Large herbivores can improve the carbon persistence of an ecosystem

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Wildlife and open-canopy ecosystems like grasslands are rarely part of discussions surrounding climate change mitigation. Now, a new review highlights interactions between wild herbivores and vegetation to show how restoration efforts could be optimized by aligning climate goals with biodiversity conservation.

The idea that herbivores are necessarily bad for carbon storage because they consume and disturb vegetation is “far too simplistic and risks making bad land management decisions with bad consequences for biodiversity,” he said. Jeppe A. Kristensen, lead author of the article and researcher at the School. of Geography and the Environment, University of Oxford.

Calling grasslands the world’s “neglected carbon pools,” the research shows how herbivores redistribute carbon from aboveground vegetation (where it’s vulnerable to disturbances like wildfire and disease) into more persistent underground soil pools. Soil pools are composed primarily of undecomposed plant and animal residues (particulate organic matter) and more resistant carbon stabilized by interaction with soil mineral particles (organic matter associated with minerals).

The article presents a holistic framework of links between vegetation, large herbivores like elephants and wild boars, smaller organisms like earthworms and dung beetles, and microbes.

By grazing, Kristensen explained, herbivores recycle plant material back into the soil via feces and urine. The earth’s decomposers (mainly microbes, as well as larger animals like earthworms) feed on this nutrient-rich resource and bury fractions of it in the soil. By increasing the amount of carbon circulating in the soil, explained Kristensen and his coauthors, ecosystems with large herbivores can store a greater fraction of the ecosystem‘s total carbon in pools that are less vulnerable to disturbance than living plant biomass.

The article presents a holistic framework of links between vegetation, large herbivores like elephants and wild boars, smaller organisms like earthworms and dung beetles, and microbes. According to the article, the carbon sequestration services above and below ground provided by these living components of an ecosystem should be considered as a whole rather than a series of singular foci.

“We focus a lot on aerial carbon. And nature management efforts are generally aimed at increasing forest area. But soil carbon is an important aspect, and herbivores enhance carbon and nitrogen sequestration in the soil,” said Judith Sitters, researcher in forest and landscape ecology at Wageningen University and Research, who did not contribute to the new article. Sitters, however, was lead author on an earlier paper that showed how megaherbivores (animals weighing more than 1,000 kilograms) increased both carbon and nitrogen stores in the soil. Observers added that megaherbivores like elephants and rhinos have a much greater impact on key ecosystem processes than smaller ones like zebras due to the amount of food they eat and the amount of manure they eat. they deposit.

An ecosystem-wide perspective

For millions of years, herbivores have been an integral part of the functioning of ecosystems. Sumanta Bagchi, an associate professor at the Center for Ecological Sciences and the Divecha Center for Climate Change at the Indian Institute of Science, said the presence of herbivores changes “the quality and quantity of the food supply of microbes in the soil. “. In the absence of herbivores, Bagchi said, “the residence time of carbon in the soil is reduced.”

Bagchi was not involved in the new study, but is one of the authors of an earlier paper suggesting why moderate levels of grazing might promote net soil carbon storage in ecosystems. Maintaining the influence of large herbivores on grazing ecosystems through conservation and reseeding efforts could be of “great importance” for soil carbon sequestration, Bagchi said.

Kristensen agreed, suggesting “a mix of climate-friendly forests, high-yield agriculture, larger semi-pastoral systems and dedicated nature parks where biodiversity is the first priority” as perhaps the best way to optimize several objectives such as climate change mitigation and biodiversity conservation. .

Scientists like Bagchi, Sitters and Kristensen are not alone in highlighting the links between biodiversity and climate change. In 2020, two United Nations bodies (the Intergovernmental Panel on Climate Change and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services) released a landmark report to highlight how the “functional separation” between the fields of climate change and biodiversity “creates a risk of incompletely identifying, understanding and addressing the links between the two.

—Rishika Pardikar (@rishpardikar), science writer

Quote: Pardikar, R. (2022), Large Herbivores Can Enhance the Carbon Persistence of an Ecosystem, Eos, 103, https://doi.org/10.1029/2022EO220029. Published on January 14, 2022.
Text © 2022. The authors. CC BY-NC-ND 3.0
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