Topography drives tree-habitat association and functional and phylogenetic structure in the northernmost tropical dry forest of the Americas

BackgroundPlant species composition and structural attributes are related to physiographic factors such as slope orientation and topographic position. This relationship is accentuated with increasing seasonality in temperature and precipitation.AimsWe quantified the relationship between topography and the taxonomic, functional and phylogenetic community composition of woody species at the northernmost distribution of seasonally dry tropical forests (STDF) in the Americas.MethodsWe related slope orientation (north-facing vs. south-facing) and position (upper slope vs. lower slope) to the distribution of species, assessed their habitat preference by life stage (juvenile vs. adult) and compared the observed phylogenetic distance of species against random species assemblages.ResultsOur results showed the segregation of two species groups in both life stages is related to slope orientation, but not to topographic position. We found a strong habitat association for 68% of the species with both juveniles and adults similarly associated with the same habitat. Slope orientation was related to taxonomic, functional and phylogenetic structure, but it differed in the two life stages.ConclusionsThe functional and evolutionary segregation of species between north-facing vs. south-facing habitats indicates that species are non-randomly distributed; suggesting that deterministic mechanisms (e.g. topographic habitat specialisation) are operating at a local scale. Slope orientation drives the species-habitat association, and functional/phylogenetic structure of the northernmost tropical dry forests on the American continent.Juveniles and adults of tree species share similar habitat association patterns, conserving habitat preference.In both life stages, the functional and phylogenetic structure of trees was clearly differentiated between north-facing and south-facing slopes, but similar within each slope.Dry forest tree species are non-randomly distributed among topographic habitats.The contrasting periods of water availability in the soil and solar radiation between slopes have revealed emerging patterns of topographic habitat specialisation.

Automated summary

The study found that slope orientation has a significant impact on the taxonomic, functional, and phylogenetic community composition of woody plant species, while topographic position does not show a clear influence. 68% of the species showed a strong habitat preference, with both juveniles and adults favoring the same habitats. The functional and evolutionary structure of tree species differs between north-facing and south-facing slopes, but remains similar within each slope.