Global field observations of tree die-off reveal hotter-drought fingerprint for Earth's forests

Tree mortality is increasing due to droughts and other climate change-related stressors, but isolating climate signals for tree mortality is challenging. Here, the authors assemble a geo-referenced global database that quantifies how drought and hotter climate drive tree mortality events. Earth's forests face grave challenges in the Anthropocene, including hotter droughts increasingly associated with widespread forest die-off events. But despite the vital importance of forests to global ecosystem services, their fates in a warming world remain highly uncertain. Lacking is quantitative determination of commonality in climate anomalies associated with pulses of tree mortality-from published, field-documented mortality events-required for understanding the role of extreme climate events in overall global tree die-off patterns. Here we established a geo-referenced global database documenting climate-induced mortality events spanning all tree-supporting biomes and continents, from 154 peer-reviewed studies since 1970. Our analysis quantifies a global hotter-drought fingerprint from these tree-mortality sites-effectively a hotter and drier climate signal for tree mortality-across 675 locations encompassing 1,303 plots. Frequency of these observed mortality-year climate conditions strongly increases nonlinearly under projected warming. Our database also provides initial footing for further community-developed, quantitative, ground-based monitoring of global tree mortality.

Automated summary

This study utilizes a geo-referenced global database to quantify the impact of drought and hotter climate on tree mortality events. The research finds a strong correlation between global hotter-drought climate signals and tree mortality, and predicts a nonlinear increase in mortality frequency under projected warming.