Tropical trees face a hydraulic trade-off that could reshape climate resilience
A new study of Puerto Rican rainforest trees reveals that species cannot simultaneously maximize water transport efficiency and drought resistance—they must choose one strategy or the other. This fundamental biological constraint could determine which tree species survive climate change and has implications for forest management, carbon storage, and watershed protection across the tropics.
Originaltitel: Wood anatomical trait correlations with hydraulic efficiency and safety in an aseasonal wet tropical forest
Valet av trädarter för långsiktig skogsbeskattning och klimatanpassad reglering beror på arter som kan balansera vattenledning med torktålighet. Uppsala universitet och internationella samarbetspartners kartlade hur växtkärlens anatomiska struktur bestämmer denna balans hos 13 tropiska arter i Puerto Rico. Forskarna identifierade en tydlig motsättning: arter med högre vattenledningsförmåga var mer känsliga för embolism (luftblockeringar som stoppar vattentransport). Motsatt vad tidigare teori förutspått var kärldiametern inte avgörande. Istället var kärlnätverkets sammanhang kritiskt — arter med fler isolerade kärl visade större embolismrisk. Resultaten visar att tropiska träd koordinerar två hydrauliska strategier: torktålighet (lågt Ψ₅₀) och torkundvikande (högt vatterlager). För investerare i klimatrobusta skogar och infrastrukturplanerare blir arten av valet nu evidensbaserat: anatomiska signaturer förutsäger vilka arter som överlevde framtida torka utan att offra tillväxt.
Abstract Xylem anatomy underpins the capacity of trees to transport water while avoiding hydraulic failure, shaping species performance and resilience to climate change. However, the specific ways anatomical traits underpin hydraulic trade‐offs in tropical forests remain debated. We investigated relationships between branch wood anatomical traits and their hydraulic properties across 78 individual trees, encompassing 13 species, in an aseasonal wet tropical forest in Puerto Rico. We combined metrics of vessel size, vessel grouping, and tissue fractions with key hydraulic traits, including theoretical hydraulic conductivity ( K th ), embolism resistance (𝜳 50 ) and stem capacitance at full turgor ( C ft ). This allowed us to address two questions. First, we tested whether species in an aseasonal wet forest exhibit a trade‐off between xylem safety and efficiency. Second, we examined which anatomical traits are associated with hydraulic safety strategies, from drought tolerance to drought avoidance. We found a high diversity of hydraulic strategies across species, with strong evidence of a trade‐off between safety and efficiency: individuals with higher K th and higher C ft were more vulnerable to embolism (less negative 𝜳 50 ). Contrary to the vessel diameter hypothesis, vessel size was not significantly related to embolism resistance. Instead, vessel connectivity emerged as a key determinant: species with a higher proportion of solitary vessels were significantly more vulnerable to embolism, supporting the vessel network hypothesis. Multivariate combinations of vessel traits also explained variation in 𝜳 50 , whereas tissue fractions, including total parenchyma and pith, did not predict variation in C ft . These findings reveal that drought tolerance (low 𝜳 50 ) and drought avoidance (high C ft ) are coordinated with water transport efficiency ( K th ), indicating that tropical tree species balance hydraulic strategies along complementary axes of safety‐efficiency. Together, this work advances understanding of the xylem structure–function link in tropical forests and emphasizes the importance of vessel network properties for predicting patterns of species co‐existence and forest resilience under intensifying climatic extremes. Read the free Plain Language Summary for this article on the Journal blog.