Besides whole discussions concerning the influence of environment heterogeneity on species distribution, communities are still treated as enclosed units. With that in mind, we sampled one grid of 100 × 30 m, aiming to analyze the composition variation of fern communities in a transition forest fragment between a tropical Brazilian savanna and the Amazonian forest. Sampling was conducted for evaluating the composition variation in riparian areas. Multivariate analysis was employed to summarize the species composition, while multiple regression analysis was used to evaluate whether the distance from a watercourse, as well as canopy openings, would influence the composition of species along these gradients. This composition was affected by the distance from the watercourse, but was not influenced by canopy opening. Species composition was diverse along the stream distance gradient, from marginal area of streams to the edge of the slope. Individual density and species richness were not influenced by canopy opening, yet they decreased as the distance from the river increased. These results highlight the significance of environmental heterogeneity in the distribution of species in riparian areas, which must be considered when planning vegetation conservation in these regions.