Importance of Quercus spp. for diversity and biomass of vascular epiphytes in a managed pine-oak forest in Southern Mexico

Abstract

Forestry management modifies the diversity, structure, and functioning of intervened forests. Timber extraction reduces tree density and basal area, leading to changes in the communities of vascular epiphytes. The objective of this study was to evaluate the diversity and biomass of vascular epiphytes in Quercus trees remaining in two pine-oak forest stands that have been subjected to two stages of the Silvicultural Development Method (release cutting, and thinning) in comparison with an unharvested old-secondary forest in southern Mexico. For each treatment, richness of epiphytes present on 60 oak trees was recorded and their dry biomass estimated. We calculated the true diversity (Hill numbers) and beta diversity using the Jaccard coefficient of similarity, and generated rank abundance curves per taxonomic epiphyte group (bromeliads, orchids, ferns and others). For each treatment, the relationships between overall diversity and epiphyte biomass to the host trees basal area were analyzed using log linear models. We recorded a total of 67 species of epiphytes species belonging to 10 families hosted by five species of oaks. The greatest species richness (0D) was recorded in the old-secondary forest. Fewer common (1D) and dominant (2D) species were recorded in the release cutting than in the other treatments. Epiphyte diversity and biomass were both slightly related to host tree basal area. Composition of epiphytes was similar (60%) among treatments, although orchids, bromeliads, and other families were more diverse in the old-secondary forest. Most bromeliad species were shared across all treatments, although orchids presented the most exclusive species in the unharvested forest. The bromeliad Tillandsia seleriana provided the greatest contribution to biomass in all treatments, followed by the orchid Camaridium densum. Generalized linear models indicated that epiphyte diversity was significantly related to treatment, and epiphyte biomass to basal area of host trees. Although forest management affects diversity, composition, and abundance of vascular epiphytes, most of their diversity and biomass can be maintained despite timber harvesting. This requires sparing some mature oaks during logging, as they contribute to conservation, establishment, and development of epiphytic communities, and maintaining untreated areas as a source of propagules for these communities.