Abstract Urbanization is a major driver of biodiversity change, yet its impacts on tropical vascular epiphyte communities remain poorly understood. We investigated how vascular epiphyte diversity responds to increasing anthropogenic pressure along an urbanization gradient in southeastern Brazil, ranging from secondary forest fragments to a managed urban park and highly urbanized street-tree environments. Using standardized field surveys and a scale-explicit framework, we quantified alpha, beta and gamma diversity and examined their relationships with host tree structure. Urban habitats—particularly the urban park and isolated street trees—supported higher local (alpha) epiphyte richness and abundance than forest fragments, while overall regional (gamma) richness remained broadly similar among habitats. This apparent maintenance of regional richness, however, was accompanied by marked biotic homogenization: urban communities were dominated by a few disturbance-tolerant generalists, resulting in low species turnover (beta diversity) among sites. In contrast, forest fragments, despite their lower alpha diversity and degraded, secondary status, preserved higher beta diversity and hosted microclimate-sensitive specialist taxa absent from urban environments. Contrary to a well-established ecological paradigm, tree size (DBH and height) was not a significant predictor of epiphyte richness in any habitat, suggesting that urbanization and landscape disturbance can override classical size–diversity relationships. Overall, our findings show that urbanization reshapes epiphyte communities in multifaceted ways, promoting richness at local scales while reducing compositional distinctiveness at broader scales. These results underscore the need to conserve even disturbed forest fragments as reservoirs of regional uniqueness, and to strategically manage urban green spaces to enhance their value for canopy biodiversity.
Vieira et al. (Wed,) studied this question.