Islands in the middle of the forest: size, distance and tree structure drive vascular epiphytes composition in Amazonia white-sand ecosystems

Abstract

Environmental factors and structural characteristics associated with tree communities influence patterns of diversity, and distribution of structurally dependent plants, such as vascular epiphytes. In this study, we investigated the diversity, composition, and structure of vascular epiphytes among five areas of white-sand ecosystems (WSEs or campinaranas), which are considered "islands" of vegetation immersed in other forest matrices, in the Central Amazon, Brazil. We tested the following hypotheses: (1) turnover is the main mechanism that drives beta diversity, (2) the epiphyte communities are geographically structured, with nearby areas sharing a greater number of species, (3) the floristic composition of vascular epiphytes differs between WSE areas and presents typical species in each of them, and (4) the size of the area, the distance from the adjacent forest matrix and the structural characteristics of the tree vegetation influence the composition and distribution of vascular epiphyte communities in the WSE. A total of 17,808 epiphyte individuals were recorded on 486 phorophytes. Our results indicate spatial turnover in the vascular epiphyte composition between WSEs studied. The size of the WSE, the distance from adjacent environments, and structural variables of vegetation (average canopy height and basal area) influence the distribution of vascular epiphytes in the WSEs. In addition, we observed that the communities have geographical structuring, with nearby areas sharing a greater number of taxa among themselves; however, the characteristic species and the epiphytic importance value are different between the areas. Differences in epiphyte communities between areas indicate that each WSe is unique; therefore, the conservation of multiple areas is necessary to preserve the diversity of epiphytes in these ecosystems.