Tree structure instead of microclimatic zones determines differences in vascular epiphyte assemblages between forest and pasture

Abstract

Land cover change threatens biodiversity by reducing species richness, altering species composition, and favouring generalist species. Pasture creation can promote the loss of original species, although this loss can be mitigated by maintaining scattered trees to reduce their structural differences with forests and thus retaining a portion of regional epiphyte diversity. We explore the negative effects of land cover change and potential factors promoting similarity of epiphyte assemblages between forests and pastures. We hypothesize that pasture epiphyte assemblages are characterized by low species richness and are dominated by xerotolerant and generalist species, with a species composition nested from the forest community, indicating a degree of overlap. We hypothesize that two main factors drive the similarity between forest and pasture epiphyte assemblages: “structural dependence”, whereby trees host similar species on their crowns and trunks independent of habitat, and “microclimatic dependence”, where pasture and forest trees are more similar in areas with comparable microclimatic conditions. We found lower species richness and higher abundance of generalist species in the pasture than in the forest, with differing species composition. However, there was still a significant overlap in species composition between the two habitats, indicating that the epiphyte assemblages in the pasture were nested from the forest assemblages. Pasture and forest trees shared more epiphyte species between crown and trunk zones rather than between shaded and sunlight-exposed zones. Hence, the similarity of vascular epiphyte assemblages between habitats is partially driven by structural factors, where certain epiphyte species preferentially occur in specific tree zones regardless of the microclimate or habitat. Considering these findings, we recommend maintaining and planting scattered trees in pastures to enhance structural complexity (e.g., longer trunks and multiple crown branching), which can foster a proportion of the vascular species from forested areas, thus maintaining the similarity in vascular epiphyte assemblages between habitats.