Variação na composição da comunidade herbácea em áreas ripárias da Amazônia central

Abstract

In spite of general agreement on the influence of environmental heterogeneity on species distribution, in Central Amazonia habitat is often delimited as rough classes, such as plateau, slope and floodplain. However, important differences in species composition may occur within seemingly “homogeneous” environments. We investigated the structure of the ground herb community occurring on floodplains in a “terra-firme” forest in Central Amazonia. Fifty 200m2 plots were distributed throughout the floodplains of Ducke Reserve (100 Km2), Manaus, Brazil. Twenty plots were sampled to detect variation in species composition from the stream margin to the edge of the slopes. Thirty plots were sampled to detect the variation from stream headwaters to larger streams. Linear regression analysis was used to determine the effects of environmental variables on species composition, which was summarized by Multidimensional Scaling. Laterally, herb species composition changes along the environmental gradient from the stream margin to the edge of the slopes. This indicates that, within one frequently-adopted broad environmental category, herb species can show niche segregation. The composition of herbs in riparian areas along watercourses was spatially auto correlated and differed between watersheds. The high species turnover indicates high Z diversity and suggests that dispersal limitation is playing an important role on shaping herb species distribution. The strong effects of environmental heterogeneity and dispersal patterns need to be taken into account in planning conservation units for riparian vegetation in central Amazonian "terra-firme" forests.