Flash droughts threaten global managed forests

Flash drought (FD), characterized by its increasing frequency and rapid onset, has emerged as a critical threat to ecosystem stability and functions.  However, a global consensus on how forests respond to FD events remains elusive.  Furthermore, the roles of FD characteristics (e.g., onset rate, peak stress, and stress duration) and forest management practices in mediating these responses have yet to be fully explored.  Here, we explored the responses of intact and managed forests to FD events using a newly produced high-resolution Standardized Precipitation-Evapotranspiration Index (SPEI) dataset from 1982 to 2022 and investigated the synergistic regulations of forest management practices, FD characteristics, background climate, and meteorological anomalies during FD events based on an interpretable machine learning framework.  Global forests have experienced faster onset, greater intensity, and prolonged duration FD events over the past four decades.  Those FD events drive the browning of managed forests worldwide, which are unable to adapt to sustained extreme high temperatures.  However, elevated temperatures during FD events leads to forest greening in the Amazon and Siberia regions due to enhanced photosynthesis.  Notably, current management practices have further exacerbated the vulnerability of managed forests to FD events globally.  Our findings underscore the escalating risks posed by more frequent and prolonged FD events to managed forests, highlighting the urgent need to incorporate forest resistance and resilience to extreme climatic events into the development of forest management strategies.