Compendium Vol. 4 No. 2: Ecological corridors and connectivity

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).