the high tree diversity and vast extent of amazonian forests challenge our understanding of how tree species abundance and composition varies across this region. information about these parameters, usually obtained from tree inventories plots, is essential for revealing patterns of tree diversity. numerous tree inventories plots have been established in amazonia, yet, tree species composition and diversity of white-sand and terra-firme forests of the upper rio negro still remain poorly understood. here, we present data from eight new one-hectare tree inventories plots established in the upper rio negro; four of which were located in white-sand forests and four in terra-firme forests. overall, we registered 4703 trees > 10 cm of diameter at breast height. these trees belong to 49 families, 215 genera, and 603 species. we found that tree communities of terra-firme and white-sand forests in the upper rio negro significantly differ from each other in their species composition. tree communities of white-sand forests show a higher floristic similarity and lower diversity than those of terra-firme forests. we argue that mechanisms driving differences between tree communities of white-sand and terra-firme forests are related to habitat size, which ultimately influences large-scale and long-term evolutionary processes.