Large Herbivores May Improve an Ecosystem’s Carbon Persistence

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Fri, Jan 14, 2022 11:34 PM

Large Herbivores May Improve an Ecosystem’s Carbon Persistence
Rishika Pardikar, Eos.
January 14, 2022

Wildlife and open-canopy ecosystems like grasslands are rarely a part of
discussions surrounding climate change mitigation. Now, a new review points
to 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 poor
land management decisions with bad consequences for biodiversity,” said
Jeppe A. Kristensen, the paper’s lead author and a fellow at the School of
Geography and the Environment, University of Oxford.

Terming grasslands as “overlooked global reservoirs of carbon,” the
research shows how herbivores redistribute carbon from aboveground
vegetation (where it is vulnerable to disturbances like wildfire and
disease) into more persistent belowground soil pools. Soil pools are
composed primarily of undecomposed plant and animal residues (particulate
organic matter) and more resistant carbon stabilized by interaction with
mineral soil particles (mineral-associated organic matter).

The paper presents a holistic framework of linkages 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 to the
soil via dung and urine. Decomposers in the earth (mostly 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 cycled
through the soil, Kristensen and his coauthors argued, ecosystems with
large herbivores may store a larger fraction of total ecosystem carbon in
pools less vulnerable to perturbations than living plant biomass.

The paper presents a holistic framework of linkages between vegetation,
large herbivores like elephants and wild boars, smaller organisms like
earthworms and dung beetles, and microbes. Aboveground and belowground
carbon sequestration services provided by these living elements of an
ecosystem ought to be viewed as a whole rather than as a series of singular
foci, the paper argues.

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

An Ecosystem-Wide Perspective
For millions of years, herbivores have been integral to how ecosystems
work. Sumanta Bagchi, an associate professor with the Centre for Ecological
Sciences and the Divecha Centre for Climate Change at the Indian Institute
of Science, said the presence of herbivores changes “the quality and
quantity of food supply for microbes in soil.” In the absence of
herbivores, Bagchi said, “carbon’s residence time in the soil is reduced.”

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

Kristensen agreed, suggesting “a mix of climate-friendly forests,
high-yielding agriculture, more extensive semipastoral systems, and
dedicated nature parks where biodiversity is given first priority” as
perhaps the best way to optimize multiple goals like 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 bodies of the United Nations (the Intergovernmental Panel on Climate
Change and the Intergovernmental Science-Policy Platform on Biodiversity
and Ecosystem Services) released a landmark report to highlight how
“functional separation” between the fields of climate change and
biodiversity “creates a risk of incompletely identifying, understanding and
dealing with the connections between the two.”

https://eos.org/articles/large-herbivores-may-improve-an-ecosystems-carbon-persistence

Large Herbivores May Improve an Ecosystem’s Carbon Persistence Rishika Pardikar, Eos. January 14, 2022 Wildlife and open-canopy ecosystems like grasslands are rarely a part of discussions surrounding climate change mitigation. Now, a new review points to 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 poor land management decisions with bad consequences for biodiversity,” said Jeppe A. Kristensen, the paper’s lead author and a fellow at the School of Geography and the Environment, University of Oxford. Terming grasslands as “overlooked global reservoirs of carbon,” the research shows how herbivores redistribute carbon from aboveground vegetation (where it is vulnerable to disturbances like wildfire and disease) into more persistent belowground soil pools. Soil pools are composed primarily of undecomposed plant and animal residues (particulate organic matter) and more resistant carbon stabilized by interaction with mineral soil particles (mineral-associated organic matter). The paper presents a holistic framework of linkages 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 to the soil via dung and urine. Decomposers in the earth (mostly 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 cycled through the soil, Kristensen and his coauthors argued, ecosystems with large herbivores may store a larger fraction of total ecosystem carbon in pools less vulnerable to perturbations than living plant biomass. The paper presents a holistic framework of linkages between vegetation, large herbivores like elephants and wild boars, smaller organisms like earthworms and dung beetles, and microbes. Aboveground and belowground carbon sequestration services provided by these living elements of an ecosystem ought to be viewed as a whole rather than as a series of singular foci, the paper argues. “There is a lot of focus on aboveground carbon. And nature management efforts are usually about increasing forest area. But soil carbon is an important aspect, and herbivores improve soil carbon and nitrogen sequestration,” said Judith Sitters, a researcher in forest and landscape ecology at Wageningen University and Research who did not contribute to the new paper. Sitters was, however, the lead author of an earlier paper that showed how megaherbivores (animals weighing more than 1,000 kilograms) increased both carbon and nitrogen pools in the soil. Sitters added that megaherbivores like elephants and rhinos have a far greater impact on key ecosystem processes than smaller ones like zebras because of the amount of food they eat and the amount of dung they deposit. An Ecosystem-Wide Perspective For millions of years, herbivores have been integral to how ecosystems work. Sumanta Bagchi, an associate professor with the Centre for Ecological Sciences and the Divecha Centre for Climate Change at the Indian Institute of Science, said the presence of herbivores changes “the quality and quantity of food supply for microbes in soil.” In the absence of herbivores, Bagchi said, “carbon’s residence time in the soil is reduced.” Bagchi was not involved in the new review but is one of the authors of an earlier paper suggesting why moderate levels of grazing could promote net soil carbon storage in ecosystems. Maintaining the influence of large herbivores on grazing ecosystems through conservation and rewilding efforts could be of “high importance” for soil carbon sequestration, Bagchi said. Kristensen agreed, suggesting “a mix of climate-friendly forests, high-yielding agriculture, more extensive semipastoral systems, and dedicated nature parks where biodiversity is given first priority” as perhaps the best way to optimize multiple goals like 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 bodies of the United Nations (the Intergovernmental Panel on Climate Change and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services) released a landmark report to highlight how “functional separation” between the fields of climate change and biodiversity “creates a risk of incompletely identifying, understanding and dealing with the connections between the two.” https://eos.org/articles/large-herbivores-may-improve-an-ecosystems-carbon-persistence