Ecosystem structure, functioning and stability under climate change and grazing in grasslands: current status and future prospects

Ongoing climate change, as well as long-term overgrazing, is threatening biodiversity and ecosystem functioning in grasslands worldwide. Climate change and grazing could directly alter ecosystem functioning and stability, or indirectly by changing species diversity, composition and plant functional traits. By synthesizing results from publications of the most recent 30-years, we found that effects of climate change and grazing on biodiversity and ecosystem functioning varied from positive to negative, depending on different scenarios. Generally, aboveground net primary production (ANPP), belowground net primary production (BNPP), and species richness showed strong negative responses to 4 degrees C warming, 50% precipitation decrease, and high grazing intensity. Responses of ANPP, BNPP and species richness to precipitation increase were mostly positive, whereas their responses to 2 degrees C warming and low-to-moderate grazing intensity varied from positive to negative. Negative effects of 2 degrees C warming on ANPP were substantially greater in grasslands that had been grazed than those that had not been grazed, and larger in arid and semi-arid grasslands than those in sub-humid and humid grasslands. Under 50% precipitation increase, ANPP responses were larger in grazed than ungrazed grasslands, and bigger in arid and semi-arid than sub-humid and humid grasslands. High levels of grazing intensity had greater effects on productivity and species richness than did warming and precipitation decrease. Currently, although there are increasing number of experiments which have included both climate change and grazing factors, more studies are needed to test the joint effects of climate change (e.g. warming, changes in precipitation patterns) and grazing (grazing intensity and livestock type) on biodiversity and multiple ecosystem functions. Multi-factor experiments would provide a more comprehensive understanding for sustainable grassland management in future.