Change on the Range: Plant species loss from over-grazing will reduce rangeland carbon storage

Anvar Sanaei, Emma J. Sayer, Zuoqiang Yuan, Hugo Saiz,Manuel Delgado-Baquerizo,Majid Sadeghinia, Parvaneh Ashouri, Sahar Ghafari, Hasan Kaboli, Mansoureh Kargar, Eric W. Seabloom, Arshad Ali

This is a plain language summary of a Functional Ecology research article which can be found here.

Livestock grazing in rangelands supports the livelihoods of millions of people in arid and semi-arid regions of the world. Unfortunately, over-grazing and climate change are threatening rangeland plant diversity, and species loss could affect the capacity of rangelands to store carbon.

Ecosystem carbon storage is often strongly related to plant diversity because different plant growth forms and strategies can boost the overall growth of the vegetation. The amounts or types of plant litter and roots also influence how much carbon is stored in soils. However, the impacts of grazing on plant diversity and carbon storage are complex. On the one hand, grazing animals can reduce diversity and carbon storage by consuming plants and trampling the soil. On the other hand, moderate grazing can promote diversity by reducing competition among plant species, and increase carbon storage by stimulating regrowth or root growth. To complicate matters further, rangelands cover large geographical areas, so differences in site characteristics like topography and climate also influence plant diversity and carbon storage.

Animals grazing in Ardabil rangelands (Credit: Sahar Ghafari)

We investigated how grazing influences plant diversity and carbon storage, taking site characteristics into account by surveying 1493 quadrats across 10 rangelands in northern Iran. Across sites, more carbon was stored in plants and soils where plant diversity was high. However, heavy grazing reduced plant diversity because animals prefer to eat the most palatable plants, especially grasses. Heavy grazing also reduced carbon storage by removing most plant material and leaving tough slow-growing plants like shrubs. Site characteristics played an important role: the impacts of grazing on plant diversity and carbon stocks tended to be lower at steep sites because they are harder for livestock to access, but the impacts of grazing animals were worse at drier sites.

Overall, our study demonstrates that plant species loss by over-grazing will reduce rangeland carbon storage. Sustainable rangeland management is therefore essential to maintain plant diversity and carbon stocks in these important ecosystems.


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