Epífitas vasculares em florestas alagáveis de várzeas e igapós de águas pretas da Amazônia Central: padrões de riqueza, composição, diversidade e distribuição de espécies

Abstract

Vascular epiphytes are important elements of the canopy of tropical forests, however, studies focused on the epiphytic component are scarce, most of all in Amazonian flooding forests. This hampers the inclusion of such plant group in conservation action plans and obscures the understanding on the dynamics of flooding ecosystems. In várzea and igapó forests in Central Amazon, we investigates 1121 individuals and approximately 242 arboreal species, from which 343 trees hosted 2922 individuals belonging to 96 species of vascular epiphytes, classified into 59 genera and 13 families. The várzea forest was the more diverse and presented more than the double of species found in igapó forests. Only 15.6% of the species were common to both environments, demonstrating that várzea and igapó contrast in their epiphytes richness and composition. The beta diversity in these environments is mainly generated by species turnover instead of nestedness. The analyses of alpha diversity revealed that tree diameter is positively correlated with epiphyte diversity in both environments, meanwhile, the arboreal and epiphytic diversity are not correlated. On the other hand, distribution analysis showed that, in várzea, epiphytes are horizontally distributed according to tree diameter, while in igapó the horizontal distribution of epiphytes seems to be influenced by the preference of epiphytes in colonizing specific tree species. The analyses of vertical distribution by ecological zones showed that in both várzea and igapó, the inner canopy presented higher species richness. Analyses of distribution using epiphyte height in relation to the soil along with tree diameter showed group of species that have their distribution determined by these two factors and that this pattern seems to reflect the physiology of each group. Our discoveries also show that, exclusively in igapó forests, the flooding cycle influences a great part of the patterns of richness and distribution of epiphytes. The flooding limits the occurrence of species where the tree is submerged, hampering specialized species to occupy the basal portion of the tree. Water level also secondarily influences the horizontal distribution of epiphytes in igapó, because it determines the distribution of trees that are preferred by epiphytes, it also seems to influence in the vertical distribution as it promotes a vertical displacement of epiphyte richness to the higher parts of the trees. We discuss that the epiphytic flora in várzea and igapó have richness patterns similar to the arboreal component of these environments, with a low similarity and the flooding influencing patterns of species richness and distribution. We suggest that other studies should be conducted in other várzea and igapó forests to verify if such patterns are consistent along the great Amazonian floodplain. Finally, the results we present here shed light on ecological and biogeographical patterns for epiphytes in the Amazon and will help in future conservation plans of epiphytes and flooding ecosystems, more and more threatened by anthropogenic actions.