Vertical Gradient of Epiphytic Bryophytes in the Amazon: the Rule and its Exception

ABSTRACT In Amazonian Terra Firme vegetation, epiphytic bryophytes present a deterministic distribution along height zones in host trees, at both local and regional scale. Recent findings about the influence of vegetation structure variation on epiphytic bryophyte assemblages suggest that the vertical gradient may also change among adjacent vegetation types. In order to analyze this influence, bryophytes were sampled in five zones from the base to the top of 24 host trees in Várzea and Igapó (flooded) and Terra Firme (non-flooded) vegetation. The species richness and diversity, distribution of guilds of tolerance to light incidence, floristic similarity, and turnover of species composition were evaluated within and between vegetation types. The vertical gradient was observed only in Igapó and Terra Firme. Species richness and diversity were higher at the base in flooded forests, and at the outer canopy in non-flooded forests. These zones also showed higher floristic similarities among vegetation types. The distribution of guilds explained the main patterns observed in assemblages. The spatial distribution of epiphytes in the studied forests is regulated by the interaction between the height zone and vegetation type, and light tolerance is one of the most important attributes explaining the distribution patterns of epiphytes in the Amazon.