A estrutura da floresta de várzea do baixo Purus e sua relação com a duração da inundação

Abstract

Forests occuring along the floodplains of the major rivers in the Amazon region harbour a diverse tree community. Tree species in these forests cope with a yearly seasonal flooding which can last up to eight months. It is therefore expected that environmental conditions limit specie occurrences. We describe the distribution pattern of α diversity of trees in relation to the environmental gradient of inundation. We also evaluated the influence of environment and space in the species composition among sites in the forest landscape of alluvial floodplain of the lower Purus river, Amazonas, Brazil. Using data from botanical inventories of trees ≥ 10 cm DBH, 16 plots of 0.315 ha, we sampled 2 951 trees in 304 species and obtained a Fisher diversity (α) of 85.05. The diversity of trees is inversely related to flood depth. The dominance of each plot directly increases with flood depth. The floristic dissimilarity is high and variation in flood depth and geographic distance between pairs of plots explain more than half of the variation in floristic composition. The most common species were not associated with a specific habitat in the floodplain. Along the gradient of inundation the tree community shows a decreasing number of species together with species replacement. The study of the distribution pattern of diversity along gradients of flooding is necessary for understanding the structure and maintenance of flooded forests in Amazonia.