Floristic composition and phytosociological structure were studied in a fragment of riverine semideciduous forest, along Passa Cinco River, Ipeúna, São Paulo State, southeastern Brazil. A total of 157 continuous plots (5 x 10 m) totalising 0.785 ha were sampled. All trees > or = 5 cm DBH were measured and mapped in 1989 and 1998. The presence of a vegetacional mosaic was observed and possible factors determining this heterogeneity are discussed. Multivariate analysis of vegetation revealed the presence of three vegetacional groups, indicating a strong relationship with edaphic features in the area. Quantitative analysis of community structure showed differences among these groups, which have not changed over time, reinforcing the correlation with soil cover. Vegetational type above alluvial soil, at river banks, showed strong floristic differences, greater diversity, basal area and density. After nine years, few changes occurred in the phytosociological structure for the most important species in the area, with an increase of 2.01% in the total density and 2.80% in total basal area.
Tropical riverine forest; tree communities; dynamics; soil; topography
