Alpine Vegetation Under Stress: Drought Impacts on Subtropical Humid High‐Mountain Plant Communities in East Asia

ABSTRACT Question Alpine regions are particularly vulnerable to climate change, with plants adapted to harsh conditions proving sensitive to shifting environmental factors. While warming can enhance productivity, the combined effects of warming and drought represent a severe threat. We investigated how concurrent warming and drought influence alpine vegetation in Taiwan, testing the hypotheses that (1) warming may increase productivity when water is sufficient, but co‐occurring severe drought and extreme heat will cause disproportionate declines and (2) severe agricultural drought events would lead to declines in mesic and cold‐adapted species, favoring drought‐tolerant species and increasing compositional homogenization. Location Fifteen summit plots in five high‐mountain regions of Taiwan. Methods We applied a multi‐scale approach integrating satellite‐based vegetation productivity indices, long‐term climate anomalies, field‐based diversity measurements, and species‐level climatic optima. Climate events were classified by intensity and frequency from 1951 to 2022, and vegetation changes were assessed using field survey and remote sensing data from 2019 to 2022. Results During 1951–2022, the study regions experienced an average of 1.08 severe droughts and 0.56 extreme drought events per decade, with a marked increase in extreme drought events since 2016. From 2019 to 2022, negative water balance and elevated temperatures led to reduced productivity. Productivity declined moderately under single‐stressor scenarios but dropped significantly when drought and warming co‐occurred. This corresponded with a decline in species richness and evenness, disappearance of mesic and cold‐adapted species, and increased vegetation homogenization. Conclusions Our findings indicate that the co‐occurring drought and extreme heat conditions substantially impact alpine vegetation resilience, driving species loss and community homogenization. With future climate scenarios projecting further decline, even humid alpine climatic region may face ongoing drought‐related threats. Our results underscore the importance of sustained field monitoring and integrated multi‐scale strategies to conserve the alpine biodiversity under climate change.