Climate-related variables and geographic distance affect fern species composition across a vegetation gradient in a shrinking hotspot

<div><p><b><i>Background:</i></b> The Atlantic Forest biome is a top hotspot for conservation priorities, but the variations in fern species composition and the factors driving these are still poorly known. The vegetation gradient found in the state of Santa Catarina, southern Brazil, constitutes an interesting environmental model for examining such patterns.</p><p><b><i>Aims:</i></b> We analysed the variation in fern species composition across a vegetation gradient in the southern Atlantic Forest and the variables that might influence it.</p><p><b><i>Methods:</i></b> We applied cluster analysis (TWINSPAN and WPGMA), ordination (DCA), regression (OLS and GWR) and variance partitioning to species occurrence, environmental and spatial data in 40 sample units (50 × 50 km<sup>2</sup>), using metadata.</p><p><b><i>Results:</i></b> Bioclimatic variables, mainly those related to humidity (water being an essential medium for fern reproduction), and geographic distance were related to variation in fern species composition. Dispersal constraints, probably related to neutral processes, could be evoked to explain the significance of the geographic distance. Overall, a great deal of uncertainty remained with regard to the determinants of floristic composition.</p><p><b><i>Conclusions:</i></b> Our study emphasises, for the first time in the Atlantic Forest, a significant role of environmental determinism and dispersal constraints on the variation of fern species composition.</p></div>