Fine-scale population dynamics help to elucidate community assembly patterns of epiphytic lichens in alpine forests

We examined the main and interactive effects of factors related to habitat filtering, dispersal dynamics, and biotic interactions, on tree-level population dynamics of a subset of species composing the epiphytic lichen pool in an alpine forest. We tested these processes evaluating the population size of 14 lichen species on six hundred and sixty-five trees within a 2 ha plot located in a high elevation alpine forest of the eastern Italian Alps. Our results indicate that community assembly patterns at the tree-level are underpinned by the simultaneous effects of habitat filtering, dispersal, and biotic interactions on the fine-scale population dynamics. These processes determine how the single species are sorted into community assemblages, contributing to tree-level community diversity and composition patterns. This corroborates the view that the response of lichen communities to environmental gradients, in terms of compositional and diversity shifts, may reflect differential species responses to different drivers.