Climate‐Driven Variability in Flowering Phenology Changes Across Subtropical Mountains: Traits, Elevation Shifts, and Biogeographic Patterns

Flowering phenology has major impacts on physiological processes, survival, and reproductive success in angiosperms, serving as a critical biological indicator of climate change impacts. However, changes in flowering phenology and their determinants in subtropical montane ecosystems remain poorly quantified at continental extents. Here we investigated the determinants of flowering phenology shifts over the past century across 11 subtropical mountains in China. Based on century-long herbarium collections of 784 flowering plant species in these mountains, we first used linear regression models to assess the magnitude and direction of changes in flowering time for each species in each mountain separately. Then, we investigated the underlying drivers of changes in flowering time, including climate changes, species traits as well as changes in species elevation range size. Our analyses revealed an average advancement in flowering phenology of 3.8 days per decade, though marked regional disparities emerged: flowering times were advanced in southeastern mountains but delayed in southwestern ones. Climate change, species functional traits, and mountain properties all had significant effects on the observed changes in flowering time. Notably, the flowering time of lowland and non-native plants was advanced more than that of alpine and native plants. A key finding was the negative correlation between flowering time changes and elevational range expansions, supporting the hypothesis that phenological plasticity facilitates range adjustments under environmental change. These findings demonstrate that flowering phenological responses are context-dependent, mediated by complex biotic-abiotic interactions. Our study provides the first biogeographical assessment of flowering phenology shifts in subtropical Asian mountains, offering critical insights for predicting ecosystem stability and informing biodiversity conservation strategies under ongoing climate change.