Corticolous liverworts and mosses in a gallery forest in Central Brazil: effects of environmental variables and space on species richness and composition

摘要

This study investigates species richness and composition of epiphytic bryophytes on tree trunks in a gallery forest near Brasilia, Brazil, assessing the effect of environmental and spatial variables in structuring the community. On each of 30 living trees with girth at breast height (gbh) 60 cm, we established two 10 cm x 30 cm plots on the lower trunk, facing opposite sides (north and south). For each plot we recorded presence/absence of bryophyte species, bark roughness, gbh. distance to the nearest creek, canopy openness and secondary metabolite content (alkaloids, tannins, flavonoids and saponins) in the bark. We found 31 species of bryophytes (18 liverworts and 13 mosses), in 21 genera and 11 families. Four species were first occurrences for the Brazilian Midwestern Region, another five species for the Federal District. Moss richness was lower in the drier north-facing plots, while liverwort richness did not respond to any of the environmental variables. Species composition of liverworts responded to distance to the creek, while moss species composition was explained by distance to the creek, gbh, bark roughness and saponins. Variation partitioning analyses also showed important differences between mosses and liverworts. Species richness of liverworts was partially explained by "pure space", but not by the environment, while the opposite happened to moss richness. Species composition of both mosses and liverworts were explained by environment as well as pure space. The results suggest that both environmental and spatial mechanisms play a role in structuring the bryophyte community.