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Species intraspecific variation drives tropical forest drought resistance

Smith-Martin, Chris12; Muscarella, Robert3; Brodribb, Timothy4; Uriarte, María2

Published Aug 10, 2026 on Dryad. https://doi.org/10.5061/dryad.r4xgxd2vb

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Abstract

Severe droughts are increasingly driving tree mortality, yet predicting forest resilience remains limited by lack of understanding of within-species variation in drought resistance. Although hydraulic traits such as embolism resistance are central to drought survival, studies conducted primarily in temperate regions have reported little intraspecific variation, implying evolutionary constraints in tree species’ adaptive potential. Here, we test this assumption using an unprecedented dataset comprising eleven hydraulic traits for 290 trees representing 18 species collected along Puerto Rico’s fourfold rainfall gradient (1,000 to 4,000 mm/yr). We find that substantial intraspecific variation, together with species turnover, drives coordinated shifts in drought resistance across the gradient. Most species exhibit significantly more embolism resistance and wider stomatal safety margins in drier forests, demonstrating a previously unrecognized level of phenotypic flexibility in tropical trees and an overlooked mechanism for adaptation to increasingly dry conditions. Species lacking such trait variability may be highly vulnerable under a future drier climate. Incorporating both inter- and intraspecific trait variation into predictive models will advance our ability to forecast forest resilience to intensifying droughts.