Amazonian epiphytic bryophytes: community matrix and tools to assess diversity across scales

Aim: Tropical forests are highly diverse at many spatial scales. In these forests, epiphytic bryophyte communities can be species-rich already within a few cm2, and their species numbers increase when expanding the sampling along the tree and the forest. Understanding how this diversity increase depends on scale and position within the tree is critical to evaluate the processes that maintain biodiversity. We, therefore, studied vertical zonation and alpha and beta diversity of epiphytic bryophytes across spatial scales ranging from 100-cm2 quadrats to 24 trees up to 10 km apart. Location: Tropical lowland forest in Yasuní National Park (Amazonian Ecuador). Methods: We sampled epiphytic bryophytes in 100-cm2 quadrats on 24 trees (15-22 sampling quadrats per tree), using a spatially hierarchical design. We applied ordination, indicator species analysis, linear mixed models, and beta partitioning to study alpha and beta diversity at different spatial grains and extents. Results: At the scale of quadrats, tree crowns held more bryophyte species than trunks. Contrastingly, all crown quadrats together held fewer species than all trunk quadrats together (77 vs. 93 species), as species turnover among trunk quadrats exceeded that among crown quadrats. Across spatial extents, species turnover consistently dominated beta diversity over nestedness. Beta diversity was higher between crowns and trunks within trees than among crowns of different trees at all studied scales, while beta diversity among trunks exceeded vertical diversity when considering all 24 trees. Main conclusions: These bryophyte communities experience two distinct vertical zones, trunks and crowns, which differ more among them than trees up to 10 km apart. Still, high species turnover makes their species composition highly unpredictable, especially on trunks. Chance processes appear to play an important role in shaping these communities, although analyses at even finer spatial grains may identify the importance of fine-scale habitat filters and species interactions.