Large trees and dense canopies: key factors for maintaining high epiphytic diversity on trunk bases (bryophytes and lichens) in tropical montane forests

The high richness of epiphytes in moist tropical montane forests is continuously decreasing due to deforestation and habitat loss. Lichens and bryophytes are important components of epiphyte diversity on trunk bases and play an important role in the water balance and nutrient cycling of tropical montane forests. As lichens and bryophytes are very sensitive to microclimatic changes, we hypothesized that their species richness and composition would change with forest alteration. We also expected their response patterns to be different given the capability of lichens to photosynthesize using water vapour. In this study, we assessed the richness and composition of epiphytes (lichens and bryophytes) on the trunk bases of 240 trees in primary and secondary forests of southern Ecuador. We found that diversity was higher in primary forests and lower in monospecific secondary forest stands. Total diversity was negatively affected by habitat loss and by the reduction of canopy cover for bryophytes. Shade epiphytes were replaced by sun epiphytes in open secondary forests. We conclude that lichen and bryophyte diversity of tropical montane forests are negatively affected by the removal of large trees and canopy disruption. The different species compositions of primary and secondary forests and the high number of species exclusive to primary forests indicate that secondary forests are of limited importance in compensating for the loss of non-vascular epiphyte species associated with primary forests.