Our knowledge of tree mortality during droughts and heat waves has increased dramatically in recent years. The evidence for hydraulic failure as a significant underlying physiological driver of mortality has become common, with abundant but more variable evidence for both carbon starvation and biotic agents. I will review the evidence for hydraulic failure, carbon starvation, and biotic agents as mortality mechanisms during drought-associated tree mortality. Through this synthesis I will provide a revised framework for investigating mortality during drought.
Results/Conclusions
Within the context of hotter droughts, it is likely that the risk of all three mechanisms will increase in most forests. The role of rising vapor pressure deficit is large. Reconciling the trade-offs of rising CO2 with rising VPD, and the possibility of more severe droughts, is a large challenge confronting the tree-mortality society. This data synthesis points to clear opportunities to revise our tests of mortality mechanisms to allow more informed results. Ultimately, the evidence that these mechanisms are interdependent is abundant, suggesting that researchers should consider as many mortality mechanisms as possible when studying tree death.