A catastrophic tropical drought kills hydraulically vulnerable tree species

Drought-related tree mortality is now a widespread phenomenon predicted to
increase in magnitude with climate change. However, the patterns of which
species and trees are most vulnerable to drought, and the underlying
mechanisms have remained elusive, in part due to the lack of relevant data
and difficulty of predicting the location of catastrophic drought years in
advance. We used long‐term demographic records and extensive databases of
functional traits and distribution patterns to understand the responses of
20 to 53 species to an extreme drought in a seasonally dry tropical forest
in Costa Rica, which occurred during the 2015 El Niño Southern Oscillation
event. Overall, species-specific mortality rates during the drought ranged
from 0% to 34%, and varied little as a function of tree size. By contrast,
hydraulic safety margins correlated well with probability of mortality
among species, while morphological or leaf economics spectrum traits did
not. This firmly suggests hydraulic traits as targets for future research.