Aim Seasonally dry tropical forest (SDTF) of the Caribbean Islands (primarily West Indies) is floristically distinct from Neotropical SDTF in Central and South America. We evaluate whether tree species composition was associated with climatic gradients or geographical distance. Turnover (dissimilarity) in species composition of different islands or among more distant sites would suggest communities structured by speciation and dispersal limitations. A nested pattern would be consistent with a steep resource gradient. Correlation of species composition with climatic variation would suggest communities structured by broad-scale environmental filtering.

Location The West Indies (The Bahamas, Cuba, Hispaniola, Jamaica, Puerto Rico, U.S. Virgin Islands, Guadeloupe, Martinique, St. Lucia), Providencia (Colombia), south Florida (USA), and Florida Keys (USA).

Taxon Seed plants -- woody taxa (primarily trees).

Methods We compiled 572 plots from 23 surveys conducted between 1969-2016. Hierarchical clustering of species in plots, and indicator species analysis for the resulting groups of sites, identified geographical patterns of turnover in species composition. Non parametric analysis of variance, applied to principal components of bioclimatic variables, determined the degree of covariation of climate with location. Nestedness versus turnover in species composition was evaluated using beta diversity partitioning. Generalized
dissimilarity modeling partitioned the effect of climate versus geographical distance on species composition.

Results Despite a set of commonly occurring species, SDTF tree community composition was distinct among islands and was characterized by spatial turnover on climatic gradients that covaried with geographical gradients. Greater Antillean islands were characterized by endemic indicator species. Northern subtropical areas supported distinct, rather than nested, SDTF communities in spite of low levels of endemism.

Main conclusions SDTF species composition was correlated with climatic variation. SDTF on large Greater Antillean islands (Hispaniola, Jamaica and Cuba) was characterized by endemic species, consistent with their geological history and the biogeography of plant lineages. These results suggest that both environmental filtering and speciation shape Caribbean SDTF tree communities.