Regime shifts and climate responses of alpine grasslands in Gannan Prefecture, China

Ecological regime shifts and resilience are critical for maintaining the stability and sustainability of grassland ecosystems under climate change. However, existing studies on alpine grasslands primarily rely on single indicators and rarely integrate ecosystem structure and function to comprehensively characterize regime dynamics. Taking the alpine grasslands of Gannan Prefecture as a case study, this study quantitatively analyzed long-term grassland dynamics from three dimensions: grassland area, vegetation structure (fractional vegetation cover, FVC), and ecosystem function (net primary productivity, NPP). The Sequential t-test Analysis of Regime Shifts (STARS) method was employed to identify regime shifts, while the "ball-and-cup" model was used to quantify ecological resilience, and the responses of regime dynamics to climate factors were further explored. The results showed that: (1) grassland area decreased by approximately 0.5% during 1995-2024, primarily converting to forest, mainly distributed in Zhuoni, Diebu, and Zhouqu counties, with a total conversion area of approximately 88,600 hm²; (2) Analyses based on FVC and NPP identified two major regime shifts in the alpine grassland ecosystem during 2001-2023, and the detected transition periods showed certain similarities. The strongest FVC-based regime shift occurred in 2018, whereas the most pronounced NPP-based shift occurred around 2006; (3) Ecological resilience exhibited a decreasing trend during the study period, decreasing by 16.03% based on FVC and by 3.85% based on NPP; (4) Furthermore, regime shifts were closely associated with both precipitation and temperature. FVC-based regime shifts suggested a possible lagged response to precipitation, whereas NPP-based regime shifts exhibited relatively synchronous patterns with temperature variability. By integrating structural and functional indicators, this study provides a more comprehensive framework for understanding alpine grassland regime dynamics and resilience under climate change. The findings provide a theoretical basis and methodological references for grassland conservation, ecological restoration, and sustainable ecosystem management in ecologically fragile alpine regions.