Associações entre epífitas vasculares e seus hospedeiros em três ambientes florestais na Amazônia Central, Brasil

Abstract

The goal of this study was to investigate how habitat type (lowland, slope, upland), host tree composition, bark characteristics and soil fertility influence community attributes of vascular epiphytic plants in a central Amazonian Forest. Previous studies in other neotropical regions have shown that these variables have different levels of influence on the composition, richness and abundance of epiphytes in relation to habitat type; however such quantitave studies have yet to be conducted in the central Amazonia. In the Adolpho Ducke Forest Reserve the abundances of all species of vascular epiphytes were recorded from 300 host trees with DBH > 30 cm. The host trees were distributed among 30 sample plots established in lowland, slope and upland habitats, and the epiphytic species were classified into 3 vegetative types (holo-epiphytes, primary hemiepiphytes and secondary hemiepiphytes). Overall 21, 000 individuals representing 122 species distributed in 66 genera and 20 families of epiphytic vascular plant taxa were registered during the course of the study. Our results show that in central Amazonia, lowland habitats are distinct in species richness, abundance and composition when compared to both slope and upland environments. Multiple regression techniques (General Additive Models) demonstrate that host tree composition, phosphorous (P) and nitrogen (N) availability together explain 70% of the variation in species richness and 73% of compositional variation for all epiphyte species, 50 % of the variation in species richness and 73% of the compositional variation for holo-epiphytes. Furthermore, null models demonstrate that a majority (76% in positive and 96% in negative associations) of the epiphyte taxa do not exhibit neither preferences nor for five types of bark texture classified in the study. In central Amazonia habitat types have a strong influence on epiphyte community attributes principally among lowland-slope and lowland-upland environments. Host plant composition in concert with edaphic conditions, specifically N and P availability, are apparently the strongest predictors of composition, richness and abundance of epiphytes in central Amazonian forests. Few significant positive and negative associations between substrate type and epiphyte taxa were detected suggesting that differences in epiphyte community structure in relation to host plant composition is due to phylogenetic or other unmeasured physical/environmental factors such as host plant architecture or microclimatic differences. This study corroborates with other experimental studies which have demonstratd both the direct (throughfall effects) and indirect (host tree composition) effects of soil fertility on epiphyte community attributes.