Tree functional traits across Caribbean island dry forests are remarkably similar

Aim: To examine the climatic and biogeographic drivers of plant trait variation across Caribbean tropical dry forests, a system characterised by high rates of plant endemism despite low moisture availability, high rainfall variability and persistent exposure to hurricanes.Location: Caribbean tropical dry forests.Taxon: Woody plants.Methods We used a database of 572 woody vegetation plots spanning across the Caribbean, including Florida. We then extracted seed mass, specific leaf area and wood density from global trait databases. We supplemented additional trait data from herbaria collections and calculated phylogenetic imputation of traits. Furthermore, we calculated presence-absence community means and functional diversity and correlated these metrics with bioclimatic variables in addition to island and dry forest area using generalised additive models.Results: Despite occurring in climatically distinct regions, Caribbean tropical dry forests are functionally similar, and the trait space of many dry forests are nested within the functional space of others. In line with island biogeographic theory, island area, dry forest area and island isolation were correlated with functional diversity. Although temperature and precipitation were important determinants of trait variation and functional diversity, environmental variables differently impacted trait variation and the variance explained was generally low.Main Conclusions: The high functional overlap among Caribbean dry forests is remarkable given the broad climatic gradient across these islands. High functional overlap suggests that environmental and biogeographic filters constrain plant form and function in these intrinsically fascinating systems. The trait space of these insular dry forest systems points to dispersal-limitation, in addition to high temperature and water limitations, and favouring persistence strategies to withstand high frequency hurricane disturbance.