FE Alan Knapp talks to Isabelle Marechaux on predicting drought tolerance for Amazonian forest trees

Droughts are predicted to become increasingly frequent and intense in Amazonia, and empirical evidence for the vulnerability of Amazonian trees to drought has grown over the past decade. Little is known, however, about the mechanisms or the diversity of drought tolerance in tropical trees and, it has been difficult to quantify drought tolerance in tropical trees, due to a lack of consensus on a relevant tree functional trait, practical to measure for the hundreds of tree species occurring in tropical forests. In this study, Isabelle Marechaux and her co-authors looked at leaf water potential at wilting or turgor loss point (πtlp), which determines tolerance of leaves to drought stress. By using a new method based on a demonstrated association between πtlp and another trait, the leaf osmotic water potential at full hydration, they were able to estimate πtlp for 165 trees of 71 species, at three sites within forests in French Guiana. This dataset represents a significant increase in information for tropical tree species, revealing a wider range of drought tolerance than previously found in the literature and indicating a potential for highly diverse species responses to drought within forest communities. Given the weak correlations between πtlp and traditionally measured plant functional traits, vegetation models seeking to predict forest response to drought should integrate improved quantification of comparative drought tolerance among tree species.