Environmental dependence of livestock grazing effects on plant diversity in grasslands

Grazing represents one of the most widespread land-use practices, and impacts plant diversity in grassland. In this study, we aim to examine its impacts on plant diversity and underlying regulatory mechanisms. We conduct a comprehensive meta-analysis of 1160 paired observations from 112 studies to synthesize grazing effects on plant diversity, and its environmental dependence in grassland ecosystems. Grazing decreased plant species richness by 3.99% while increasing functional diversity (Rao's quadratic entropy) by 18.20%. Grazing significantly altered community-weighted mean (CWM) trait values, reducing plant stature by 27.87% and leaf dry matter content by 5.86%, but increasing specific leaf area by 14.99%. Crucially, we found that the magnitude and direction (positive or negative) of grazing effects were strongly moderated by environmental context: prolonged grazing duration and small-bodied livestock exacerbated richness loss, particularly under low mean annual precipitation (<400 mm) and temperature (<5 °C) conditions. Elevation emerged as a key moderating variable, exhibiting distinct moderating patterns from climatic factors. Notably, mean annual precipitation (MAP) fundamentally altered the direction of grazing duration effects on both specific leaf area and leaf dry matter content. These results demonstrate that grazing effects on grassland plant communities are fundamentally context-dependent, varying across biodiversity dimensions and environmental gradients. Our findings provide critical insights for developing spatially explicit, sustainable grassland management strategies that account for these complex interacting factors in the face of environmental change.