Exotic tree monocultures play a limited role in the conservation of Atlantic Forest epiphytes

The Brazilian Atlantic Forest suffered a severe geographic contraction along the last five centuries that reduced drastically most vascular epiphyte populations. Among the range of man-made matrixes, tree monocultures have the potential to contribute positively to the maintenance of the regional epiphyte diversity. Here, we test the similarity in abundance, richness, and species composition between vascular epiphytic communities established in managed monocultures of exotic and native species with natural communities occurring in neighboring native Araucaria Forest patches. In the São Francisco de Paula National Forest (Rio Grande do Sul state, Brazil), we recorded 62 epiphyte species from 300 phorophytes occurring in 12, one-hectare plots of Araucaria Forest and managed plantations of Pinus, Eucalyptus and Araucaria. Species richness, rarefied richness and abundance were significantly higher in Araucaria Forest in comparison to the exotic stands. Species composition was also substantially differentiated as Araucaria Forest patches harbored a greater number of zoochorous species than those of the exotic stands. Additionally, plantations of Araucariaangustifolia, a native species, sustained more individuals and more species than the exotic plantations. Neither tree height nor DBH explained epiphyte richness; however, both phorophyte diversity and stand age together accounted for 92% of the among-site variation in epiphytic species richness. We conclude that substrate heterogeneity in combination with time available for colonization contribute significantly to beta-diversity of epiphytes in Araucaria forests. However, demographic experimental studies are necessary in order to disentangle the role of substrate quality from metapopulation processes, such as dispersal limitation, at both temporal and spatial scales.