Monday, March 4, 2024

Abundant Wildlife amplifies Nature’s Carbon Sequestration Power

The following extracts are from the research paper ‘Trophic rewilding can expand natural climate solutions‘ published in the journal Nature

The Paris Climate Agreement is celebrated for spurring the development of climate solutions that would hold global mean temperature rise to 1.5°C. The proposed solutions focus on reaching net-zero fossil fuel CO2 emissions by a complete transition to renewable energy generation by 2050, together with a halt to deforestation and land conversion to prevent the emissions of carbon already stored in ecosystems. However, these solutions alone will be insufficient because the heat trapping capacity of the CO2 that remains in the atmosphere will challenge the current efforts to hold the global mean temperature rise even to below 2°C. To prevent this requires ‘negative emissions’ solutions that remove and store 500Gt of atmospheric CO2 between now and 2100 (6.5GtCO2/yr).

To this end, natural climate solutions (NCS) are being proposed as cost-effective and relatively safe ways to capture the excess atmospheric CO2 and store it within terrestrial and aquatic ecosystems. These solutions are inspired by the recognition that natural biogeochemical processes within terrestrial and marine ecosystems already remove up to 50% of all human-caused CO2 emissions annually. Natural climate solutions aim to do more, first by protecting forest, wetland, coastal and grassland ecosystems to avoid emissions of 4GtCO2/yr, and second by restoring and managing plants, soils and sediments in these ecosystems to capture and store 5–6GtCO2 more each year. If guidelines to avoid negative impacts are followed, such efforts could co-benefit biodiversity conservation and the provision of ecosystem services that support human livelihoods and welfare.  The current 5–6GtCO2/yr goal is a major step forward. However, the solutions still fall short of reaching the 6.5Gt CO2/yr  removal target by 0.5–1.5Gt CO2/yr. To overcome this shortfall with additional natural climate solutions requires thinking differently about biotic controls over ecosystem carbon capture and storage.

Usually NCS are said to arrest climate warming by protecting and enhancing carbon capture and storage in plants, soils and sediments in ecosystems.  These solutions are viewed as having only ancillary benefit of protecting habitats and landscapes, which in turn conserve animal species diversity.  However, this study shows that this reasoning undervalues the role animals play in controlling the carbon cycle.  The researchers present scientific evidence showing that protecting and restoring wild animals and their functional roles can enhance natural carbon capture and storage.  They call for new thinking that includes the restoration and conservation of wild animals and their ecosystem roles as a key component of natural climate solutions that can enhance the ability to prevent climate warming beyond 1.5°C.

When it comes to climate solutions, your first thought may not be the wildebeest. But in the Serengeti, these buffalo-looking antelopes are the key to carbon capture.  Wildebeest eat large amounts of grass and recycle it back into the soil as dung. So when their population plummeted in the early 1900s due to a disease transmitted from domestic cattle, the loss of natural grazing led to more frequent and intense wildfires, turning the Serengeti into a carbon source.  Efforts to bring back or “rewild” the wildebeest population through disease management were a huge success, helping reduce the frequency and intensity of wildfires, and restoring the Serengeti back into a carbon sink.

Similarly, intensive sampling of 650 plots of 100m2 in a 48,000km2 tropical forest region in Guyana revealed that tree and soil carbon storage increased by 3.5–4 times across a gradient from 10 to 70 tree species.  Yet, across a gradient from 5 to 35 mammal species within this same region, tree and soil carbon storage in the sampling plots increased 4–5 times. This additional boost in carbon storage is attributable to a diversity of animal species with medium-to-large bodies that have a diversity of functional roles in the ecosystem. Animals play a significant role in how much carbon plants, soil and sediments can capture, as they redistribute seeds and nutrients and disturb soil through digging, trampling, and nest-building. This is one of a growing number of examples from various land and ocean ecosystems showing that wild animals can substantially enhance negative emissions.

The data show the added atmospheric CO2 that could be held in ecosystems by using trophic rewilding as a natural climate solution. Additional ecosystem CO2 uptake represents amounts of carbon storage above levels estimated or measured in the absence of the focal animal.

Bison, which once numbered over 30 million and occupied 22 ecosystem types within 9.4 million km2 of the North American landscapes, now exist at 2% of their historical numbers, restricted to 1% of their historical range. Restoring populations to even a fraction of the landscape—places where conflict with humans would be minimal (that is, 1–16% of six shortgrass and tallgrass prairie regions) – could add an estimated 595Mt CO2 annually to prairie ecosystem storage primarily by reducing soil emissions.

Rewilding just nine wildlife species or species groups (African forest elephants, American bison, fish, gray wolves, musk oxen, sea otters, sharks, whales and wildebeest) in different ecosystems around the world, would contribute more than 95% of the annual requirement to achieve the global target of extracting 500 billion metric tons of carbon dioxide from the atmosphere by 2100. This in turn would help cap the global temperature rise at less than 1.5° Celsius (2.7° Fahrenheit) below pre-industrial levels, as called for in the Paris Agreement.

Trophic Rewilding

Using wild animal conservation explicitly to enhance carbon capture and storage is known as ‘animating the carbon cycle’.  To do this certainly requires protecting and restoring species presences in ecosystems. However—and this is key—it requires protecting and restoring the ability of animal species to reach ecologically meaningful densities so that as they move and interact with each other they can fulfil their functional roles across landscapes and seascapes. To restore and protect animal functional roles in ecosystems is known as trophic rewilding.

The report suggests that to successfully reintroduce wildlife into areas where humans live, it’s important to work closely with local communities to address the complex social issues that can affect conservation efforts. This may include involving the local community in decision-making and governance processes, and taking into account their knowledge, values and attitudes toward rewilded species, as well as their cultural heritage, land rights and access to natural resources.


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