Overgrazing impacts plant species diversity in alpine wetlands indirectly by altering its environmental dependency

Abstract

Grazing is a significant disturbance in alpine wetlands that affects plant species diversity directly through livestock activity and indirectly by altering environmental factors. Although the direct effects of grazing are well understood, indirect pathways remain underexplored. We conducted a comparative study of plant species diversity and their environmental dependencies in the ungrazed and overgrazed areas of a typical alpine wetland on the Qinghai-Tibet Plateau to address this. Our results showed that the average Q value (representing the explanatory power of environmental factors on plant species diversity) for hydrological regimes was 0.29 in ungrazed areas and 0.47 in overgrazed areas. The proportion of the Q value attributed to hydrological regimes relative to the total Q value of environmental variables increased from 11.6 % in the ungrazed areas to 26.3 % in the overgrazed areas. Furthermore, the interaction Q values (representing the extent to which the interaction between two environmental factors explains plant species diversity) among the environmental variables in both regions were significantly higher than those of individual variables. The average interaction Q value exceeded 0.5 in the ungrazed areas, whereas it fell below 0.5 in the overgrazed areas. Overgrazing also shifted the impact of hydrological regimes on plant species diversity to a significantly positive effect (β = 0.64, P < 0.001), with soil factors indirectly influencing plant species diversity through hydrological pathways. Our study demonstrated that overgrazing modifies the environmental dependencies of plant species diversity in alpine wetlands. Specifically, it amplified the role of hydrological regimes, which have emerged as critical mediators influencing the effects of both biotic and abiotic soil factors on plant species diversity. Additionally, the direct relationship between soil factors and plant species diversity was significantly weakened, and the overall environmental interactions were suppressed. Both environmental interactions and plant species diversity should be considered key indicators to better assess the health of alpine wetland ecosystems. Our findings underscored the substantial impact of overgrazing on alpine wetland ecosystems, with important implications for biodiversity management and conservation in fragile environments.