Time-series characterization of forest resistance to extreme drought in southern China

Frequent droughts in the context of global change pose an increasing threat to forest growth. However， the response of karst forests to drought remains poorly characterized. This study proposed a daily 500 m standardized precipitation evapotranspiration index (SPEI) product and utilized solar-induced chlorophyll fluorescence (SIF) as an indicator to quantify the resistance of the karst forest (KF) and the non-karst forest (NKF) in southern China. The mean absolute percentage error (MAPE) of the SPEI calculation results was 8.153%， the Nash-Sutcliffe efficiency (NSE) was 0.71， and the overall estimation accuracy for different wet and dry events was 74%. From 2001 to 2022， the resistance to extreme drought for KFs and NKFs averaged 20.6 and 19.1， respectively， with a decreasing trend in resistance over time. The results indicate that: (1) potential evapotranspiration (PET) products based on satellite observations can enhance the spatial resolution of SPEI products and provide detailed spatial information; (2)time-series SIF products enable the effective characterization of forest disturbances by tracking variations in canopy photosynthetic capacity; and (3) the interannual fluctuation of NKF resistance was significantly higher than that of KF. This study improved the spatial resolution of existing SPEI products and proposed a method to quantify forest resistance to extreme drought based on SIF. The findings can provide a reference for forest management under different geological conditions in the context of climate change.