Bark traits affect epiphytic bryophyte community assembly in a temperate forest

Bark traits of trees often serve as a key factor determining the community structure of epiphytes. However, the extent to which barks modulate the relative importance of abiotic and biotic assembly processes of epiphytes is poorly understood. Here, using a community phylogenetic approach, we aimed to infer the assembly processes of epiphytic mosses and liverworts on tree species with varying bark traits in a temperate forest of central Japan. We observed a total of 56 moss and 35 liverwort species on 150 trees. Moss communities showed decreasing species richness and a tendency toward phylogenetic overdispersion, that is, higher phylogenetic diversity than expected by chance, in relation to increasing bark roughness, acidity, and wetness. Along the same bark gradients, liverwort communities became phylogenetically clustered. Species richness of both mosses and liverworts increased with the nitrogen content of barks. The results indicate non-random assembly processes such as interspecific competition on resource-rich barks and abiotic filtering associated with environmental harshness and microhabitat variety determined by barks. Our findings imply that bark traits modulate community assembly processes through which epiphyte diversity is maintained.