This study compares tree species diversity and community structure between the annually flooded forest (MV) and the submontane semideciduous forest (MS) situated along rivers but outside the frequently flooded area. Fifteen forest fragments were studied along the Jacaré-Pepira River (state of São Paulo) to make this comparison. We used the point-centred-quarter method for floristic survey to record all trees with a diameter greater than 3 cm at breast height (1.3 m). Fragments of MV presented a low species diversity (1.6 nats/tree <FONT FACE="Symbol">£</font> H’ <FONT FACE="Symbol">£</font> 2.9 nats/tree) in relation to fragments of MS (3.0 nats/tree <FONT FACE="Symbol">£</font> H’ <FONT FACE="Symbol">£</font> 4.3 nats/tree). This difference was significant in a discriminant analysis (F= 9.544, p= 0.013). Nevertheless, some fragments presented both forest types (MV and MS), and, as a consequence, had high levels of diversity (H’ near 3.9 nats/tree). The amounts of total density (DT) and total basal area (ABT) presented a wide range of variation, particularly for MS (2040 trees/ha <FONT FACE="Symbol">£</font> DT <FONT FACE="Symbol">£</font> 5479 trees/ha; 21.05 m2/ha <FONT FACE="Symbol">£</font> ABT <FONT FACE="Symbol">£</font> 65.35 m2/ha). In a discriminant analysis, MV and MS could not be distinguished using DT and ABT figures (p> 0.05). The Cover Value Index (sum of relative figures for density and basal-area coverage) showed that the fragments of MV presented always the same most important species (Croton urucurana e Inga affinis ), while the fragments of MS presented a high variety of the most important species, despite the fact that the surveys had been carried out in a short river reach and in similar edaphic and topographic conditions. In the riparian areas there was a strip of transitional forest, which presented intermediate structures between MV and MS, and presented different widths according to topographic conditions and river discharges.
Phytosociological structure; species diversity; riparian forests
