Mixed grazing maintains the spatial invariability of alpine grassland biomass by fostering a more diversified community structure and spatial heterogeneity

Abstract

Grazing by large herbivores is widely recognized as an important driver of plant diversity, function and community stability (invariability) in grassland ecosystems. However, previous studies have focused primarily on the community temporal invariability of biomass under single herbivore grazing regimes. Since different herbivores have different foraging strategies, we hypothesize that mixed grazing can increase grassland heterogeneity and community spatial invariability of biomass. Using a 3-year field experiment in an alpine grassland implementing moderate grazing (medium grazing intensity) across various grazing types (including yaks grazing, sheep grazing and mixed grazing), we quantified the impact of different grazing types on the community spatial invariability of biomass and underlying processes including spatial covariation and invariability at the species level. We found that moderate grazing increased the community spatial invariability of biomass by reducing species-level spatial covariation. Furthermore, single grazing indirectly promoted community spatial invariability of biomass by increasing the spatial invariability of dominant species. Specifically, yaks grazing achieved this by suppressing species spatial covariation and improving species spatial invariability, while sheep grazing contributed primarily by improving species spatial invariability. On the contrary, mixed grazing improved the community spatial invariability of biomass by regulating species-level spatial covariation and invariability, independent of the influence of the dominant species. These results suggest that mixed grazing may diminish the disproportionate role of dominant species fostering multi-dominant species coexistence and greater spatial heterogeneity through the diverse behaviours of large herbivores. Synthesis and applications. Our study underscores the critical role of mixed grazing in improving the community spatial invariability of biomass in alpine grasslands. Our research reveals that yaks, sheep and mixed grazing under moderate intensity consistently improve spatial stability by reducing species-level spatial covariation. These findings highlight that mixed grazing, by integrating a variety of herbivore foraging strategies, not only increases the community spatial invariability of biomass but also promotes a resilient, heterogeneous ecosystem structure. Such integrated management practices can be crucial to maintaining the long-term functionality and stability of alpine grasslands, providing valuable insights for grassland conservation and sustainable grazing management.