From Delay to Advance: The Impact of Increasing Drought on Autumn Photosynthetic Phenology in Subtropical and Tropical Forests

Abstract Drought dramatically impacts the autumn phenology of vegetation. However, the underlying mechanisms of vegetation autumn phenology responses to drought in tropical and subtropical forests remain unclear. Here, we employed three fitting methods to extract the end‐of‐photosynthetic‐growing‐season (EOPS) dates and quantified their responses to drought intensity using ridge regression and correlation analysis. Our analysis revealed a general delay in the trend of EOPS at an average rate of 3.6 days per decade from 2001 to 2020 in southern China. The standardized precipitation evapotranspiration index (SPEI) emerged as the primary influencing predictor of EOPS processes, surpassing the impacts of temperature, precipitation, and radiation. Notably, our analysis highlighted a shift in the response of EOPS to drought from delay to advancement when drought intensity exceeded 0.38. Incorporating this reversal phenomenon into EOPS models is crucial for accurately predicting autumn phenology under future escalating drought conditions.