Elevation-dependent regulation of alpine vegetation productivity by snow cover and grazing on the Tibetan Plateau under a warming–wetting climate

Grassland productivity on the Tibetan Plateau (TP) is fundamental to regional carbon cycling and ecosystem functioning and is strongly regulated by snow dynamics and grazing under a changing climate. However, the mechanisms by which alpine grassland productivity responds to interacting climatic, cryospheric, and anthropogenic drivers remain poorly constrained. Here, we integrated long-term multi-source Earth observation data to quantify the spatiotemporal trends of grassland gross primary productivity (GPP) across the TP from 1982 to 2018 and examined the relationships between GPP and snow dynamics, climate, and grazing intensity, with an explicit emphasis on elevation-dependent controls. Our results reveal a pronounced nonlinear reorganization of GPP controls along elevation gradients, with a critical transition zone at mid-elevations (∼3500–4000 m). Within this zone, warming exerted the strongest positive association with GPP, while grazing intensity also showed a positive spatial association with GPP. In contrast, at higher elevations (>4500 m), snow dynamics emerged as dominant constraints on GPP. Structural equation modeling further indicates that snow cover duration showed the strongest negative total effect among the modeled environmental variables, whereas grazing intensity showed an elevation – dependent association with GPP, shifting from a positive spatial correlation at mid – elevations to a negative correlation at high elevations. Across all elevation zones, soil moisture-mediated pathways consistently exert stronger controls on GPP than soil temperature pathways, highlighting water availability as the more direct and dominant constraint on alpine grassland productivity. These findings demonstrate that elevation fundamentally regulates the spatial organization of ecosystem productivity controls on the TP and underscore the importance of explicitly accounting for cryosphere–biosphere–human interactions when assessing alpine carbon dynamics under a warming and wetting climate.