Grazing Exclusion Effects on Grassland Community Diversity Vary Along Altitudinal Gradient: A Case Study From Mount Gongga

Understanding the dynamic process of community diversity after grazing exclusion is crucial for the management and conservation of alpine grassland ecosystems. This study conducted a ten-year grazing exclusion experiment across four altitudinal gradients on Mount Gongga, ranging from 3000 to 4130 m, and surveyed community diversity during the years 2012–2016, 2020, and 2022. Several key findings were revealed: (1) the linear mixed-effects models showed that the interaction between altitude and time was significantly correlated with α-diversity, which decrease during the long-term grazing exclusion period across all altitudes. However, the changes in community composition at low altitudes occurred at a slower pace compared to those at higher altitudes; (2) across all altitudes, β-diversity significantly increased under long-term grazing exclusion compared to short-term grazing exclusion, primarily due to species replacement, as evidenced by the seven newly emerged species observed in 2022 relative to 2012; and (3) overall, the coverage of livestock-favored plants, including sedges (Cyperaceae) and grasses (Poaceae), has increased under long-term grazing exclusion, whereas the coverage of other forbs has declined. Pioneer species (e.g., Potentilla leuconota and Plantago asiatica) played a crucial role at low altitudes. These results highlight the complexity of ecological replacement and how factors such as altitude and grazing exclusion influence the dynamics and composition of alpine grassland communities over time.