Biogeographic distributions of neotropical trees reflect their directly measured drought tolerances

Adriane Esquivel-Muelbert,Antonio Carlos Lola Da Costa,Daniel Nepstad,Oliver L Phillips,Lucy Rowland,Patrick Meir,Kyle G Dexter,David Galbraith,Simon L Lewis,Timothy R Baker

doi:10.1038/s41598-017-08105-8

Abstract

High levels of species diversity hamper current understanding of how tropical forests may respond to environmental change. In the tropics, water availability is a leading driver of the diversity and distribution of tree species, suggesting that many tropical taxa may be physiologically incapable of tolerating dry conditions, and that their distributions along moisture gradients can be used to predict their drought tolerance. While this hypothesis has been explored at local and regional scales, large continental-scale tests are lacking. We investigate whether the relationship between drought-induced mortality and distributions holds continentally by relating experimental and observational data of drought-induced mortality across the Neotropics to the large-scale bioclimatic distributions of 115 tree genera. Across the different experiments, genera affiliated to wetter climatic regimes show higher drought-induced mortality than dry-affiliated ones, even after controlling for phylogenetic relationships. This pattern is stronger for adult trees than for saplings or seedlings, suggesting that the environmental filters exerted by drought impact adult tree survival most strongly. Overall, our analysis of experimental, observational, and bioclimatic data across neotropical forests suggests that increasing moisture-stress is indeed likely to drive significant changes in floristic composition.

Highlights

The future composition and structure of tropical forests may be substantially altered by periods of high moisture stress, such as droughts
The water deficit affiliations (WDA) of neotropical tree genera, which display more strongly negative values for genera that occur in drier conditions, are significantly associated with their tolerances to drought
We compared the bioclimatic distribution of 115 tree genera along a continental scale moisture gradient with drought-induced mortality rates from experimental and natural drought events across the Neotropics

Summary

Introduction

The future composition and structure of tropical forests may be substantially altered by periods of high moisture stress, such as droughts. Similar results were observed in Ghana at the lower end of the rainfall gradient (1000–1800 mm y−1) in a study of 21 plots distributed across that country’s forest zone, which represents the largest scale study of this question in the tropics[22] These studies suggest that the distribution vs tolerance relationship holds for tropical forests at local scales, no direct analysis of this relationship that covers a broad range of precipitation values and different life history stages has yet been attempted. Such an approach would provide insights into the potential responses of tropical forest taxa to increasing moisture stress. Given the predictions of drier conditions, better delimitation of the drought vulnerability of different tree taxa would improve our understanding of how tropical forest communities will respond to future changes in climate

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Conclusion