Flash droughts threaten global managed forests

Flash drought (FD), characterized by its rapid onset and increasing frequency, has emerged as a significant 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 explore the responses of intact and managed forests to FD events using a newly produced high-resolution Standardized Precipitation-Evapotranspiration Index (SPEI) dataset spanning from 1982 to 2022 and investigate the synergistic effects of forest management practices, FD characteristics, background climate, and meteorological anomalies during FD events based on an interpretable machine learning framework. Global forests have been experiencing FD events with faster onsets, greater intensity, and prolonged duration over the past four decades. These FD events drive the browning of managed forests worldwide, which appear less able to adapt to sustained extreme high temperatures. However, elevated temperatures during FD events lead to forest greening in the Amazon and Siberia regions due to enhanced photosynthesis. Notably, current management practices further exacerbate 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.