Dominant grasses buffer the fluctuation of plant productivity to long-term grazing pressure in a desert steppe grassland

Abstract

Grazing by livestock can influence the diversity and productivity of plants in an ecosystem, as well as the relationship between productivity and diversity. Furthermore, these effects or their relationship can be strongly influenced by variation in the intensity of grazing as well as external environmental conditions, such as rainfall amount. We used observations over an 18-year period in a desert steppe grassland in Inner Mongolia to evaluate how different intensities of grazing influenced productivity, diversity and the underlying mechanism of their relationship through time. Increasing intensity of grazing led to decreased species richness, primarily via the loss of subordinate and rare species, and a decrease in aboveground net primary productivity [ANPP: g m^-2], primarily due to a reduction in dominant species (especially the forb species, A. frigida). We found a positive association between diversity and productivity in most experimental years (14 out of 18 years), with the slope being strongest in wetter years. This suggests that their positive relationship may be affected by precipitation. We used a random forest model to show that variation in ANPP was mainly driven by variation in dominant species, not species richness. Dominant species may be the key driver in regulating plant primary productivity in these species-poor, water-limited grassland ecosystems, and that less intense grazing may be an appropriate management regime to balance ecosystem functions and herder's income.