Grazing animals key in stabilising soil carbon levels: Study

Grazing by mammalian herbivores significantly helped stabilising soil carbon pools in grazing ecosystems such as the Spiti region in the Himalayas, a 16-year-long study has found.

The Indian Institute of Science (IISc) said on Tuesday that a study by researchers at the Centre for Ecological Sciences (CES) and the Divecha Centre for Climate Change found large mammalian herbivores like the yak and ibex as crucial in stabilisation of the carbon pools.

An IISc statement said experimental removal of grazing by herbivores from such ecosystems was found to increase fluctuations in soil carbon levels, which could set off negative consequences for the global carbon cycle. The study was published in the Proceedings of the National Academy of Sciences.

Sumanta Bagchi, Associate Professor at CES and senior author of the study, said the soil pool was a reliable sink for trapping carbon and maintaining stable levels of soil carbon was key to offsetting the effects of climate change.

Bagchi began studying the impact of grazing animals on Himalayan ecosystems during his PhD, in 2005. He and his team established fenced plots, where animals were excluded, as well as plots in which animals like yak and ibex grazed. Soil samples were collected from the region over the following decade and their chemical composition was analysed, year after year.

The statement said from one year to the next, soil carbon was found to fluctuate 30-40% more in the fenced plots where animals were absent, compared to the grazed plots where it remained more stable each year.

“Depending on the soil conditions, nitrogen can either stabilise or destabilise the carbon pool. Grazing by herbivores, however, changes their interactions in ways that tip the balance in favour of the former, the researchers found,” the statement said.

The researchers suggested that since grazing ecosystems make up about 40% of the earth’s land surface, protecting herbivores that keep the soil carbon stable should remain a key priority for mitigating climate change.