Compendium Vol. 3 No. 1: Worthy miscellany

Compendium Volume 3 Number 1 July 2019

Indigenous hunters have positive impacts on food webs in desert Australia, Penn State 2019

When Australian authorities removed indigenous Martu people from their traditional lands in the desertic center of the continent in the mid-1900s, endemic species there declined or went extinct. Researchers observed that the Martu’s hunting regime of small burning patches of land reduced the size of wildfires while also boosting populations of native species such as dingo, monitor lizard and kangaroo. The absence of the Martu after the 1950s resulted in domination by invasive species, which killed much of the native wildlife.

Blue carbon stocks of Great Barrier Reef deep-water seagrasses, York et al. 2018

The Great Barrier Reef (GBR) protects northeast Australia from wave exposure, while also creating habitat for a vast expanse of shallow- and deep-water seagrasses between the reef and the shoreline. Deep-water seagrasses here occupy an area roughly the size of Switzerland. While the carbon storage capacity of shallow-water seagrasses, dubbed ‘blue carbon,’ are known to be extremely high, the amounts of carbon stored in deep-water seagrasses (greater than 15 meters depth) is less well known, and expected to be lower due to these plants’ smaller stature and relative sparseness.

The authors found, however, that “deep-water seagrass contained similar levels of organic carbon (OC) to shallow-water species, despite being much sparser and smaller in stature” [York 2018: 1]. Furthermore, deep-water seagrass sediments contained about nine times more OC than surrounding bare areas.

If the OC stocks reported in this study are similar to deep-water [seagrass] meadows elsewhere within the GBR lagoon, then OC bound within this system is roughly estimated at 27.4 million tons [York 2018: 1].

Vegetation as a major conductor of geomorphic changes on the Earth surface: toward evolutionary geomorphology, Corenblit & Steiger 2009

Geomorphology is the study of landforms and processes and how they developed. This conceptual commentary proposes that the emergence and evolution of life, especially vegetation, has played a major role in physically shaping the Earth. For example, plant roots trap and hold sediment (preventing erosion), resulting in the formation of hillsides, sand dunes, fluvial islands, river banks, floodplains, and river channels, for example. Without vegetation to hold sediment in place, it would be blown or washed away, creating different land patterns. Roots also contribute to rock weathering, resulting in soil formation and even the formation of marine black shale, while aboveground, plants create a rough surface which affects flows of matter and energy. Indirectly, in being the primary source of energy for animals and microorganisms, plants “also control geomorphic processes through their engineering activities in soils and at the surface of the Earth.”

Trees play a central geomorphological role:

In particular the development of the lignin-containing plants (shrubs and trees) in the middle Devonian (380 Ma[9]) have produced the most significant geomorphic changes. Their complex and resistant root and stem systems combined with their slower decomposition has contributed to increase global sediment stability and storage in time and in space on the Earth’s surface [Corenblit & Steiger 2009: 894].

The authors contextualize the role of life in geomorphology in terms of energy sources available to do geomorphic work. Vegetation dynamics, driven by photosynthesis, which converts solar energy into stored chemical energy, is one of four such energy sources. The other three are: gravity, solar energy, and geothermal activity. This article helps us to visualize Earth’s systems (in particular lithosphere and biosphere) as interwoven, where biology drives not only life processes, but land formation process as well.

Gaia and natural selection, Lenton 1998

The Gaia hypothesis invites us to imagine Earth as an integral living system in order to explore the mechanisms by which life helps create and maintain the conditions for life, such as an oxygenated atmosphere.

“The Gaia theory proposes that organisms contribute to self-regulating feedback mechanisms that have kept the Earth’s surface environment stable and habitable to life” [Lenton 2000: 439]. This theory was developed by James Lovelock, a chemist who observed that Earth’s atmosphere is in a constant state of disequilibrium,

in which highly reactive gases, such as methane and oxygen, exist together at levels that are different by many orders of magnitude from photochemical steady states. Large, biogenic fluxes of gases are involved in maintaining such disequilibrium. This perturbed state is remarkable in that the atmospheric composition is fairly stable over periods of time that are much longer than the residence times of the constituent gases, indicating that life may regulate the composition of the Earth’s atmosphere. This concept became the foundation of Gaia theory [Lenton 2000: 439].

The theory is based on the evolutionary biology concept of natural selection, focusing on traits that alter the environment and the resulting feedback from that environmental change on the organisms with the traits that produced it. Lenton offers a few examples to illustrate such feedbacks, starting with the “Daisyworld” model, where black pigment in daisies confers advantage in an environment with below-optimal temperatures. By absorbing heat, the black daisies grow better than their white counterparts and their population dominates. The global effect of a growing population of individually warm daisies raises the overall temperature of the world. At this point, the population of white daisies begins to rebound and the global temperatures cool again.

Gaia theory aims to be consistent with evolutionary biology and views the evolution of organisms and their material environment as so closely coupled that they form a single, indivisible, process. Organisms possess environment-altering traits because the benefit that these traits confer (to the fitness of the organisms) outweighs the cost in energy to the individual [Lenton 2000: 440].

Some activities that alter the environment are so advantageous (to the organisms carrying out the activities) that they become widespread, fundamental properties of organisms. (An example is photosynthesis, the implications of which have been studied by modelling the Archaean–Proterozoic transition.) Other activities are favorable only under particular environmental conditions and hence are subject to selection. In such cases, it is often changes in one environmental variable that determine whether a trait remains selectively favorable. If the spread of the trait alters this environmental variable, it also alters the forces of selection determining its own value [Lenton 2000: 442].

Furthermore, ecosystems-level environmental feedbacks can be understood in terms of natural selection. For example:

The trees of the Amazon rainforest, through generating a high level of water cycling, maintain the moist environmental conditions in which they can persist (a positive feedback on growth and selection). Nutrients are also effectively retained and recycled. If too much forest is removed, the water-regulation system can collapse, the topsoil is washed away and the region reverts to arid semi-desert, a change that may be difficult to reverse [Lenton 2000: 445].

Lenton explains that while there are geochemical mechanisms involved in regulating the climate, “it is clear that organisms are involved in many environmental feedbacks on Earth, and their effects need to be considered” [Lenton 2000: 441]. For example, acid rain weathers calcium-silicate rocks resulting in the formation of calcium carbonate by removing carbon dioxide from the atmosphere, thus cooling the Earth. Warmer average global temperatures would lead to more rain, thus more weathering and the cooling effects of that negative, self-correcting feedback. “However, geochemical feedbacks [such as this one] operate slowly and are not very responsive to perturbation” [Lenton 2000: 441]. Rock weathering organisms can amplify the weathering effects of the rain, hastening the negative feedback. Thus, there’s an intertwining of processes that regulate the climate.

The significance of this article is that if life has been at least partly responsible for creating and maintaining the habitability of Earth’s climate for the past 3.5 billion years, then it has a key role to play today as we grapple with how to keep global temperatures from rising above 1.5C. Ecosystems are clearly victimized by climate chaos, while also being directly damaged by avoidable human activity, such as land-clearing for development and agriculture and the ubiquitous use of chemical toxins and plastics. Yet if ecosystems are also a driver of climatic conditions, then it is critical to protect them from further harm and to nurture their growth and stability. Humans can become Gaia’s nursing team – we can improve the conditions for her recovery to the point when her own systems kick in and bring her back to health.

Corenblit, Dov & Johannes Steiger, 2009, Vegetation as a major conductor of geomorphic changes on the Earth surface: toward evolutionary geomorphology, Earth Surface Processes and Landforms 34,

York, Paul H., Peter I. Macreadie & Michael A. Rasheed, 2018, Blue Carbon stocks of Great Barrier Reef deep-water seagrasses, Biological Letters 14,

[9] “Ma” means millions of years ago.

For the full PDF version of the compendium issue where this article appears, visit Compendium Volume 3 Number 1 July 2019