Corticolous bryophytes in managed Douglas-fir forests: habitat differentiation and responses to thinning and fertilization

Corticolous bryophytes, that is, mosses and liverworts that inhabit tree trunks, represent an important component of plant diversity in temperate ecosystems, but little is known of their ecology in managed forests. In this study, we quantified community composition and habitat differentiation of corticolous bryophytes in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantations subjected to experimental thinning and fertilization treatments. Twenty-four bryophyte species were recorded in a sample of 480, 225 cm2 quadrats on 60 tree trunks. All moss species and obligately epiphytic liverworts (those with a primary habitat preference for tree trunks) showed highest cover values on south and west exposures. In contrast, facultatively epiphytic liverworts occurred only at the tree base, and mainly on north and west exposures. Pairwise correlations among species cover values were nearly always positive, and cover of the most abundant species, Isothecium myosuroides, was also positively correlated with local species richness of other bryophyte taxa. These patterns suggest that competitive interactions among bryophyte species are not strong in this community. There was little evidence for fertilization or thinning effects on total bryophyte cover or species richness. However, analyses of community composition and species-specific responses indicated significant negative effects of thinning on some bryophyte species. Observed patterns of habitat differentiation, interspecific associations, and treatment responses suggest that stand hydrology and microclimate are of primary importance in determining the distribution and abundance of corticolous bryophytes in managed forests.