Wood anatomical trait correlations with hydraulic efficiency and safety in an aseasonal wet tropical forest

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 (ψ₅₀) 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 ψ₅₀). 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 ψ₅₀, whereas tissue fractions, including total parenchyma and pith, did not predict variation in C_ft. These findings reveal that drought tolerance (low ψ₅₀) 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.