Seasonally asymmetric warming reshapes grassland stability across timescales.

Climate change can alter ecosystem stability, yet how seasonally asymmetric warming or drought reshapes stability across timescales remains unresolved. To address this, we conducted two multiyear field experiments in Tibetan alpine grasslands, investigating how season-specific warming or drought alters the seasonal and interannual stability of plant community biomass. Spring warming increased both seasonal and interannual stability, whereas year-round warming only enhanced seasonal stability. Summer drought also enhanced seasonal stability, but season-specific droughts showed only weak effects on interannual stability. The increases in seasonal stability were primarily driven by greater species-level stability rather than stronger species asynchrony. In contrast, the increases in interannual stability under spring warming resulted from asynchronous responses among functional groups. These results identify season-specific climate forcing as a key determinant of stability mechanisms, motivating seasonally explicit projections of ecosystem dynamics.