Drought Vulnerability of Neotropical Canopy Trees and Lianas

International audienceThe high diversity of tropical forests complicates predictions of how canopy trees and lianas will respond to drought. Detail ed physiological measurements are necessary to improve predictions, yet these measurements are tedious and time-consuming, so relatively little data is available. The DROUGHT Project, initiated in 2016, aims to elucidate how hydraulic traits related to drought vulnerability are coordinated among canopy species across the Neotropics by increasing the scope of data available. Method: So far, we have performed detailed measures of hydraulic conductivity, xylem vulnerability curves, sapwood pressure-volume curves, and wood density on emergent branches of 35 common liana and tree species from French Guiana and Panama. Our measurements were stratified across a broad range of wood density. Objectives included determining the range of hydraulic traits, evaluating coordination among hydraulic traits to identify strategies, and providing trait values for inclusion in predictive models. Result: Wood density was correlated with sapwood pressure-volume traits, including capacitance, sapwood water content and turgor loss point. Xylem hydraulic conductivity was related to xylem vulnerability to embolism at some sites, but not others, indicating variation in the xylem safety versus efficiency trade-off. Relationships between wood density and xylem vulnerability to embolism varied among sites. In general, wood density showed greater correlation with sapwood pressure-volume traits than with xylem vulnerability to embolism. Conclusion: Detailed physiological traits offer a way forward for predicting tropical liana and tree responses to drought. An understanding of the trade-offs and coordinated functions that separate tropical canopy species along an axis of drought vulnerability may be an important component for parameterizing Earth system models