Generalizing among seasonally dry tropical forests remains challenging due to their inherent ecological complexity. Functional shifts in plant water-use have been predicted to occur across climatic gradients which if true, could lead to a trait-based approach to classifying these systems. A wide range of water-use strategies have been documented in wetter, seasonally distinct regions however whether this extends to much drier, seasonally variable regions is uncertain. We describe the water-use strategies and response to drought conditions of a taxonomically diverse group of 31 dominant tree species in Puerto Rico using a large set of physiological and morphological traits to determine: (i) if stressful environmental conditions due to low, inconsistent rainfall select for reduced trait variation within the tree community and; (ii) whether water-use is associated with leaf habit or growth form.
Results/Conclusions
We found a large diversity of water-use adaptations among species with interspecific differences accounting for 67-94% of the total variation in traits. Although tree species fell along a continuum of strict isohydric to extreme anisohydric, a surprisingly large proportion exhibited maintenance or increases in gas-exchange under strong drought conditions. Such drought-tolerance was strongly tied to investment in wood density and leaf dry matter content. Relatively few species were considered strong drought avoiders (strict isohydric). Generally, evergreens were found to exhibit more negative maximum and greater diurnal variation of leaf water potential, greater wood density and lower water-use efficiency and leaf dry matter content than deciduous species but a surprising number of deciduous trees also showed impressive drought-tolerance. Semi-deciduous leaf habits were less distinguishable due to a wide variety of trait combinations. No relationship was found between measured traits and growth form. These findings contribute to a trait-based understanding of functional distributions along Neotropical dry forest climatic gradients by: (i) underscoring that trees employ similarly wide ranges of water-use behaviors across sites characterized by contrasting precipitation regimes and; (ii) leaf habit and stem count alone have limited utility as a way to classify dry forest species into ecologically meaningful groups.