Flush to Crush: The Paradox of Favourable Springs Leading to Tree Mortality

European forests are increasingly vulnerable to climate change, with mortality rates rising across major tree species. Using data from the French National Forest Inventory (NFI), we examined mortality trends between 2014 and 2023 for over 600,000 trees spanning 52 species and major climate zones. Mortality rates significantly increased, particularly in northeastern France matching spatial patterns of warming temperatures and declining precipitation. Employing explainable machine learning, we identified forest demography (e.g., tree size, competition) and climate anomaly variables as the primary contributors to a tree’s probability of dying. In addition to warmer, drier summers being associated with higher mortality through intensified drought stress, an unexpected contributor to mortality was the occurrence of warmer and wetter springs. This result is consistent with the ‘structural overshoot’ hypothesis that rapid canopy growth during favorable warmer, wetter springs predisposes trees to hydraulic failure during subsequent droughts. Species-specific analysis revealed diverse responses, with drought-adapted Mediterranean tree species showing a lower risk of structural overshoot than temperate trees. Different drought stress mechanisms revealed by our empirical data appear to play compounding roles, with emerging drivers of mortality being chronic dryness (possibly depleting tree reserves and weakening them), acute droughts (causing hydraulic failure), and insufficient post-drought rainfall (hindering recovery). Milder winters and springs also contributed to increased mortality, likely because they enhanced pest survival and disrupted winter dormancy, further exerting stress. With rainfall projected to shift from summer to winter and rising temperatures, future droughts are expected to become increasingly harmful. These findings underscore the urgent need for adaptive policies to safeguard forest ecosystems and their essential functions.