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

• Published in: Geophysical research letters Vol. 51; no. 20
• Main Authors: Xu, Yue, Li, Mingwei, Liu, Zunchi, Gong, Yufeng, Wu, Zhaofei, Pu, Xiao, Fu, Yongshuo H.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.10.2024; Wiley
• Subjects: Autumn; autumn phenology; Carbon; Climate change; Climate models; Climate prediction; Constraint modelling; Correlation analysis; Delay; Drought; Drought conditions; drought intensity; Evapotranspiration; Evapotranspiration-precipitation relationships; Forest ecosystems; Forests; Phenology; Photosynthesis; Precipitation; SPEI; subtropical and tropical forests; Terrestrial ecosystems; threshold; Tropical forests; Vegetation; Water balance
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL112054

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. Plain Language Summary Ongoing climate change is substantially altering autumn phenology, and subsequently impacting terrestrial carbon and water balance. Tropical and subtropical forests, being major reservoirs of global carbon, are experiencing notable effects due to escalating drought conditions. However, the underlying mechanisms of its autumn phenology responses to drought remain unclear. We employed three fitting methods to extract the end‐of‐photosynthetic‐growing‐season (EOPS) dates of subtropical and tropical forests and quantified their response to drought intensity through ridge regression and correlation analysis. Our analysis revealed a delay in EOPS across over 70% of the studied forests during the period 2001–2020, and we found that the standardized precipitation evapotranspiration index (SPEI) primarily determined the EOPS processes. Interestingly, our analysis demonstrated a shift in the response of EOPS to drought from delay to advancement when drought intensity exceeded 0.38. These findings underscore the existence of a critical threshold in drought severity, beyond which a reversal in the response of EOPS to drought is anticipated. This reversal effect may stem from vegetation's adaptive strategies and environmental constraints. Incorporating this reversal phenomenon into EOPS modeling is imperative for enhancing predictions of autumn phenology and advancing our comprehension of carbon and water balances in forest ecosystems. Key Points The standardized precipitation evapotranspiration index (SPEI) emerged as the primary influencing predictor factor on EOPS processes Increasing drought induces contrasting shifts in the autumnal photosynthetic phenology of tropical and subtropical forests The effect of drought on autumn photosynthetic vegetation phenology shifts from delay to advancement as drought intensity exceeds 0.38