Vascular epiphyte assemblages in a Brazilian Atlantic Forest fragment: investigating the effect of host tree features

This study investigates the relative importance of dispersal- and niche-related mechanisms structuring the assemblages of vascular epiphytes in a 10-ha secondary Atlantic Forest patch in So Paulo city, Brazil. We tested for the effect of characteristics of host trees (species, height, trunk diameter, presence of lianas, and distance to a near stream) and of space on epiphyte abundance, species richness, and species composition of vascular epiphytes. Inside a 0.2-ha plot, all 86 trees with diameter at breast height > 13 cm (27 species) were recorded, as well as all epiphytes larger than 15 cm in length on those trees (380 individuals, 22 species). Twenty-eight trees (32.6 %) did not carry epiphytes. On individual trees, tree species showed a significant effect on epiphyte abundance, richness, and species composition. The bark-shedding Piptadenia gonoacantha carried less epiphytes than other tree species. Distance to the stream showed effects on abundance and species composition, with lower abundance farther from the stream. Tree height had a positive effect on abundance, richness, and species composition, but trunk diameter had none, supporting the importance of vertical stratification in controlling epiphyte richness. Variation partitioning analyses showed little or no effect of "pure space" on abundance, richness, and species composition (explaining 6.7, 4.5, and 0.7 % of variation, respectively), as compared to environmental effects (26, 30, and 14.5 %), generally supporting a higher importance of niche-based processes in structuring epiphytic assemblages on host trees in the plot.