, slow the flow, hold water up in the landscape and have you growing grass for longer’ [Major 2020].

Rehydrating landscapes can improve their resilience to extreme events, and improve their quality in the face of chronic problems like erosion. According to the Mulloon Institute Chairman Gary Nairn, the issue of degraded gullies and streams is a national concern. Gullies are created when parched land is unable to absorb rainwater, allowing it to run off. The sediment-filled runoff ends up in the ocean, polluting it.

Nairn sees land rehydration through planned grazing and related techniques as a better solution than building a massive, industrial-scale dam to retain water. The Australian government has been looking into building new large dams. Levels at Warragamba Dam, which supplies about 80 percent of Sydney’s water, have dropped to less than half capacity.

‘We’ve been able to demonstrate in Mulloon, if we repaired and rehydrated the catchment through to the Sydney water supply, you could store the equivalent of Warragamba Dam,’ he said [Major 2020].

Well-watered mulberry tree credited with saving home on NSW South Coast from summer bushfires, Aubrey 2020

A well-watered mulberry tree has been credited with averting the danger of destructive wildfires from destroying Brett Hawkins’ home during 2020’s unprecedented fire season in Australia. When massive fires raged through the bush through the summer, many homes were completely engulfed. However, Hawkins attested that when he returned to his home after evacuating,

‘I could see straight away the house was intact — the roof was intact, but everything else around it was burnt, with the exception of the mulberry tree.’ He described the stark scene greeting him upon arriving back home, ‘It was apocalyptic,’ Mr. Hawkins said. ‘There was not a tree left, ash on the ground and smouldering embers everywhere.’ But among the blackened trees, Mr. Hawkins found his mudbrick house and mulberry tree in full leaf [Aubrey 2020].

In the season’s drought, he had been rationing water, but sparing some to keep his tree hydrated and healthy, which may have been a contributing factor in its resistance. According to the article, “Mr. Hawkins believed that by heavily watering the tree, combined with luck regarding which direction the fires came, the full heat of the bushfires was shifted.” [Aubrey 2020]

Another important feature is the mulberry’s lack of dried leaves and brush at its base that might pose a danger of igniting. Other species, like eucalyptus, with oily leaves that could dry out, or pine trees whose long branches catch dry leaves, are less ideal.

A tree expert from the Fenner School of Environment at the Australian National University analyzed some of the possible factors leading to the survival of this mulberry tree and what it might teach those wishing to fortify the fire resilience of their homes and properties. “While there does not seem to be a clear answer on what to plant to ‘fire-proof’ your house, Professor Brack said a well-watered tree, with a clear trunk and no loose, dry leaves or branches is a good start” [Aubrey 2020].

All over the world, from Australia to Europe to North and South America, wildfires have waged destruction on natural landscapes and human settlements alike. The devastation of these disasters is heartbreaking, and the images of catastrophe – walls of flame, scorched wildlife, a world gone red – are unforgettable. There is no more potent image of the climate crisis than the towering infernos and eerie, hellish, smoke-filled skies that we’ve seen in this past year.

The question is how we best confront the issue, keeping people safe and ecosystems intact as much as possible. Given that the hotter, drier conditions that climate change causes are exacerbating wildfire seasons in both duration and destructiveness, it is urgent that we better understand fire’s natural role in ecosystems and the conditions that cause fires to become ultra-destructive. Wildfire is a complicated global problem that requires locally-informed responses adapted to local ecosystems.

“Fuel load” reduction is a major solution, and this may be part of the answer in certain cases. However, to the extent that hauling out vegetation from a fire-prone site further degrades that ecosystem, this practice may only exacerbate the problem in the long run. Fortunately, many alternative and complementary practices to diminish wildfire ferocity are known. This includes, for example, indigenous prescribed burning, promoting ecosystem health to reduce dryness and drought, favoring native species, and enacting land use policies that discourage development in fire-prone areas.

In discussion of fire and its risks, it is important to first note that not all fire is problematic, and the ideal healthy ecosystem would not necessarily be one without any fire. For example, species in fire-evolved landscapes depend on cyclical fires, and burning can also increase landscape heterogeneity and biodiversity.

In discussion of fire and its risks, it is important to first note that not all fire is problematic, and the ideal healthy ecosystem would not necessarily be one without any fire.

Moreover, a world without fire is impossible, and focusing on total fire suppression is misguided. As environmental historian Stephen Pyne warns, “Removing fire from landscapes that have co-evolved or co-existed with it can be as ruinous as putting fire into landscapes that have no history of it” [Pyne 2020]. In fact, we can fight fire with fire by planning controlled burns, part of the strategy of managing the vegetative fuel available to wildfires.

Since grasses, shrubs, and trees become fuel for a fire, much scientific literature on wildfire examines how to reduce this fuel so that when wildfire does occur, it is less destructive and less far-reaching. Invasive plants are a particularly problematic form of fuel, because they haven’t necessarily evolved in fire-shaped landscapes. Fires can quickly gain in intensity when consuming them, and invasive grasses alter the cyclical availability of fuel and increase the frequency of fires [Fusco 2020].

In contrast, native plants in fire-prone ecosystems often evolve with fire playing an ecological role in their habitat, leading them to be more resistant and hardy in destructive blazes. Thus there is a clear advantage to favoring native species over invasive ones, especially since native species also perform ecological functions necessary for the health of the ecosystem and its inhabitants.

It is important to understand that more plant life does not necessarily translate to more fire fuel.  The quality of landscape and details such as height, density, fuel bed depth and fuel moisture all matter for fire spread [Nader 2007]. Furthermore, not all vegetation is equally vulnerable. This is not just a matter of the differences between species, but also how landscape differs in its spacing, density, and topological features, making some landscapes more vulnerable to fire spread than others.

Often, our problems with fire are also problems of water. How well hydrated a landscape is can make a crucial difference to its vulnerability to wildfire. In fact, the capacity of land to retain water is linked to vegetation, and specifically to biodiverse vegetated areas. A healthy and hydrated tree or patch of forest may withstand fire that drier and more brittle vegetation does not. Healthy trees may even protect properties from fire, as anecdotes attest [Aubrey 2020].

Plant roots, along with the mycorrhiza and microbes that make up a symbiotic web of linked organisms within healthy soil, create a porous soil structure that water infiltrates when it rains; the soil thus acts as a sort of natural sponge. Unlike dehydrated and degraded soil, which do not absorb and retain water effectively, living soil soaks up precipitation; this reduces runoff and erosion during heavy deluges. Water infiltrating healthy soil hydrates organic matter, is retained in topsoil pores, or makes its way to the water table below ground, which can be thought of as a bank for water. When dry seasons or droughts arrive, this bank provides the moisture needed to keep vegetation healthy–and, when rains arrive again, this bank refills.

Plant presence helps build healthy soil, and it also contributes to the small water cycle (the circulation of water evaporating from land and falling in the form of precipitation over the same environment). For example, scientists have found that many plants release microbes which are borne up on evaporated water droplets and catalyze cloud formation and precipitation in the atmosphere, a phenomenon known as bioprecipitation [Morris 2014]. Plants don’t just need rain – they help create it too. Well-hydrated, fire-resistant plants are part of the key to retaining moisture in landscapes and sapping wildfire of its power.

Beavers also contribute to water retention on the landscapes they inhabit. They play a major ecological role by creating and preserving wetlands, so much so that they are sometimes called ecosystem architects or engineers.The hydrating effects of beaver activities have even been found to create areas that resist fire even while neighboring landscapes burn. Some experts suggest that “perhaps instead of relying solely on human engineering and management to create and maintain fire-resistant landscape patches, we could benefit from beavers’ ecosystem engineering to achieve the same goals at a lower cost” [Fairfax and Whittle 2020: 7].

Beavers are not the only type of animal life that can help in fire management. Ruminants like goats, cows and sheep can control vegetation, while also improving soil health and promoting water retention in well-managed grazing systems. The movement of hoofed grazing animals across grasslands breaks up soil, making it easier for water to infiltrate, while the animal manure provides natural fertilizer.

Another benefit to controlling vegetation through animal grazing is the retention of biomass on the landscape in the form of nourishing manure, rather than clearing it away via logging or burning, for example [Nader 2007]. Grazing also presents opportunities for diversified economic activity within agricultural or silvopasture (the practice of integrating trees, forage, and the grazing of domesticated animals in a mutually beneficial way) systems. In case studies, managed grazing has made farm operations more productive and profitable while at the same time promoting ecological health [Major 2020]. Grazing animals also can increase ecosystem biodiversity^[2].

Finally, there is the role of humans and where we choose to live. Part of the reason fires cause such harm to human settlements is because we build houses in fire-prone areas. The wildland-urban interface (WUI) is the site of a large percentage of fires, including particularly destructive fires, and increasing human encroachment of wild areas means that more people are brought into closer range of wildfires, while also negatively impacting ecosystems and their biodiversity. Of course, one bold strategy to reduce fire risk is to change our land use [Syphard 2013].

Part of the reason fires cause such harm to human settlements is because we build houses in fire-prone areas.

As modern human settlements have expanded, we have designed our fire management strategies to focus almost exclusively on suppression in most places, enforcing a dominant paradigm that fire is always bad and should be eliminated from landscapes. Unfortunately, such policy allows the very buildup of vegetation that can fuel increasingly destructive wildfires.

However, alternative relationships to fire have been practiced across human history, such as the controlled burning used by Indigenous communities across the world, from California to Australia. Recently, the depth of these communities’ ecological knowledge is beginning to gain the respect it deserves and to be considered and implemented in mainstream fire practices. In certain circumstances, it is now accepted that controlled burns can help ensure healthy ecosystems by decreasing the destructiveness and frequency of wildfires.

Although the use of prescribed fire is one way to manage vegetation and shape a varied landscape, any strategy that combines fire management and ecological stewardship will be full of site-specific complexity. Thus, it is critical to understand how Indigenous stewardship has been carried out over generations on given landscapes and to factor this knowledge into strategies to combat wildfire and ensure ecological health.

Much of the world’s remaining biodiversity resides in land inhabited by Indigenous groups, whose fire and land management practices come from a deep cultural and spiritual context. That is, “Indigenous fire management is effective in that it is an emergent property of a linked social-ecological system where Indigenous knowledge and culture, and associated livelihoods, are intimately interconnected with landscape management practices” [Mistry 2016: 4].

A path forward into a fire-resilient age might be led by Indigenous groups implementing local, community-owned solutions. Society at large would benefit from supporting and learning from the local communities who have generational knowledge of local ecosystems and fire management. In addition, land stewardship using practices that favor native species, biodiversity, living soils, and aim to retain moisture on the land should be applied on a wide scale. The articles that follow offer detail and insight into these approaches.

Wildfire article summaries

Our burning planet: why we must learn to live with fire, Pyne 2020

Steven J. Pyne is an emeritus professor at Arizona State University and the author of several books on fire history and policy. He wrote this opinion piece as a protest against the prevention and suppression of wildfires in our land management process. He argues that revising our perception of fire and accepting its presence in ecosystems is critical to our ongoing relationship with our planet.

He describes “a paradox at the core of Earth’s unraveling firescapes,” that “we have too many bad fires — fires that kill people, burn towns, and trash valued landscapes. We have too few good ones — fires that enhance ecological integrity and hold fires within their historic ranges” [Pyne 2020]. Operating under a paradigm of total fire suppression leads us astray in managing landscapes, while we so readily accept fire in the form of fossil fuel combustion in so much of our lives. Pyne sees these behaviors as evidence that our relationship with fire is out of whack.

He stresses the importance of distinguishing between burning in living ecosystems and burning the fossils of life from past ages.

The critical contrast lies in a deeper dialectic than burned and unburned landscapes. It is a dialectic between burning living biomass and burning fossil biomass. We are taking stuff out of the geologic past, burning it in the present with all kinds of little understood consequences, and passing the effluent into the geologic future.

…

Fires in living landscapes come with ecological checks and balances. Fires in lithic landscapes have no boundaries save those humans impose on themselves [Pyne 2020].

Pyne associates three paradoxes with our current fire policies. First, abandoning a traditional lore of “light burning” has removed good fires and left us with only bad and harmful ones. When controlled burns are not practiced regularly to manage landscapes, vegetation can build up and fuel the intensity and spread of uncontrolled blazes that spark.

Second and surprisingly: “The Earth does not have more fire today than before fossil fuels emerged as a primary source of energy: It has significantly less” [Pyne 2020]. That is, the amount of land burned in fires has actually decreased, while the presence of intense “feral flames” has increased. The decrease in the scope of fire is largely due to the move away from fire’s use in agriculture and its replacement with modern techniques, including machinery powered by combustion. As Pyne describes,

Farmers had relied on fire to fertilize, fumigate, and alter microclimates. Fire did all this in one catalytic process that self-propagated. But with the transition to fossil biomass, modern agriculture found surrogates with artificial fertilizers, pesticides, and herbicides, and it now had the fossil-fuel-powered machines to distribute them. Production became more efficient; transport, more dense. As agriculture joins a modern economy, working flames recede [Pyne 2020].

What we are left with is intense, destructive wildfire, rather than helpful working fire. Pyne points out that we now only see one half of fire’s possibilities, since the working fire shaping landscapes and agricultural systems is notably absent. He says: “Landscape fire fades; what fire persists tends to be outbreaks of feral fire. We see those oft-disastrous flames. We don’t see the lost fires or the sublimated fires in machines that removed them” [Pyne 2020].

The third paradox is that as we reduce our use of fossil fuels going forward (as one sort of fire), we will have a greater need “to manage fire in living landscapes.” So Pyne calls for us “to reinstate the right kind of fire, and … adapt to fire’s presence and let it do the work for us.” He pushes for the recognition that transitioning away from our reliance on fossil fuel burning is an important but incomplete step in balancing ecosystem health. Fires in living systems have an important role to play, and according to Pyne, “the need is not just to reduce fuels to help contain wildfires; those missing fires did biological work for which no single surrogate exists” [Pyne 2020]. He asserts that we will need to reintroduce fire as a staple tool on our landscapes.

Fires in living systems have an important role to play, and according to Pyne, “the need is not just to reduce fuels to help contain wildfires; those missing fires did biological work for which no single surrogate exists.” He asserts that we will need to reintroduce fire as a staple tool on our landscapes.

Pyne concludes with a call for the overhaul of our conceptual and policy treatment of fire.

Anthropogenic fire needs more room to maneuver – more geographic space, more legal space, more political space, more conceptual space. … Equally, society needs to rethink liability law to reduce the risks incurred by fire officers doing a necessary job …; adapt air quality regulations …; and tweak National Environmental Policy Act review processes … [to] accommodate the realities of restored fire at a landscape scale. … Communities in the fire equivalents of floodplains need hardening [Pyne 2020].

He proposes that fire restoration jobs can replace those lost from forestry and fire suppression. He admits that our understanding of fire biology requires more research, and that our greatest need is for “a working fire culture … that ensures fire’s proper place in the landscape” by renewing “our ancient alliance” with fire and making it “an indispensable friend.”

Fire Myths, Hanson 2018

In this podcast interview, Dr. Chad Hanson, an ecologist and fire researcher, shares his perspective on the 2018 wildfires in the American West and some myths that have circulated about fire management in their wake.

First, there is a perception that wildfires in forested regions are so devastating that they reverse the ‘carbon sink’ effect of forests, releasing the carbon of the burned biomass back into the atmosphere. Forests still sequester large amounts of carbon, even if they experience wildfires, because most of the forest remains intact even through blazes. Models that fault wildfires for turning forests into net carbon emitters rest on the assumption that all of the carbon that would usually be stored in a forest is combusted during a fire, but this is far from the reality, in which just a small fraction of a forest’s biomass is consumed. As Hanson says,

In fact, even in the most intensely burned patches where a fire kills all the trees (which in reality, even in the biggest fires, it’s only a small portion, a minor portion of the overall fire)… But even in those areas, only about two or three percent of the above ground biomass is actually consumed, in other words, ends up as carbon. The trees are still standing there [Hanson 2018].

Second, the intensity of fires has not been universally increasing in recent years. We are experiencing a lot of geographically large fires, but these are not necessarily high intensity fires. The percentage of high intensity fire today is similar to historical precedent, and overall, there is much less fire in our landscapes now than in Earth’s geological history. Further, even in the highest intensity fires, forests are never decimated past the point of no return. Trees and vegetation are reestablished after fires, and the ash left behind is dense with nutrients, promoting new growth. Even dead trees, which have long been thought to be responsible for contributing to high intensity fires, are actually not shown to drive fire intensity, according to Hanson.

This series of myths – that forest fires are raging with high intensities, that they burn up so much biomass as to make forests ineffective sources of carbon sequestration, and that the only way to manage forests to avoid these outcomes is to thin out the trees – hinder our understanding of forest management and allow false and harmful solutions to propagate. As a result of these perceptions, proponents of logging have pushed to expand logging operations, purportedly as a fire management strategy. However, according to Hanson, logging is actually linked to greater fire intensity. He explains that small materials, like twigs, are more flammable than trunks.

Tree trunks are not combustible. They really just don’t burn. Again, outer bark can burn, but the trees themselves don’t burn. What logging does is it removes noncombustible material essentially from the forest and leaves behind very combustible kindling, like slash debris – the branches and small twigs and things like that that are not possible to get up off the forest floor after the tree trunks are removed and that’s very combustible.

The other thing that logging does is that it reduces the cooling shade of the forest canopy. By removing a lot of trees, you have more sunlight reaching the forest floor, and what that does is it creates hotter and drier conditions and that means everything on the forest floor gets more dried out, more potentially combustible, and logging also spreads invasive weeds like cheatgrass, which is very, very flammable. Cheatgrass loves a lot of sunlight and so you get a lot of that after intensive logging.

And the last [problem with logging] is a little bit more technical, but basically when you have a lot more trees, it cuts down on the wind speeds that drive fires. It has a buffering effect in a sense. And when a lot of the trees are removed, that buffering effect is reduced or eliminated and fire spreads through those forests faster [Hanson 2018].

This three-fold effect of logging makes forests more vulnerable, and it is important to dispel the concept that removing trees is the best way to keep people safe from fires. Hanson criticizes the opportunism of using these fire myths to advance an agenda of logging. He cautions that when fire science and policy emerge from the U.S. Forest Service, which manages national forests and gains a good deal of revenue from logging, there is a perverse incentive to keep practicing logging as fire management. He calls for clearer and more public communication from scientists to dispel fire myths and share recent findings that have been shifting so much of what we know about fire science.

Hanson says that the best strategy to ensure the protection of homes from wildfire is to focus on the homes themselves. This can be done by using fire resistant building materials, fire-proofing roofs, erecting rain gutter guards to prevent the accumulation of small fuels like pine needles, pruning the vegetation in a 100-foot radius of a house, and removing small shrubs and branches of mature trees, while leaving those trees standing. Fire management interventions at this level are shown to be far more effective at preventing damage than attempts to control the fuel load of fires within forests.

Hanson points out the need to decouple fires that occur in remote forest ecosystems and those that rage through human settlements and urban communities, because thinning out vegetation in attempts to suppress the former do not actually protect against the latter. In fact, thinning forests undermines the ecological processes that fire serves in forest systems. When discussing fires that have devastated homes and lives, he says

I mean, where’s the forest in Malibu? There’s no forest. These are chaparral ecosystems, most of the fires that are burned homes and lives have been lost are not in forest. In fact, they’re mostly nowhere near forests. They’re in grasslands, chaparral shrub habitat, oak woodlands. But the areas that are in forest, where we’ve had tragic loss of homes and lives, these are mostly areas where we’ve had intensive logging, and it’s like I mentioned earlier, you know, more logging is typically associated with more intense fire at a faster rate of spread. [Hanson 2018]

He advocates for a greater focus on fire prevention around homes and communities themselves, in what is known as ‘defensible space.’ He points out that such measures are a great source of jobs, as well as an effective intervention curbing the destructiveness of fires. With a shift in focus from forest thinning to fire-proofing, and better understanding and communication of fire science, we can let go of some of the fire myths that have been dictating policy and failing to meet public needs.

More logging is typically associated with more intense fire at a faster rate of spread [Hanson 2018].

Land use planning and wildfire: development policies influence future probability of housing loss, Syphard et al. 2013

Wildfire is a challenge that threatens human settlement at an increasing scale, but planning and development does not always address this threat. In fact, policy around land use is in large part responsible for the destruction of homes and property and the threat to human life that occurs in wildland-urban interfaces (WUIs). While there is much literature on how to suppress fires, mitigate their damage, or manage for less destructive fire seasons, a more far-reaching strategy would be to stop building in fire prone areas. Land use decisions can be improved to lessen the risk of infrastructure loss and foster healthy ecosystem function.

Land use planning is an alternative that represents a further shift in thinking, beyond the preparation of communities to withstand an inevitable fire, to preventing new residential structures from being exposed to fire in the first place. The reason homes are vulnerable to fires at the wildland-urban interface is a function of its very definition: “where homes meet or intermingle with wildland vegetation”. In other words, the location and pattern of homes influence their fire risk, and past land-use decision-making has allowed homes to be constructed in highly flammable areas. [Syphard 2013: 1-2]

In many areas, including in California, we have come to expect fire, but have not necessarily learned to live with it. The authors of this study analyzed what types of human development carried out in the next several years might contribute to or avert the risk of fire damage. They examined the South Coast Ecoregion of San Diego County, which they describe as:

topographically diverse with high levels of biodiversity, and urban development has been the primary cause of natural habitat loss and species extinction. Owing to the Mediterranean climate, with mild, wet winters and long summer droughts, the native shrublands dominating the landscape are extremely fire-prone [Syphard et al. 2013: 2].

This study acknowledges the responsibility humans have in shaping the landscape and its biodiversity, and in contributing to fire activity by building into wild areas and expanding WUI. They sought to understand how patterns of development and housing density might influence future fire spread and intensity. They found that

structures in areas with low- to intermediate- housing density were most likely to burn, potentially due to intermingling with wildland vegetation or difficulty of firefighter access. Fire frequency also tends to be highest at low to intermediate housing density, at least in regions where humans are the primary cause of ignitions [Syphard 2013: 2].

Though it is impossible to reverse the effects of policies that have shaped the fire landscape we have today, understanding the way human behavior contributes to our own risk of harm from wildfire can help us plan intelligently going forward. The authors conclude that

With projections of substantial global change in climate and human development, we recommend that land use planning should be considered as an important component to fire risk management, potentially to become as successful as the prevention of building on flood plains. History has shown us that preventing fires is impossible in areas where large wildfires are a natural ecological process. As Roger Kennedy put it, “the problem isn’t fires; the problem is people in the wrong places [Syphard 2013: 10-11].

Community owned solutions for fire management in tropical ecosystems: case studies from Indigenous communities of South America, Mistry et al. 2016

Indigenous groups across the world have developed ecological knowledge linked to the places they inhabit, including prescribed fire practices used to maintain healthy ecosystems. Mistry et al. examine the challenges Indigenous communities in South America face in managing the landscape through fire and preserving such knowledge across generations in sometimes hostile political climates. However, there is growing recognition that Indigenous people have a vital role to play in combating climate change and supporting biodiversity and healthy ecosystems.

Emerging research shows the fundamental role of Indigenous land-use practices for controlling deforestation and reducing CO2 emissions—analysis of satellite imagery suggests that Indigenous lands have reduced rates of deforestation and habitat conversion, and lower greenhouse gas (GHG) emissions, compared with surrounding areas [Mistry 2016: 1].

While indigenous groups’ use of prescribed fire early in the dry season to prevent destructive out-of-control fires is gaining broad recognition, that hasn’t necessarily translated into greater respect or autonomy for those communities. Instead, Indigenous people may be given auxiliary roles in fire management, or have their knowledge utilized but implemented by non-local organizations in structures that fail to benefit or empower the local communities themselves. While this may still achieve desired wildfire management results, it weakens intergenerational knowledge transfer and undermines the social and spiritual role of prescribed fire within communities.

Mistry et al. argue that “Indigenous fire management is effective in that it is an emergent property of a linked social-ecological system where Indigenous knowledge and culture, and associated livelihoods, are intimately interconnected with landscape management practices” [Mistry 2016: 4]. Precisely because prescribed fire matters to Indigenous communities as something more than a tool in the toolkit of managing wildfires, it is effective when carried out by those communities in reducing risk of destructive wildfires and supporting healthy and biodiverse ecosystems.

Importantly, the numerous uses of fire mean that burning is a relatively constant activity, particularly during the dry season, generally at low levels, thereby helping to prevent the build-up of flammable fuel and incidents of large-scale uncontrollable wildfires. Experimental studies of fire behaviour suggest that this patch mosaic burning not only reduces the occurrence of dangerous fires, but also increases spatial and temporal vegetation heterogeneity and biodiversity [Mistry 2016: 4].

These authors distinguish between Indigenous relationships to ecosystems and market-based approaches to ecosystem services valuation, which attempt to incentivize conservation through payment. While the goal of the market-based approach is to monitor and preserve functioning ecosystems, “their ideological foundations within a neoliberal agenda that promotes ‘selling nature to save it’ is in stark contradiction with Indigenous ontologies based on human–nonhuman–spiritual relationships” [Mistry 2016: 2].

Within Indigenous communities, fire plays a role in social bonding, intergenerational knowledge transfer, and agricultural practices. Mistry et al. argue that

savanna and forest ecosystems are being protected within Indigenous lands not because they are being ‘managed’ in a direct and active way, but as the indirect outcome of a healthy social–ecological system, i.e. the outcome of practices that maintain social and ecological integrity, or what can be termed ‘community owned solutions [Mistry 2016: 4].

But challenges, including loss of fire knowledge by younger generations within Indigenous groups because of outside pressures and encroachment, pose a threat to these fire management practices. For example, in Venezuela and Brazil,

young Wapishana and Makushi and some community leaders were more critical about the use of fire as they had more regular contact with state natural resource management officials and environmental organizations that promoted antifire discourses. As with the Krahô, changing Indigenous values to focus on fire prevention and suppression could have the effect of making the problem worse [Mistry 2016: 4].

That is, when prescribed burning is taken out of its original context and represented to younger generations of Indigenous people and land stewards as simply a well-incentivized tool, the Indigenous communities themselves are diminished, along with the robustness of their ecological knowledge that gets passed forward.

In spite of lingering antagonistic views in Brazil and Venezuela toward indigenous fire management, attitudes are changing.

Not only is there a move away from categorizing all fire as ‘bad’; there is also a recognition that Indigenous fire knowledge is a valid form of knowledge that could inform policy-making [Mistry et al. 2016: 6].

Mistry et al. suggest the best way to achieve both ecological and communal health might be through power-sharing arrangements. By empowering Indigenous communities, national governments could in turn work toward their fire management and biodiversity conservation goals. This might require evaluating ecological health in ways beyond just quantitative metrics, which reduce these complex systems down to a set of standardized numbers, as well as the recognition that the well-being of these ecosystems is tied to the Indigenous communities that inhabit them, according to the authors:

There needs to be enabling policies that focus on legitimizing and strengthening Indigenous fire management as a community owned solution. Critically, as community owned fire management is intricately linked with Indigenous survival strategies, so too must firefighting and prescribed burning be grounded in local social–ecological systems. We believe it is necessary to define long-term actions to support the integrated functioning and survival of Indigenous communities as a whole, rather than focusing on isolated issues (e.g. carbon retention) or benefits for some individuals (e.g. hiring Indigenous firefighters) [Mistry 2016: 8].

This systems approach may well be the key to successful long-term fire management. The authors offer this challenge:

What we want to do is not promote one over the other, but encourage decision-makers to engage with, and appreciate, Indigenous perspectives and worldviews on fire management. Community owned solutions acknowledge collectivity, spirituality, process orientation and locality, whereas many expert-led fire management interventions often result in promoting individualism, ethnocentrism, rationality, efficiency, commercialism and globalization. The question we raise is this: can the ‘community owned solutions’ approach be the mechanism through which Indigenous perspectives can be represented within fire management [Mistry et al. 2016: 8]?

Invasive grasses increase fire occurrence and frequency across US ecoregions, Fusco et al. 2019

It has long been suspected that the increasing abundance of invasive grass species may contribute to wildfires in the United States by adding abundant new fuels to ecosystems, increasing the range of conditions that lead to fire ignition, and enabling the development of larger, hotter fires. The new fire regimes (patterns of fire duration, intensity, and spread) that emerge can in turn destabilize wildlife and lead to local extinctions while expanding favorable habitat for the invasive species, for many of these grasses recover quickly after fires, providing renewed fuel and potentially increasing the frequency of fires.

The authors of this paper provide a comprehensive analysis on the impact of 12 non-native grasses on the occurrence (whether a fire occurred in a particular place), frequency (how many times a place burned), and size of wildfires. The research was conducted across 29 US ecoregions, including deserts, temperate forests, wetlands, woodlands, river valleys, shrublands, and coastal plains. Data were collected and combined from fire records and records of invasive grasses, and results from “invaded” regions and nearby “uninvaded” regions were compared. The authors also considered human activities and ecological factors related to fire.

One of the most notorious impacts of nonnative, invasive grasses is the alteration of fire regimes. Yet, most evidence of these impacts comes from local-scale studies, making it unclear whether they have broader implications for national and regional fire management. Our analysis of 12 invasive grasses documents regional-scale alteration of fire regimes for 8 species, which are already increasing fire occurrence by up to 230% and fire frequency by up to 150%. These impacts were demonstrated across US ecoregions and vegetation types, suggesting that many ecosystems are vulnerable to a novel grass-fire cycle. Managing existing grass invasions and preventing future introductions presents a key opportunity to remediate the ecological and economic consequences of invasive species and fire [Fusco 2019: 23594]

The results of this analysis showed that 8 of the 12 invasive grass species examined were associated with significantly higher fire occurrence and fire frequency, and that fire occurrence more than doubled for two of these species. Three of the species did not impact fire occurrence, and a decrease in fires was associated with one species (a wetlands grass species). The impact on fire size was variable, with two species associated with larger fires, three species associated with smaller fires.

Individually, climate change is expected to increase the potential for fire occurrence by 150% by the end of the century based on projected changes in temperature and precipitation. Here we show that 8 invasive grass species are already associated with increased rates of fire occurrence by 27 to 230%, and 6 invasive grass species are associated with increased mean fire frequency by 24 to 150%, compounding current and future fire risk across the United States. [Fusco et al. 2019: 23595]

The authors suggest that fire and invasive species managers work together to create integrated management plans; otherwise, the convergence of human activities, climate change, and invasive species will continue to promote wildfires across the United States.

Smokey the Beaver: beaver‐dammed riparian corridors stay green during wildfire throughout the western USA, Fairfax and Whittle 2020

This study examines the positive effects of beaver damming on the resistance of landscapes to wildfire damage. The authors find that in riparian corridors (areas along rivers), the presence of beavers and their dams can create refuges that withstand blazes that consume surrounding vegetation.

Beavers play an important role in wetland habitats and are known as ecosystem engineers for the way they can shape landscapes with their activities. Beaver dams slow down water moving across a landscape, holding it in place for longer and allowing water to infiltrate into the soil, which raises water tables.

The combination of building flow obstructions (dams), accumulating water (ponds), and spreading that water out in the landscape (channels) gives beavers the unique potential to modulate environmental extremes such as flood and drought. When it comes to water, beavers slow it, spread it, and store it.

Due to the fact that beaver channels and dams spread water out in the landscape and store it broadly in adjacent soils, the vegetation near beaver ponds doesn’t experience as much reduced water availability during drought. Drought-stricken vegetation burns more easily than lush, green vegetation, so it follows that the vegetation around beaver ponds would be more difficult to burn than vegetation around undammed creeks [Fairfax and Whittle 2020: 1].

Fairfax and Whittle observed the effects of beaver dams on preventing fire spread to the areas where they had built dams, examples of which are shown in satellite imagery below.

The authors quantify the effects of beaver activity in fireproofing areas by examining the Normalized Difference Vegetation Index (NDVI) observed in satellite imagery before, during, and after wildfire years in the American West. They found that while vegetation is able to reestablish itself a year after fire damage regardless of beaver activity due to its own resilience to fire, areas in beaver dammed zones maintained vegetation even during wildfires, demonstrating actual resistance to blazes, not just the ability to recover after damage. They note how vital this is for those ecosystems and the life within them.         

These ribbons of fire-resistant riparian corridor may be particularly important for species that are unable to physically escape wildfire. They can provide temporary habitat for fish, amphibians, reptiles, small mammals, wild and domestic ungulates, and birds that are unable to outrun/outfly the spread of flames. While we found that beaver activity does play a significant role in maintaining vegetation greenness during wildfires, it does not appear to play a significant role in the ability for a riparian corridor to rebound in the year following fire. Riparian vegetation NDVI rebounded in the year following the fire regardless of proximity to beaver activity. Thus, we would describe beaver activity as creating refugia during wildfire, but not necessarily changing the long-term landscape outcomes [Fairfax and Whittle 2020: 7].

The survival of wildlife is crucial to these ecosystems, and beaver activity uniquely contributes to the creation of refuge areas that resist burning and can provide shelter for animals during these destructive events. The authors conclude,

As it stands today, wetland habitat is very limited and beavers can create and maintain wetland habitat that persists through flood, drought, and, as we have shown in this study, fire. This has immediate relevance to scientists and practitioners across North America and Eurasia, particularly in places with increasing wildfire risk and existing or planned beaver populations. Perhaps instead of relying solely on human engineering and management to create and maintain fire-resistant landscape patches, we could benefit from beavers’ ecosystem engineering to achieve the same goals at a lower cost [Fairfax and Whittle 2020: 7].

Planned Herbivory in the Management of Wildfire Fuels, Nader et al. 2007

Nader et al. survey herbicides, prescribed fire, mechanized treatments, hand cutting, and grazing animals as fire management techniques. Managing vegetation involves “changing the plant community to decrease the flame height when fire occurs,” favoring native species that may be more resilient to fire, and altering the landscape to create fuel breaks, which are patches across which it is hard for fire to jump [Nader 2007: 18].

Focusing their analysis on grazing and the contexts in which it is most useful, the authors note that there are many site and animal specific factors to take into account for successful implementation.

[Grazing] is a complex, dynamic tool with many plant and animal variables, and it requires sufficient knowledge of the critical control points to reach treatment objectives. Those control points involve the species of livestock grazed (cattle, sheep, goats, or a combination); the animals’ previous grazing experience (which can affect their preferences for certain plants); time of year as it relates to plant physiology (animal consumption is directed by the seasonal nutrient content); animal concentration or stocking density during grazing; grazing duration; plant secondary compounds; and animal physiological state [Nader 2007: 19].

Grazing has the advantage of keeping nutrients in the ecosystem, unlike mechanical methods that harvest vegetation to be sold as biomass chips (like wood chips). This means that when animals digest vegetation and excrete on the landscape, they participate in the local nutrient cycle. Animals also trample soil, which can crush fine fuel and mix it into the soil, where it cannot contribute to ignition, which reduces one contributing factor to persistent and destructive blazes.  Animals do more than just remove extra vegetation – they can have many beneficial interactions within a given ecosystem.

Any grazing plan designed for fuel reduction needs to consider the grazing impacts on parameters other than just simply reduction. The effects of the grazing management should be studied for their impact on water quality, compaction, riparian vegetation, disease interaction with wildlife (bluetongue, pasturella), and weed transmission. The positive aspects of grazing over other treatments also should be weighed, including recycling of nutrients into the products of food and fiber [Nader 2007: 22].

By introducing grazing animals into a landscape or agricultural system, managers can affect biodiversity in complex ways. The authors mention that “Hadar et al. reported that light grazing increased plant diversity on treated sites. Thus, when proposing a stocking rate for treatment consumption, the environmental impact needs to be considered” [Nader 2007: 22].

Nader et al. conclude that “grazing is best used when addressing vegetation with stems of smaller diameters that make up the 1- and 10-hour fuels. These two fuel classes are important because they can greatly impact the rate of spread of a fire, as well as flame height” [Nader 2007: 19]. While they call for further research to validate anecdotal accounts supporting grazing and understand its best practice, they maintain that “prescribed grazing has the potential to be an ecologically and economically sustainable management tool for reduction of fuel loads” [Nader 2007: 20].

Landscape rehydration ‘better than dams’ in improving farm production, reducing fire risk, Major 2020

A project in Queensland, Australia has met with success in its efforts to rehydrate the landscape on the farmland property of Worona Station, improving biodiversity, water retention, and resistance to erosion and fire. Worona Station had been degraded and faced serious erosion issues, so Chris Le Feuvre, the owner, partnered with consultancy groups of NQ Dry Tropics and the Mulloon Institute in a project to rehydrate his land.

The project team has used a combination of planned grazing and small, low-tech dams to combat erosion problems. The grazing technique involves:

Splitting paddocks into small sizes and using large mobs of cattle grazing on rotation … grazing pasture more intensively while giving it longer to rest, [thereby] increasing carrying capacity.

Grazing in this way (which is evocative of Allan Savory’s Holistic Planned Grazing methodology) has resulted in increased pasture species diversity and boosted plant growth, allowing the Le Feuvre to double his herd size. Planned grazing has also reduced sediment runoff from the property. Sam Skeat, a grazing officer with NQ Dry Tropics, attests to the importance of grazing.

The plug-and-pond technique — also known as leaky weirs — involves small dam-like structures to lift the bed level of the water, which is then run onto the floodplain to grow pasture and recharge aquifers. While weirs have been strategically constructed, Mr. Skeat said grazing management was the most important tool to improve water retention in a landscape. ‘If you can use cattle as a tool to regenerate the grassland, you’ll get more infiltration, slow the flow, hold water up in the landscape and have you growing grass for longer’ [Major 2020].

Rehydrating landscapes can improve their resilience to extreme events, and improve their quality in the face of chronic problems like erosion. According to the Mulloon Institute Chairman Gary Nairn, the issue of degraded gullies and streams is a national concern. Gullies are created when parched land is unable to absorb rainwater, allowing it to run off. The sediment-filled runoff ends up in the ocean, polluting it.

Nairn sees land rehydration through planned grazing and related techniques as a better solution than building a massive, industrial-scale dam to retain water. The Australian government has been looking into building new large dams. Levels at Warragamba Dam, which supplies about 80 percent of Sydney’s water, have dropped to less than half capacity.

‘We’ve been able to demonstrate in Mulloon, if we repaired and rehydrated the catchment through to the Sydney water supply, you could store the equivalent of Warragamba Dam,’ he said [Major 2020].

Well-watered mulberry tree credited with saving home on NSW South Coast from summer bushfires, Aubrey 2020

A well-watered mulberry tree has been credited with averting the danger of destructive wildfires from destroying Brett Hawkins’ home during 2020’s unprecedented fire season in Australia. When massive fires raged through the bush through the summer, many homes were completely engulfed. However, Hawkins attested that when he returned to his home after evacuating,

‘I could see straight away the house was intact — the roof was intact, but everything else around it was burnt, with the exception of the mulberry tree.’ He described the stark scene greeting him upon arriving back home, ‘It was apocalyptic,’ Mr. Hawkins said. ‘There was not a tree left, ash on the ground and smouldering embers everywhere.’ But among the blackened trees, Mr. Hawkins found his mudbrick house and mulberry tree in full leaf [Aubrey 2020].

In the season’s drought, he had been rationing water, but sparing some to keep his tree hydrated and healthy, which may have been a contributing factor in its resistance. According to the article, “Mr. Hawkins believed that by heavily watering the tree, combined with luck regarding which direction the fires came, the full heat of the bushfires was shifted.” [Aubrey 2020]

Another important feature is the mulberry’s lack of dried leaves and brush at its base that might pose a danger of igniting. Other species, like eucalyptus, with oily leaves that could dry out, or pine trees whose long branches catch dry leaves, are less ideal.

A tree expert from the Fenner School of Environment at the Australian National University analyzed some of the possible factors leading to the survival of this mulberry tree and what it might teach those wishing to fortify the fire resilience of their homes and properties. “While there does not seem to be a clear answer on what to plant to ‘fire-proof’ your house, Professor Brack said a well-watered tree, with a clear trunk and no loose, dry leaves or branches is a good start” [Aubrey 2020].

https://www.yesmagazine.org/environment/2020/05/20/garden-advice-indigenous-food-growers/

Covid19 has been an additional stressor on many Native American communities already burdened by deprivations from centuries of ongoing injustice. According to Julie Garreau, project coordinator of Cheyenne River Youth Project, which operates a 2.5-acre youth garden in South Dakota, gardens are a source of both food and healing. “Gardens represent so much more,” she said. “Food, yes, but a belief in our future. Gardens represent resiliency, strength, wellness, culture.” During the pandemic, the Youth Project delivered garden produce and other foods to the homes of Cheyenne River Sioux Reservation children.

Another youth-focused gardening organization is Dream of Wild Health. Based in Minneapolis/St. Paul, MN, this Native-led organization operates a 30-acre biodiverse suburban farm that supplies food, learning experiences, and the chance to reconnect with nature. Kids learn cooking and seed saving, and student interns called Garden Warriors help grow food. Due to Covid19, workshops moved online, with the organization delivering ingredients to kids’ homes and then leading them in an online cooking class.  

“Working in a garden develops your relationship to the land,” says Aubrey Skye, a Hunkpapa Lakota gardener who for many years ran a gardening program on Standing Rock Reservation on the border of North and South Dakota. “Our ancestors understood that. Look at the old pictures. It’s etched on their faces. When you understand it as well, a sense of scarcity and insecurity transforms into a feeling of abundance and control—something we all need these days.”

Some tips from the gardeners mentioned in this article:

1. Start small if you’re a beginner (in a few pots or a raised bed).
2. Favor companion planting. (“Look at nature, and figure out combinations that mimic it,” recommends Traditional Native American Farmers Association Director Clayton Brascoupé.)
3. Embellish your garden with colorful native flowers to attract and nourish pollinators.
4. Use rocks to keep crops cozy and supported; rocks act as heat sink and can protect seedlings from early frost.
5. Reuse discarded materials – you’ll get for free while building a network in the collection process: mulch with used cardboard and paper; create drip irrigation from soda pop bottles pierced with a needle at the neck, fill with water then bury the neck in the soil close to the plant.
6. Make compacted soil soft and plant friendly using dandelions, a supposed weed with nutritional value, whose taproot breaks up hardened soil enabling earthworm activity.
7. Include healing herbs, especially native varieties.
8. Save the seeds of the plants that thrive best and are favorites, which not only enables future food supply, but also, as Aubrey Skye says, preserves history like little time capsules.

https://news.mongabay.com/2020/05/in-south-korea-centuries-of-farming-point-to-the-future-for-sustainable-agriculture/?utm_source=Mongabay+Newsletter&utm_campaign=624a4d7680-Newsletter_2020_04_30_COPY_01&utm_medium=email&utm_term=0_940652e1f4-624a4d7680-77145713

In South Korea, knowledge of ancient farming techniques adapted to various harsh conditions, along with a sense of urgency about the need to adapt to even harsher conditions as the global climate system deteriorates, is bringing about the blossoming of an environmentally friendly agriculture movement.

Farmers draw on traditional knowledge of “nitrogen-fixing plants, soil bacteria, micro-organisms, and the relations between all of them to optimize yields by increasing soil fertility, boost crop health and biomass for livestock grazing, and reduce weed and pest infestations.” These practices are combined with intercropping (planting multiple crops together in a field) and crop rotation (constantly changing crops over time in a field) in a developing agricultural ethic that favors biodiversity and soil health.

Interestingly, the role of soil microorganisms is understood and valued in a way that intersects a fermentation-based food culture.

Traditional Korean knowledge of soil nutrients and food fermentation techniques is also used by some farmers to create natural fertilizer and pesticide. This is done by culturing and proliferating indigenous microorganisms – fungi, bacteria and yeast – to enhance the soil’s fertility without the need for livestock waste.

Such practices are supported both by national policy aiming to facilitate transition to organic and environmentally friendly methods, and by community-led organic farming movements. From participating in national climate strikes to demanding protections of native seeds to facilitating organic food commerce, consumer coops are doing their part to help make South Korea a global model for sustainable farming.

Similarly, both government and grassroots groups have established initiatives to recruit youth into agricultural careers.

The South Korean Ministry of Agriculture, Food and Rural Affairs has set up a Back-to-Earth Promotion Project, Youth Farmer Fostering Policy, and the Farmland Banking Project, aiming to promote and fund startups and businesses in the agricultural sector and in farming villages. …

Grassroots initiatives that are part of a similar movement can be seen in the Milmeori Farm School in Yeoju county and the Geumsan Gandhi School in Geumsan county. These are boarding school programs that bring youth from cities to experience the countryside, learn Korean organic farming, and cook plant-rich dishes from their harvests.

https://www.yesmagazine.org/issue/just-transition/2017/10/12/the-hopeful-work-of-turning-appalachias-mountaintop-coal-mines-into-farms/

In Mingo County, West Virginia, the soil on a flat expanse of what had been a mountaintop is compacted, composed mainly of blasted rocks, and lacks organic matter, due to several years of coal mining. The ground is harder than anticipated; even the soil scientists say they are not sure how long it will take to bring the soil back to life. Besides, the ground does not retain water very well as it was engineered to drain water into the valley. Furthermore, there is the problem of aggressive invaders (autumn olive, multiflora rose, and tall fescue), making it difficult to penetrate the terrain.

As Ben Gilmer, president of Refresh Appalachia, which helps convert post-mine lands into agriculture and forestry enterprises, says, “it’s a long-term science project.” Refresh Appalachia provides job training and encourages farming systems that form a loop between the animals and plants, where one nourishes the other, cutting down on feed and fertilizer, providing food and land management, and helping ensure food sovereignty in an economically depressed region. Refresh farms raise poultry, goats, pigs, and honey bees, along with fruits, nuts, vegetables, and herbs.

Appalachia is a temperate region with heavy rainfall, not a barren moonscape. Each site being restored “just needs some care and management appropriate to their characteristics,” says Carl Zipper, Virginia Tech crop and soil science professor specializing in mine-land restoration.

The workers previously responsible for blowing up are now trying to put back together that which was blown up. Many are working on associate degrees in conjunction with job training in sustainable agriculture and related fields. “I’m living the dream,” Refresh member Wilburn Jude exclaimed. Former miner Chris Farley is excited to be part of the first group to attempt to farm these lands. Everyone was eager for the arrival of a mulcher to remove and chew the invasive shrubs into the wood chip. The clearing would then be planted with over 2,000 berry, pawpaw, and hazelnut seedlings.

In continuation of the “blessed unrest” section of previous issues of the Compendium, the following sketches illustrate how people everywhere are seeing that humanity depends on nature for both our physical and spiritual wellbeing and our survival. As this awareness takes hold, people act to protect and restore not only the land, but also our relationship to it. As the stories below show, growing food in an eco-friendly way does that. Adopting Paul Hawken’s terminology and characterization of “blessed unrest” as a spontaneous, decentralized global social movement, we here present a diverse series of vignettes of everyday heroes. May such stories light the fire for new heroes to perpetually emerge in defense of all life on Earth.

The hopeful work of turning Appalachia’s mountaintop coal mines into farms

https://www.yesmagazine.org/issue/just-transition/2017/10/12/the-hopeful-work-of-turning-appalachias-mountaintop-coal-mines-into-farms/

In Mingo County, West Virginia, the soil on a flat expanse of what had been a mountaintop is compacted, composed mainly of blasted rocks, and lacks organic matter, due to several years of coal mining. The ground is harder than anticipated; even the soil scientists say they are not sure how long it will take to bring the soil back to life. Besides, the ground does not retain water very well as it was engineered to drain water into the valley. Furthermore, there is the problem of aggressive invaders (autumn olive, multiflora rose, and tall fescue), making it difficult to penetrate the terrain.

As Ben Gilmer, president of Refresh Appalachia, which helps convert post-mine lands into agriculture and forestry enterprises, says, “it’s a long-term science project.” Refresh Appalachia provides job training and encourages farming systems that form a loop between the animals and plants, where one nourishes the other, cutting down on feed and fertilizer, providing food and land management, and helping ensure food sovereignty in an economically depressed region. Refresh farms raise poultry, goats, pigs, and honey bees, along with fruits, nuts, vegetables, and herbs.

Appalachia is a temperate region with heavy rainfall, not a barren moonscape. Each site being restored “just needs some care and management appropriate to their characteristics,” says Carl Zipper, Virginia Tech crop and soil science professor specializing in mine-land restoration.

The workers previously responsible for blowing up are now trying to put back together that which was blown up. Many are working on associate degrees in conjunction with job training in sustainable agriculture and related fields. “I’m living the dream,” Refresh member Wilburn Jude exclaimed. Former miner Chris Farley is excited to be part of the first group to attempt to farm these lands. Everyone was eager for the arrival of a mulcher to remove and chew the invasive shrubs into the wood chip. The clearing would then be planted with over 2,000 berry, pawpaw, and hazelnut seedlings.

In South Korea, centuries of farming point to the future for sustainable agriculture

https://news.mongabay.com/2020/05/in-south-korea-centuries-of-farming-point-to-the-future-for-sustainable-agriculture/?utm_source=Mongabay+Newsletter&utm_campaign=624a4d7680-Newsletter_2020_04_30_COPY_01&utm_medium=email&utm_term=0_940652e1f4-624a4d7680-77145713

In South Korea, knowledge of ancient farming techniques adapted to various harsh conditions, along with a sense of urgency about the need to adapt to even harsher conditions as the global climate system deteriorates, is bringing about the blossoming of an environmentally friendly agriculture movement.

Farmers draw on traditional knowledge of “nitrogen-fixing plants, soil bacteria, micro-organisms, and the relations between all of them to optimize yields by increasing soil fertility, boost crop health and biomass for livestock grazing, and reduce weed and pest infestations.” These practices are combined with intercropping (planting multiple crops together in a field) and crop rotation (constantly changing crops over time in a field) in a developing agricultural ethic that favors biodiversity and soil health.

Interestingly, the role of soil microorganisms is understood and valued in a way that intersects a fermentation-based food culture.

Traditional Korean knowledge of soil nutrients and food fermentation techniques is also used by some farmers to create natural fertilizer and pesticide. This is done by culturing and proliferating indigenous microorganisms – fungi, bacteria and yeast – to enhance the soil’s fertility without the need for livestock waste.

Such practices are supported both by national policy aiming to facilitate transition to organic and environmentally friendly methods, and by community-led organic farming movements. From participating in national climate strikes to demanding protections of native seeds to facilitating organic food commerce, consumer coops are doing their part to help make South Korea a global model for sustainable farming.

Similarly, both government and grassroots groups have established initiatives to recruit youth into agricultural careers.

The South Korean Ministry of Agriculture, Food and Rural Affairs has set up a Back-to-Earth Promotion Project, Youth Farmer Fostering Policy, and the Farmland Banking Project, aiming to promote and fund startups and businesses in the agricultural sector and in farming villages. …

Grassroots initiatives that are part of a similar movement can be seen in the Milmeori Farm School in Yeoju county and the Geumsan Gandhi School in Geumsan county. These are boarding school programs that bring youth from cities to experience the countryside, learn Korean organic farming, and cook plant-rich dishes from their harvests.

Gardening advice from indigenous food growers

https://www.yesmagazine.org/environment/2020/05/20/garden-advice-indigenous-food-growers/

Covid19 has been an additional stressor on many Native American communities already burdened by deprivations from centuries of ongoing injustice. According to Julie Garreau, project coordinator of Cheyenne River Youth Project, which operates a 2.5-acre youth garden in South Dakota, gardens are a source of both food and healing. “Gardens represent so much more,” she said. “Food, yes, but a belief in our future. Gardens represent resiliency, strength, wellness, culture.” During the pandemic, the Youth Project delivered garden produce and other foods to the homes of Cheyenne River Sioux Reservation children.

Another youth-focused gardening organization is Dream of Wild Health. Based in Minneapolis/St. Paul, MN, this Native-led organization operates a 30-acre biodiverse suburban farm that supplies food, learning experiences, and the chance to reconnect with nature. Kids learn cooking and seed saving, and student interns called Garden Warriors help grow food. Due to Covid19, workshops moved online, with the organization delivering ingredients to kids’ homes and then leading them in an online cooking class.  

“Working in a garden develops your relationship to the land,” says Aubrey Skye, a Hunkpapa Lakota gardener who for many years ran a gardening program on Standing Rock Reservation on the border of North and South Dakota. “Our ancestors understood that. Look at the old pictures. It’s etched on their faces. When you understand it as well, a sense of scarcity and insecurity transforms into a feeling of abundance and control—something we all need these days.”

Some tips from the gardeners mentioned in this article:

1. Start small if you’re a beginner (in a few pots or a raised bed).
2. Favor companion planting. (“Look at nature, and figure out combinations that mimic it,” recommends Traditional Native American Farmers Association Director Clayton Brascoupé.)
3. Embellish your garden with colorful native flowers to attract and nourish pollinators.
4. Use rocks to keep crops cozy and supported; rocks act as heat sink and can protect seedlings from early frost.
5. Reuse discarded materials – you’ll get for free while building a network in the collection process: mulch with used cardboard and paper; create drip irrigation from soda pop bottles pierced with a needle at the neck, fill with water then bury the neck in the soil close to the plant.
6. Make compacted soil soft and plant friendly using dandelions, a supposed weed with nutritional value, whose taproot breaks up hardened soil enabling earthworm activity.
7. Include healing herbs, especially native varieties.
8. Save the seeds of the plants that thrive best and are favorites, which not only enables future food supply, but also, as Aubrey Skye says, preserves history like little time capsules.

While several studies have shown that biodiversity within a trophic level (among plants, for example) increases ecosystem function (such as productivity), this study examines the effects of increased plant diversity on multi-trophic networks (encompassing plants, soil microorganisms, and above- and belowground invertebrates). The authors compared monoculture plots (with one plant species) to plots containing 60 plant species, and found that:

higher plant diversity leads to more energy stored, greater energy flow and higher community-energy-use efficiency across the entire trophic network. These effects of biodiversity on energy dynamics were not restricted to only plants but were also expressed by other trophic groups and, to a similar degree, in aboveground and belowground parts of the ecosystem, even though plants are by far the dominating group in the system [Buzhdygan 2020: 1].

“More energy stored” means there is more standing biomass in the system, including plants, plant litter, microorganisms, insects and other invertebrates – in short, more life.

Compared to monoculture plots, high-diversity plots also had 50% greater energy flow, which implies “that the overall amount of resources consumed and recycled by the community increased with greater plant diversity” [Buzhdygan 2020: 2].

A community with “higher energy-use efficiency” has lower “maintenance costs,” referring to the amount of energy expended (through respiration) “to support the energetic demands of the living biomass stored in the system” [Buzhdygan 2020: 2]. In other words, organisms in an ecological community with high energy-use efficiency collectively work less hard to sustain themselves compared to, collectively, the organisms in a community with low energy-use efficiency. Biodiversity increases energy-use efficiency by increasing the quantity and variety of resources available to consumers.

Plant communities with a high plant diversity are typically more productive than low-diversity communities and, therefore, provide a larger quantity and variety of resources to consumers. This increase in resource availability can reduce competition and increase energy flow to consumers. A larger variety of resources can also attract a higher number of specialized species, supporting trophic complementarity across the network and resulting in a reduction of community maintenance costs [Buzhdygan 2020: 4].

In this way, higher energy-use efficiency boosts ecosystem function.

Higher energy use efficiency at high plant species richness may be an additional mechanism that contributes to the resilience of ecosystems because communities with low maintenance costs have a higher potential to compensate for energy loss during disturbance. … Moreover, lower community maintenance costs may imply a reduced ‘leakiness’ of ecosystems at high biodiversity. Indeed, evidence is mounting that high-biodiversity ecosystems lose less soil nitrogen, store more carbon in the soil and have more efficient soil microbial communities [Buzhdygan 2020: 7].

Inversely,

the reduced community-energy-use efficiency and standing stock biomass in species-poor ecosystems indicates that more carbon is released into the atmosphere; this implies potential feedback effects of the ongoing global biodiversity loss on carbon sequestration and climate change [Buzhdygan 2020: 8].

Biodiversity increases multitrophic energy use efficiency, flow and storage in grasslands, Buzhdygan 2020

While several studies have shown that biodiversity within a trophic level (among plants, for example) increases ecosystem function (such as productivity), this study examines the effects of increased plant diversity on multi-trophic networks (encompassing plants, soil microorganisms, and above- and belowground invertebrates). The authors compared monoculture plots (with one plant species) to plots containing 60 plant species, and found that:

higher plant diversity leads to more energy stored, greater energy flow and higher community-energy-use efficiency across the entire trophic network. These effects of biodiversity on energy dynamics were not restricted to only plants but were also expressed by other trophic groups and, to a similar degree, in aboveground and belowground parts of the ecosystem, even though plants are by far the dominating group in the system [Buzhdygan 2020: 1].

“More energy stored” means there is more standing biomass in the system, including plants, plant litter, microorganisms, insects and other invertebrates – in short, more life.

Compared to monoculture plots, high-diversity plots also had 50% greater energy flow, which implies “that the overall amount of resources consumed and recycled by the community increased with greater plant diversity” [Buzhdygan 2020: 2].

A community with “higher energy-use efficiency” has lower “maintenance costs,” referring to the amount of energy expended (through respiration) “to support the energetic demands of the living biomass stored in the system” [Buzhdygan 2020: 2]. In other words, organisms in an ecological community with high energy-use efficiency collectively work less hard to sustain themselves compared to, collectively, the organisms in a community with low energy-use efficiency. Biodiversity increases energy-use efficiency by increasing the quantity and variety of resources available to consumers.

Plant communities with a high plant diversity are typically more productive than low-diversity communities and, therefore, provide a larger quantity and variety of resources to consumers. This increase in resource availability can reduce competition and increase energy flow to consumers. A larger variety of resources can also attract a higher number of specialized species, supporting trophic complementarity across the network and resulting in a reduction of community maintenance costs [Buzhdygan 2020: 4].

In this way, higher energy-use efficiency boosts ecosystem function.

Higher energy use efficiency at high plant species richness may be an additional mechanism that contributes to the resilience of ecosystems because communities with low maintenance costs have a higher potential to compensate for energy loss during disturbance. … Moreover, lower community maintenance costs may imply a reduced ‘leakiness’ of ecosystems at high biodiversity. Indeed, evidence is mounting that high-biodiversity ecosystems lose less soil nitrogen, store more carbon in the soil and have more efficient soil microbial communities [Buzhdygan 2020: 7].

Inversely,

the reduced community-energy-use efficiency and standing stock biomass in species-poor ecosystems indicates that more carbon is released into the atmosphere; this implies potential feedback effects of the ongoing global biodiversity loss on carbon sequestration and climate change [Buzhdygan 2020: 8].

This article analyzes the policy context for forest ecosystem restoration, arguing that it is heavily shaped by the way we define a forest. The use of a forest definition lacking ecological considerations severely undermines conservation and restoration initiatives.  

We live in an era of unprecedented environmental change, motivating equally unprecedented global actions to protect and restore forest ecosystems. These efforts could fail to achieve their ambitious goals if they are not informed by clear and appropriate concepts and definitions of forests [Chazdon 2016: 1].

There are multiple definitions of a forest. Early European and internationally adopted definitions tended to define forests according to their usage for timber. FAO’s 1948 definition created for assessing wood harvesting potential of the world’s forests is still in use today. Yet new definitions have since been created that emphasize conservation, carbon sequestration and biodiversity values of forests.

However, national and global forest assessments tend to use narrow technical definitions that ignore ecological values of forested land.

In many cases, forest assessments do not distinguish between land covered by natural and planted forests. Thus, if natural forests are cleared and replaced with plantations, no net loss of forest cover is reported [Chazdon 2016: 6].

In other words, areas that should not be considered forest in ecological terms are counted as forest – an obfuscation with disastrous environmental outcomes. Similarly, ecologically important yet small patches of trees that are not counted in forest inventories and lack legal protection are at risk of being lost.

Areas classified as ‘‘non-forests’’ are as important to forest definitions as are forests. More than 43 % of agricultural land globally is in agroforestry systems with 10 % tree cover. In Rwanda and Brazil, forest inventories using a 0.5-ha threshold ignore substantial areas of small forest fragments, agroforests, and woodlots, leading to underestimates of actual tree cover. Small patches of trees and even isolated remnant trees can hold high ecological and conservation value, and can play an important role in enhancing landscape connectivity, local biodiversity, and local livelihoods [Chazdon 2016: 7].

Information from participatory local monitoring and remote sensing technology that distinguishes “among successional stages of forests, selectively logged forests, and single-species plantations” [Chazdon 2016: 10] is needed.

Access to this information will allow countries and international agencies to track changes in natural forest cover, and to monitor processes of restoration, rehabilitation, and afforestation within a landscape context and, consequently, make informed policy decisions. We are on the frontier of developing new ways of monitoring and assessing land cover that will provide robust indicators of the quality and origins of tree cover and enable new ways of viewing and defining forests and reforests. To see beyond the overly simplified categories of forest loss, forest degradation, and forest gain, we need to develop and apply more adapted and nuanced definitions that will deepen our understanding of the drivers and outcomes of land-use change and forest dynamics within landscapes [Chazdon 2016: 10].

This study tested the Miyawaki method of rapid natural forest regeneration (which has been shown to work in Japan and elsewhere) in the arid Mediterranean. In this area, millennia of human civilization have resulted in degraded soils and reduced and changed forest cover, traditional reforestation efforts have often failed, and desertification is a looming threat. The Miyawaki method speeds up the process of ecological succession by densely planting a multilayer forest made up of a wide diversity of indigenous species.

In a natural forest cycle, as Clements (1916) described, annual plants on barren land are succeeded by perennial grass, sun-tolerant shrubs, light-demanding, fast-growing trees, and finally natural forests; each step may require decades, and the climax vegetation could be formed after two centuries or more. Currently, most forest reforestation programs adopt a scheme of planting one or more early successional species; after successful establishment, they are gradually replaced by intermediate species (either naturally or by planting), until late successional species arise. This pattern tries to simulate natural processes of ecological succession, from pioneer species to climax vegetation. However, it requires several silvicultural practices and normally takes a long time [Shirone 2011: 82].

In the Miyawaki method, by contrast, one plants all at once the many plant species normally present in a native forest community, thus bypassing the earliest stages of ecological succession. Other tree-planting methods favor fast-growing non-native tree species, while omitting understory species – in other words, creating a simple plantation rather than a forest community that functions ecologically and can evolve and sustain itself.

Multilayer forests, and natural biocoenosis [ecological community] is possible, and well-developed ecosystems can be quickly established because of the simultaneous use of intermediate and late successional species in plantations. The Miyawaki method involves surveying the potential natural vegetation of the area to be reforested and recovering topsoil to a depth of 20– 30 cm by mixing the soil and a compost from organic materials, such as fallen leaves, mowed grass, etc. In this way, the time of the natural process of soil evolution, established by the vegetational succession itself, is reduced [Shirone 2011: 82].

The authors of this study found that compared to traditional reforestation, there was “a more rapid development of trees on the Miyawaki plots, in particular, early-successional species [especially maritime pine]. The benefits over previous methods are remarkable and comparable with those obtained by Miyawaki in Asia and South America.” The Miyawaki method favoring denser plantings works even in arid climates, in spite of traditional views favoring sparse plantings in arid places, although the optimal density for the Mediterranean still needs testing, according to the authors.

In fact, low plant density has been traditionally retained as appropriate in arid and semiarid environments in order to avoid competition for water resources between plants, but it is now evident that cooperative processes, e.g., mutual shading, prevail over competitive processes. High plant density also reduces the impact of acorn predators, thus encouraging oak regeneration, i.e., the main late-successional forest species in Mediterranean environments. In addition, excellent plant stock remains fundamental for planting success in harsh environments [Shirone 2011: 91].

This article assesses the ecological value of small woodlands relative to larger ones. The authors conclude that:

…smaller woodlands potentially deliver multiple services at higher performance levels on a per area basis than larger woodlands of a similar age, even if the larger woodlands harbor a higher biodiversity [Valdes 2020: 12].

Because of their high edge-to-core ratio, smaller woodlots get more sunlight and more nutrient input from surrounding farmland, resulting in denser vegetation cover and higher biomass production at edges.

This altered functioning in turn increases the delivery potential of some services, such as game production potential, due to an increased quantity of food available for game, and topsoil carbon storage, due to the faster incorporation of organic matter in the soil. Tick-borne disease risk is, however, lower, likely due to decreased larval densities in the unfavorable (e.g. hotter and drier) microclimatic conditions at the edge [Valdes 2020: 12].

While smaller woodlands were more apt to deliver “multiple services at higher levels of performance per area than larger woodlands of a similar age,” the greater biodiversity of larger woodlands increased certain individual ecosystem services.

The supply potential of several individual ecosystem services indirectly increased in larger and more ancient woodlands because it was dependent on higher levels of biodiversity. For example, abundance of usable plants and game production potential might have increased due to a positive correlation with vascular plant diversity, while pest control potential probably increased due to bottom-up effects through the trophic chain. On the contrary, tick-borne disease risk, topsoil carbon storage and stemwood volume were unrelated to multidiversity, probably because they depended on particular environmental conditions or on the presence and abundance of specific species rather than on species richness per se.

Finally, it should be noted that we focused on the service delivery potential on a per area basis and that the total amount of services provided by large patches might still be larger than that of small patches. Our findings should therefore not be interpreted as a trade-off between large, biodiverse patches versus small patches that have a higher potential to deliver services, but rather as an observation that small woodlands in agricultural landscapes have the potential to deliver a high flow of services relative to their size [Valdes 2020: 12].

This study tested biodiversity effects on ecosystem function in the process of reviving severely degraded and contaminated land, and found that “increasing plant diversity greatly enhanced the reclamation of these lands” [Jia 2020: 1].  

Prior to implementing the reclamation experiment, the degraded mine wasteland investigated in this study was heavily impacted by past mining activities and was devoid of vegetation for more than a decade and the soil lacked structure, contained high levels of toxic metals and low levels of nutrients. … our results showed that higher plant species richness enhanced land reclamation across all standard measures of reclamation success and specifically resulted in higher vegetation coverage, biomass yield and stability for all 3 years [of the experiment] [Jia 2020: 6].

Furthermore, higher biodiversity plots had higher levels of organic carbon in the soil, higher soil microorganism abundance, lower fungal pathogens, and lower heavy metal concentrations in plant tissue.

The most striking impact of plant diversity on soil was on the microbial communities. Both soil fungal and bacterial OTUs [operational taxonomic units^[8]] increased significantly with plant species richness. More importantly, we found that higher plant species richness significantly increased the relative abundance of soil cellulolytic bacteria that degrade cellulose and are thus essential components of nutrient cycling [Jia 2020: 7].

The concept of “proforestation” presented here means letting existing forests continue to grow and reach their full ecological potential. Due to intensive management practices, most existing forests sequester carbon at only half (or less) of their potential rate. In addition to storing (embodying) more carbon than their smaller counterparts, large trees also sequester carbon at a faster rate. For example, “Each year a single tree that is 100 cm in diameter adds the equivalent biomass of an entire 10-20 cm diameter tree, further underscoring the role of large trees” [Moomaw 2019: 4]. Imagine, reader, that every year you planted a whole new medium-sized tree – that’s essentially what large trees are doing.

“Each year a single tree that is 100 cm in diameter adds the equivalent biomass of an entire 10-20 cm diameter tree, further underscoring the role of large trees” [Moomaw 2019: 4].

Much of Maine’s forests have been harvested continuously for 200 years and have a carbon density less than one-third of the forests of Southern Vermont and New Hampshire, Northwestern Connecticut and Western Massachusetts – a region that has not been significantly harvested over the past 75-150 years. …

Ecosystem services accrue as forests age for centuries. Far from plateauing in terms of carbon sequestration (or added wood) at a relatively young age as was long believed, older forests (e.g., >200 years of age without intervention) contain a variety of habitats, typically continue to sequester additional carbon for many decades or even centuries, and sequester significantly more carbon than younger and managed stands [Moomaw 2019: 5].

Because existing forests are already sequestering carbon, and will continue at an increasing rate as tree size grows, the author argues that proforestation is a more effective immediate solution than either reforestation (planting new trees where they had been cleared for agriculture, etc.) or afforestation (planting trees in new places), though these other two approaches are important for longer term ecosystem function. Moomaw et al. argue that the urgency of removing CO2 makes it imperative to keep existing forests growing.

Globally, existing forests only store approximately half of their potential due to past and present management, and many existing forests are capable of immediate and even more extensive growth for many decades. During the timeframe while seedlings planted for afforestation and reforestation are growing (yet will never achieve the carbon density of an intact forest), proforestation is a safe, highly effective, immediate natural solution that does not rely on uncertain discounted future benefits inherent in other options [Moomaw 2019: 7].

Furthermore, existing, older forests are critical habitats for threatened wildlife, even small intact woods.

Forest bird guilds also benefit from small intact forests in urban landscapes relative to unprotected matrix forests. Several bird species in the U.S. that are globally threatened – including the wood thrush, cerulean warbler, marbled murrelet, and spotted owl are, in part, dependent on intact, older forests with large trees [Moomaw 2019: 5].

In sum, proforestation provides the most effective solution to dual global crises – climate change and biodiversity loss. It is the only practical, rapid, economical, and effective means for atmospheric CDR [carbon dioxide removal] among the multiple options that have been proposed because it removes more atmospheric carbon dioxide in the immediate future and continues to sequester it long-term. Proforestation will increase the diversity of many groups of organisms and provide numerous additional and important ecosystem services. While multiple strategies will be needed to address global environmental crises, proforestation is a very low-cost option for increasing carbon sequestration that does not require additional land beyond what is already forested and provides new forest related jobs and opportunities along with a wide array of quantifiable ecosystem services, including human health [Moomaw 2019: 8].

This perspective piece argues against scientific or public adoption of the term “rewilding,” which the authors view as being generally synonymous with the classical and better-understood concept of ecological restoration. Definitions of restoration are sufficient to encompass practices espoused in rewilding.

Early definitions of restoration describe the practice as “the process of repairing damage caused by humans to the diversity and dynamics of indigenous ecosystems” (Jackson et al., 1995). Although at the time of this definition, restoration science was still developing, it was clear that it had established itself under the broad banner of repairing damaged ecosystems. … More recently, restoration has been defined as “any activity whose aim it is to ultimately achieve ecosystem recovery, insofar as possible and relative to an appropriate local native model (termed here a reference ecosystem), regardless of the period of time required to achieve the recovery outcome” (McDonald et al., 2016) [Hayward 2019: 257].

The term rewilding, which has evolved over time, “was arguably conceived to promote the original authors’ view of conservation via cores [habitats], corridors, and carnivores” [Hayward 2019: 256]. In this early context,

‘rewilding’ referred to conservation and management interventions that focused on reintroducing keystone predators and ensuring that they had sufficient interconnected space to live. The authors emphasized within their original work that rewilding was “one essential element in most efforts to restore fully functioning ecosystems” (Soulé and Noss, 1998). As such, it is clear that rewilding was originally aimed to be a term that referred to one component of ecological restoration [Hayward 2019: 256].

Since then, rewilding has come to refer to practices involving “translocating substitute species to fill vacant ecological niches left by extinct species” [Hayward 2019: 257] or reintroducing locally extinct species, or simply allowing natural succession to occur on abandoned land. Given multiple definitions, all of which relate to the idea of restoration, the term rewilding is seen here as superfluous and confusing.

Given the lack of clear differences between rewilding and restoration in both definition and practice, we see little need for these competing terms within scientific discourse [Hayward 2019: 257].

However, the authors suggest two positive contributions from the rewilding discourse. Because of its overall focus on large fauna, rewilding has captured public imagination and interest in conservation, while also helping to shift a potential vegetation bias among restoration practitioners/scientists toward equal emphasis on the ecosystem role of animals.

Therefore, rather than adopting a new term with copious definitions that lack clarity, this debate can be used as an opportunity to adaptively improve current restoration practice by incorporating a more equal focus between flora and fauna [Hayward 2019: 258].

Because of its overall focus on large fauna, rewilding has captured public imagination and interest in conservation, while also helping to shift a potential vegetation bias among restoration practitioners/scientists toward equal emphasis on the ecosystem role of animals.

This commentary distinguishes between restoration and rewilding of ecosystems, explaining that the latter aims at ecological adaptation to novel local environmental conditions wrought by global climate change. By contrast, restoration, as defined here, aims to recreate and maintain an historical state or condition of an ecosystem, regardless of current environmental conditions.

Although the two words are often conflated,

Rewilding is thus conceptually different from restoring. It is an adaptive approach to conserving ecological functionality under changing environmental conditions, to which historical benchmarks are less relevant than to restoring. It inherently acknowledges and promotes unpredictability, while placing the emphasis on function over species composition [du Toit & Pettorelli 2019: 2].

The authors assert that rewilding is better suited to preserving biodiversity and ecosystem function under present and future conditions.

It is difficult to imagine how conserving biodiversity and ecosystem services could be possible in predicted future scenarios without rewilding. Simply stated, anthropogenic environmental forcing makes ecosystem restoration a diminishing option [du Toit & Pettorelli 2019: 4].

Rewilding is gaining traction as an approach to conservation. However, many different perspectives about which species and ecological processes to focus rewilding efforts on and how deeply to intervene in systems has created some confusion and contention within the field. Furthermore, the most ambitious and extreme rewilding proposals (for example, recreating communities that went extinct millennia ago) have often attracted more attention, while the more pragmatic and immediate solutions in the field are overlooked.

This article attempts to clarify the concept. The authors emphasize that rewilding is a process-oriented approach to biodiversity conservation “focused on preserving and restoring the structural and functional complexity of degraded ecosystems” [Fernandez 2017: 276].

Rewilding pursues the goal of restoring wild species interactions and their regulation of key ecosystem processes including nutrient and energy flows, vegetation succession and disturbances, drawing specific attention to the key roles of large-bodied species that are especially sensitive to the human appropriation of landscapes [Fernandez 2017: 277].

The authors suggest further research is needed. They note that while the negative effects on ecosystems of the loss of biodiversity and keystone species is well documented, ecosystem responses to species reintroduction and other rewilding efforts are not as well studied. To guide future research, the authors                                               

propose an unequivocally process-oriented formulation of the “rewilding hypothesis” as a general guidance: that the large-scale restoration of apex consumers and large herbivores promotes self-regulation in community assemblages, and increases the complexity of ecological processes in ecosystems [Fernandez 2016: 277].

Also needed is policy and management practice support, particularly in terms of protecting the areas and species in question. Proactive policies could ensure that gains made toward ecological restoration are not undermined by damaging human activity.

Policies and practices should be developed in order to enforce the idea that rewilding is about reducing the human control on ecosystem processes. It must begin to include varied objectives to alleviate pressures on wildlife populations such as a full legal protection of large predators based on their unique ecological roles and not just depending on their conservation status; the eradication of predator control programs; or the elimination of game management practices such as wildlife fencing, introduction of alien game populations, supplementary feeding and others that profoundly alter the natural regulation and the genetic structure of large herbivore populations [Fernandez 2016: 278].

A growing body of literature emphasizes the need for novel, process-oriented approaches to restoring ecosystems in our rapidly changing world. Dynamic and process-oriented approaches focus on the adaptive capacity of ecosystems and the restoration of ecosystem processes promoting biodiversity, rather than aiming to maintain or restore particular ecosystem states characterized by predefined species compositions or particular bundles of ecosystem services [Perino 2019: 1].

In contrast to other types of restoration efforts aiming to recreate the composition and appearance of an historical ecological community, rewilding focuses on ecosystem function and recognizes the dynamic and unpredictable nature of ecosystems. This article highlights three key ecological processes that rewilding aims to activate: trophic complexity, natural disturbances and dispersal.

Rewilding aims to restore these three ecological processes to foster complex and self-organizing ecosystems that require minimum human management in the long term [Perino 2019: 2].

Trophic complexity implies the presence of large vertebrates, including herbivores that modify the landscape through grazing or dam building and predators that control the herbivore populations. These keystone species can promote biodiversity in the landscapes they inhabit.

Stochastic (random) natural disturbance (such as fire or flooding) can increase ecosystem heterogeneity and complexity, allowing less competitive species to survive. Rewilding involves discontinuing both controlled anthropogenic disturbances and suppression of natural disturbances.

Rewilding actions aim to release ecosystems from continued and controlled anthropogenic disturbances to allow for natural variability and sources of stochasticity. Mowing of grassland can be reduced or replaced by natural grazing. Dams can be removed or their management modified to restore natural flood regimes. Logging can be replaced by allowing natural fire and pest regimes [Perino 2019: 4].

Dispersal – rewilding aims to remove anthropogenic barriers that limit the movement of plants and animals and thus the dispersal of their genetic material and potential for recolonization after a disturbance event. The creation of ecological corridors is an example of a rewilding activity that enhances dispersal.

The interaction of these ecological processes boosts the functioning of each. For example, the presence of larger animals facilitates seed dispersal throughout the system. High levels of dispersal, in turn, can facilitate ecosystem recovery following a disturbance.

Rewilding projects can be passive (allowing abandoned agricultural fields to recover on their own) or active (species reintroductions, for example), and are most effective when conducted in a manner that engages the local community in the process.

This meta-analysis of 400 studies compared passive and active ecosystem repair outcomes in terms of the speed and completeness of recovery, and found little difference between the two approaches.

Active restoration did not result in faster or more complete recovery than simply ending the disturbances ecosystems face [Jones 2018: 1].

Passive recovery simply means ending the anthropogenic disturbance that was causing the degradation, while active restoration here includes anything from fertilizer application to recontouring/dredging to planting a desired species mix.

The authors speculate that the lack of different outcomes between the two approaches could be due to restoration managers correctly choosing to actively restore the ecosystems that “are not recovering on their own and require active restoration to improve recovery outcomes relative to passively recovering systems” [Jones 2018: 6]. Also, the actively managed sites in the study had, on average, less time to recover than the passively managed sites. Finally, the authors suggest there may be right and wrong ways to actively restore ecosystems, and “recommend that restoration strategies be tailored more closely to overcome the specific barriers to recovery in individual sites” [Jones 2018: 6].  

Assuming active and passive restoration achieve comparable outcomes in many cases, then passive restoration deserves serious consideration, given limited resources available for the vast amount of ecosystem repair required in the world today.

Letting ecosystems repair themselves in many cases may be the most effective restoration strategy – a counterintuitive yet critical finding that could help society allocate restoration funds more efficiently in the future [Jones 2018: 6].

The study also consistently found that across systems, ecosystems didn’t fully recover, at least not within the timeframe of the studies.

Our results expand those findings to a broader range of ecosystems and geographies, and, together with previous work, suggest the majority of ecosystems have not yet recovered fully following disturbance and may not in the future. Thus, restoration should not be considered a substitute for conservation, which is a key strategy to ensure sustained support of biodiversity and delivery of ecosystem services in the future [Jones 2018: 4].

Ecological restoration success is higher for natural regeneration than for active restoration in tropical forests, Crouzeilles et al. 2017

This meta-analysis comparing active restoration to natural ecosystem regeneration found the latter to be more effective. The authors conclude that “lower-cost natural regeneration surpasses active restoration in achieving tropical forest restoration success for biodiversity and vegetation structure^[7]” [Crouzeilles 2017: 4]. This conclusion runs counter to conventional wisdom that active restoration is preferable despite being more expensive.

Natural forest regeneration is the spontaneous recovery of native tree species that colonize and establish in abandoned fields or natural disturbances; this process can also be assisted through human interventions such as fencing to control livestock grazing, weed control, and fire protection. In contrast, active restoration requires planting of nursery-grown seedlings, direct seeding, and/or the manipulation of disturbance regimes (for example, thinning and burning) to speed up the recovery process, often at a high cost to establish structural features of the vegetation (hereafter termed vegetation structure), reassemble local species composition, and/or catalyze ecological succession [Crouzeilles 2017: 1].

However, “restoration success for biodiversity and vegetation structure was significantly lower in both natural regeneration and active restoration than in reference systems” [Crouzeilles 2017: 2], underscoring the importance of conserving existing intact ecosystems.  

“Restoration success for biodiversity and vegetation structure was significantly lower in both natural regeneration and active restoration than in reference systems” [Crouzeilles 2017: 2], underscoring the importance of conserving existing intact ecosystems.

Part of the explanation for the lower success of active restoration compared to natural regeneration is that the composition and/or diversity of species chosen for planting in active restoration may be inappropriate, while the species that colonize abandoned land are likely to be diverse and locally adapted.

Natural regeneration is initiated through the colonization of opportunistic and locally adapted species, resulting in a stochastic dynamic process of forest restoration that ultimately leads to higher diversity of native, locally adapted plant species than in tree planting schemes (that is, active restoration). Active restoration also can create a highly diverse habitat through human introduction of up to 6000 seedlings/ha, but tree species used in plantings often lack the full range of functional traits found in natural regrowth forests. In addition, most tropical forest plantings for restoration or forest plantations use relatively few species, that is, these plantations may not be planted primarily for biodiversity outcomes. Thus, the higher plant biodiversity in naturally regenerated systems creates more habitats and resources, which provide additional sources of food, shelter, nesting, and breeding sites, to support higher animal biodiversity [Crouzeilles 2017: 2].

Restoration and repair of Earth’s damaged ecosystems, Jones et al. 2018

This meta-analysis of 400 studies compared passive and active ecosystem repair outcomes in terms of the speed and completeness of recovery, and found little difference between the two approaches.

Active restoration did not result in faster or more complete recovery than simply ending the disturbances ecosystems face [Jones 2018: 1].

Passive recovery simply means ending the anthropogenic disturbance that was causing the degradation, while active restoration here includes anything from fertilizer application to recontouring/dredging to planting a desired species mix.

The authors speculate that the lack of different outcomes between the two approaches could be due to restoration managers correctly choosing to actively restore the ecosystems that “are not recovering on their own and require active restoration to improve recovery outcomes relative to passively recovering systems” [Jones 2018: 6]. Also, the actively managed sites in the study had, on average, less time to recover than the passively managed sites. Finally, the authors suggest there may be right and wrong ways to actively restore ecosystems, and “recommend that restoration strategies be tailored more closely to overcome the specific barriers to recovery in individual sites” [Jones 2018: 6].  

Assuming active and passive restoration achieve comparable outcomes in many cases, then passive restoration deserves serious consideration, given limited resources available for the vast amount of ecosystem repair required in the world today.

Letting ecosystems repair themselves in many cases may be the most effective restoration strategy – a counterintuitive yet critical finding that could help society allocate restoration funds more efficiently in the future [Jones 2018: 6].

The study also consistently found that across systems, ecosystems didn’t fully recover, at least not within the timeframe of the studies.

Our results expand those findings to a broader range of ecosystems and geographies, and, together with previous work, suggest the majority of ecosystems have not yet recovered fully following disturbance and may not in the future. Thus, restoration should not be considered a substitute for conservation, which is a key strategy to ensure sustained support of biodiversity and delivery of ecosystem services in the future [Jones 2018: 4].

Rewilding complex ecosystems, Perino et al. 2019

A growing body of literature emphasizes the need for novel, process-oriented approaches to restoring ecosystems in our rapidly changing world. Dynamic and process-oriented approaches focus on the adaptive capacity of ecosystems and the restoration of ecosystem processes promoting biodiversity, rather than aiming to maintain or restore particular ecosystem states characterized by predefined species compositions or particular bundles of ecosystem services [Perino 2019: 1].

In contrast to other types of restoration efforts aiming to recreate the composition and appearance of an historical ecological community, rewilding focuses on ecosystem function and recognizes the dynamic and unpredictable nature of ecosystems. This article highlights three key ecological processes that rewilding aims to activate: trophic complexity, natural disturbances and dispersal.

Rewilding aims to restore these three ecological processes to foster complex and self-organizing ecosystems that require minimum human management in the long term [Perino 2019: 2].

Trophic complexity implies the presence of large vertebrates, including herbivores that modify the landscape through grazing or dam building and predators that control the herbivore populations. These keystone species can promote biodiversity in the landscapes they inhabit.

Stochastic (random) natural disturbance (such as fire or flooding) can increase ecosystem heterogeneity and complexity, allowing less competitive species to survive. Rewilding involves discontinuing both controlled anthropogenic disturbances and suppression of natural disturbances.

Rewilding actions aim to release ecosystems from continued and controlled anthropogenic disturbances to allow for natural variability and sources of stochasticity. Mowing of grassland can be reduced or replaced by natural grazing. Dams can be removed or their management modified to restore natural flood regimes. Logging can be replaced by allowing natural fire and pest regimes [Perino 2019: 4].

Dispersal – rewilding aims to remove anthropogenic barriers that limit the movement of plants and animals and thus the dispersal of their genetic material and potential for recolonization after a disturbance event. The creation of ecological corridors is an example of a rewilding activity that enhances dispersal.

The interaction of these ecological processes boosts the functioning of each. For example, the presence of larger animals facilitates seed dispersal throughout the system. High levels of dispersal, in turn, can facilitate ecosystem recovery following a disturbance.

Rewilding projects can be passive (allowing abandoned agricultural fields to recover on their own) or active (species reintroductions, for example), and are most effective when conducted in a manner that engages the local community in the process.

Rewilding: a call for boosting ecological complexity in conservation, Fernández et al. 2017

Rewilding is gaining traction as an approach to conservation. However, many different perspectives about which species and ecological processes to focus rewilding efforts on and how deeply to intervene in systems has created some confusion and contention within the field. Furthermore, the most ambitious and extreme rewilding proposals (for example, recreating communities that went extinct millennia ago) have often attracted more attention, while the more pragmatic and immediate solutions in the field are overlooked.

This article attempts to clarify the concept. The authors emphasize that rewilding is a process-oriented approach to biodiversity conservation “focused on preserving and restoring the structural and functional complexity of degraded ecosystems” [Fernandez 2017: 276].

Rewilding pursues the goal of restoring wild species interactions and their regulation of key ecosystem processes including nutrient and energy flows, vegetation succession and disturbances, drawing specific attention to the key roles of large-bodied species that are especially sensitive to the human appropriation of landscapes [Fernandez 2017: 277].

The authors suggest further research is needed. They note that while the negative effects on ecosystems of the loss of biodiversity and keystone species is well documented, ecosystem responses to species reintroduction and other rewilding efforts are not as well studied. To guide future research, the authors                                               

propose an unequivocally process-oriented formulation of the “rewilding hypothesis” as a general guidance: that the large-scale restoration of apex consumers and large herbivores promotes self-regulation in community assemblages, and increases the complexity of ecological processes in ecosystems [Fernandez 2016: 277].

Also needed is policy and management practice support, particularly in terms of protecting the areas and species in question. Proactive policies could ensure that gains made toward ecological restoration are not undermined by damaging human activity.

Policies and practices should be developed in order to enforce the idea that rewilding is about reducing the human control on ecosystem processes. It must begin to include varied objectives to alleviate pressures on wildlife populations such as a full legal protection of large predators based on their unique ecological roles and not just depending on their conservation status; the eradication of predator control programs; or the elimination of game management practices such as wildlife fencing, introduction of alien game populations, supplementary feeding and others that profoundly alter the natural regulation and the genetic structure of large herbivore populations [Fernandez 2016: 278].

The differences between rewilding and restoring an ecologically degraded landscape, du Toit & Pettorelli 2019

This commentary distinguishes between restoration and rewilding of ecosystems, explaining that the latter aims at ecological adaptation to novel local environmental conditions wrought by global climate change. By contrast, restoration, as defined here, aims to recreate and maintain an historical state or condition of an ecosystem, regardless of current environmental conditions.

Although the two words are often conflated,

Rewilding is thus conceptually different from restoring. It is an adaptive approach to conserving ecological functionality under changing environmental conditions, to which historical benchmarks are less relevant than to restoring. It inherently acknowledges and promotes unpredictability, while placing the emphasis on function over species composition [du Toit & Pettorelli 2019: 2].

The authors assert that rewilding is better suited to preserving biodiversity and ecosystem function under present and future conditions.

It is difficult to imagine how conserving biodiversity and ecosystem services could be possible in predicted future scenarios without rewilding. Simply stated, anthropogenic environmental forcing makes ecosystem restoration a diminishing option [du Toit & Pettorelli 2019: 4].

Reintroducing rewilding to restoration – rejecting the search for novelty, Hayward et al. 2019

This perspective piece argues against scientific or public adoption of the term “rewilding,” which the authors view as being generally synonymous with the classical and better-understood concept of ecological restoration. Definitions of restoration are sufficient to encompass practices espoused in rewilding.

Early definitions of restoration describe the practice as “the process of repairing damage caused by humans to the diversity and dynamics of indigenous ecosystems” (Jackson et al., 1995). Although at the time of this definition, restoration science was still developing, it was clear that it had established itself under the broad banner of repairing damaged ecosystems. … More recently, restoration has been defined as “any activity whose aim it is to ultimately achieve ecosystem recovery, insofar as possible and relative to an appropriate local native model (termed here a reference ecosystem), regardless of the period of time required to achieve the recovery outcome” (McDonald et al., 2016) [Hayward 2019: 257].

The term rewilding, which has evolved over time, “was arguably conceived to promote the original authors’ view of conservation via cores [habitats], corridors, and carnivores” [Hayward 2019: 256]. In this early context,

‘rewilding’ referred to conservation and management interventions that focused on reintroducing keystone predators and ensuring that they had sufficient interconnected space to live. The authors emphasized within their original work that rewilding was “one essential element in most efforts to restore fully functioning ecosystems” (Soulé and Noss, 1998). As such, it is clear that rewilding was originally aimed to be a term that referred to one component of ecological restoration [Hayward 2019: 256].

Since then, rewilding has come to refer to practices involving “translocating substitute species to fill vacant ecological niches left by extinct species” [Hayward 2019: 257] or reintroducing locally extinct species, or simply allowing natural succession to occur on abandoned land. Given multiple definitions, all of which relate to the idea of restoration, the term rewilding is seen here as superfluous and confusing.

Given the lack of clear differences between rewilding and restoration in both definition and practice, we see little need for these competing terms within scientific discourse [Hayward 2019: 257].

However, the authors suggest two positive contributions from the rewilding discourse. Because of its overall focus on large fauna, rewilding has captured public imagination and interest in conservation, while also helping to shift a potential vegetation bias among restoration practitioners/scientists toward equal emphasis on the ecosystem role of animals.

Therefore, rather than adopting a new term with copious definitions that lack clarity, this debate can be used as an opportunity to adaptively improve current restoration practice by incorporating a more equal focus between flora and fauna [Hayward 2019: 258].

Because of its overall focus on large fauna, rewilding has captured public imagination and interest in conservation, while also helping to shift a potential vegetation bias among restoration practitioners/scientists toward equal emphasis on the ecosystem role of animals.

Intact forests in the United States: proforestation mitigates climate change and serves the greatest good, Moomaw 2019

The concept of “proforestation” presented here means letting existing forests continue to grow and reach their full ecological potential. Due to intensive management practices, most existing forests sequester carbon at only half (or less) of their potential rate. In addition to storing (embodying) more carbon than their smaller counterparts, large trees also sequester carbon at a faster rate. For example, “Each year a single tree that is 100 cm in diameter adds the equivalent biomass of an entire 10-20 cm diameter tree, further underscoring the role of large trees” [Moomaw 2019: 4]. Imagine, reader, that every year you planted a whole new medium-sized tree – that’s essentially what large trees are doing.

“Each year a single tree that is 100 cm in diameter adds the equivalent biomass of an entire 10-20 cm diameter tree, further underscoring the role of large trees” [Moomaw 2019: 4].

Much of Maine’s forests have been harvested continuously for 200 years and have a carbon density less than one-third of the forests of Southern Vermont and New Hampshire, Northwestern Connecticut and Western Massachusetts – a region that has not been significantly harvested over the past 75-150 years. …

Ecosystem services accrue as forests age for centuries. Far from plateauing in terms of carbon sequestration (or added wood) at a relatively young age as was long believed, older forests (e.g., >200 years of age without intervention) contain a variety of habitats, typically continue to sequester additional carbon for many decades or even centuries, and sequester significantly more carbon than younger and managed stands [Moomaw 2019: 5].

Because existing forests are already sequestering carbon, and will continue at an increasing rate as tree size grows, the author argues that proforestation is a more effective immediate solution than either reforestation (planting new trees where they had been cleared for agriculture, etc.) or afforestation (planting trees in new places), though these other two approaches are important for longer term ecosystem function. Moomaw et al. argue that the urgency of removing CO2 makes it imperative to keep existing forests growing.

Globally, existing forests only store approximately half of their potential due to past and present management, and many existing forests are capable of immediate and even more extensive growth for many decades. During the timeframe while seedlings planted for afforestation and reforestation are growing (yet will never achieve the carbon density of an intact forest), proforestation is a safe, highly effective, immediate natural solution that does not rely on uncertain discounted future benefits inherent in other options [Moomaw 2019: 7].

Furthermore, existing, older forests are critical habitats for threatened wildlife, even small intact woods.

Forest bird guilds also benefit from small intact forests in urban landscapes relative to unprotected matrix forests. Several bird species in the U.S. that are globally threatened – including the wood thrush, cerulean warbler, marbled murrelet, and spotted owl are, in part, dependent on intact, older forests with large trees [Moomaw 2019: 5].

In sum, proforestation provides the most effective solution to dual global crises – climate change and biodiversity loss. It is the only practical, rapid, economical, and effective means for atmospheric CDR [carbon dioxide removal] among the multiple options that have been proposed because it removes more atmospheric carbon dioxide in the immediate future and continues to sequester it long-term. Proforestation will increase the diversity of many groups of organisms and provide numerous additional and important ecosystem services. While multiple strategies will be needed to address global environmental crises, proforestation is a very low-cost option for increasing carbon sequestration that does not require additional land beyond what is already forested and provides new forest related jobs and opportunities along with a wide array of quantifiable ecosystem services, including human health [Moomaw 2019: 8].

Plant diversity enhances the reclamation of degraded lands by stimulating plant-soil feedbacks, Jia et al. 2020

This study tested biodiversity effects on ecosystem function in the process of reviving severely degraded and contaminated land, and found that “increasing plant diversity greatly enhanced the reclamation of these lands” [Jia 2020: 1].  

Prior to implementing the reclamation experiment, the degraded mine wasteland investigated in this study was heavily impacted by past mining activities and was devoid of vegetation for more than a decade and the soil lacked structure, contained high levels of toxic metals and low levels of nutrients. … our results showed that higher plant species richness enhanced land reclamation across all standard measures of reclamation success and specifically resulted in higher vegetation coverage, biomass yield and stability for all 3 years [of the experiment] [Jia 2020: 6].

Furthermore, higher biodiversity plots had higher levels of organic carbon in the soil, higher soil microorganism abundance, lower fungal pathogens, and lower heavy metal concentrations in plant tissue.

The most striking impact of plant diversity on soil was on the microbial communities. Both soil fungal and bacterial OTUs [operational taxonomic units^[8]] increased significantly with plant species richness. More importantly, we found that higher plant species richness significantly increased the relative abundance of soil cellulolytic bacteria that degrade cellulose and are thus essential components of nutrient cycling [Jia 2020: 7].

High ecosystem service delivery potential of small woodlands in agricultural landscapes, Valdes 2020

This article assesses the ecological value of small woodlands relative to larger ones. The authors conclude that:

…smaller woodlands potentially deliver multiple services at higher performance levels on a per area basis than larger woodlands of a similar age, even if the larger woodlands harbor a higher biodiversity [Valdes 2020: 12].

Because of their high edge-to-core ratio, smaller woodlots get more sunlight and more nutrient input from surrounding farmland, resulting in denser vegetation cover and higher biomass production at edges.

This altered functioning in turn increases the delivery potential of some services, such as game production potential, due to an increased quantity of food available for game, and topsoil carbon storage, due to the faster incorporation of organic matter in the soil. Tick-borne disease risk is, however, lower, likely due to decreased larval densities in the unfavorable (e.g. hotter and drier) microclimatic conditions at the edge [Valdes 2020: 12].

While smaller woodlands were more apt to deliver “multiple services at higher levels of performance per area than larger woodlands of a similar age,” the greater biodiversity of larger woodlands increased certain individual ecosystem services.

The supply potential of several individual ecosystem services indirectly increased in larger and more ancient woodlands because it was dependent on higher levels of biodiversity. For example, abundance of usable plants and game production potential might have increased due to a positive correlation with vascular plant diversity, while pest control potential probably increased due to bottom-up effects through the trophic chain. On the contrary, tick-borne disease risk, topsoil carbon storage and stemwood volume were unrelated to multidiversity, probably because they depended on particular environmental conditions or on the presence and abundance of specific species rather than on species richness per se.

Finally, it should be noted that we focused on the service delivery potential on a per area basis and that the total amount of services provided by large patches might still be larger than that of small patches. Our findings should therefore not be interpreted as a trade-off between large, biodiverse patches versus small patches that have a higher potential to deliver services, but rather as an observation that small woodlands in agricultural landscapes have the potential to deliver a high flow of services relative to their size [Valdes 2020: 12].

Effectiveness of the Miyawaki method in Mediterranean forest restoration programs, Shirone, Salis & Vessela 2011

This study tested the Miyawaki method of rapid natural forest regeneration (which has been shown to work in Japan and elsewhere) in the arid Mediterranean. In this area, millennia of human civilization have resulted in degraded soils and reduced and changed forest cover, traditional reforestation efforts have often failed, and desertification is a looming threat. The Miyawaki method speeds up the process of ecological succession by densely planting a multilayer forest made up of a wide diversity of indigenous species.

In a natural forest cycle, as Clements (1916) described, annual plants on barren land are succeeded by perennial grass, sun-tolerant shrubs, light-demanding, fast-growing trees, and finally natural forests; each step may require decades, and the climax vegetation could be formed after two centuries or more. Currently, most forest reforestation programs adopt a scheme of planting one or more early successional species; after successful establishment, they are gradually replaced by intermediate species (either naturally or by planting), until late successional species arise. This pattern tries to simulate natural processes of ecological succession, from pioneer species to climax vegetation. However, it requires several silvicultural practices and normally takes a long time [Shirone 2011: 82].

In the Miyawaki method, by contrast, one plants all at once the many plant species normally present in a native forest community, thus bypassing the earliest stages of ecological succession. Other tree-planting methods favor fast-growing non-native tree species, while omitting understory species – in other words, creating a simple plantation rather than a forest community that functions ecologically and can evolve and sustain itself.

Multilayer forests, and natural biocoenosis [ecological community] is possible, and well-developed ecosystems can be quickly established because of the simultaneous use of intermediate and late successional species in plantations. The Miyawaki method involves surveying the potential natural vegetation of the area to be reforested and recovering topsoil to a depth of 20– 30 cm by mixing the soil and a compost from organic materials, such as fallen leaves, mowed grass, etc. In this way, the time of the natural process of soil evolution, established by the vegetational succession itself, is reduced [Shirone 2011: 82].

The authors of this study found that compared to traditional reforestation, there was “a more rapid development of trees on the Miyawaki plots, in particular, early-successional species [especially maritime pine]. The benefits over previous methods are remarkable and comparable with those obtained by Miyawaki in Asia and South America.” The Miyawaki method favoring denser plantings works even in arid climates, in spite of traditional views favoring sparse plantings in arid places, although the optimal density for the Mediterranean still needs testing, according to the authors.

In fact, low plant density has been traditionally retained as appropriate in arid and semiarid environments in order to avoid competition for water resources between plants, but it is now evident that cooperative processes, e.g., mutual shading, prevail over competitive processes. High plant density also reduces the impact of acorn predators, thus encouraging oak regeneration, i.e., the main late-successional forest species in Mediterranean environments. In addition, excellent plant stock remains fundamental for planting success in harsh environments [Shirone 2011: 91].

When is a forest a forest? Forest concepts and definitions in the era of forest and landscape restoration, Chazdon et al. 2016

This article analyzes the policy context for forest ecosystem restoration, arguing that it is heavily shaped by the way we define a forest. The use of a forest definition lacking ecological considerations severely undermines conservation and restoration initiatives.  

We live in an era of unprecedented environmental change, motivating equally unprecedented global actions to protect and restore forest ecosystems. These efforts could fail to achieve their ambitious goals if they are not informed by clear and appropriate concepts and definitions of forests [Chazdon 2016: 1].

There are multiple definitions of a forest. Early European and internationally adopted definitions tended to define forests according to their usage for timber. FAO’s 1948 definition created for assessing wood harvesting potential of the world’s forests is still in use today. Yet new definitions have since been created that emphasize conservation, carbon sequestration and biodiversity values of forests.

However, national and global forest assessments tend to use narrow technical definitions that ignore ecological values of forested land.

In many cases, forest assessments do not distinguish between land covered by natural and planted forests. Thus, if natural forests are cleared and replaced with plantations, no net loss of forest cover is reported [Chazdon 2016: 6].

In other words, areas that should not be considered forest in ecological terms are counted as forest – an obfuscation with disastrous environmental outcomes. Similarly, ecologically important yet small patches of trees that are not counted in forest inventories and lack legal protection are at risk of being lost.

Areas classified as ‘‘non-forests’’ are as important to forest definitions as are forests. More than 43 % of agricultural land globally is in agroforestry systems with 10 % tree cover. In Rwanda and Brazil, forest inventories using a 0.5-ha threshold ignore substantial areas of small forest fragments, agroforests, and woodlots, leading to underestimates of actual tree cover. Small patches of trees and even isolated remnant trees can hold high ecological and conservation value, and can play an important role in enhancing landscape connectivity, local biodiversity, and local livelihoods [Chazdon 2016: 7].

Information from participatory local monitoring and remote sensing technology that distinguishes “among successional stages of forests, selectively logged forests, and single-species plantations” [Chazdon 2016: 10] is needed.

Access to this information will allow countries and international agencies to track changes in natural forest cover, and to monitor processes of restoration, rehabilitation, and afforestation within a landscape context and, consequently, make informed policy decisions. We are on the frontier of developing new ways of monitoring and assessing land cover that will provide robust indicators of the quality and origins of tree cover and enable new ways of viewing and defining forests and reforests. To see beyond the overly simplified categories of forest loss, forest degradation, and forest gain, we need to develop and apply more adapted and nuanced definitions that will deepen our understanding of the drivers and outcomes of land-use change and forest dynamics within landscapes [Chazdon 2016: 10].

The UN’s Decade of Ecosystem Restoration declaration aims to “prevent, halt and reverse the degradation of ecosystems worldwide,” stating that “there has never been a more urgent need to restore damaged ecosystems than now” [UNEP/FAO Factsheet 2020].

Estimates of global land degradation range from 25% to 75% of Earth’s land surface. The uncertainty is due to different ideas about what counts as degraded land and different methodologies for quantifying it (expert opinion, satellite data, or modeling, for example). Generally, degradation is defined as “a reduction in productivity of the land or soil due to human activity” [Gibbs & Salmon 2015: 13].

Another global assessment [IPBES 2019] states that 75% of the land surface “is significantly altered, 66 percent of the ocean area is experiencing increasing cumulative impacts, and over 85 percent of wetlands (area) has been lost” [IPBES 2019: 11]. Meanwhile, wilderness remains on just 23% of Earth’s land surface [Watson 2016]. Wilderness areas are defined as

biologically and ecologically largely intact landscapes that are mostly free of human disturbance. These areas do not exclude people, as many are in fact critical to certain communities, including indigenous peoples. Rather, they have lower levels of impacts from the kinds of human uses that result in significant biophysical disturbance to natural habitats, such as large-scale land conversion, industrial activity, or infrastructure development [Watson 2016: 1].

Degraded lands have reduced ecosystem function, upon which humans and other beings depend for clean water and air, shelter, food, and habitable local and global climate systems. In fact, half of Earth’s surface (including ocean and land) should be maintained or restored to intact ecosystems, in addition to cutting fossil fuel emissions, for any chance of keeping global warming from surpassing 1.5C above pre-industrial levels and averting catastrophic climate change [Dinerstein 2019].

This means existing wilderness needs to be protected and degraded lands regenerated. Currently less than 15% of land surface is formally protected and 2% of oceans [Dinerstein 2019]. Furthermore, intact ecosystems need to be connected by wildlife corridors to allow for migration and dispersal of diverse species. Quantifying a few of the direct human benefits from large-scale restoration, the UN estimates that:

Restoration of 350 million hectares of degraded land between now and 2030 could generate USD 9 trillion in ecosystem services and take an additional 13-26 gigatons of greenhouse gases out of the atmosphere [UNEP 2019].

So how does ecosystem restoration happen? There are critical social, political and cultural responses to this question that are beyond the scope of this review – except to stress that all hands are needed on deck. As the UN says:

This incredible challenge can only be met if everyone – including member states, local governments, partners from the private sector, academia and civil society – come together to find viable, lasting solutions [UNEP/FAO Factsheet 2020: 1].

Here we present a handful of the solutions as discussed in a growing body of ecological restoration literature, such as the articles summarized in the following section. There are two overarching approaches – active versus passive restoration. The latter aims simply to remove the anthropogenic disturbance causing the degradation and allow abandoned or no-longer-disturbed land to regenerate on its own. Sometimes simple removal of the disturbance (such as a dam) involves plenty of human energy, and may not seem passive at all. By contrast, though, active restoration actively facilitates land regeneration. Activities may include installing hollow logs, wood piles or other habitat features; planting; dredging; prescribed burning; reintroducing key species; or controlling invasive species, for example.

A somewhat intermediate approach of planting “tree islands” to restore tropical forests is another option [Holl 2020]. Instead of planting rows of trees throughout a given plot, clusters of trees are planted on just a fraction of the area, costing just a fraction of the price of a plantation-style restoration effort. Tree islands simulate the patchiness of natural forest recovery, while speeding up the process, and rely on animals to disperse tree seeds. In a study in Costa Rica of the tree island restoration method, cover of trees and shrubs had increased from 20% to over 90% over 15 years [Holl 2020].

Deciding which approach is best may depend on the situation – the degree of degradation needing to be reversed or the proximity of adjacent ecosystems as a seed source to kickstart colonization. Funding may also be a factor as active restoration projects typically cost more than do passive ones. Interestingly, in spite of being less expensive and often less work, passive regeneration projects are comparable to or more effective than active restoration in terms of achieving outcomes, according to two meta-studies [Jones 2018, Crouzeilles 2017]. Desired outcomes for restoration projects relate to measures of biodiversity, density and height of vegetation, amount of biomass produced, and speed of recovery, for example.

Letting ecosystems repair themselves in many cases may be the most effective restoration strategy – a counterintuitive yet critical finding that could help society allocate restoration funds more efficiently in the future [Jones 2018: 6].

The most effective strategy for a given situation is not always taken, and projects sometimes fail or only partially succeed. One reason for underperformance is simply that ecosystems are complex and restoring them requires “significant time, resources, and knowledge,” which may not always be available [Gann 2019: 14]. Necessary follow up after activities are completed may never happen, such as when trees are planted and then abandoned in the first few critical years of establishment. Another potential roadblock to ecological recovery is competing goals for a project, which may be skewed toward economic concerns.

For instance, the Bonn Challenge to restore 330 million hectares of deforested and degraded land by 2030 has been criticized for counting monoculture timber plantations in progress toward reforestation goals [Lewis & Wheeler 2019]. Such woodlots offer little in the way of wildlife habitat and store an estimated 40 times less carbon than do natural forests [Lewis & Wheeler 2019]. Part of the problem of allowing such practices to count as restoration lies in the definition of “forest” used in setting goals and making policy; definitions may lack consideration of biodiversity or other essential elements of natural forests. The UN Food and Agriculture Organization’s definition in use today was originally created to facilitate timber inventories [Chazdon 2016].

Early afforestation efforts in arid and semi-arid northern China reveals how restoration can go wrong when natural ecosystem characteristics are ignored [Cao 2008]. Much of the area, whose natural state is grasslands, had become desertified by the middle of the 20th Century due to agriculture, overgrazing and monoculture timber plantations. Large-scale afforestation began in 1978, when modern restoration science was not yet well established. Plantings involved fast-growing water-use inefficient tree species not well adapted to arid environments, which only exacerbated dry conditions, rather than native grassland shrubs.

The natural vegetation of much of the region was desert steppe vegetation or dryland shrub communities, which have a much higher water-use efficiency than most tree communities and which have evolved to use soil water sustainably under these environmental conditions [Cao 2008: 1828].

 In his analysis of the project, Shixiong Cao [2008] recommends a change of practice.

In terms of revegetation strategies, planners must understand that different environments will support different vegetation communities and that forests are not a suitable choice in all areas. To successfully revegetate an area, planners must determine which vegetation types a given environment can naturally sustain and target restoration activities at creating such communities. For example, stable communities of natural desert steppe and grassland vegetation, and possibly even lichen species in more severely degraded environments, can develop in arid and semiarid areas as a result of natural processes, thereby increasing vegetation cover beyond the levels that could be sustained for trees, and can thereby provide better protection for the soil [Cao 2008: 1830].

The concept of rewilding, which entered ecological restoration discourse a couple of decades ago, has sparked confusion and controversy due to its multiple definitions [Hayward 2019]. However, the concept has also perhaps served to reinforce ecological principles within the larger restoration movement. Rewilding is an approach to restoring ecosystems that “aims to restore self-sustaining and complex ecosystems with interlinked ecological processes that promote and support one another while minimizing or gradually reducing human interventions” [Perino 2019: 1].

For example, rewilding has often focused on the roles of top predators in ecosystem processes, and proposed their reintroduction as a key tactic. The addition of large animals to a system enhances trophic complexity and dispersal. Along with natural disturbances (like natural fires), these are key ecosystem processes rewilding aims to activate.

Rewilding aims to restore these three ecological processes [trophic complexity, dispersal and natural disturbances] to foster complex and self-organizing ecosystems that require minimum human management in the long term [Perino 2019: 2].

Establishing ecological corridors that connect larger intact ecosystems can facilitate migration and dispersal of plants and animals to colonize new areas. The value of ecological corridors highlights the role of small-scale, local restoration and conservation projects in rebuilding landscape-level ecological integrity. Protecting and expanding hedges, river systems and roadsides contributes to the success of the larger wilderness areas they connect. Similarly, even small woodlots in agricultural landscapes can have unexpectedly high ecosystem functionality [Valdes 2019]. The relevance of small projects to overall ecological wellbeing means that almost anybody anywhere has a role to play.

Lastly, the importance of conserving existing ecosystems cannot be overstated, and restoration projects should never serve to justify destruction elsewhere – mature intact ecosystems are irreplaceable. Rather, ecosystem restoration should be viewed as a strategy that “seeks to advance conservation by rebuilding nature” [Young & Schwartz 2019: 1]. Many restoration projects achieve only partial recovery during relevant time periods, meaning they may not ever become as fully functional as mature intact ecosystems during our lifetimes [Jones 2018]. Existing mature forests and other ecosystems are major carbon sinks in terms of the large amount of carbon they contain and in terms of the superior sequestration rates of older larger trees [Moomaw 2019]. Intact forests are also home to about two thirds of all species on Earth [Dinerstein 2019].

Both conservation and restoration are essential – they are an inseparable two-part solution to a dire global ecological crisis.

Lastly, the importance of conserving existing ecosystems cannot be overstated, and restoration projects should never serve to justify destruction elsewhere – mature intact ecosystems are irreplaceable. Rather, ecosystem restoration should be viewed as a strategy that “seeks to advance conservation by rebuilding nature” [Young & Schwartz 2019: 1].

Approaches to ecosystem restoration article summaries

Ecological restoration success is higher for natural regeneration than for active restoration in tropical forests, Crouzeilles et al. 2017

This meta-analysis comparing active restoration to natural ecosystem regeneration found the latter to be more effective. The authors conclude that “lower-cost natural regeneration surpasses active restoration in achieving tropical forest restoration success for biodiversity and vegetation structure^[7]” [Crouzeilles 2017: 4]. This conclusion runs counter to conventional wisdom that active restoration is preferable despite being more expensive.

Natural forest regeneration is the spontaneous recovery of native tree species that colonize and establish in abandoned fields or natural disturbances; this process can also be assisted through human interventions such as fencing to control livestock grazing, weed control, and fire protection. In contrast, active restoration requires planting of nursery-grown seedlings, direct seeding, and/or the manipulation of disturbance regimes (for example, thinning and burning) to speed up the recovery process, often at a high cost to establish structural features of the vegetation (hereafter termed vegetation structure), reassemble local species composition, and/or catalyze ecological succession [Crouzeilles 2017: 1].

However, “restoration success for biodiversity and vegetation structure was significantly lower in both natural regeneration and active restoration than in reference systems” [Crouzeilles 2017: 2], underscoring the importance of conserving existing intact ecosystems.  

“Restoration success for biodiversity and vegetation structure was significantly lower in both natural regeneration and active restoration than in reference systems” [Crouzeilles 2017: 2], underscoring the importance of conserving existing intact ecosystems.

Part of the explanation for the lower success of active restoration compared to natural regeneration is that the composition and/or diversity of species chosen for planting in active restoration may be inappropriate, while the species that colonize abandoned land are likely to be diverse and locally adapted.

Natural regeneration is initiated through the colonization of opportunistic and locally adapted species, resulting in a stochastic dynamic process of forest restoration that ultimately leads to higher diversity of native, locally adapted plant species than in tree planting schemes (that is, active restoration). Active restoration also can create a highly diverse habitat through human introduction of up to 6000 seedlings/ha, but tree species used in plantings often lack the full range of functional traits found in natural regrowth forests. In addition, most tropical forest plantings for restoration or forest plantations use relatively few species, that is, these plantations may not be planted primarily for biodiversity outcomes. Thus, the higher plant biodiversity in naturally regenerated systems creates more habitats and resources, which provide additional sources of food, shelter, nesting, and breeding sites, to support higher animal biodiversity [Crouzeilles 2017: 2].

Restoration and repair of Earth’s damaged ecosystems, Jones et al. 2018

This meta-analysis of 400 studies compared passive and active ecosystem repair outcomes in terms of the speed and completeness of recovery, and found little difference between the two approaches.

Active restoration did not result in faster or more complete recovery than simply ending the disturbances ecosystems face [Jones 2018: 1].

Passive recovery simply means ending the anthropogenic disturbance that was causing the degradation, while active restoration here includes anything from fertilizer application to recontouring/dredging to planting a desired species mix.

The authors speculate that the lack of different outcomes between the two approaches could be due to restoration managers correctly choosing to actively restore the ecosystems that “are not recovering on their own and require active restoration to improve recovery outcomes relative to passively recovering systems” [Jones 2018: 6]. Also, the actively managed sites in the study had, on average, less time to recover than the passively managed sites. Finally, the authors suggest there may be right and wrong ways to actively restore ecosystems, and “recommend that restoration strategies be tailored more closely to overcome the specific barriers to recovery in individual sites” [Jones 2018: 6].  

Assuming active and passive restoration achieve comparable outcomes in many cases, then passive restoration deserves serious consideration, given limited resources available for the vast amount of ecosystem repair required in the world today.

Letting ecosystems repair themselves in many cases may be the most effective restoration strategy – a counterintuitive yet critical finding that could help society allocate restoration funds more efficiently in the future [Jones 2018: 6].

The study also consistently found that across systems, ecosystems didn’t fully recover, at least not within the timeframe of the studies.

Our results expand those findings to a broader range of ecosystems and geographies, and, together with previous work, suggest the majority of ecosystems have not yet recovered fully following disturbance and may not in the future. Thus, restoration should not be considered a substitute for conservation, which is a key strategy to ensure sustained support of biodiversity and delivery of ecosystem services in the future [Jones 2018: 4].

Rewilding complex ecosystems, Perino et al. 2019

A growing body of literature emphasizes the need for novel, process-oriented approaches to restoring ecosystems in our rapidly changing world. Dynamic and process-oriented approaches focus on the adaptive capacity of ecosystems and the restoration of ecosystem processes promoting biodiversity, rather than aiming to maintain or restore particular ecosystem states characterized by predefined species compositions or particular bundles of ecosystem services [Perino 2019: 1].

In contrast to other types of restoration efforts aiming to recreate the composition and appearance of an historical ecological community, rewilding focuses on ecosystem function and recognizes the dynamic and unpredictable nature of ecosystems. This article highlights three key ecological processes that rewilding aims to activate: trophic complexity, natural disturbances and dispersal.

Rewilding aims to restore these three ecological processes to foster complex and self-organizing ecosystems that require minimum human management in the long term [Perino 2019: 2].

Trophic complexity implies the presence of large vertebrates, including herbivores that modify the landscape through grazing or dam building and predators that control the herbivore populations. These keystone species can promote biodiversity in the landscapes they inhabit.

Stochastic (random) natural disturbance (such as fire or flooding) can increase ecosystem heterogeneity and complexity, allowing less competitive species to survive. Rewilding involves discontinuing both controlled anthropogenic disturbances and suppression of natural disturbances.

Rewilding actions aim to release ecosystems from continued and controlled anthropogenic disturbances to allow for natural variability and sources of stochasticity. Mowing of grassland can be reduced or replaced by natural grazing. Dams can be removed or their management modified to restore natural flood regimes. Logging can be replaced by allowing natural fire and pest regimes [Perino 2019: 4].

Dispersal – rewilding aims to remove anthropogenic barriers that limit the movement of plants and animals and thus the dispersal of their genetic material and potential for recolonization after a disturbance event. The creation of ecological corridors is an example of a rewilding activity that enhances dispersal.

The interaction of these ecological processes boosts the functioning of each. For example, the presence of larger animals facilitates seed dispersal throughout the system. High levels of dispersal, in turn, can facilitate ecosystem recovery following a disturbance.

Rewilding projects can be passive (allowing abandoned agricultural fields to recover on their own) or active (species reintroductions, for example), and are most effective when conducted in a manner that engages the local community in the process.

Rewilding: a call for boosting ecological complexity in conservation, Fernández et al. 2017

Rewilding is gaining traction as an approach to conservation. However, many different perspectives about which species and ecological processes to focus rewilding efforts on and how deeply to intervene in systems has created some confusion and contention within the field. Furthermore, the most ambitious and extreme rewilding proposals (for example, recreating communities that went extinct millennia ago) have often attracted more attention, while the more pragmatic and immediate solutions in the field are overlooked.

This article attempts to clarify the concept. The authors emphasize that rewilding is a process-oriented approach to biodiversity conservation “focused on preserving and restoring the structural and functional complexity of degraded ecosystems” [Fernandez 2017: 276].

Rewilding pursues the goal of restoring wild species interactions and their regulation of key ecosystem processes including nutrient and energy flows, vegetation succession and disturbances, drawing specific attention to the key roles of large-bodied species that are especially sensitive to the human appropriation of landscapes [Fernandez 2017: 277].

The authors suggest further research is needed. They note that while the negative effects on ecosystems of the loss of biodiversity and keystone species is well documented, ecosystem responses to species reintroduction and other rewilding efforts are not as well studied. To guide future research, the authors                                               

propose an unequivocally process-oriented formulation of the “rewilding hypothesis” as a general guidance: that the large-scale restoration of apex consumers and large herbivores promotes self-regulation in community assemblages, and increases the complexity of ecological processes in ecosystems [Fernandez 2016: 277].

Also needed is policy and management practice support, particularly in terms of protecting the areas and species in question. Proactive policies could ensure that gains made toward ecological restoration are not undermined by damaging human activity.

Policies and practices should be developed in order to enforce the idea that rewilding is about reducing the human control on ecosystem processes. It must begin to include varied objectives to alleviate pressures on wildlife populations such as a full legal protection of large predators based on their unique ecological roles and not just depending on their conservation status; the eradication of predator control programs; or the elimination of game management practices such as wildlife fencing, introduction of alien game populations, supplementary feeding and others that profoundly alter the natural regulation and the genetic structure of large herbivore populations [Fernandez 2016: 278].

The differences between rewilding and restoring an ecologically degraded landscape, du Toit & Pettorelli 2019

This commentary distinguishes between restoration and rewilding of ecosystems, explaining that the latter aims at ecological adaptation to novel local environmental conditions wrought by global climate change. By contrast, restoration, as defined here, aims to recreate and maintain an historical state or condition of an ecosystem, regardless of current environmental conditions.

Although the two words are often conflated,

Rewilding is thus conceptually different from restoring. It is an adaptive approach to conserving ecological functionality under changing environmental conditions, to which historical benchmarks are less relevant than to restoring. It inherently acknowledges and promotes unpredictability, while placing the emphasis on function over species composition [du Toit & Pettorelli 2019: 2].

The authors assert that rewilding is better suited to preserving biodiversity and ecosystem function under present and future conditions.

It is difficult to imagine how conserving biodiversity and ecosystem services could be possible in predicted future scenarios without rewilding. Simply stated, anthropogenic environmental forcing makes ecosystem restoration a diminishing option [du Toit & Pettorelli 2019: 4].

Reintroducing rewilding to restoration – rejecting the search for novelty, Hayward et al. 2019

This perspective piece argues against scientific or public adoption of the term “rewilding,” which the authors view as being generally synonymous with the classical and better-understood concept of ecological restoration. Definitions of restoration are sufficient to encompass practices espoused in rewilding.

Early definitions of restoration describe the practice as “the process of repairing damage caused by humans to the diversity and dynamics of indigenous ecosystems” (Jackson et al., 1995). Although at the time of this definition, restoration science was still developing, it was clear that it had established itself under the broad banner of repairing damaged ecosystems. … More recently, restoration has been defined as “any activity whose aim it is to ultimately achieve ecosystem recovery, insofar as possible and relative to an appropriate local native model (termed here a reference ecosystem), regardless of the period of time required to achieve the recovery outcome” (McDonald et al., 2016) [Hayward 2019: 257].

The term rewilding, which has evolved over time, “was arguably conceived to promote the original authors’ view of conservation via cores [habitats], corridors, and carnivores” [Hayward 2019: 256]. In this early context,

‘rewilding’ referred to conservation and management interventions that focused on reintroducing keystone predators and ensuring that they had sufficient interconnected space to live. The authors emphasized within their original work that rewilding was “one essential element in most efforts to restore fully functioning ecosystems” (Soulé and Noss, 1998). As such, it is clear that rewilding was originally aimed to be a term that referred to one component of ecological restoration [Hayward 2019: 256].

Since then, rewilding has come to refer to practices involving “translocating substitute species to fill vacant ecological niches left by extinct species” [Hayward 2019: 257] or reintroducing locally extinct species, or simply allowing natural succession to occur on abandoned land. Given multiple definitions, all of which relate to the idea of restoration, the term rewilding is seen here as superfluous and confusing.

Given the lack of clear differences between rewilding and restoration in both definition and practice, we see little need for these competing terms within scientific discourse [Hayward 2019: 257].

However, the authors suggest two positive contributions from the rewilding discourse. Because of its overall focus on large fauna, rewilding has captured public imagination and interest in conservation, while also helping to shift a potential vegetation bias among restoration practitioners/scientists toward equal emphasis on the ecosystem role of animals.

Therefore, rather than adopting a new term with copious definitions that lack clarity, this debate can be used as an opportunity to adaptively improve current restoration practice by incorporating a more equal focus between flora and fauna [Hayward 2019: 258].

Because of its overall focus on large fauna, rewilding has captured public imagination and interest in conservation, while also helping to shift a potential vegetation bias among restoration practitioners/scientists toward equal emphasis on the ecosystem role of animals.

Intact forests in the United States: proforestation mitigates climate change and serves the greatest good, Moomaw 2019

The concept of “proforestation” presented here means letting existing forests continue to grow and reach their full ecological potential. Due to intensive management practices, most existing forests sequester carbon at only half (or less) of their potential rate. In addition to storing (embodying) more carbon than their smaller counterparts, large trees also sequester carbon at a faster rate. For example, “Each year a single tree that is 100 cm in diameter adds the equivalent biomass of an entire 10-20 cm diameter tree, further underscoring the role of large trees” [Moomaw 2019: 4]. Imagine, reader, that every year you planted a whole new medium-sized tree – that’s essentially what large trees are doing.

“Each year a single tree that is 100 cm in diameter adds the equivalent biomass of an entire 10-20 cm diameter tree, further underscoring the role of large trees” [Moomaw 2019: 4].

Much of Maine’s forests have been harvested continuously for 200 years and have a carbon density less than one-third of the forests of Southern Vermont and New Hampshire, Northwestern Connecticut and Western Massachusetts – a region that has not been significantly harvested over the past 75-150 years. …

Ecosystem services accrue as forests age for centuries. Far from plateauing in terms of carbon sequestration (or added wood) at a relatively young age as was long believed, older forests (e.g., >200 years of age without intervention) contain a variety of habitats, typically continue to sequester additional carbon for many decades or even centuries, and sequester significantly more carbon than younger and managed stands [Moomaw 2019: 5].

Because existing forests are already sequestering carbon, and will continue at an increasing rate as tree size grows, the author argues that proforestation is a more effective immediate solution than either reforestation (planting new trees where they had been cleared for agriculture, etc.) or afforestation (planting trees in new places), though these other two approaches are important for longer term ecosystem function. Moomaw et al. argue that the urgency of removing CO2 makes it imperative to keep existing forests growing.

Globally, existing forests only store approximately half of their potential due to past and present management, and many existing forests are capable of immediate and even more extensive growth for many decades. During the timeframe while seedlings planted for afforestation and reforestation are growing (yet will never achieve the carbon density of an intact forest), proforestation is a safe, highly effective, immediate natural solution that does not rely on uncertain discounted future benefits inherent in other options [Moomaw 2019: 7].

Furthermore, existing, older forests are critical habitats for threatened wildlife, even small intact woods.

Forest bird guilds also benefit from small intact forests in urban landscapes relative to unprotected matrix forests. Several bird species in the U.S. that are globally threatened – including the wood thrush, cerulean warbler, marbled murrelet, and spotted owl are, in part, dependent on intact, older forests with large trees [Moomaw 2019: 5].

In sum, proforestation provides the most effective solution to dual global crises – climate change and biodiversity loss. It is the only practical, rapid, economical, and effective means for atmospheric CDR [carbon dioxide removal] among the multiple options that have been proposed because it removes more atmospheric carbon dioxide in the immediate future and continues to sequester it long-term. Proforestation will increase the diversity of many groups of organisms and provide numerous additional and important ecosystem services. While multiple strategies will be needed to address global environmental crises, proforestation is a very low-cost option for increasing carbon sequestration that does not require additional land beyond what is already forested and provides new forest related jobs and opportunities along with a wide array of quantifiable ecosystem services, including human health [Moomaw 2019: 8].

Plant diversity enhances the reclamation of degraded lands by stimulating plant-soil feedbacks, Jia et al. 2020

This study tested biodiversity effects on ecosystem function in the process of reviving severely degraded and contaminated land, and found that “increasing plant diversity greatly enhanced the reclamation of these lands” [Jia 2020: 1].  

Prior to implementing the reclamation experiment, the degraded mine wasteland investigated in this study was heavily impacted by past mining activities and was devoid of vegetation for more than a decade and the soil lacked structure, contained high levels of toxic metals and low levels of nutrients. … our results showed that higher plant species richness enhanced land reclamation across all standard measures of reclamation success and specifically resulted in higher vegetation coverage, biomass yield and stability for all 3 years [of the experiment] [Jia 2020: 6].

Furthermore, higher biodiversity plots had higher levels of organic carbon in the soil, higher soil microorganism abundance, lower fungal pathogens, and lower heavy metal concentrations in plant tissue.

The most striking impact of plant diversity on soil was on the microbial communities. Both soil fungal and bacterial OTUs [operational taxonomic units^[8]] increased significantly with plant species richness. More importantly, we found that higher plant species richness significantly increased the relative abundance of soil cellulolytic bacteria that degrade cellulose and are thus essential components of nutrient cycling [Jia 2020: 7].

High ecosystem service delivery potential of small woodlands in agricultural landscapes, Valdes 2020

This article assesses the ecological value of small woodlands relative to larger ones. The authors conclude that:

…smaller woodlands potentially deliver multiple services at higher performance levels on a per area basis than larger woodlands of a similar age, even if the larger woodlands harbor a higher biodiversity [Valdes 2020: 12].

Because of their high edge-to-core ratio, smaller woodlots get more sunlight and more nutrient input from surrounding farmland, resulting in denser vegetation cover and higher biomass production at edges.

This altered functioning in turn increases the delivery potential of some services, such as game production potential, due to an increased quantity of food available for game, and topsoil carbon storage, due to the faster incorporation of organic matter in the soil. Tick-borne disease risk is, however, lower, likely due to decreased larval densities in the unfavorable (e.g. hotter and drier) microclimatic conditions at the edge [Valdes 2020: 12].

While smaller woodlands were more apt to deliver “multiple services at higher levels of performance per area than larger woodlands of a similar age,” the greater biodiversity of larger woodlands increased certain individual ecosystem services.

The supply potential of several individual ecosystem services indirectly increased in larger and more ancient woodlands because it was dependent on higher levels of biodiversity. For example, abundance of usable plants and game production potential might have increased due to a positive correlation with vascular plant diversity, while pest control potential probably increased due to bottom-up effects through the trophic chain. On the contrary, tick-borne disease risk, topsoil carbon storage and stemwood volume were unrelated to multidiversity, probably because they depended on particular environmental conditions or on the presence and abundance of specific species rather than on species richness per se.

Finally, it should be noted that we focused on the service delivery potential on a per area basis and that the total amount of services provided by large patches might still be larger than that of small patches. Our findings should therefore not be interpreted as a trade-off between large, biodiverse patches versus small patches that have a higher potential to deliver services, but rather as an observation that small woodlands in agricultural landscapes have the potential to deliver a high flow of services relative to their size [Valdes 2020: 12].

Effectiveness of the Miyawaki method in Mediterranean forest restoration programs, Shirone, Salis & Vessela 2011

This study tested the Miyawaki method of rapid natural forest regeneration (which has been shown to work in Japan and elsewhere) in the arid Mediterranean. In this area, millennia of human civilization have resulted in degraded soils and reduced and changed forest cover, traditional reforestation efforts have often failed, and desertification is a looming threat. The Miyawaki method speeds up the process of ecological succession by densely planting a multilayer forest made up of a wide diversity of indigenous species.

In a natural forest cycle, as Clements (1916) described, annual plants on barren land are succeeded by perennial grass, sun-tolerant shrubs, light-demanding, fast-growing trees, and finally natural forests; each step may require decades, and the climax vegetation could be formed after two centuries or more. Currently, most forest reforestation programs adopt a scheme of planting one or more early successional species; after successful establishment, they are gradually replaced by intermediate species (either naturally or by planting), until late successional species arise. This pattern tries to simulate natural processes of ecological succession, from pioneer species to climax vegetation. However, it requires several silvicultural practices and normally takes a long time [Shirone 2011: 82].

In the Miyawaki method, by contrast, one plants all at once the many plant species normally present in a native forest community, thus bypassing the earliest stages of ecological succession. Other tree-planting methods favor fast-growing non-native tree species, while omitting understory species – in other words, creating a simple plantation rather than a forest community that functions ecologically and can evolve and sustain itself.

Multilayer forests, and natural biocoenosis [ecological community] is possible, and well-developed ecosystems can be quickly established because of the simultaneous use of intermediate and late successional species in plantations. The Miyawaki method involves surveying the potential natural vegetation of the area to be reforested and recovering topsoil to a depth of 20– 30 cm by mixing the soil and a compost from organic materials, such as fallen leaves, mowed grass, etc. In this way, the time of the natural process of soil evolution, established by the vegetational succession itself, is reduced [Shirone 2011: 82].

The authors of this study found that compared to traditional reforestation, there was “a more rapid development of trees on the Miyawaki plots, in particular, early-successional species [especially maritime pine]. The benefits over previous methods are remarkable and comparable with those obtained by Miyawaki in Asia and South America.” The Miyawaki method favoring denser plantings works even in arid climates, in spite of traditional views favoring sparse plantings in arid places, although the optimal density for the Mediterranean still needs testing, according to the authors.

In fact, low plant density has been traditionally retained as appropriate in arid and semiarid environments in order to avoid competition for water resources between plants, but it is now evident that cooperative processes, e.g., mutual shading, prevail over competitive processes. High plant density also reduces the impact of acorn predators, thus encouraging oak regeneration, i.e., the main late-successional forest species in Mediterranean environments. In addition, excellent plant stock remains fundamental for planting success in harsh environments [Shirone 2011: 91].

When is a forest a forest? Forest concepts and definitions in the era of forest and landscape restoration, Chazdon et al. 2016

This article analyzes the policy context for forest ecosystem restoration, arguing that it is heavily shaped by the way we define a forest. The use of a forest definition lacking ecological considerations severely undermines conservation and restoration initiatives.  

We live in an era of unprecedented environmental change, motivating equally unprecedented global actions to protect and restore forest ecosystems. These efforts could fail to achieve their ambitious goals if they are not informed by clear and appropriate concepts and definitions of forests [Chazdon 2016: 1].

There are multiple definitions of a forest. Early European and internationally adopted definitions tended to define forests according to their usage for timber. FAO’s 1948 definition created for assessing wood harvesting potential of the world’s forests is still in use today. Yet new definitions have since been created that emphasize conservation, carbon sequestration and biodiversity values of forests.

However, national and global forest assessments tend to use narrow technical definitions that ignore ecological values of forested land.

In many cases, forest assessments do not distinguish between land covered by natural and planted forests. Thus, if natural forests are cleared and replaced with plantations, no net loss of forest cover is reported [Chazdon 2016: 6].

In other words, areas that should not be considered forest in ecological terms are counted as forest – an obfuscation with disastrous environmental outcomes. Similarly, ecologically important yet small patches of trees that are not counted in forest inventories and lack legal protection are at risk of being lost.

Areas classified as ‘‘non-forests’’ are as important to forest definitions as are forests. More than 43 % of agricultural land globally is in agroforestry systems with 10 % tree cover. In Rwanda and Brazil, forest inventories using a 0.5-ha threshold ignore substantial areas of small forest fragments, agroforests, and woodlots, leading to underestimates of actual tree cover. Small patches of trees and even isolated remnant trees can hold high ecological and conservation value, and can play an important role in enhancing landscape connectivity, local biodiversity, and local livelihoods [Chazdon 2016: 7].

Information from participatory local monitoring and remote sensing technology that distinguishes “among successional stages of forests, selectively logged forests, and single-species plantations” [Chazdon 2016: 10] is needed.

Access to this information will allow countries and international agencies to track changes in natural forest cover, and to monitor processes of restoration, rehabilitation, and afforestation within a landscape context and, consequently, make informed policy decisions. We are on the frontier of developing new ways of monitoring and assessing land cover that will provide robust indicators of the quality and origins of tree cover and enable new ways of viewing and defining forests and reforests. To see beyond the overly simplified categories of forest loss, forest degradation, and forest gain, we need to develop and apply more adapted and nuanced definitions that will deepen our understanding of the drivers and outcomes of land-use change and forest dynamics within landscapes [Chazdon 2016: 10].

Increasing agricultural production to feed >11 billion people by 2100 raises several challenges for effectively managing infectious disease. Of many factors examined in this article linking agricultural expansion to infectious disease, one is conversion of natural habitat to cropland or rangeland. Land conversion increases contact between wild animals, livestock and humans.

As natural ecosystems are converted to crop land or range land, interactions among humans, and domesticated and wild animals, could increase. … These interactions are crucial because 77% of livestock pathogens are capable of infecting multiple host species, including wildlife and humans, and based on published estimates from the 2000s, over half of all recognized human pathogens are currently or originally zoonotic, as are 60–76% of recent emerging infectious disease events [Rohr 2019: 451].

“As natural ecosystems are converted to crop land or range land, interactions among humans, and domesticated and wild animals, could increase” [Rohr 2019: 451].

Land conversion pushes humans and livestock up against wilderness areas, increasing contact between species with previously little to no contact. The jumping of a pathogen to a new host species is called “spillover.”

Spillover appears to be a function of the frequency, duration and intimacy of interactions between a reservoir and novel host population. For example, influenza is believed to have jumped from horses to humans soon after domesticating horses and then made additional jumps to humans from other domesticated animals, such as poultry and swine [Rohr 2019: 451].

Furthermore, agricultural intensification tends to involve greater concentrations of a single variety of a single species, increasing the risk that any new disease will spread quickly in the population.

A central tenet of epidemiology is that the incidence of many infectious diseases should increase proportionally with host density because of increased contact rates and thus transmission among hosts. Hence, increasing human and livestock densities could cause increases in infectious diseases unless investments in disease prevention are sufficient to prevent these increases [Rohr 2019: 451].

Industrial-scale confined livestock production is

vulnerable to devastating losses of animals to disease. For instance, in just the last 25 years, an influenza A virus (H5N1) and a foot-and-mouth outbreak led to the destruction of more than 1.2 million chickens and 6 million livestock in China and Great Britain, respectively, and a ‘mad cow disease’ epizootic led to the slaughter of 11 million cattle worldwide [Rohr 2019: 449].

Increased agricultural production tends to be accompanied by new irrigation infrastructure and increased pesticide, fertilizer and antibiotic use, all of which increase infectious disease risk. Dams (often created for irrigation schemes) increase risk of mosquito-borne disease. Antibiotic overuse for livestock fosters resistance among pathogens that can also infect humans. Greater pesticide use leads to resistance among disease vectors such as mosquitoes to insecticides, while also weakening immune systems among exposed humans and wildlife hosts, increasing infection rates/severity. Nutrient enrichment caused by fertilizer can also contribute to the spread of infectious disease, for example, through mosquitos or snail vectors.

Finally, the urbanization and globalization associated with agricultural intensification/expansion elongates food supply chains, which increases movement of people and goods over borders, spreading food-born illness, flu and other infections.

In short,

These analyses revealed that agricultural drivers were associated with 25% of all diseases and nearly 50% of zoonotic diseases that emerged in humans since 1940. These values are even higher if we include the use of antimicrobial agents as an agricultural driver of human disease emergence, given that agricultural uses of antibiotics outpace medical uses in the developed world nearly nine to one [Rohr 2019: 451].

The authors recommend numerous measures for improving agricultural production while limiting infectious disease, including reducing antibiotic use for livestock, conserving biodiversity, improving and diversifying livestock and crop genetic material, investing in urban agriculture, social investments, and inter-disciplinary research and collaboration.

This article introduces the concept of One Health, a public health framework adopted by the Centers for Disease Control in 2009, which recognizes the interdependence of humans, animals and our shared environment. The concept has gained traction as a way to address health problems arising from global environmental change.

Climate change, loss of biodiversity, habitat fragmentation and pollution, and subsequent degradation of natural environments threaten the range of ecosystem services that support all life on this planet [Sleeman 2019: 91].

…

It was the challenge of responding to these complex [environmental] problems that led to the emergence of the concept of One Health, which is defined by the Centers for Disease Control and Prevention (CDC) as the collaborative effort of multiple disciplines and sectors – working locally, nationally, regionally and globally – with the goal of achieving optimal health outcomes, recognizing the interconnection among people, animals, plants and our shared environment. This definition acknowledges that human, domestic animal and wildlife health are interconnected within the context of ecosystem/environmental health and provides a useful conceptual framework for the development of solutions to global health and environmental challenges. Given this interconnection, it follows that actions aimed primarily at improving the health of one part of the human-animal-environmental triad may have unanticipated consequences for the system as a whole if the harms they may cause to the other components are not considered. However, previous authors have noted that, despite the acknowledged interdependencies, few public or livestock health interventions include a consideration of biodiversity conservation or ecosystem/environmental health. Instead, health-promoting interventions focus largely on single-sector outcomes and, thus, may miss the opportunity to concurrently optimize outcomes in the other two sectors [Sleeman 2019: 92].

The authors suggest that despite its potential, the One Health approach does not as yet fully integrate wildlife and environmental health, instead favoring human health. Yet failure to optimize the health of all three realms can lead to unexpected and outcomes, ironically increasing risk to humans in some cases. Therefore, the authors propose the clarification of One Health values and goals, and integration of a systems approach and a harm reduction perspective into the One Health framework.

Systems biology provides methods to understand how interactions among [interrelated and interdependent] parts [livestock, humans and wildlife, for example] give rise to the function and behavior of that system [Sleeman 2019: 96].

A harm reduction perspective recognizes that solutions to complex problems require a broad societal response and that elimination of risk is not feasible for most issues. Consequently, this perspective promotes collaborative, multisectoral approaches whereby reducing harm, despite uncertainty regarding the outcome, is valued over inaction spurred by a desire for a perfect solution [Sleeman 2019: 94].

Habitat loss reduces biodiversity, which leads to infectious disease emergence. The way a habitat is fragmented (how many patches it is divided into, how those patches are shaped, and what the distance is between them) further affects the extent of disease emergence. Both the number of divisions of habitat into smaller patches and the irregularity of patch shapes tend to increase habitat perimeter, which in turn increases contact between disease agents and humans.

The hazard is greatest in places with greater pre-existing biodiversity, where there is a greater diversity of microbial pathogens and associated hosts. There is a double risk of developing wilderness areas in these places because there are more pathogens to begin with, and the resulting biodiversity loss tends to amplify disease transmission.

Human encroachment into species-rich habitats may simultaneously decrease biodiversity and increase exposure of people to novel microbes [Wilkinson 2018: 1].

Ebola virus disease outbreaks in West and Central Africa have been linked to spillover from potential disease reservoirs such as bats, apes, and duikers (an antelope-like animal). Spillover has been thought to be related to population density, vegetation cover, and human activities such as hunting, poaching, and bushmeat consumption. In this study, forest data from satellites coupled with disease outbreak records identify a nexus between forest fragmentation and Ebola.

The researchers identified 11 sites of the first human infection of Ebola from a wild species having occurred since 2004. Changes in forest cover between the year 2000 (baseline year) and the years of first infection for each of these outbreaks were determined using high-resolution satellite data on tree cover. All 11 centers of infection were found to be located in forested areas where the rate of forest fragmentation was greater than the regional average. Similarly, forest fragmentation decreased with increasing distance from the centers of infection.

All 11 centers of infection were found to be located in forested areas where the rate of forest fragmentation was greater than the regional average.

The centers of first infection … tend to occur in areas where on the outbreak year the average degree of forest fragmentation (e.g., within a 25 km, 50 km or 100 km distance from the infection center) was significantly higher than in the rest of the region [Rulli 2017: 2].

Furthermore, eight of the 11 centers of infection were located in fragmentation “hotspots,” meaning within a cluster of highly fragmented forest areas.

Bats are the commonly accepted host to filoviruses such as Ebola and tend to increase in population in fragmented habitats. The geographic distribution of potential bat hosts was consistent with the distribution of the zoonotic niche of Ebola. A decline in the population of insectivorous bats and an increase in the frugivorous (fruit-eating) bat species as a result of forest fragmentation was observed. Reshaping forest boundaries, habitat disruption, and biodiversity loss may enhance the likelihood of zoonotic infection by increasing the abundance of a particular species and thus the prevalence of that species’ pathogens.

The fact that spillover tends to occur in hotspots of forest fragmentation rather than in clearcut areas suggests that chances of human interactions with host wildlife are higher in areas where human encroachment leaves forest fragments that provide habitat for reservoir species [Rulli 2017: 5].

Pressure on land and its products is increasingly pushing people into forested areas. Given the danger of zoonotic disease outbreak, any evaluation of the costs, risk, and benefits of forest loss and fragmentation should include global health considerations.

This article very pragmatically addresses the question of whether biodiversity conservation could be an effective public health tool against infectious disease emergence and transmission.

Determining whether biodiversity conservation is an effective public health strategy requires answering four questions: (1) Is there a general, causal relationship between host biodiversity and disease risk? (2) If the link is causal and negative for most pathogens, does the increased diversity of pathogens with more diverse host communities result in net total increase or decrease in infectious disease burden? (3) Is the net benefit of biodiversity conservation greater than the net benefit of diversity-degrading processes (agricultural land-use change and wild animal harvesting)? (4) Are conservation interventions feasible and cost-effective compared to standard public health approaches (vaccines and treatments)?

Regarding the first question, experimental and observational research shows that increased biodiversity is associated with reduced disease burden.

Overall, the available data suggests that there is some correlational support in many zoonotic systems for a dilution effect, and that some species or species groups are more important than others in transmission [Kilpatrick 2017: 4].

The dilution effect hypothesis originated to explain the Lyme disease system. Greater numbers of hosts that are less “competent” (at spreading Lyme disease) – opossums, birds, raccoons and skunks – dilutes the transmission of Lyme bacteria to larval ticks by more competent hosts – white-footed mice, eastern chipmunks and shrews. Changes in community diversity affect, for example, host-vector encounter rates and host and vector abundances.

However,

much more research is needed to show that observed correlations are causal and to identify the mechanisms by which diversity is influencing disease risk [Kilpatrick 2017: 4].

The possibility of confounding factors in observational field studies is high because the same disturbances that change host diversity alters other aspects of transmission as well. For example, an ecosystem disturbance may, in addition to decreasing host diversity, also increase vector abundance, making it difficult to discern the proximate cause of increased disease rates. The authors note that the dilution effect may well cause decreased disease rates – more research is needed to determine this. But they caution that if the dilution effect turns out not to be the direct cause of decreased disease rates in any given pathogen system, then interventions to increase host diversity could be in vain with respect to that desired outcome.

Examples of potential conservation interventions to improve public health include preserving or restoring forest land, reintroducing top predators to control host populations, installing bat or owl boxes to increase predation of mosquitos (vectors) or rodents (hosts). Our still limited understanding of the mechanisms driving disease incidence patterns, however, make it difficult to predict outcomes for broad-scale land-use interventions, according to the authors. They argue instead that more targeted interventions aiming to reduce populations of key hosts in transmission may be more feasible public health tools than general land preservation. Even this, however, requires “deep understanding of both disease and population ecology.”

Further research to address this knowledge gap may be worth the investment, both for human wellbeing and for the planet. Exposure to nature has been shown to improve human mental and physical health and wellbeing, the authors note, regardless of biodiversity’s potential to reduce infectious disease. Furthermore,

If diverse communities can be shown to provide net benefits to human wellbeing, this could provide a powerful motivation for preserving Earth’s remaining biodiversity [Kilpatrick 2017: 7].

This status-quo-challenging editorial is written for the American Society of Clinical Pathology, a group seemingly unrelated to the Bio4Climate community. The authors suggest that medical training in pathology over-emphasizes oncology at the expense of an adequate coverage of infectious disease, even though “between 1940 and 2004, a total of 335 human infectious diseases ‘emerged,’ and 60% of these were zoonotic” [Granter 2016: 645]. Having explained biodiversity loss as a factor driving disease rates, the authors make a plea for diagnosticians to become aware of the human health implications of environmental destruction.

Knowledge and prowess with infectious diseases for diagnosticians must be incorporated back into training with a reimagined lens crafted from the information we have gained by studying our environment, its destruction, and the ultimate resulting human infections. As loss of habitat, habitat fragmentation, and consequent biodiversity loss continue unabated, tools and skills will need to be in the hands of all diagnosticians if we hope to minimize the effect of these infections as they continually emerge [Granter 2016: 645].

This paper provides a particularly clear explanation of how biodiversity loss increases human infection risk.

The relationship between loss of biodiversity and human disease was first illustrated by Lyme disease. Its cause, the Borrelia burgdorferi bacterium, has the opportunity to encounter numerous vertebrate hosts – in one study estimated to be at least 125 species – in a diverse and healthy ecosystem. The potential hosts vary tremendously in their ability to harbor and transmit the bacteria, that is, their “reservoir competence.” Studies estimate the white-footed mouse infects more than 90% of ticks that complete their blood meal. While a few other hosts, such as eastern chipmunks and short-tailed shrews, are moderately competent, most tick hosts are marginally competent or dead-end hosts that are highly unlikely to transmit the infection. Since the white-footed mouse tends to thrive in impoverished ecosystems lacking biodiversity, infected ticks and, consequently, risk of human infection show a strong negative relationship with biodiversity. Because a diverse ecosystem with a range of vertebrate hosts – including many incompetent and dead-end hosts – “dilutes” the representation of the white-footed mouse and reduces human infection risk, this phenomenon has been termed the dilution effect [Granter 2016: 644].

“Because a diverse ecosystem with a range of vertebrate hosts – including many incompetent and dead-end hosts – “dilutes” the representation of the white-footed mouse and reduces human infection risk, this phenomenon has been termed the dilution effect” [Granter 2016: 644].

Human activities are dramatically reducing biodiversity, and the frequency and severity of infectious disease outbreaks in human, wildlife, and domesticated species are increasing. These concurrent patterns have prompted suggestions that biodiversity and the spread of diseases may be causally linked. For example, the dilution effect hypothesis proposes that diverse host communities inhibit the abundance of parasites through several mechanisms, such as regulating populations of susceptible hosts or interfering with the transmission process. Thus, diverse communities may inhibit the proliferation of parasites, thereby promoting the stability of ecological communities and ecosystem services (e.g., nutrient cycling, carbon sequestration, and natural product production) [Civitello 2015: 8667].

This meta-analysis concludes that as a general rule across ecosystems, biodiversity inhibits parasitism. Previous studies had focused on particular host-parasite systems, and found that greater host diversity dilutes, or limits, the spread of disease. “Consequently, anthropogenic declines in biodiversity could increase human and wildlife diseases and decrease crop and forest production” [Civitello 2015: 8667].

This paper contextualizes reduced transmission of infectious disease as one of the many ecosystem services provided by biodiversity. Changes in biodiversity affect infectious disease transmission by changing the abundance of the host and/or vector; the loss of non-host species may increase the density of host species, increasing the encounter rates between pathogen and host.

Often, the species that remain when biodiversity is lost are those which are better pathogen hosts, while the lost species tend to be more resistant to infectious disease.

In several case studies, the species most likely to be lost from ecological communities as diversity declines are those most likely to reduce pathogen transmission [Keesing 2010: 648].

For example, the white-footed mouse, which are high-quality hosts both for the bacteria causing Lyme Disease and for the tick vectors, are abundant in both biodiverse systems and impoverished systems, while opossums, a poorer host for the Lyme bacterium that also kill/eat most ticks attempting to feed on them, do poorly in lower-biodiversity conditions.

Therefore, as biodiversity is lost, the host with a strong buffering effect – the opossum – disappears, while the host with a strong amplifying effect – the mouse – remains [Keesing 2010: 650].

There may be a causal link between a species’ susceptibility to biodiversity loss and its quality as a disease host. Among vertebrates,

resilience in the face of disturbances that cause biodiversity loss, such as habitat destruction and fragmentation, is facilitated by life history features such as high reproductive output and intrinsic rates of increase. Vertebrates with these features tend to invest minimally in some aspects of adaptive immunity; we hypothesize that this may make them more competent hosts for pathogens and vectors [Keesing 2010: 650].

Biodiversity also affects the emergence of infectious disease, such as the evolution of a new strain of pathogen in the same host (due to antibiotic resistance, for example), and the spillover to a new host species. Pathogen establishment in humans from other animal hosts is related to mammal species richness (a larger source pool), and land-use change (such as deforestation), which increases contact between humans and pathogen hosts. The pathogen then becomes an epidemic due to the new host species’ density (domesticated animals and humans).

The authors recommend preserving biodiversity by protecting natural habitat, while also preserving microbial diversity within organisms by limiting the use of antimicrobial agents. A diverse microbiome within an organism serves as a buffer against pathogens.

West Nile Virus is an infectious disease that arrived in New York City in 1999, and subsequently spread across the country to the west coast. It is transmitted to humans from passerine (perching) birds via mosquito vectors. This study tested the dilution effect hypothesis, which posits that greater diversity (of birds in this case) reduces the concentration of species that are the primary disease reservoirs (American robin, American crow, blue jay, western scrub jay, common grackle, house finch, and house sparrow), thus reducing vector contact with infected individuals, and ultimately transmission to humans. The study analyzed the incidence of human infection during 2003-2004, and found that biodiversity was indeed associated with reduced WNV infection rates among humans.

For all 3 years, the county-level human incidence of WNV disease was strongly, and significantly, negatively correlated with bird diversity within that county [Ostfeld 2009: 41].

Similar results are reported for studies of the dilution effect of biodiversity on Lyme disease risk. Furthermore, having collected data on the competence of various mammalian hosts to infect ticks with Lyme disease, as well as each host species’ average tick burden, the authors state that “we can project the number of ticks that will feed on them and the proportion of those ticks that will become infected” [Ostfeld 2009: 42].

We conclude from these studies that high vertebrate diversity is negatively correlated with human risk of exposure to Lyme disease. Furthermore, knowledge of the species composition of these communities, beyond simple measures of species richness or evenness, strongly enhances our ability to predict risk [Ostfeld 2009: 42].

In summary,

Evidence for a protective dilution effect of high diversity has been obtained for numerous infectious diseases of humans, wildlife, and plants. The weight of evidence suggests that protection against exposure to infectious diseases should be added to the list of utilitarian functions of biodiversity [Ostfeld 2009: 42].

“Evidence for a protective dilution effect of high diversity has been obtained for numerous infectious diseases of humans, wildlife, and plants. The weight of evidence suggests that protection against exposure to infectious diseases should be added to the list of utilitarian functions of biodiversity [Ostfeld 2009: 42].

This review article describes the potential mechanisms by which biodiversity affects disease risk. The authors explore the mechanisms at play in simple systems with only host and pathogen, as well as in more complex systems that include a vector species and/or multiple hosts. The reduction of disease risk by increased diversity is called the “dilution effect.” The opposite, termed the “amplification effect,” is when disease risk increases. “Both models and literature reviews suggest that high host diversity is more likely to decrease than increase disease risk” [Keesing 2006: 485].

The mechanisms by which diversity affects disease risk are as follows:

Encounter reduction: An additional species (such as a predator) suppresses the movement of host species or vector species, thereby reducing contact between susceptible hosts and infected hosts or vectors. (Alternatively, if the presence of a different species causes host species to clump together more among their own kind, then transmission could increase in an encounter augmentation.)

Transmission reduction: An additional species in a system (such as a prey) reduces host stress, boosting immune system response and lowering pathogen load. An added species could also modify host behavior in a way that reduces the duration of their encounters and thus limits transmission.

Vector or susceptible host [population] regulation: The addition of any species that reduces birth rates or increases death rates, limiting overall population, among hosts susceptible to the pathogen or among pathogen vectors. Transmission rates may be reduced, for example, with the addition of host species predators or with the addition of species that attract vectors (ticks, for instance), but then groom themselves in a way that kills many vector individuals.

Infected host mortality: An added species outcompetes infected hosts for resources or targets infected hosts for predation.

Recovery augmentation: The addition of a prey species as an added resource for host species could, for example, increase full recovery rates of host species, creating a dilution effect, or, by contrast, increase the longevity of sick hosts in an amplification effect.

When there are many hosts for a particular pathogen, some species transmit the disease more readily than others. Often, the species that most effectively spread the disease (the most competent reservoirs) are present in species-poor, degraded ecosystems, meaning that any additional host species is likely to dilute the presences of the more contagious species.

One key question in multi-host disease systems is whether the most competent reservoir is present in species-poor communities. If so, species added to these communities have, by definition, lower (if any) reservoir competence and thus have the potential to decrease disease risk. If the most competent reservoir is not present in species-poor communities, by contrast, then an increase in diversity could include the addition of the most competent reservoir itself, which is likely to result in an amplification of disease risk. Ostfeld & Keesing (2000b) considered evidence that the most competent reservoir for a variety of vector-borne zoonoses was typically present in species-poor communities [Keesing 2006: 495].

Humans are not the only species to suffer global pandemics. Planetwide, fungal disease ravages amphibians, just as honeybees are ravaged by varroasis. A herpes virus caused mass mortality of pilchard fish off the coast of Australia and New Zealand in 1995, and seals from Antarctica to the Caspian Sea have contracted canine distemper viruses, for which domestic dogs are also hosts.

The authors point to multiple anthropogenic environmental changes as the underlying causes of disease emergence among wildlife, livestock and humans.

Emerging infectious diseases (EIDs) are defined as diseases that have recently increased in incidence or geographic range, recently moved into new host populations, recently been discovered or are caused by newly-evolved pathogens [Daszak 2001: 103].

Two major known causes of disease emergence in wildlife are (1) “spillover” of livestock disease into wild populations; and (2) pathogen pollution, which stems from the global transport of domestic and wild animals, and contaminated products and materials. In addition, habitat destruction and fragmentation, and toxic pollution, are likely to contribute to disease emergence, although these factors hadn’t been as well studied (at least at the time of the writing in 2001).

The authors conclude with the following observation:

We have described a group of wildlife diseases that can be classified as emerging in the same way as human EIDs. These represent a link in the chain of emergence of human and domestic animal diseases, with pathogens, habitats and environmental changes shared between these populations. Parallels between causes of emergence across these groups of diseases demonstrates an important concept: that human environmental change may be the most significant driver of wildlife, domestic animal and human EIDs [Daszak 2001: 112].

Anthropogenic environmental change and the emergence of infectious diseases in wildlife, Daszak, Cunningham & Hyatt 2001

Humans are not the only species to suffer global pandemics. Planetwide, fungal disease ravages amphibians, just as honeybees are ravaged by varroasis. A herpes virus caused mass mortality of pilchard fish off the coast of Australia and New Zealand in 1995, and seals from Antarctica to the Caspian Sea have contracted canine distemper viruses, for which domestic dogs are also hosts.

The authors point to multiple anthropogenic environmental changes as the underlying causes of disease emergence among wildlife, livestock and humans.

Emerging infectious diseases (EIDs) are defined as diseases that have recently increased in incidence or geographic range, recently moved into new host populations, recently been discovered or are caused by newly-evolved pathogens [Daszak 2001: 103].

Two major known causes of disease emergence in wildlife are (1) “spillover” of livestock disease into wild populations; and (2) pathogen pollution, which stems from the global transport of domestic and wild animals, and contaminated products and materials. In addition, habitat destruction and fragmentation, and toxic pollution, are likely to contribute to disease emergence, although these factors hadn’t been as well studied (at least at the time of the writing in 2001).

The authors conclude with the following observation:

We have described a group of wildlife diseases that can be classified as emerging in the same way as human EIDs. These represent a link in the chain of emergence of human and domestic animal diseases, with pathogens, habitats and environmental changes shared between these populations. Parallels between causes of emergence across these groups of diseases demonstrates an important concept: that human environmental change may be the most significant driver of wildlife, domestic animal and human EIDs [Daszak 2001: 112].

Effects of species diversity on disease risk, Keesing, Holt & Ostfeld 2006

This review article describes the potential mechanisms by which biodiversity affects disease risk. The authors explore the mechanisms at play in simple systems with only host and pathogen, as well as in more complex systems that include a vector species and/or multiple hosts. The reduction of disease risk by increased diversity is called the “dilution effect.” The opposite, termed the “amplification effect,” is when disease risk increases. “Both models and literature reviews suggest that high host diversity is more likely to decrease than increase disease risk” [Keesing 2006: 485].

The mechanisms by which diversity affects disease risk are as follows:

Encounter reduction: An additional species (such as a predator) suppresses the movement of host species or vector species, thereby reducing contact between susceptible hosts and infected hosts or vectors. (Alternatively, if the presence of a different species causes host species to clump together more among their own kind, then transmission could increase in an encounter augmentation.)

Transmission reduction: An additional species in a system (such as a prey) reduces host stress, boosting immune system response and lowering pathogen load. An added species could also modify host behavior in a way that reduces the duration of their encounters and thus limits transmission.

Vector or susceptible host [population] regulation: The addition of any species that reduces birth rates or increases death rates, limiting overall population, among hosts susceptible to the pathogen or among pathogen vectors. Transmission rates may be reduced, for example, with the addition of host species predators or with the addition of species that attract vectors (ticks, for instance), but then groom themselves in a way that kills many vector individuals.

Infected host mortality: An added species outcompetes infected hosts for resources or targets infected hosts for predation.

Recovery augmentation: The addition of a prey species as an added resource for host species could, for example, increase full recovery rates of host species, creating a dilution effect, or, by contrast, increase the longevity of sick hosts in an amplification effect.

When there are many hosts for a particular pathogen, some species transmit the disease more readily than others. Often, the species that most effectively spread the disease (the most competent reservoirs) are present in species-poor, degraded ecosystems, meaning that any additional host species is likely to dilute the presences of the more contagious species.

One key question in multi-host disease systems is whether the most competent reservoir is present in species-poor communities. If so, species added to these communities have, by definition, lower (if any) reservoir competence and thus have the potential to decrease disease risk. If the most competent reservoir is not present in species-poor communities, by contrast, then an increase in diversity could include the addition of the most competent reservoir itself, which is likely to result in an amplification of disease risk. Ostfeld & Keesing (2000b) considered evidence that the most competent reservoir for a variety of vector-borne zoonoses was typically present in species-poor communities [Keesing 2006: 495].

Biodiversity loss and the rise of zoonotic pathogens, Ostfeld 2009

West Nile Virus is an infectious disease that arrived in New York City in 1999, and subsequently spread across the country to the west coast. It is transmitted to humans from passerine (perching) birds via mosquito vectors. This study tested the dilution effect hypothesis, which posits that greater diversity (of birds in this case) reduces the concentration of species that are the primary disease reservoirs (American robin, American crow, blue jay, western scrub jay, common grackle, house finch, and house sparrow), thus reducing vector contact with infected individuals, and ultimately transmission to humans. The study analyzed the incidence of human infection during 2003-2004, and found that biodiversity was indeed associated with reduced WNV infection rates among humans.

For all 3 years, the county-level human incidence of WNV disease was strongly, and significantly, negatively correlated with bird diversity within that county [Ostfeld 2009: 41].

Similar results are reported for studies of the dilution effect of biodiversity on Lyme disease risk. Furthermore, having collected data on the competence of various mammalian hosts to infect ticks with Lyme disease, as well as each host species’ average tick burden, the authors state that “we can project the number of ticks that will feed on them and the proportion of those ticks that will become infected” [Ostfeld 2009: 42].

We conclude from these studies that high vertebrate diversity is negatively correlated with human risk of exposure to Lyme disease. Furthermore, knowledge of the species composition of these communities, beyond simple measures of species richness or evenness, strongly enhances our ability to predict risk [Ostfeld 2009: 42].

In summary,

Evidence for a protective dilution effect of high diversity has been obtained for numerous infectious diseases of humans, wildlife, and plants. The weight of evidence suggests that protection against exposure to infectious diseases should be added to the list of utilitarian functions of biodiversity [Ostfeld 2009: 42].

“Evidence for a protective dilution effect of high diversity has been obtained for numerous infectious diseases of humans, wildlife, and plants. The weight of evidence suggests that protection against exposure to infectious diseases should be added to the list of utilitarian functions of biodiversity [Ostfeld 2009: 42].

Impacts of biodiversity on the emergence and transmission of infectious diseases, Keesing et al. 2010

This paper contextualizes reduced transmission of infectious disease as one of the many ecosystem services provided by biodiversity. Changes in biodiversity affect infectious disease transmission by changing the abundance of the host and/or vector; the loss of non-host species may increase the density of host species, increasing the encounter rates between pathogen and host.

Often, the species that remain when biodiversity is lost are those which are better pathogen hosts, while the lost species tend to be more resistant to infectious disease.

In several case studies, the species most likely to be lost from ecological communities as diversity declines are those most likely to reduce pathogen transmission [Keesing 2010: 648].

For example, the white-footed mouse, which are high-quality hosts both for the bacteria causing Lyme Disease and for the tick vectors, are abundant in both biodiverse systems and impoverished systems, while opossums, a poorer host for the Lyme bacterium that also kill/eat most ticks attempting to feed on them, do poorly in lower-biodiversity conditions.

Therefore, as biodiversity is lost, the host with a strong buffering effect – the opossum – disappears, while the host with a strong amplifying effect – the mouse – remains [Keesing 2010: 650].

There may be a causal link between a species’ susceptibility to biodiversity loss and its quality as a disease host. Among vertebrates,

resilience in the face of disturbances that cause biodiversity loss, such as habitat destruction and fragmentation, is facilitated by life history features such as high reproductive output and intrinsic rates of increase. Vertebrates with these features tend to invest minimally in some aspects of adaptive immunity; we hypothesize that this may make them more competent hosts for pathogens and vectors [Keesing 2010: 650].

Biodiversity also affects the emergence of infectious disease, such as the evolution of a new strain of pathogen in the same host (due to antibiotic resistance, for example), and the spillover to a new host species. Pathogen establishment in humans from other animal hosts is related to mammal species richness (a larger source pool), and land-use change (such as deforestation), which increases contact between humans and pathogen hosts. The pathogen then becomes an epidemic due to the new host species’ density (domesticated animals and humans).

The authors recommend preserving biodiversity by protecting natural habitat, while also preserving microbial diversity within organisms by limiting the use of antimicrobial agents. A diverse microbiome within an organism serves as a buffer against pathogens.

Biodiversity inhibits parasites: Broad evidence for the dilution effect, Civitello et al. 2015

Human activities are dramatically reducing biodiversity, and the frequency and severity of infectious disease outbreaks in human, wildlife, and domesticated species are increasing. These concurrent patterns have prompted suggestions that biodiversity and the spread of diseases may be causally linked. For example, the dilution effect hypothesis proposes that diverse host communities inhibit the abundance of parasites through several mechanisms, such as regulating populations of susceptible hosts or interfering with the transmission process. Thus, diverse communities may inhibit the proliferation of parasites, thereby promoting the stability of ecological communities and ecosystem services (e.g., nutrient cycling, carbon sequestration, and natural product production) [Civitello 2015: 8667].

This meta-analysis concludes that as a general rule across ecosystems, biodiversity inhibits parasitism. Previous studies had focused on particular host-parasite systems, and found that greater host diversity dilutes, or limits, the spread of disease. “Consequently, anthropogenic declines in biodiversity could increase human and wildlife diseases and decrease crop and forest production” [Civitello 2015: 8667].

Where the Wild Things Aren’t: Loss of Biodiversity, Emerging Infectious Diseases, and Implications for Diagnosticians, Granter 2016

This status-quo-challenging editorial is written for the American Society of Clinical Pathology, a group seemingly unrelated to the Bio4Climate community. The authors suggest that medical training in pathology over-emphasizes oncology at the expense of an adequate coverage of infectious disease, even though “between 1940 and 2004, a total of 335 human infectious diseases ‘emerged,’ and 60% of these were zoonotic” [Granter 2016: 645]. Having explained biodiversity loss as a factor driving disease rates, the authors make a plea for diagnosticians to become aware of the human health implications of environmental destruction.

Knowledge and prowess with infectious diseases for diagnosticians must be incorporated back into training with a reimagined lens crafted from the information we have gained by studying our environment, its destruction, and the ultimate resulting human infections. As loss of habitat, habitat fragmentation, and consequent biodiversity loss continue unabated, tools and skills will need to be in the hands of all diagnosticians if we hope to minimize the effect of these infections as they continually emerge [Granter 2016: 645].

This paper provides a particularly clear explanation of how biodiversity loss increases human infection risk.

The relationship between loss of biodiversity and human disease was first illustrated by Lyme disease. Its cause, the Borrelia burgdorferi bacterium, has the opportunity to encounter numerous vertebrate hosts – in one study estimated to be at least 125 species – in a diverse and healthy ecosystem. The potential hosts vary tremendously in their ability to harbor and transmit the bacteria, that is, their “reservoir competence.” Studies estimate the white-footed mouse infects more than 90% of ticks that complete their blood meal. While a few other hosts, such as eastern chipmunks and short-tailed shrews, are moderately competent, most tick hosts are marginally competent or dead-end hosts that are highly unlikely to transmit the infection. Since the white-footed mouse tends to thrive in impoverished ecosystems lacking biodiversity, infected ticks and, consequently, risk of human infection show a strong negative relationship with biodiversity. Because a diverse ecosystem with a range of vertebrate hosts – including many incompetent and dead-end hosts – “dilutes” the representation of the white-footed mouse and reduces human infection risk, this phenomenon has been termed the dilution effect [Granter 2016: 644].

“Because a diverse ecosystem with a range of vertebrate hosts – including many incompetent and dead-end hosts – “dilutes” the representation of the white-footed mouse and reduces human infection risk, this phenomenon has been termed the dilution effect” [Granter 2016: 644].

Conservation of biodiversity as a strategy for improving human health and wellbeing, Kilpatrick et al. 2017

This article very pragmatically addresses the question of whether biodiversity conservation could be an effective public health tool against infectious disease emergence and transmission.

Determining whether biodiversity conservation is an effective public health strategy requires answering four questions: (1) Is there a general, causal relationship between host biodiversity and disease risk? (2) If the link is causal and negative for most pathogens, does the increased diversity of pathogens with more diverse host communities result in net total increase or decrease in infectious disease burden? (3) Is the net benefit of biodiversity conservation greater than the net benefit of diversity-degrading processes (agricultural land-use change and wild animal harvesting)? (4) Are conservation interventions feasible and cost-effective compared to standard public health approaches (vaccines and treatments)?

Regarding the first question, experimental and observational research shows that increased biodiversity is associated with reduced disease burden.

Overall, the available data suggests that there is some correlational support in many zoonotic systems for a dilution effect, and that some species or species groups are more important than others in transmission [Kilpatrick 2017: 4].

The dilution effect hypothesis originated to explain the Lyme disease system. Greater numbers of hosts that are less “competent” (at spreading Lyme disease) – opossums, birds, raccoons and skunks – dilutes the transmission of Lyme bacteria to larval ticks by more competent hosts – white-footed mice, eastern chipmunks and shrews. Changes in community diversity affect, for example, host-vector encounter rates and host and vector abundances.

However,

much more research is needed to show that observed correlations are causal and to identify the mechanisms by which diversity is influencing disease risk [Kilpatrick 2017: 4].

The possibility of confounding factors in observational field studies is high because the same disturbances that change host diversity alters other aspects of transmission as well. For example, an ecosystem disturbance may, in addition to decreasing host diversity, also increase vector abundance, making it difficult to discern the proximate cause of increased disease rates. The authors note that the dilution effect may well cause decreased disease rates – more research is needed to determine this. But they caution that if the dilution effect turns out not to be the direct cause of decreased disease rates in any given pathogen system, then interventions to increase host diversity could be in vain with respect to that desired outcome.

Examples of potential conservation interventions to improve public health include preserving or restoring forest land, reintroducing top predators to control host populations, installing bat or owl boxes to increase predation of mosquitos (vectors) or rodents (hosts). Our still limited understanding of the mechanisms driving disease incidence patterns, however, make it difficult to predict outcomes for broad-scale land-use interventions, according to the authors. They argue instead that more targeted interventions aiming to reduce populations of key hosts in transmission may be more feasible public health tools than general land preservation. Even this, however, requires “deep understanding of both disease and population ecology.”

Further research to address this knowledge gap may be worth the investment, both for human wellbeing and for the planet. Exposure to nature has been shown to improve human mental and physical health and wellbeing, the authors note, regardless of biodiversity’s potential to reduce infectious disease. Furthermore,

If diverse communities can be shown to provide net benefits to human wellbeing, this could provide a powerful motivation for preserving Earth’s remaining biodiversity [Kilpatrick 2017: 7].

The nexus between forest fragmentation in Africa and Ebola virus disease outbreaks, Rulli et al. 2017

Ebola virus disease outbreaks in West and Central Africa have been linked to spillover from potential disease reservoirs such as bats, apes, and duikers (an antelope-like animal). Spillover has been thought to be related to population density, vegetation cover, and human activities such as hunting, poaching, and bushmeat consumption. In this study, forest data from satellites coupled with disease outbreak records identify a nexus between forest fragmentation and Ebola.

The researchers identified 11 sites of the first human infection of Ebola from a wild species having occurred since 2004. Changes in forest cover between the year 2000 (baseline year) and the years of first infection for each of these outbreaks were determined using high-resolution satellite data on tree cover. All 11 centers of infection were found to be located in forested areas where the rate of forest fragmentation was greater than the regional average. Similarly, forest fragmentation decreased with increasing distance from the centers of infection.

All 11 centers of infection were found to be located in forested areas where the rate of forest fragmentation was greater than the regional average.

The centers of first infection … tend to occur in areas where on the outbreak year the average degree of forest fragmentation (e.g., within a 25 km, 50 km or 100 km distance from the infection center) was significantly higher than in the rest of the region [Rulli 2017: 2].

Furthermore, eight of the 11 centers of infection were located in fragmentation “hotspots,” meaning within a cluster of highly fragmented forest areas.

Bats are the commonly accepted host to filoviruses such as Ebola and tend to increase in population in fragmented habitats. The geographic distribution of potential bat hosts was consistent with the distribution of the zoonotic niche of Ebola. A decline in the population of insectivorous bats and an increase in the frugivorous (fruit-eating) bat species as a result of forest fragmentation was observed. Reshaping forest boundaries, habitat disruption, and biodiversity loss may enhance the likelihood of zoonotic infection by increasing the abundance of a particular species and thus the prevalence of that species’ pathogens.

The fact that spillover tends to occur in hotspots of forest fragmentation rather than in clearcut areas suggests that chances of human interactions with host wildlife are higher in areas where human encroachment leaves forest fragments that provide habitat for reservoir species [Rulli 2017: 5].

Pressure on land and its products is increasingly pushing people into forested areas. Given the danger of zoonotic disease outbreak, any evaluation of the costs, risk, and benefits of forest loss and fragmentation should include global health considerations.

Habitat fragmentation, biodiversity loss and the risk of novel infectious disease emergence, Wilkinson 2018

Habitat loss reduces biodiversity, which leads to infectious disease emergence. The way a habitat is fragmented (how many patches it is divided into, how those patches are shaped, and what the distance is between them) further affects the extent of disease emergence. Both the number of divisions of habitat into smaller patches and the irregularity of patch shapes tend to increase habitat perimeter, which in turn increases contact between disease agents and humans.

The hazard is greatest in places with greater pre-existing biodiversity, where there is a greater diversity of microbial pathogens and associated hosts. There is a double risk of developing wilderness areas in these places because there are more pathogens to begin with, and the resulting biodiversity loss tends to amplify disease transmission.

Human encroachment into species-rich habitats may simultaneously decrease biodiversity and increase exposure of people to novel microbes [Wilkinson 2018: 1].

Integration of wildlife and environmental health into a One Health approach, Sleeman et al. 2019

This article introduces the concept of One Health, a public health framework adopted by the Centers for Disease Control in 2009, which recognizes the interdependence of humans, animals and our shared environment. The concept has gained traction as a way to address health problems arising from global environmental change.

Climate change, loss of biodiversity, habitat fragmentation and pollution, and subsequent degradation of natural environments threaten the range of ecosystem services that support all life on this planet [Sleeman 2019: 91].

…

It was the challenge of responding to these complex [environmental] problems that led to the emergence of the concept of One Health, which is defined by the Centers for Disease Control and Prevention (CDC) as the collaborative effort of multiple disciplines and sectors – working locally, nationally, regionally and globally – with the goal of achieving optimal health outcomes, recognizing the interconnection among people, animals, plants and our shared environment. This definition acknowledges that human, domestic animal and wildlife health are interconnected within the context of ecosystem/environmental health and provides a useful conceptual framework for the development of solutions to global health and environmental challenges. Given this interconnection, it follows that actions aimed primarily at improving the health of one part of the human-animal-environmental triad may have unanticipated consequences for the system as a whole if the harms they may cause to the other components are not considered. However, previous authors have noted that, despite the acknowledged interdependencies, few public or livestock health interventions include a consideration of biodiversity conservation or ecosystem/environmental health. Instead, health-promoting interventions focus largely on single-sector outcomes and, thus, may miss the opportunity to concurrently optimize outcomes in the other two sectors [Sleeman 2019: 92].

The authors suggest that despite its potential, the One Health approach does not as yet fully integrate wildlife and environmental health, instead favoring human health. Yet failure to optimize the health of all three realms can lead to unexpected and outcomes, ironically increasing risk to humans in some cases. Therefore, the authors propose the clarification of One Health values and goals, and integration of a systems approach and a harm reduction perspective into the One Health framework.

Systems biology provides methods to understand how interactions among [interrelated and interdependent] parts [livestock, humans and wildlife, for example] give rise to the function and behavior of that system [Sleeman 2019: 96].

A harm reduction perspective recognizes that solutions to complex problems require a broad societal response and that elimination of risk is not feasible for most issues. Consequently, this perspective promotes collaborative, multisectoral approaches whereby reducing harm, despite uncertainty regarding the outcome, is valued over inaction spurred by a desire for a perfect solution [Sleeman 2019: 94].

Emerging human infectious diseases and the links to global food production, Rohr et al. 2019

Increasing agricultural production to feed >11 billion people by 2100 raises several challenges for effectively managing infectious disease. Of many factors examined in this article linking agricultural expansion to infectious disease, one is conversion of natural habitat to cropland or rangeland. Land conversion increases contact between wild animals, livestock and humans.

As natural ecosystems are converted to crop land or range land, interactions among humans, and domesticated and wild animals, could increase. … These interactions are crucial because 77% of livestock pathogens are capable of infecting multiple host species, including wildlife and humans, and based on published estimates from the 2000s, over half of all recognized human pathogens are currently or originally zoonotic, as are 60–76% of recent emerging infectious disease events [Rohr 2019: 451].

“As natural ecosystems are converted to crop land or range land, interactions among humans, and domesticated and wild animals, could increase” [Rohr 2019: 451].

Land conversion pushes humans and livestock up against wilderness areas, increasing contact between species with previously little to no contact. The jumping of a pathogen to a new host species is called “spillover.”

Spillover appears to be a function of the frequency, duration and intimacy of interactions between a reservoir and novel host population. For example, influenza is believed to have jumped from horses to humans soon after domesticating horses and then made additional jumps to humans from other domesticated animals, such as poultry and swine [Rohr 2019: 451].

Furthermore, agricultural intensification tends to involve greater concentrations of a single variety of a single species, increasing the risk that any new disease will spread quickly in the population.

A central tenet of epidemiology is that the incidence of many infectious diseases should increase proportionally with host density because of increased contact rates and thus transmission among hosts. Hence, increasing human and livestock densities could cause increases in infectious diseases unless investments in disease prevention are sufficient to prevent these increases [Rohr 2019: 451].

Industrial-scale confined livestock production is

vulnerable to devastating losses of animals to disease. For instance, in just the last 25 years, an influenza A virus (H5N1) and a foot-and-mouth outbreak led to the destruction of more than 1.2 million chickens and 6 million livestock in China and Great Britain, respectively, and a ‘mad cow disease’ epizootic led to the slaughter of 11 million cattle worldwide [Rohr 2019: 449].

Increased agricultural production tends to be accompanied by new irrigation infrastructure and increased pesticide, fertilizer and antibiotic use, all of which increase infectious disease risk. Dams (often created for irrigation schemes) increase risk of mosquito-borne disease. Antibiotic overuse for livestock fosters resistance among pathogens that can also infect humans. Greater pesticide use leads to resistance among disease vectors such as mosquitoes to insecticides, while also weakening immune systems among exposed humans and wildlife hosts, increasing infection rates/severity. Nutrient enrichment caused by fertilizer can also contribute to the spread of infectious disease, for example, through mosquitos or snail vectors.

Finally, the urbanization and globalization associated with agricultural intensification/expansion elongates food supply chains, which increases movement of people and goods over borders, spreading food-born illness, flu and other infections.

In short,

These analyses revealed that agricultural drivers were associated with 25% of all diseases and nearly 50% of zoonotic diseases that emerged in humans since 1940. These values are even higher if we include the use of antimicrobial agents as an agricultural driver of human disease emergence, given that agricultural uses of antibiotics outpace medical uses in the developed world nearly nine to one [Rohr 2019: 451].

The authors recommend numerous measures for improving agricultural production while limiting infectious disease, including reducing antibiotic use for livestock, conserving biodiversity, improving and diversifying livestock and crop genetic material, investing in urban agriculture, social investments, and inter-disciplinary research and collaboration.

The subject of infectious disease became both fascinating and uncomfortably relevant with the global breakout of Covid-19 in early 2020. Are bats to blame, hunting and selling of wild game or seafood markets? It turns out that the destruction of nature is the root problem, according to the UN environment chief and lead scientists for the Intergovernmental Panel on Biodiversity and Ecosystem Services (IPBES). “Covid-19 is nature sending us a message,” writes the UN environment chief and colleague [Dasgupta & Anderson 2020]. They continue:

In fact, it reads like an SOS signal for the human enterprise, bringing into sharp focus the need to live within the planet’s means. The environmental, health and economic consequences of failing to do so are disastrous [Dasgupta & Anderson 2020].

“Covid-19 is nature sending us a message. In fact, it reads like an SOS signal for the human enterprise, bringing into sharp focus the need to live within the planet’s means. The environmental, health and economic consequences of failing to do so are disastrous.” – Sir Partha Dasgupta & Ingar Anderson

An April 2020 IPBES article [Settele 2020] echoes this alert:

As with the climate and biodiversity crises, recent pandemics are a direct consequence of human activity – particularly our global financial and economic systems, based on a limited paradigm that prizes economic growth at any cost.

… Our actions have significantly impacted more than three quarters of the Earth’s land surface, destroyed more than 85% of wetlands and dedicated more than a third of all land and almost 75% of available freshwater to crops and livestock production [Settele 2020].

“With more than 70% of all emerging diseases affecting people having originated in wildlife and domesticated animals,” the IPBES team explains, “activities that bring increasing numbers of people into direct contact and often conflict with the animals that carry these pathogens” lead to pandemics [Settele 2020].

A study [Rulli 2017] linking forest fragmentation with outbreaks of Ebola virus disease in West and Central Africa bears out this assessment. The authors stress that infectious disease emergence is among the many dangers stemming from ecosystem destruction.

The impact of forest loss on ecosystems and the services they provide is often evaluated in terms of habitat destruction, losses of biodiversity, carbon stock and emissions, land degradation, or altered climate and hydrologic conditions. This study, however, highlights that deforestation and forest fragmentation potentially have another important class of externalities associated with global health and zoonotic^[3] disease outbreaks [Rulli 2017: 5].

Using satellite data on forest cover change from 2000 to 2014, these researchers found that all 11 sites of the first human Ebola infections since 2004 occurred in close proximity (within 25 km) to areas with higher rates of forest fragmentation than the regional average. Similarly, the closer one approached to the centers of first infection, the greater the fragmentation.

What is forest fragmentation? It is the cutting of forest into isolated patches and irregular shapes, resulting in greater lengths of edge between forested and non-forested areas. The increased length of forest perimeter in turn increases contact between humans and the wildlife that are potential disease agents, which would not otherwise be crossing our paths.

In addition to increasing human-wildlife contact, forest fragmentation favors some species while harming or obliterating others, throwing the whole system out of balance. Various studies have shown that the animals that thrive in degraded ecosystems are the same ones that constitute reservoirs of diseases communicable to humans. For example, in the case of West and Central Africa, the species suspected in the emergence of Ebola in humans include gorillas, chimpanzees, duikers (similar to an antelope) and a handful of bat species, all of which have been observed to increase in density following forest disturbance.

In addition to increasing human-wildlife contact, forest fragmentation favors some species while harming or obliterating others, throwing the whole system out of balance.

Thus, it could be argued that while disturbance by deforestation destroys the habitat of specialist^[4] species, generalists – possibly including reservoirs of some zoonotic pathogens – thrive, thereby further enhancing the risk of infection in human populations close to the forest margins [Rulli 2017: 5].

A similar observation was made in North America. The white-footed mouse, an extremely “competent” host for Lyme Disease – meaning highly capable of harboring and transmitting the Lyme bacteria – does well in degraded forests, while many less competent hosts require more diverse, intact forests to thrive. Opossums, for instance, do poorly in impoverished ecosystems and also do not transmit the Lyme bacterium as readily as mice do. Furthermore, opossums kill ticks attempting to feed on them, making them a poorer host for the tick vector^[5] as well.

There may be a direct link between a species’ susceptibility to habitat degradation and its quality as a disease host^[6]. Among vertebrates,

resilience in the face of disturbances that cause biodiversity loss, such as habitat destruction and fragmentation, is facilitated by life history features such as high reproductive output and intrinsic rates of increase. Vertebrates with these features tend to invest minimally in some aspects of adaptive immunity; we hypothesize that this may make them more competent hosts for pathogens and vectors [Keesing 2010: 650].

The loss of less-competent disease host species, or of predators, for example, that would otherwise control a competent host population, thus allowing the latter to flourish, can create an “amplification effect.” The resulting higher concentration of competent hosts increases the likelihood of vector contact with infected hosts, thus increases disease transmission.

The amplification effect was observed also in the case of West Nile Virus (WNV) in North America in 2003-2004 [Ostfeld 2009]. Counties with higher passerine (perching) bird diversity were found to have lower human incidence of WNV disease, presumably due to lower concentrations of the bird species that were the primary disease reservoirs. With higher bird diversity, mosquito vectors were less likely to get infected due to a greater prevalence of uninfected birds upon which to feed.

With higher bird diversity, mosquito vectors were less likely to get infected due to a greater prevalence of uninfected birds upon which to feed.

Given multiple studies of particular disease systems like the ones described above indicating that biodiversity inhibits the spread of disease, another group of scientists [Civitello 2015] wanted to know how broadly and generally the amplification effect applies. Were these disease systems special cases, or do they suggest an inherent relationship between biodiversity and disease? Inverse of the amplification effect, “the dilution effect hypothesis suggests that diverse ecological communities limit disease spread via several mechanisms. Therefore, biodiversity losses could worsen epidemics that harm humans and wildlife” [Civitello 2015: 8667], the authors state to contextualize their research. They analyzed 202 studies of biodiversity and parasite abundance, and found “overwhelming evidence of dilution, which is independent of host density, study design, and type and specialization of parasites” [Civitello 2015: 8667]. From these results, it can be inferred that biodiversity generally limits infectious disease.  

This message has not gone unheard by some in the public health field. An article [Granter 2016] published in the American Society of Clinical Pathology argues for health practitioners to become aware of the human health implications of environmental destruction, stating that:

Knowledge and prowess with infectious diseases for diagnosticians must be incorporated back into training with a reimagined lens crafted from the information we have gained by studying our environment, its destruction, and the ultimate resulting human infections [Granter 2016: 645].

A research team that included ecologists and a Center for Disease Control staff member [Kilpatrick 2017] analyzed the inclusion of biodiversity conservation among key public health tools. Without further research, the authors remain hesitant to recommend conservation generally as a public health tool (except insofar as exposure to nature boosts human wellbeing). However, they suggest that targeted interventions, such as reintroducing top predators to control host populations, installing bat or owl boxes to increase predation of mosquitos (vectors) or rodents (hosts) could be feasible public health interventions against infectious disease.

In their IPBES letter, Settele and colleagues [2020] recommend the adoption of a “One Health” approach to public health. This concept recognizes the fundamental interdependence of humans, animals, plants and our shared environment, and stresses the importance to human health of the overall health of nature. Some assessments paint that interdependence in even starker terms: “Zoonoses [human diseases of animal origin] reveal that environmental stewardship is not simply related to public health; in many cases, they are the same,” writes science journalist Ferris Jabr [2020].

In their IPBES letter, Settele and colleagues [2020] recommend the adoption of a “One Health” approach to public health. This concept recognizes the fundamental interdependence of humans, animals, plants and our shared environment, and stresses the importance to human health of the overall health of nature.

Indeed, humans are not the only species to experience disease epidemics. Bovine tuberculosis, honeybee varroasis, rabbit hemorrhagic disease virus, herpes virus in pilchard fish, West Nile virus in birds, and amphibians worldwide ravaged by a fungal disease are a few examples of how other species suffer. The underlying factors causing livestock, wildlife and human epidemics are anthropogenic environmental change driven by globalization of agriculture, commerce and human travel, all of which spread disease. Habitat destruction and toxic pollution are additional factors [Daszek 2001].

Compendium readers will be aware that biodiverse, intact ecosystems provide multiple vital functions. Healthy ecosystems absorb stormwater, forestall drought, generate rain, cool the air and land, purify air and groundwater, and pollinate crops, for example, not to mention contributing to human psychological wellbeing by providing recreational opportunities and beauty. What pandemics like Covid19 have now made us aware of is that biodiversity also plays a key role in limiting the emergence and spread of infectious disease.

Biodiversity loss and pandemics article summaries

Anthropogenic environmental change and the emergence of infectious diseases in wildlife, Daszak, Cunningham & Hyatt 2001

Humans are not the only species to suffer global pandemics. Planetwide, fungal disease ravages amphibians, just as honeybees are ravaged by varroasis. A herpes virus caused mass mortality of pilchard fish off the coast of Australia and New Zealand in 1995, and seals from Antarctica to the Caspian Sea have contracted canine distemper viruses, for which domestic dogs are also hosts.

The authors point to multiple anthropogenic environmental changes as the underlying causes of disease emergence among wildlife, livestock and humans.

Emerging infectious diseases (EIDs) are defined as diseases that have recently increased in incidence or geographic range, recently moved into new host populations, recently been discovered or are caused by newly-evolved pathogens [Daszak 2001: 103].

Two major known causes of disease emergence in wildlife are (1) “spillover” of livestock disease into wild populations; and (2) pathogen pollution, which stems from the global transport of domestic and wild animals, and contaminated products and materials. In addition, habitat destruction and fragmentation, and toxic pollution, are likely to contribute to disease emergence, although these factors hadn’t been as well studied (at least at the time of the writing in 2001).

The authors conclude with the following observation:

We have described a group of wildlife diseases that can be classified as emerging in the same way as human EIDs. These represent a link in the chain of emergence of human and domestic animal diseases, with pathogens, habitats and environmental changes shared between these populations. Parallels between causes of emergence across these groups of diseases demonstrates an important concept: that human environmental change may be the most significant driver of wildlife, domestic animal and human EIDs [Daszak 2001: 112].

Effects of species diversity on disease risk, Keesing, Holt & Ostfeld 2006

This review article describes the potential mechanisms by which biodiversity affects disease risk. The authors explore the mechanisms at play in simple systems with only host and pathogen, as well as in more complex systems that include a vector species and/or multiple hosts. The reduction of disease risk by increased diversity is called the “dilution effect.” The opposite, termed the “amplification effect,” is when disease risk increases. “Both models and literature reviews suggest that high host diversity is more likely to decrease than increase disease risk” [Keesing 2006: 485].

The mechanisms by which diversity affects disease risk are as follows:

Encounter reduction: An additional species (such as a predator) suppresses the movement of host species or vector species, thereby reducing contact between susceptible hosts and infected hosts or vectors. (Alternatively, if the presence of a different species causes host species to clump together more among their own kind, then transmission could increase in an encounter augmentation.)

Transmission reduction: An additional species in a system (such as a prey) reduces host stress, boosting immune system response and lowering pathogen load. An added species could also modify host behavior in a way that reduces the duration of their encounters and thus limits transmission.

Vector or susceptible host [population] regulation: The addition of any species that reduces birth rates or increases death rates, limiting overall population, among hosts susceptible to the pathogen or among pathogen vectors. Transmission rates may be reduced, for example, with the addition of host species predators or with the addition of species that attract vectors (ticks, for instance), but then groom themselves in a way that kills many vector individuals.

Infected host mortality: An added species outcompetes infected hosts for resources or targets infected hosts for predation.

Recovery augmentation: The addition of a prey species as an added resource for host species could, for example, increase full recovery rates of host species, creating a dilution effect, or, by contrast, increase the longevity of sick hosts in an amplification effect.

When there are many hosts for a particular pathogen, some species transmit the disease more readily than others. Often, the species that most effectively spread the disease (the most competent reservoirs) are present in species-poor, degraded ecosystems, meaning that any additional host species is likely to dilute the presences of the more contagious species.

One key question in multi-host disease systems is whether the most competent reservoir is present in species-poor communities. If so, species added to these communities have, by definition, lower (if any) reservoir competence and thus have the potential to decrease disease risk. If the most competent reservoir is not present in species-poor communities, by contrast, then an increase in diversity could include the addition of the most competent reservoir itself, which is likely to result in an amplification of disease risk. Ostfeld & Keesing (2000b) considered evidence that the most competent reservoir for a variety of vector-borne zoonoses was typically present in species-poor communities [Keesing 2006: 495].

Biodiversity loss and the rise of zoonotic pathogens, Ostfeld 2009

West Nile Virus is an infectious disease that arrived in New York City in 1999, and subsequently spread across the country to the west coast. It is transmitted to humans from passerine (perching) birds via mosquito vectors. This study tested the dilution effect hypothesis, which posits that greater diversity (of birds in this case) reduces the concentration of species that are the primary disease reservoirs (American robin, American crow, blue jay, western scrub jay, common grackle, house finch, and house sparrow), thus reducing vector contact with infected individuals, and ultimately transmission to humans. The study analyzed the incidence of human infection during 2003-2004, and found that biodiversity was indeed associated with reduced WNV infection rates among humans.

For all 3 years, the county-level human incidence of WNV disease was strongly, and significantly, negatively correlated with bird diversity within that county [Ostfeld 2009: 41].

Similar results are reported for studies of the dilution effect of biodiversity on Lyme disease risk. Furthermore, having collected data on the competence of various mammalian hosts to infect ticks with Lyme disease, as well as each host species’ average tick burden, the authors state that “we can project the number of ticks that will feed on them and the proportion of those ticks that will become infected” [Ostfeld 2009: 42].

We conclude from these studies that high vertebrate diversity is negatively correlated with human risk of exposure to Lyme disease. Furthermore, knowledge of the species composition of these communities, beyond simple measures of species richness or evenness, strongly enhances our ability to predict risk [Ostfeld 2009: 42].

In summary,

Evidence for a protective dilution effect of high diversity has been obtained for numerous infectious diseases of humans, wildlife, and plants. The weight of evidence suggests that protection against exposure to infectious diseases should be added to the list of utilitarian functions of biodiversity [Ostfeld 2009: 42].

“Evidence for a protective dilution effect of high diversity has been obtained for numerous infectious diseases of humans, wildlife, and plants. The weight of evidence suggests that protection against exposure to infectious diseases should be added to the list of utilitarian functions of biodiversity [Ostfeld 2009: 42].

Impacts of biodiversity on the emergence and transmission of infectious diseases, Keesing et al. 2010

This paper contextualizes reduced transmission of infectious disease as one of the many ecosystem services provided by biodiversity. Changes in biodiversity affect infectious disease transmission by changing the abundance of the host and/or vector; the loss of non-host species may increase the density of host species, increasing the encounter rates between pathogen and host.

Often, the species that remain when biodiversity is lost are those which are better pathogen hosts, while the lost species tend to be more resistant to infectious disease.

In several case studies, the species most likely to be lost from ecological communities as diversity declines are those most likely to reduce pathogen transmission [Keesing 2010: 648].

For example, the white-footed mouse, which are high-quality hosts both for the bacteria causing Lyme Disease and for the tick vectors, are abundant in both biodiverse systems and impoverished systems, while opossums, a poorer host for the Lyme bacterium that also kill/eat most ticks attempting to feed on them, do poorly in lower-biodiversity conditions.

Therefore, as biodiversity is lost, the host with a strong buffering effect – the opossum – disappears, while the host with a strong amplifying effect – the mouse – remains [Keesing 2010: 650].

There may be a causal link between a species’ susceptibility to biodiversity loss and its quality as a disease host. Among vertebrates,

resilience in the face of disturbances that cause biodiversity loss, such as habitat destruction and fragmentation, is facilitated by life history features such as high reproductive output and intrinsic rates of increase. Vertebrates with these features tend to invest minimally in some aspects of adaptive immunity; we hypothesize that this may make them more competent hosts for pathogens and vectors [Keesing 2010: 650].

Biodiversity also affects the emergence of infectious disease, such as the evolution of a new strain of pathogen in the same host (due to antibiotic resistance, for example), and the spillover to a new host species. Pathogen establishment in humans from other animal hosts is related to mammal species richness (a larger source pool), and land-use change (such as deforestation), which increases contact between humans and pathogen hosts. The pathogen then becomes an epidemic due to the new host species’ density (domesticated animals and humans).

The authors recommend preserving biodiversity by protecting natural habitat, while also preserving microbial diversity within organisms by limiting the use of antimicrobial agents. A diverse microbiome within an organism serves as a buffer against pathogens.

Biodiversity inhibits parasites: Broad evidence for the dilution effect, Civitello et al. 2015

Human activities are dramatically reducing biodiversity, and the frequency and severity of infectious disease outbreaks in human, wildlife, and domesticated species are increasing. These concurrent patterns have prompted suggestions that biodiversity and the spread of diseases may be causally linked. For example, the dilution effect hypothesis proposes that diverse host communities inhibit the abundance of parasites through several mechanisms, such as regulating populations of susceptible hosts or interfering with the transmission process. Thus, diverse communities may inhibit the proliferation of parasites, thereby promoting the stability of ecological communities and ecosystem services (e.g., nutrient cycling, carbon sequestration, and natural product production) [Civitello 2015: 8667].

This meta-analysis concludes that as a general rule across ecosystems, biodiversity inhibits parasitism. Previous studies had focused on particular host-parasite systems, and found that greater host diversity dilutes, or limits, the spread of disease. “Consequently, anthropogenic declines in biodiversity could increase human and wildlife diseases and decrease crop and forest production” [Civitello 2015: 8667].

Where the Wild Things Aren’t: Loss of Biodiversity, Emerging Infectious Diseases, and Implications for Diagnosticians, Granter 2016

This status-quo-challenging editorial is written for the American Society of Clinical Pathology, a group seemingly unrelated to the Bio4Climate community. The authors suggest that medical training in pathology over-emphasizes oncology at the expense of an adequate coverage of infectious disease, even though “between 1940 and 2004, a total of 335 human infectious diseases ‘emerged,’ and 60% of these were zoonotic” [Granter 2016: 645]. Having explained biodiversity loss as a factor driving disease rates, the authors make a plea for diagnosticians to become aware of the human health implications of environmental destruction.

Knowledge and prowess with infectious diseases for diagnosticians must be incorporated back into training with a reimagined lens crafted from the information we have gained by studying our environment, its destruction, and the ultimate resulting human infections. As loss of habitat, habitat fragmentation, and consequent biodiversity loss continue unabated, tools and skills will need to be in the hands of all diagnosticians if we hope to minimize the effect of these infections as they continually emerge [Granter 2016: 645].

This paper provides a particularly clear explanation of how biodiversity loss increases human infection risk.

The relationship between loss of biodiversity and human disease was first illustrated by Lyme disease. Its cause, the Borrelia burgdorferi bacterium, has the opportunity to encounter numerous vertebrate hosts – in one study estimated to be at least 125 species – in a diverse and healthy ecosystem. The potential hosts vary tremendously in their ability to harbor and transmit the bacteria, that is, their “reservoir competence.” Studies estimate the white-footed mouse infects more than 90% of ticks that complete their blood meal. While a few other hosts, such as eastern chipmunks and short-tailed shrews, are moderately competent, most tick hosts are marginally competent or dead-end hosts that are highly unlikely to transmit the infection. Since the white-footed mouse tends to thrive in impoverished ecosystems lacking biodiversity, infected ticks and, consequently, risk of human infection show a strong negative relationship with biodiversity. Because a diverse ecosystem with a range of vertebrate hosts – including many incompetent and dead-end hosts – “dilutes” the representation of the white-footed mouse and reduces human infection risk, this phenomenon has been termed the dilution effect [Granter 2016: 644].

“Because a diverse ecosystem with a range of vertebrate hosts – including many incompetent and dead-end hosts – “dilutes” the representation of the white-footed mouse and reduces human infection risk, this phenomenon has been termed the dilution effect” [Granter 2016: 644].

Conservation of biodiversity as a strategy for improving human health and wellbeing, Kilpatrick et al. 2017

This article very pragmatically addresses the question of whether biodiversity conservation could be an effective public health tool against infectious disease emergence and transmission.

Determining whether biodiversity conservation is an effective public health strategy requires answering four questions: (1) Is there a general, causal relationship between host biodiversity and disease risk? (2) If the link is causal and negative for most pathogens, does the increased diversity of pathogens with more diverse host communities result in net total increase or decrease in infectious disease burden? (3) Is the net benefit of biodiversity conservation greater than the net benefit of diversity-degrading processes (agricultural land-use change and wild animal harvesting)? (4) Are conservation interventions feasible and cost-effective compared to standard public health approaches (vaccines and treatments)?

Regarding the first question, experimental and observational research shows that increased biodiversity is associated with reduced disease burden.

Overall, the available data suggests that there is some correlational support in many zoonotic systems for a dilution effect, and that some species or species groups are more important than others in transmission [Kilpatrick 2017: 4].

The dilution effect hypothesis originated to explain the Lyme disease system. Greater numbers of hosts that are less “competent” (at spreading Lyme disease) – opossums, birds, raccoons and skunks – dilutes the transmission of Lyme bacteria to larval ticks by more competent hosts – white-footed mice, eastern chipmunks and shrews. Changes in community diversity affect, for example, host-vector encounter rates and host and vector abundances.

However,

much more research is needed to show that observed correlations are causal and to identify the mechanisms by which diversity is influencing disease risk [Kilpatrick 2017: 4].

The possibility of confounding factors in observational field studies is high because the same disturbances that change host diversity alters other aspects of transmission as well. For example, an ecosystem disturbance may, in addition to decreasing host diversity, also increase vector abundance, making it difficult to discern the proximate cause of increased disease rates. The authors note that the dilution effect may well cause decreased disease rates – more research is needed to determine this. But they caution that if the dilution effect turns out not to be the direct cause of decreased disease rates in any given pathogen system, then interventions to increase host diversity could be in vain with respect to that desired outcome.

Examples of potential conservation interventions to improve public health include preserving or restoring forest land, reintroducing top predators to control host populations, installing bat or owl boxes to increase predation of mosquitos (vectors) or rodents (hosts). Our still limited understanding of the mechanisms driving disease incidence patterns, however, make it difficult to predict outcomes for broad-scale land-use interventions, according to the authors. They argue instead that more targeted interventions aiming to reduce populations of key hosts in transmission may be more feasible public health tools than general land preservation. Even this, however, requires “deep understanding of both disease and population ecology.”

Further research to address this knowledge gap may be worth the investment, both for human wellbeing and for the planet. Exposure to nature has been shown to improve human mental and physical health and wellbeing, the authors note, regardless of biodiversity’s potential to reduce infectious disease. Furthermore,

If diverse communities can be shown to provide net benefits to human wellbeing, this could provide a powerful motivation for preserving Earth’s remaining biodiversity [Kilpatrick 2017: 7].

The nexus between forest fragmentation in Africa and Ebola virus disease outbreaks, Rulli et al. 2017

Ebola virus disease outbreaks in West and Central Africa have been linked to spillover from potential disease reservoirs such as bats, apes, and duikers (an antelope-like animal). Spillover has been thought to be related to population density, vegetation cover, and human activities such as hunting, poaching, and bushmeat consumption. In this study, forest data from satellites coupled with disease outbreak records identify a nexus between forest fragmentation and Ebola.

The researchers identified 11 sites of the first human infection of Ebola from a wild species having occurred since 2004. Changes in forest cover between the year 2000 (baseline year) and the years of first infection for each of these outbreaks were determined using high-resolution satellite data on tree cover. All 11 centers of infection were found to be located in forested areas where the rate of forest fragmentation was greater than the regional average. Similarly, forest fragmentation decreased with increasing distance from the centers of infection.

All 11 centers of infection were found to be located in forested areas where the rate of forest fragmentation was greater than the regional average.

The centers of first infection … tend to occur in areas where on the outbreak year the average degree of forest fragmentation (e.g., within a 25 km, 50 km or 100 km distance from the infection center) was significantly higher than in the rest of the region [Rulli 2017: 2].

Furthermore, eight of the 11 centers of infection were located in fragmentation “hotspots,” meaning within a cluster of highly fragmented forest areas.

Bats are the commonly accepted host to filoviruses such as Ebola and tend to increase in population in fragmented habitats. The geographic distribution of potential bat hosts was consistent with the distribution of the zoonotic niche of Ebola. A decline in the population of insectivorous bats and an increase in the frugivorous (fruit-eating) bat species as a result of forest fragmentation was observed. Reshaping forest boundaries, habitat disruption, and biodiversity loss may enhance the likelihood of zoonotic infection by increasing the abundance of a particular species and thus the prevalence of that species’ pathogens.

The fact that spillover tends to occur in hotspots of forest fragmentation rather than in clearcut areas suggests that chances of human interactions with host wildlife are higher in areas where human encroachment leaves forest fragments that provide habitat for reservoir species [Rulli 2017: 5].

Pressure on land and its products is increasingly pushing people into forested areas. Given the danger of zoonotic disease outbreak, any evaluation of the costs, risk, and benefits of forest loss and fragmentation should include global health considerations.

Habitat fragmentation, biodiversity loss and the risk of novel infectious disease emergence, Wilkinson 2018

Habitat loss reduces biodiversity, which leads to infectious disease emergence. The way a habitat is fragmented (how many patches it is divided into, how those patches are shaped, and what the distance is between them) further affects the extent of disease emergence. Both the number of divisions of habitat into smaller patches and the irregularity of patch shapes tend to increase habitat perimeter, which in turn increases contact between disease agents and humans.

The hazard is greatest in places with greater pre-existing biodiversity, where there is a greater diversity of microbial pathogens and associated hosts. There is a double risk of developing wilderness areas in these places because there are more pathogens to begin with, and the resulting biodiversity loss tends to amplify disease transmission.

Human encroachment into species-rich habitats may simultaneously decrease biodiversity and increase exposure of people to novel microbes [Wilkinson 2018: 1].

Integration of wildlife and environmental health into a One Health approach, Sleeman et al. 2019

This article introduces the concept of One Health, a public health framework adopted by the Centers for Disease Control in 2009, which recognizes the interdependence of humans, animals and our shared environment. The concept has gained traction as a way to address health problems arising from global environmental change.

Climate change, loss of biodiversity, habitat fragmentation and pollution, and subsequent degradation of natural environments threaten the range of ecosystem services that support all life on this planet [Sleeman 2019: 91].

…

It was the challenge of responding to these complex [environmental] problems that led to the emergence of the concept of One Health, which is defined by the Centers for Disease Control and Prevention (CDC) as the collaborative effort of multiple disciplines and sectors – working locally, nationally, regionally and globally – with the goal of achieving optimal health outcomes, recognizing the interconnection among people, animals, plants and our shared environment. This definition acknowledges that human, domestic animal and wildlife health are interconnected within the context of ecosystem/environmental health and provides a useful conceptual framework for the development of solutions to global health and environmental challenges. Given this interconnection, it follows that actions aimed primarily at improving the health of one part of the human-animal-environmental triad may have unanticipated consequences for the system as a whole if the harms they may cause to the other components are not considered. However, previous authors have noted that, despite the acknowledged interdependencies, few public or livestock health interventions include a consideration of biodiversity conservation or ecosystem/environmental health. Instead, health-promoting interventions focus largely on single-sector outcomes and, thus, may miss the opportunity to concurrently optimize outcomes in the other two sectors [Sleeman 2019: 92].

The authors suggest that despite its potential, the One Health approach does not as yet fully integrate wildlife and environmental health, instead favoring human health. Yet failure to optimize the health of all three realms can lead to unexpected and outcomes, ironically increasing risk to humans in some cases. Therefore, the authors propose the clarification of One Health values and goals, and integration of a systems approach and a harm reduction perspective into the One Health framework.

Systems biology provides methods to understand how interactions among [interrelated and interdependent] parts [livestock, humans and wildlife, for example] give rise to the function and behavior of that system [Sleeman 2019: 96].

A harm reduction perspective recognizes that solutions to complex problems require a broad societal response and that elimination of risk is not feasible for most issues. Consequently, this perspective promotes collaborative, multisectoral approaches whereby reducing harm, despite uncertainty regarding the outcome, is valued over inaction spurred by a desire for a perfect solution [Sleeman 2019: 94].

Emerging human infectious diseases and the links to global food production, Rohr et al. 2019

Increasing agricultural production to feed >11 billion people by 2100 raises several challenges for effectively managing infectious disease. Of many factors examined in this article linking agricultural expansion to infectious disease, one is conversion of natural habitat to cropland or rangeland. Land conversion increases contact between wild animals, livestock and humans.

As natural ecosystems are converted to crop land or range land, interactions among humans, and domesticated and wild animals, could increase. … These interactions are crucial because 77% of livestock pathogens are capable of infecting multiple host species, including wildlife and humans, and based on published estimates from the 2000s, over half of all recognized human pathogens are currently or originally zoonotic, as are 60–76% of recent emerging infectious disease events [Rohr 2019: 451].

“As natural ecosystems are converted to crop land or range land, interactions among humans, and domesticated and wild animals, could increase” [Rohr 2019: 451].

Land conversion pushes humans and livestock up against wilderness areas, increasing contact between species with previously little to no contact. The jumping of a pathogen to a new host species is called “spillover.”

Spillover appears to be a function of the frequency, duration and intimacy of interactions between a reservoir and novel host population. For example, influenza is believed to have jumped from horses to humans soon after domesticating horses and then made additional jumps to humans from other domesticated animals, such as poultry and swine [Rohr 2019: 451].

Furthermore, agricultural intensification tends to involve greater concentrations of a single variety of a single species, increasing the risk that any new disease will spread quickly in the population.

A central tenet of epidemiology is that the incidence of many infectious diseases should increase proportionally with host density because of increased contact rates and thus transmission among hosts. Hence, increasing human and livestock densities could cause increases in infectious diseases unless investments in disease prevention are sufficient to prevent these increases [Rohr 2019: 451].

Industrial-scale confined livestock production is

vulnerable to devastating losses of animals to disease. For instance, in just the last 25 years, an influenza A virus (H5N1) and a foot-and-mouth outbreak led to the destruction of more than 1.2 million chickens and 6 million livestock in China and Great Britain, respectively, and a ‘mad cow disease’ epizootic led to the slaughter of 11 million cattle worldwide [Rohr 2019: 449].

Increased agricultural production tends to be accompanied by new irrigation infrastructure and increased pesticide, fertilizer and antibiotic use, all of which increase infectious disease risk. Dams (often created for irrigation schemes) increase risk of mosquito-borne disease. Antibiotic overuse for livestock fosters resistance among pathogens that can also infect humans. Greater pesticide use leads to resistance among disease vectors such as mosquitoes to insecticides, while also weakening immune systems among exposed humans and wildlife hosts, increasing infection rates/severity. Nutrient enrichment caused by fertilizer can also contribute to the spread of infectious disease, for example, through mosquitos or snail vectors.

Finally, the urbanization and globalization associated with agricultural intensification/expansion elongates food supply chains, which increases movement of people and goods over borders, spreading food-born illness, flu and other infections.

In short,

These analyses revealed that agricultural drivers were associated with 25% of all diseases and nearly 50% of zoonotic diseases that emerged in humans since 1940. These values are even higher if we include the use of antimicrobial agents as an agricultural driver of human disease emergence, given that agricultural uses of antibiotics outpace medical uses in the developed world nearly nine to one [Rohr 2019: 451].

The authors recommend numerous measures for improving agricultural production while limiting infectious disease, including reducing antibiotic use for livestock, conserving biodiversity, improving and diversifying livestock and crop genetic material, investing in urban agriculture, social investments, and inter-disciplinary research and collaboration.

In a fitting juxtaposition, 2020 has brought us both the Covid-19 pandemic and the eve of the United Nations (UN) Decade of Ecosystem Restoration (2021-2030). As we have learned from infectious disease research, ecosystem degradation drives the emergence of novel human diseases that become pandemic. In this issue of the compendium we delve into research examining the connection between biodiversity loss and infectious disease, along with another set of articles on how best to restore the increasingly dangerous degraded lands that surround us. Perhaps a decade of restoring ecosystems as if our lives depend on it will deliver us to a gentler world come 2030.

Sacred forests/groves are not uncommon in India, especially in the biodiverse Western Ghats mountain range. These groves are community-protected patches of forest ranging in size from less than a hectare to several hundred hectares, and they are often believed to house gods [Ormsby & Bhagwat 2010]. A particular temple in the Western Ghats just outside the small town of Meenangadi in the state of Kerala owns 30 acres of forested hillside regarded as sacred.

In a clearing at the bottom of these hills, the people of the temple erected a shrine over a small stream flowing from their forest. Eventually, they built an elegant structure around the shrine with an opening in the roof to allow rain to wash onto the shrine. Praying involves touching the sacred stream water.

A few decades ago, however, in need of revenue, the temple cut a few acres at the uphill edge of their 30-acre plot and sold the wood. Following the loss of this portion of forest came a decline in the flow of the stream connecting the remaining sacred forest with the shrine. During the seasonally dry months of March and April, the stream had begun to run dry.

Concerned, temple officials went to the mayor in search of a solution to the drying of their stream. Town officials connected the temple with Kerala’s forestry department, whose mission includes increasing “the inflow of water to the reservoirs by improving the tree cover / forest cover over catchment areas,” “managing forests in such a way that it protects and enriches the social and cultural values of the state,” “protection and expansion of mangroves, sacred groves and other highly sensitive ecosystem,” and taking “Kerala to greater heights in the matter of biodiversity conservation,” among other goals [Kerala Forests and Wildlife Department website].

Given a mission such as this, the forest department knew what to do. They agreed to help by reforesting the clear-cut uphill edge of the sacred forest. Using only indigenous species, they planted some 89 different varieties of trees and shrubs, including medicinal varieties, on 1.6 hectares. This project was completed about five years ago.

On an afternoon in late January this year, as a Paradise Flycatcher darted in and out from the edge of the sacred grove to drink and bathe a few meters upstream of the shrine, a trained ear could hear another couple of dozen different bird species calling from the surrounding forest. Temple staff members said they have indeed seen more birds now that the cleared forest has been replanted. And the stream no longer runs dry, not even in March and April.

https://e360.yale.edu/features/the-science-and-art-of-restoring-a-damaged-wetland

“It was a stink hole,” says Al Rizzo, the refuge manager of Prime Hook National Wildlife Refuge in Delaware Bay. Humans had messed with hydrology in an ill-conceived project aimed to convert salt marsh into a large open freshwater impoundment system to attract migrating waterfowl among others. Lines of dunes and tidal gates were constructed to barricade the inflow of salt water. However, severe storms, including Hurricane Sandy, tore open gaps in dune lines, inundating the re-engineered system with salt water, killing fresh-water marsh grass, and turning a healthy riparian forest into a wasteland of dead trees.

In order to reverse the damage of this unnatural disaster, government agencies and conservation groups used the Hurricane Sandy Disaster Relief Fund to embark on a $38 million attempt to restore 4000 acres of damaged wetland. Engineering with nature is how Rizzo and Bart Wilson, restoration project manager, describe their approach, in which they are taking cues from nature to create a more resilient ecosystem. The objective is to allow the system to adjust itself and to work based on normal coastal dynamics.

Relying on existing data, extensive hydrodynamic modeling was applied to find out what actually works. The refuge was found to have no elevation problem but rather a plumbing challenge. Work started with closing up the breaches by reconstructing the beach and dunes. The restored dunes are now 10ft high, allowing for overwash to dissipate storm and wave power. Sediments produced were cast onto the banks creating sand flats that are being colonized naturally by native grass. A neural network of channels was opened on historic waterways to let the tide flow back in and out. The result is a healthy tidal marsh with meandering channels, lush salt-tolerant grasses and mudflats that attract rich diversity of fish and birdlife. The Prime Hook is becoming a model for wetland restoration globally.

https://news.mongabay.com/2019/09/for-one-indonesian-village-mangrove-restoration-has-been-all-upside/?n3wsletter&utm_source=Mongabay+Newsletter&utm_campaign=a1cff7d467-Newsletter_2019_09_26&utm_medium=email&utm_term=0_940652e1f4-a1cff7d467-77145713

Demand for firewood in recent years led to the depletion of the mangrove forest in the Indonesia village of Paremas. For years the people’s occupations were agriculture and fishing. Depleted fish stock, poor irrigation and challenges associated with land ownership drove most of the men to work overseas in order to raise money to care for their loved ones, while some women went abroad to work as domestic servants. The women who stayed home have depended on their husbands’ remittances in addition to collecting fish and other sea life in pools.

However, about 10 years ago, the local government and environmental NGOs emphasized the significance of restoring the mangrove. With the help of the locals, everyone got to work replanting Paremas mangrove forest, which in turn now cushions the effect of tidal waves, limits coastal flooding, saves arable land from coastal erosion, reduces plastic and garbage deposit on the beach, and increases biodiversity. With the availability of crabs, vegetables and fruits, the women started making crab crackers, as well as cakes made from the flour of mangrove fruits, creating a source of income for the women to support their families. “There are many benefits now,” says Hanieti, a resident mother, “even the mosquitoes are gone.”

https://news.mongabay.com/2019/09/sri-lanka-wields-mangroves-its-tsunami-shield-against-climate-change/?n3wsletter&utm_source=Mongabay+Newsletter&utm_campaign=a1cff7d467-Newsletter_2019_09_26&utm_medium=email&utm_term=0_940652e1f4-a1cff7d467-77145713

Sri Lanka is home to 82 lagoons and estuaries and is among the top five countries that will be impacted by climate risk. Thilakaratne De Silva, a 63-year old local fisherman, saw the Tsunami of December 2004 sweep off half his home village. He was among the first to join hands with other community members on a coastal natural buffer initiative of replanting the mangroves. In the aftermath of the tsunami, it became apparent that those who lived behind a thick buffer of mangrove forest were better shielded from the destructive waves.

The government and NGOs initiated the mangrove replanting, as well as implementing regulations aimed at curbing mangrove clearing, coral reef destruction and sand excavation. But after the Government and NGOs moved on, it’s been the local community’s engagement and consistency that is ensuring the success of a green belt along the south coast.

The critical goal now is to sustain the positive conservation effort already in place. Sustainable use enables gathering of edible mangrove varieties and collecting twigs and branches rather than cutting down trees and shrubs, according to Sarathchandra de Silva, an international agency worker involved in the replanting program.

Sugunawathi, a 51-year-old villager says that they are mindful of not cutting mangrove for fuelwood, though the burning efficiency of mangrove is preferred to forest wood, gas or kerosene. The frequency and extent to which communities access mangrove forest has much to do with poverty and lack of livelihood. However, growing tourism employs more rural men, creating livelihoods and boosting mangrove appreciation by the local community. A local NGO has sought to incentivize women because of their influence on children and the community on the need for the sustainable use of mangroves. The Galle success is now a model for replication, which inspires authorities to want to boost coastal buffer owning to the resilient nature of mangrove forest in climate risk, with an addition of 10,000 hectares to the existing 15,670 hectares already in place.

In continuation of the “blessed unrest” section of Compendium V3N1, the following sketches illustrate how people throughout the world are coming to recognise the enormous value of intact ecosystems, and are doing their part to protect and restore. Adopting Paul Hawken’s terminology and characterization of “blessed unrest” as a spontaneous, decentralized global social movement, we here present a diverse series of vignettes of everyday heroes. May such stories light the fire for new heroes to perpetually emerge in defense of all life on Earth.

Sri Lanka wields mangroves, its tsunami shield, against climate change, summarized from Mongabay News, September 2019

https://news.mongabay.com/2019/09/sri-lanka-wields-mangroves-its-tsunami-shield-against-climate-change/?n3wsletter&utm_source=Mongabay+Newsletter&utm_campaign=a1cff7d467-Newsletter_2019_09_26&utm_medium=email&utm_term=0_940652e1f4-a1cff7d467-77145713

Sri Lanka is home to 82 lagoons and estuaries and is among the top five countries that will be impacted by climate risk. Thilakaratne De Silva, a 63-year old local fisherman, saw the Tsunami of December 2004 sweep off half his home village. He was among the first to join hands with other community members on a coastal natural buffer initiative of replanting the mangroves. In the aftermath of the tsunami, it became apparent that those who lived behind a thick buffer of mangrove forest were better shielded from the destructive waves.

The government and NGOs initiated the mangrove replanting, as well as implementing regulations aimed at curbing mangrove clearing, coral reef destruction and sand excavation. But after the Government and NGOs moved on, it’s been the local community’s engagement and consistency that is ensuring the success of a green belt along the south coast.

The critical goal now is to sustain the positive conservation effort already in place. Sustainable use enables gathering of edible mangrove varieties and collecting twigs and branches rather than cutting down trees and shrubs, according to Sarathchandra de Silva, an international agency worker involved in the replanting program.

Sugunawathi, a 51-year-old villager says that they are mindful of not cutting mangrove for fuelwood, though the burning efficiency of mangrove is preferred to forest wood, gas or kerosene. The frequency and extent to which communities access mangrove forest has much to do with poverty and lack of livelihood. However, growing tourism employs more rural men, creating livelihoods and boosting mangrove appreciation by the local community. A local NGO has sought to incentivize women because of their influence on children and the community on the need for the sustainable use of mangroves. The Galle success is now a model for replication, which inspires authorities to want to boost coastal buffer owning to the resilient nature of mangrove forest in climate risk, with an addition of 10,000 hectares to the existing 15,670 hectares already in place.

For one Indonesian village, mangrove restoration has been all upside, summarized from Mongabay News, September 2019

https://news.mongabay.com/2019/09/for-one-indonesian-village-mangrove-restoration-has-been-all-upside/?n3wsletter&utm_source=Mongabay+Newsletter&utm_campaign=a1cff7d467-Newsletter_2019_09_26&utm_medium=email&utm_term=0_940652e1f4-a1cff7d467-77145713

Demand for firewood in recent years led to the depletion of the mangrove forest in the Indonesia village of Paremas. For years the people’s occupations were agriculture and fishing. Depleted fish stock, poor irrigation and challenges associated with land ownership drove most of the men to work overseas in order to raise money to care for their loved ones, while some women went abroad to work as domestic servants. The women who stayed home have depended on their husbands’ remittances in addition to collecting fish and other sea life in pools.

However, about 10 years ago, the local government and environmental NGOs emphasized the significance of restoring the mangrove. With the help of the locals, everyone got to work replanting Paremas mangrove forest, which in turn now cushions the effect of tidal waves, limits coastal flooding, saves arable land from coastal erosion, reduces plastic and garbage deposit on the beach, and increases biodiversity. With the availability of crabs, vegetables and fruits, the women started making crab crackers, as well as cakes made from the flour of mangrove fruits, creating a source of income for the women to support their families. “There are many benefits now,” says Hanieti, a resident mother, “even the mosquitoes are gone.”

Coastal recovery: bringing a damaged wetland back to life, summarized from Yale Environment 360, May 2019

https://e360.yale.edu/features/the-science-and-art-of-restoring-a-damaged-wetland

“It was a stink hole,” says Al Rizzo, the refuge manager of Prime Hook National Wildlife Refuge in Delaware Bay. Humans had messed with hydrology in an ill-conceived project aimed to convert salt marsh into a large open freshwater impoundment system to attract migrating waterfowl among others. Lines of dunes and tidal gates were constructed to barricade the inflow of salt water. However, severe storms, including Hurricane Sandy, tore open gaps in dune lines, inundating the re-engineered system with salt water, killing fresh-water marsh grass, and turning a healthy riparian forest into a wasteland of dead trees.

In order to reverse the damage of this unnatural disaster, government agencies and conservation groups used the Hurricane Sandy Disaster Relief Fund to embark on a $38 million attempt to restore 4000 acres of damaged wetland. Engineering with nature is how Rizzo and Bart Wilson, restoration project manager, describe their approach, in which they are taking cues from nature to create a more resilient ecosystem. The objective is to allow the system to adjust itself and to work based on normal coastal dynamics.

Relying on existing data, extensive hydrodynamic modeling was applied to find out what actually works. The refuge was found to have no elevation problem but rather a plumbing challenge. Work started with closing up the breaches by reconstructing the beach and dunes. The restored dunes are now 10ft high, allowing for overwash to dissipate storm and wave power. Sediments produced were cast onto the banks creating sand flats that are being colonized naturally by native grass. A neural network of channels was opened on historic waterways to let the tide flow back in and out. The result is a healthy tidal marsh with meandering channels, lush salt-tolerant grasses and mudflats that attract rich diversity of fish and birdlife. The Prime Hook is becoming a model for wetland restoration globally.

Indian temple restores sacred forest stream flow

Sacred forests/groves are not uncommon in India, especially in the biodiverse Western Ghats mountain range. These groves are community-protected patches of forest ranging in size from less than a hectare to several hundred hectares, and they are often believed to house gods [Ormsby & Bhagwat 2010]. A particular temple in the Western Ghats just outside the small town of Meenangadi in the state of Kerala owns 30 acres of forested hillside regarded as sacred.

In a clearing at the bottom of these hills, the people of the temple erected a shrine over a small stream flowing from their forest. Eventually, they built an elegant structure around the shrine with an opening in the roof to allow rain to wash onto the shrine. Praying involves touching the sacred stream water.

A few decades ago, however, in need of revenue, the temple cut a few acres at the uphill edge of their 30-acre plot and sold the wood. Following the loss of this portion of forest came a decline in the flow of the stream connecting the remaining sacred forest with the shrine. During the seasonally dry months of March and April, the stream had begun to run dry.

Concerned, temple officials went to the mayor in search of a solution to the drying of their stream. Town officials connected the temple with Kerala’s forestry department, whose mission includes increasing “the inflow of water to the reservoirs by improving the tree cover / forest cover over catchment areas,” “managing forests in such a way that it protects and enriches the social and cultural values of the state,” “protection and expansion of mangroves, sacred groves and other highly sensitive ecosystem,” and taking “Kerala to greater heights in the matter of biodiversity conservation,” among other goals [Kerala Forests and Wildlife Department website].

Given a mission such as this, the forest department knew what to do. They agreed to help by reforesting the clear-cut uphill edge of the sacred forest. Using only indigenous species, they planted some 89 different varieties of trees and shrubs, including medicinal varieties, on 1.6 hectares. This project was completed about five years ago.

On an afternoon in late January this year, as a Paradise Flycatcher darted in and out from the edge of the sacred grove to drink and bathe a few meters upstream of the shrine, a trained ear could hear another couple of dozen different bird species calling from the surrounding forest. Temple staff members said they have indeed seen more birds now that the cleared forest has been replanted. And the stream no longer runs dry, not even in March and April.

In climate policy and financing, the goals of adaptation (helping communities and ecosystems adapt to the effects of climate change) and mitigation (reducing carbon emissions and increasing carbon sinks) are often separate. This is because “adaptation and mitigation are driven by different interests and political economies, with distinct international donors and national institutions. These differences are reflected in the guidelines and requirements that climate change project developers have to follow” [Kongsager 2019: 279].

This present study, however, found that many climate change projects do or could address adaptation and mitigation jointly.

PDDs [Project Design Documents] integrating adaptation and mitigation shared several common features. They recognized ecosystems as providers of multiple services for both mitigation (carbon) and adaptation (watershed protection, forest products for livelihood diversification or safety nets, mangrove protection against storms and waves, microclimate regulation in agricultural fields) [Kongsager 2019: 278].

Ninety percent of mitigation projects mentioned adaptation goals while 30% of adaptation projects had mitigation goals. The authors speculate on the reason for this discrepancy:

There appears to be an intrinsic value in integrating adaptation into mitigation projects even without incentives provided by funders, because of reduced climatic risks and increased sustainability, as mentioned by a few project developers … By contrast, there is no clear rationale for a project developer to integrate mitigation into adaptation projects, beyond the perspective of receiving additional support from mitigation funding by selling carbon credits [Kongsager 2019: 279].

The authors recommend adjusting the institutional framework to encourage deeper, better coordinated integration of mitigation and adaptation goals into climate-related projects.

With a synergetic approach, AFOLU [agriculture, forests, and other land use] projects would be designed to combine adaptation and mitigation in a way that project components interact with each other to generate additional climate benefits compared to projects in which adaptation and mitigation are separated. Mainstreaming climate compatible development (i.e., adaptation, mitigation, and development) may avoid that projects respond to adaptation and mitigation urgencies separately. Scarce resources could be more efficiently spent, for instance, by not establishing separate institutions and processes to support adaptation and mitigation, and by avoiding conflicting policies, because a current major challenge in integrating adaptation and mitigation is the institutional complexity [Kongsager 2019: 279].

Forests currently cover a quarter of Earth’s terrestrial surface, although at least 82% of that remaining forest is degraded by human activity. While a handful of international accords rightly encourage forest conservation and reforestation to limit global warming, these agreements fail to prioritize protection specifically of intact forests, or forests that are free from human activities “known to cause physical changes in a forest that lead to declines in ecological function” [Watson 2018: 1].

The authors argue for the protection of all forests, including degraded ones, as well as reforestation, to stem global ecological collapse, while here they particularly emphasize the exceptional value of intact forests. They present these key arguments:

• Carbon sequestration and storage. “Intact forests store more carbon than logged, degraded or planted forests in ecologically comparable locations. Industrial logging and conversion of forest to cropland causes heavy erosion and contributes to the loss of belowground carbon” [Watson 2018: 3].
• Local climate. “Intact tropical forests are critical for rain generation because air that passes over these forests produces at least twice as much rain as air that passes over degraded or non-forest areas” [Watson 2018: 4]. By contrast, deforestation and forest degradation can increase the frequency of hot, dry days, leading to drought.
• Biodiversity. Forested ecosystems support the majority of global terrestrial biodiversity, and “beyond outright forest clearance, forest degradation from logging is the most pervasive threat facing species inhabiting intact forests” [Watson 2018: 4]. “For example, a recent global analysis of nearly 20,000 vertebrate species showed that even minimal initial deforestation within an intact landscape had severe consequences for vertebrate biodiversity in a given region, emphasizing the special value of intact forests in minimizing extinction risk” [Watson 2018: 5].
• Indigenous peoples. “Industrial-scale degradation of intact forest erodes the material basis for the livelihoods of indigenous forest peoples, depleting wildlife and other resources. It also renders traditional resource management strategies ineffective, and undermines the value of traditional knowledge and authority” [Watson 2018: 5], ultimately driving indigenous peoples off their land.
• Human health. “Forested ecosystems are major sources of many medicinal compounds that supply millions of people with medicines worldwide” [Watson 2018: 6]. Forest degradation results in the decline or loss of medically relevant species, while also directly harming human health through increased wildfire severity and spread of disease.
• Forest resilience. Forest degradation reduces the resilience of forests to climate change, leading to even greater ultimate loss of ecosystem function.

The authors warn that intact forests could soon disappear unless action is taken to protect them, which must necessarily start with greater recognition of their value compared to degraded forests.

There are still significant tracts of forest that are free from the damaging impacts of large-scale human activities. These intact forests typically provide more environmental and social values than forests that have been degraded by human activities. Despite these values, it is possible to envisage, within the current century, a world with few or no significant remaining intact forests. Humanity may be left with only degraded, damaged forests, in need of costly and sometimes unfeasible restoration, open to a cascade of further threats and lacking the resilience needed to weather the stresses of climate change. The practical tools required to address this challenge are generally well understood and include well-located and managed protected areas, indigenous territories that exemplify sound stewardship, regulatory controls and responsible behavior by logging, mining, and agricultural companies and consumers, and targeted restoration. Currently these tools are insufficiently applied, and inadequately supported by governance, policy and financial arrangements designed to incentivize conservation. Losing the remaining intact forests would exacerbate climate change effects through huge carbon emissions and the decline of a crucial, under-appreciated carbon sink. It would also result in the extinction of many species, harm communities worldwide by disrupting regional weather and hydrology, and devastate the cultures of many indigenous communities. Increased awareness of the scale and urgency of this problem is a necessary precondition for more effective conservation efforts across a wide range of spatial scales [Watson 2018: 8].

Despite their total area having increased by 10% since 1750, European forests have failed to achieve a net removal of CO2 from the atmosphere because of how they’ve been managed over that time. Eighty-five percent of Europe’s once largely unmanaged forest has been subjected to tree species conversion, wood extraction via thinning and harvesting, and litter raking, resulting in a large overall loss of carbon from biomass and soil.

Putting 417,000 km2 of previously unmanaged forest into production is estimated to have released 3.5 Pg of carbon to the atmosphere, because the carbon stock in living biomass, coarse woody debris, litter, and soil was simulated to be, respectively, 24, 43, 8, and 6% lower in managed forests compared with unmanaged forests [Naudts 2016: 598].

The sweeping change in Europe’s forest species from broad leaf trees to conifers represents a shift to a production-oriented approach to forestry undertaken to satisfy demands of a population that quadrupled between 1750 and 2010.

Whereas deforestation between 1750 and 1850 mainly replaced broadleaved forests with agricultural land, afforestation from 1850 onward was often with coniferous species. Broadleaved forests were also directly converted to coniferous forests, resulting in a total increase of 633,000 km2 in conifers at the expense of broadleaved forests (decreasing by 436,000 km2). For centuries, foresters have favored a handful of commercially successful tree species (Scots pine, Norway spruce, and beech) and, in doing so, are largely responsible for the current distribution of conifers and broadleaved species in Europe [Naudts 2016: 598].

The authors note that many other parts of the world have followed a similar path,

Wood extraction occurs in 64 to 72% of the 26.5 to 29.4 million km2 of global forest area, and substantial species changes have occurred in China (216,000 km2), Brazil (71,000 km2), Chile (24,000 km2), New Zealand (18,000 km2), and South Africa (17,000 km2) [Naudts 2016: 599].

This global trend has resulted in limiting the ability of many managed forests to sequester carbon, compared to their wild or better-managed counterparts.

Hence, any climate framework that includes land management as a pathway for climate mitigation should not only account for land-cover changes but also should equally address changes in forest management, because not all forest management contributes to climate change mitigation [Naudts 2016: 599].

The growth rate of trees – and thus their accumulation of carbon – increases continuously with tree size. Even though the leaves of smaller, younger trees are more efficient (more productive per unit area of leaf surface), larger trees have more total leaf surface area and thereby grow at a faster rate than their smaller counterparts. “For example, in our western USA old-growth forest plots, trees > 100cm in diameter comprised 6% of trees, yet contributed 33% of the annual forest mass growth” [Stephenson 2014: 92].

Since trees use atmospheric carbon to grow, the more they grow, the more carbon they sequester. “Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees” [Stephenson 2014: 90].

Phylogenetic^[10] measures of diversity contain information on evolutionary divergences amongst species, thus representing the diversity of phylogenetically conserved traits related to resource use, acquisition and storage. Thereby, distantly related species are expected to respond differently to changing environmental conditions. These functional traits can be general traits related to the fast–slow growth rate spectrum, such as specific leaf area and wood density, and also physiological traits triggering plant responses to climatic fluctuations, such as flowering and leafing phenologies^[11]. [Mazzochini 2019: 1431].

This study shows that (phylogenetic) plant diversity helps to stabilize ecosystem productivity – even at the landscape scale. Previous experiments have shown that plant diversity increases the stability of ecosystem productivity in small patches of vegetation where plant interaction boosts overall productivity, as does difference in response to environmental fluctuations among different species. The present study increases the scale of observation to the landscape level, and finds that biodiversity increases ecosystem stability due to varied or “asynchronous responses of distantly related species during environmental fluctuations” [Mazzochini 2019: 1431].

Our results expand by several orders of magnitude the spatial scale of evidence that high biodiversity strengthens the resistance of key ecosystem features to climatic fluctuations. Specifically, we show that the positive relationship between phylogenetic diversity and stability reported in local experiments can also be observed at larger spatial extents and grain sizes using available biodiversity databases and modelling techniques. As we expected, in the analyses at the landscape resolution, phylogenetic diversity correlates with vegetation productivity stability mainly due to a reduction in productivity variability across the years, and not by increasing average productivity, which was mostly driven by climatic variables [Mazzochini 2019: 1435].

This long-term experiment measured the difference in colonization and extinction rates of connected habitat fragments versus isolated fragments. The connected fragments were linked by a narrow (150m by 25m) strip of habitat. These habitat corridors increased the biodiversity of connected fragments by 14% after 18 years compared to their isolated counterparts.

In a large and well-replicated habitat fragmentation experiment, we find that annual colonization rates for 239 plant species in connected fragments are 5% higher and annual extinction rates 2% lower than in unconnected fragments. This has resulted in a steady, non-asymptotic increase in diversity, with nearly 14% more species in connected fragments after almost two decades. Our results show that the full biodiversity value of connectivity is much greater than previously estimated, cannot be effectively evaluated at short time scales, and can be maximized by connecting habitat sooner rather than later [Damschen 2019: 1479].

The authors note that 70% of the world’s forest area is within 1 km of an edge – meaning Earth’s forests are very fragmented. They stress that connecting habitat fragments is critical to the success of habitat and biodiversity conservation.

Conservation plans that ignore connectivity, such as plans that focus solely on habitat area, will leave unrealized the substantial, complementary, and persistent gains in biodiversity attributable specifically to landscape connectivity [Damschen 2019: 1480].

We found that wilderness areas act as a buffer against extinction risk. The global probability of species extinction in non-wilderness communities is over twice as high as that of species in wilderness communities. The buffering effect that wilderness has on extinction risk was found in every biogeographical realm, but was higher for realms with larger remaining extents of wilderness such as the Palaearctic^[9] [Di Marco 2019: 26].

The remaining intact ecosystems of Earth—which are increasingly seen as essential for providing ecosystem services on which humanity relies and maintaining the bio-cultural connections of indigenous communities—have been neglected in efforts to conserve biodiversity. This is largely due to a belief that these areas are less vulnerable to threatening processes and less rich in threatened biodiversity, thereby having lower conservation value [Di Marco 2019: 585].

However,

These areas are important because they host highly unique biological communities and/or represent the majority of remaining natural habitats for biological communities that have suffered high levels of habitat loss elsewhere [Di Marco 2019: 585].

Indigenous people make up less than 5% of the global population, but their lands encompass 37% of the planet’s remaining natural lands and (partially overlapping with natural lands) 40% of Earth’s protected area, much of this in sparsely inhabited places. Like everyone, indigenous people have multiple interests (economic, political, cultural), which don’t necessarily always support conservation interests. However, “Indigenous Peoples often express deep spiritual and cultural ties to their land and contend that local ecosystems reflect millennia of their stewardship” [Garnett 2018: 369]. Indeed, “Countless Indigenous management institutions have already proven to be remarkably persistent and resilient, suggesting that such governance forms can shape sustainable human landscape relationships in many places” [Garnett 2018: 370].

Thus, the authors argue for indigenous voices to be prominent in land-use decision-making processes at global and local levels. “There is already good evidence that recognition of the practices, institutions and rights of Indigenous Peoples in global environmental governance is essential if we are to develop and achieve the next generation of global biodiversity targets” [Garnett 2018: 372].

In total, Indigenous Peoples influence land management across at least 28.1% of the land area.

About 7.8 million km2 (20.7%) of Indigenous Peoples’ lands are within protected areas, encompassing at least 40% of the global protected area with the proportion of Indigenous land in protected areas significantly higher than the proportion of other lands that are protected. The relationship between Indigenous Peoples and conserved areas varies in nature. While some protected areas (as defined by states and/or the International Union for Conservation of Nature (IUCN)) are under the governance of Indigenous Peoples themselves, others are governed by state authorities with varying degrees of respect for the presence of Indigenous Peoples. This respect ranges from collaborative governance where Indigenous Peoples are consulted on decisions, to de facto management and use of protected areas by Indigenous Peoples despite threats of eviction [Garnett 2018: 370].

Around half of the global terrestrial environment can be classified as human-dominated. Using this as a measure of human influence, we estimated that Indigenous Peoples’ lands account for 37% of all remaining natural lands across the Earth. A higher proportion (67%) of Indigenous Peoples’ lands was classified as natural compared with 44% of other lands. Even though no global data are available on other anthropogenic pressures such as grazing, burning, hunting or fishing, the drivers assessed by the Human Footprint (which range from roads, access, population density and different agricultural land use activity) are suitable surrogates. Consistent with this, most parts of the planet managed and/or owned by Indigenous Peoples have low intensity land uses: less than 3.8 million km2 (10.2%) of the world’s urban areas, villages and non-remote croplands are on Indigenous Peoples’ lands, whereas, in contrast, they encompass 24.9 million km2 (65.7%) of the remotest and least inhabited anthromes. Many of these remote Indigenous areas are nevertheless under pressure from intensive development [Garnett 2018: 370].

A spatial overview of the global importance of Indigenous lands for conservation, Garnett et al. 2018

Indigenous people make up less than 5% of the global population, but their lands encompass 37% of the planet’s remaining natural lands and (partially overlapping with natural lands) 40% of Earth’s protected area, much of this in sparsely inhabited places. Like everyone, indigenous people have multiple interests (economic, political, cultural), which don’t necessarily always support conservation interests. However, “Indigenous Peoples often express deep spiritual and cultural ties to their land and contend that local ecosystems reflect millennia of their stewardship” [Garnett 2018: 369]. Indeed, “Countless Indigenous management institutions have already proven to be remarkably persistent and resilient, suggesting that such governance forms can shape sustainable human landscape relationships in many places” [Garnett 2018: 370].

Thus, the authors argue for indigenous voices to be prominent in land-use decision-making processes at global and local levels. “There is already good evidence that recognition of the practices, institutions and rights of Indigenous Peoples in global environmental governance is essential if we are to develop and achieve the next generation of global biodiversity targets” [Garnett 2018: 372].

In total, Indigenous Peoples influence land management across at least 28.1% of the land area.

About 7.8 million km2 (20.7%) of Indigenous Peoples’ lands are within protected areas, encompassing at least 40% of the global protected area with the proportion of Indigenous land in protected areas significantly higher than the proportion of other lands that are protected. The relationship between Indigenous Peoples and conserved areas varies in nature. While some protected areas (as defined by states and/or the International Union for Conservation of Nature (IUCN)) are under the governance of Indigenous Peoples themselves, others are governed by state authorities with varying degrees of respect for the presence of Indigenous Peoples. This respect ranges from collaborative governance where Indigenous Peoples are consulted on decisions, to de facto management and use of protected areas by Indigenous Peoples despite threats of eviction [Garnett 2018: 370].

Around half of the global terrestrial environment can be classified as human-dominated. Using this as a measure of human influence, we estimated that Indigenous Peoples’ lands account for 37% of all remaining natural lands across the Earth. A higher proportion (67%) of Indigenous Peoples’ lands was classified as natural compared with 44% of other lands. Even though no global data are available on other anthropogenic pressures such as grazing, burning, hunting or fishing, the drivers assessed by the Human Footprint (which range from roads, access, population density and different agricultural land use activity) are suitable surrogates. Consistent with this, most parts of the planet managed and/or owned by Indigenous Peoples have low intensity land uses: less than 3.8 million km2 (10.2%) of the world’s urban areas, villages and non-remote croplands are on Indigenous Peoples’ lands, whereas, in contrast, they encompass 24.9 million km2 (65.7%) of the remotest and least inhabited anthromes. Many of these remote Indigenous areas are nevertheless under pressure from intensive development [Garnett 2018: 370].

Wilderness areas halve the extinction risk of terrestrial biodiversity, DiMarco et al. 2019

We found that wilderness areas act as a buffer against extinction risk. The global probability of species extinction in non-wilderness communities is over twice as high as that of species in wilderness communities. The buffering effect that wilderness has on extinction risk was found in every biogeographical realm, but was higher for realms with larger remaining extents of wilderness such as the Palaearctic^[9] [Di Marco 2019: 26].

The remaining intact ecosystems of Earth—which are increasingly seen as essential for providing ecosystem services on which humanity relies and maintaining the bio-cultural connections of indigenous communities—have been neglected in efforts to conserve biodiversity. This is largely due to a belief that these areas are less vulnerable to threatening processes and less rich in threatened biodiversity, thereby having lower conservation value [Di Marco 2019: 585].

However,

These areas are important because they host highly unique biological communities and/or represent the majority of remaining natural habitats for biological communities that have suffered high levels of habitat loss elsewhere [Di Marco 2019: 585].

Ongoing accumulation of plant diversity through habitat connectivity in an 18-year experiment, Damschen et al. 2019

This long-term experiment measured the difference in colonization and extinction rates of connected habitat fragments versus isolated fragments. The connected fragments were linked by a narrow (150m by 25m) strip of habitat. These habitat corridors increased the biodiversity of connected fragments by 14% after 18 years compared to their isolated counterparts.

In a large and well-replicated habitat fragmentation experiment, we find that annual colonization rates for 239 plant species in connected fragments are 5% higher and annual extinction rates 2% lower than in unconnected fragments. This has resulted in a steady, non-asymptotic increase in diversity, with nearly 14% more species in connected fragments after almost two decades. Our results show that the full biodiversity value of connectivity is much greater than previously estimated, cannot be effectively evaluated at short time scales, and can be maximized by connecting habitat sooner rather than later [Damschen 2019: 1479].

The authors note that 70% of the world’s forest area is within 1 km of an edge – meaning Earth’s forests are very fragmented. They stress that connecting habitat fragments is critical to the success of habitat and biodiversity conservation.

Conservation plans that ignore connectivity, such as plans that focus solely on habitat area, will leave unrealized the substantial, complementary, and persistent gains in biodiversity attributable specifically to landscape connectivity [Damschen 2019: 1480].

Plant phylogenetic diversity stabilizes large‐scale ecosystem productivity, Mazzochini et al. 2019

Phylogenetic^[10] measures of diversity contain information on evolutionary divergences amongst species, thus representing the diversity of phylogenetically conserved traits related to resource use, acquisition and storage. Thereby, distantly related species are expected to respond differently to changing environmental conditions. These functional traits can be general traits related to the fast–slow growth rate spectrum, such as specific leaf area and wood density, and also physiological traits triggering plant responses to climatic fluctuations, such as flowering and leafing phenologies^[11]. [Mazzochini 2019: 1431].

This study shows that (phylogenetic) plant diversity helps to stabilize ecosystem productivity – even at the landscape scale. Previous experiments have shown that plant diversity increases the stability of ecosystem productivity in small patches of vegetation where plant interaction boosts overall productivity, as does difference in response to environmental fluctuations among different species. The present study increases the scale of observation to the landscape level, and finds that biodiversity increases ecosystem stability due to varied or “asynchronous responses of distantly related species during environmental fluctuations” [Mazzochini 2019: 1431].

Our results expand by several orders of magnitude the spatial scale of evidence that high biodiversity strengthens the resistance of key ecosystem features to climatic fluctuations. Specifically, we show that the positive relationship between phylogenetic diversity and stability reported in local experiments can also be observed at larger spatial extents and grain sizes using available biodiversity databases and modelling techniques. As we expected, in the analyses at the landscape resolution, phylogenetic diversity correlates with vegetation productivity stability mainly due to a reduction in productivity variability across the years, and not by increasing average productivity, which was mostly driven by climatic variables [Mazzochini 2019: 1435].

Rate of tree carbon accumulation increases continuously with tree size, Stephenson et al. 2014

The growth rate of trees – and thus their accumulation of carbon – increases continuously with tree size. Even though the leaves of smaller, younger trees are more efficient (more productive per unit area of leaf surface), larger trees have more total leaf surface area and thereby grow at a faster rate than their smaller counterparts. “For example, in our western USA old-growth forest plots, trees > 100cm in diameter comprised 6% of trees, yet contributed 33% of the annual forest mass growth” [Stephenson 2014: 92].

Since trees use atmospheric carbon to grow, the more they grow, the more carbon they sequester. “Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees” [Stephenson 2014: 90].

Europe’s forest management did not mitigate climate warming, Naudts et al. 2016

Despite their total area having increased by 10% since 1750, European forests have failed to achieve a net removal of CO2 from the atmosphere because of how they’ve been managed over that time. Eighty-five percent of Europe’s once largely unmanaged forest has been subjected to tree species conversion, wood extraction via thinning and harvesting, and litter raking, resulting in a large overall loss of carbon from biomass and soil.

Putting 417,000 km2 of previously unmanaged forest into production is estimated to have released 3.5 Pg of carbon to the atmosphere, because the carbon stock in living biomass, coarse woody debris, litter, and soil was simulated to be, respectively, 24, 43, 8, and 6% lower in managed forests compared with unmanaged forests [Naudts 2016: 598].

The sweeping change in Europe’s forest species from broad leaf trees to conifers represents a shift to a production-oriented approach to forestry undertaken to satisfy demands of a population that quadrupled between 1750 and 2010.

Whereas deforestation between 1750 and 1850 mainly replaced broadleaved forests with agricultural land, afforestation from 1850 onward was often with coniferous species. Broadleaved forests were also directly converted to coniferous forests, resulting in a total increase of 633,000 km2 in conifers at the expense of broadleaved forests (decreasing by 436,000 km2). For centuries, foresters have favored a handful of commercially successful tree species (Scots pine, Norway spruce, and beech) and, in doing so, are largely responsible for the current distribution of conifers and broadleaved species in Europe [Naudts 2016: 598].

The authors note that many other parts of the world have followed a similar path,

Wood extraction occurs in 64 to 72% of the 26.5 to 29.4 million km2 of global forest area, and substantial species changes have occurred in China (216,000 km2), Brazil (71,000 km2), Chile (24,000 km2), New Zealand (18,000 km2), and South Africa (17,000 km2) [Naudts 2016: 599].

This global trend has resulted in limiting the ability of many managed forests to sequester carbon, compared to their wild or better-managed counterparts.

Hence, any climate framework that includes land management as a pathway for climate mitigation should not only account for land-cover changes but also should equally address changes in forest management, because not all forest management contributes to climate change mitigation [Naudts 2016: 599].

The exceptional value of intact forest ecosystems, Watson et al. 2018

Forests currently cover a quarter of Earth’s terrestrial surface, although at least 82% of that remaining forest is degraded by human activity. While a handful of international accords rightly encourage forest conservation and reforestation to limit global warming, these agreements fail to prioritize protection specifically of intact forests, or forests that are free from human activities “known to cause physical changes in a forest that lead to declines in ecological function” [Watson 2018: 1].

The authors argue for the protection of all forests, including degraded ones, as well as reforestation, to stem global ecological collapse, while here they particularly emphasize the exceptional value of intact forests. They present these key arguments:

• Carbon sequestration and storage. “Intact forests store more carbon than logged, degraded or planted forests in ecologically comparable locations. Industrial logging and conversion of forest to cropland causes heavy erosion and contributes to the loss of belowground carbon” [Watson 2018: 3].
• Local climate. “Intact tropical forests are critical for rain generation because air that passes over these forests produces at least twice as much rain as air that passes over degraded or non-forest areas” [Watson 2018: 4]. By contrast, deforestation and forest degradation can increase the frequency of hot, dry days, leading to drought.
• Biodiversity. Forested ecosystems support the majority of global terrestrial biodiversity, and “beyond outright forest clearance, forest degradation from logging is the most pervasive threat facing species inhabiting intact forests” [Watson 2018: 4]. “For example, a recent global analysis of nearly 20,000 vertebrate species showed that even minimal initial deforestation within an intact landscape had severe consequences for vertebrate biodiversity in a given region, emphasizing the special value of intact forests in minimizing extinction risk” [Watson 2018: 5].
• Indigenous peoples. “Industrial-scale degradation of intact forest erodes the material basis for the livelihoods of indigenous forest peoples, depleting wildlife and other resources. It also renders traditional resource management strategies ineffective, and undermines the value of traditional knowledge and authority” [Watson 2018: 5], ultimately driving indigenous peoples off their land.
• Human health. “Forested ecosystems are major sources of many medicinal compounds that supply millions of people with medicines worldwide” [Watson 2018: 6]. Forest degradation results in the decline or loss of medically relevant species, while also directly harming human health through increased wildfire severity and spread of disease.
• Forest resilience. Forest degradation reduces the resilience of forests to climate change, leading to even greater ultimate loss of ecosystem function.

The authors warn that intact forests could soon disappear unless action is taken to protect them, which must necessarily start with greater recognition of their value compared to degraded forests.

There are still significant tracts of forest that are free from the damaging impacts of large-scale human activities. These intact forests typically provide more environmental and social values than forests that have been degraded by human activities. Despite these values, it is possible to envisage, within the current century, a world with few or no significant remaining intact forests. Humanity may be left with only degraded, damaged forests, in need of costly and sometimes unfeasible restoration, open to a cascade of further threats and lacking the resilience needed to weather the stresses of climate change. The practical tools required to address this challenge are generally well understood and include well-located and managed protected areas, indigenous territories that exemplify sound stewardship, regulatory controls and responsible behavior by logging, mining, and agricultural companies and consumers, and targeted restoration. Currently these tools are insufficiently applied, and inadequately supported by governance, policy and financial arrangements designed to incentivize conservation. Losing the remaining intact forests would exacerbate climate change effects through huge carbon emissions and the decline of a crucial, under-appreciated carbon sink. It would also result in the extinction of many species, harm communities worldwide by disrupting regional weather and hydrology, and devastate the cultures of many indigenous communities. Increased awareness of the scale and urgency of this problem is a necessary precondition for more effective conservation efforts across a wide range of spatial scales [Watson 2018: 8].

Addressing change mitigation and adaptation together: a global assessment of agriculture and forestry projects, Kongsager, Locatelli & Chazarin 2019

In climate policy and financing, the goals of adaptation (helping communities and ecosystems adapt to the effects of climate change) and mitigation (reducing carbon emissions and increasing carbon sinks) are often separate. This is because “adaptation and mitigation are driven by different interests and political economies, with distinct international donors and national institutions. These differences are reflected in the guidelines and requirements that climate change project developers have to follow” [Kongsager 2019: 279].

This present study, however, found that many climate change projects do or could address adaptation and mitigation jointly.

PDDs [Project Design Documents] integrating adaptation and mitigation shared several common features. They recognized ecosystems as providers of multiple services for both mitigation (carbon) and adaptation (watershed protection, forest products for livelihood diversification or safety nets, mangrove protection against storms and waves, microclimate regulation in agricultural fields) [Kongsager 2019: 278].

Ninety percent of mitigation projects mentioned adaptation goals while 30% of adaptation projects had mitigation goals. The authors speculate on the reason for this discrepancy:

There appears to be an intrinsic value in integrating adaptation into mitigation projects even without incentives provided by funders, because of reduced climatic risks and increased sustainability, as mentioned by a few project developers … By contrast, there is no clear rationale for a project developer to integrate mitigation into adaptation projects, beyond the perspective of receiving additional support from mitigation funding by selling carbon credits [Kongsager 2019: 279].

The authors recommend adjusting the institutional framework to encourage deeper, better coordinated integration of mitigation and adaptation goals into climate-related projects.

With a synergetic approach, AFOLU [agriculture, forests, and other land use] projects would be designed to combine adaptation and mitigation in a way that project components interact with each other to generate additional climate benefits compared to projects in which adaptation and mitigation are separated. Mainstreaming climate compatible development (i.e., adaptation, mitigation, and development) may avoid that projects respond to adaptation and mitigation urgencies separately. Scarce resources could be more efficiently spent, for instance, by not establishing separate institutions and processes to support adaptation and mitigation, and by avoiding conflicting policies, because a current major challenge in integrating adaptation and mitigation is the institutional complexity [Kongsager 2019: 279].