<p>Identifying suitable habitats for riparian tree colonization is important for optimizing natural resource management programmes around reservoirs. We investigated the floristic relationships among riparian ecosystems associated with hydroelectric dams constructed in the Brazilian Amazon and selected predictors of biodiversity variation in these ecosystems. We addressed the following questions: (1) How are ecosystems in the Brazilian Amazon affected by hydroelectric dams related floristically? and (2) How do large- and small-scale environmental variations affect tree composition and richness? We accessed floristic data from 62 sites in areas influenced by hydroelectric dams, collected after the start of their operation, for which we obtained data on climatic, topographic and edaphic variables, and distance from the nearest water course. We found that the floristic variation among different ecosystems in the Amazon basin affected by hydroelectric dams is conditioned by the synergistic action of environmental predictors and spatial filters. The composition and richness of tree species are strongly predicted by edaphic and topographic gradients, especially by elevation and slope of the terrain, in addition to intrinsic hydrological characteristics of dams. Although they are crucial for survival and serve as reservoirs of species that must be preserved along rivers, hills and slopes are exposed to deforestation, geological instability and soil erosion, making it necessary to carry out complementary studies that will help predict the potential risk of species loss in these environments.</p>