PATTERN OF TREE SPECIES-DIVERSITY IN RIPARIAN FOREST FRAGMENTS OF DIFFERENT WIDTHS (SE BRAZIL)

Width is an essential element of the spatial configuration of riparian forests and may be fundamental in determining their corridor function . In the present study we tested the effect of forest width on florist ic structure (tree species composition and diversity) in 15 fragments of riparian forest in an agricultural fragmented landscape of SE Brazi l. All these fragments were chosen in a geomorphological homogeneous r iver reach under similar soil, topographic and human disturbance condi tions in order to minimize the influence of these factors. The forest widths considered ranged from 30 to 650 m. The results showed that tot al species richness and climax species richness were significantly gre ater when we consider larger fragments, as has been observed in other studies. Nevertheless, species diversity and evenness were not signifi cantly correlated with forest width. The analysis of species compositi on showed that the narrowest fragments were characterized by species w ell adapted to temporary flood conditions, while medium and wide fragm ents showed a composition typical of drier upland areas. Therefore, th e effect of forest width on floristic structure appears to be more str ongly linked to the effect of river floods in the case of the fragment s studied. The existence in riparian corridors of a drier forest, in g eneral richer and more diversified than the annually flooded forest, s eems to favor the maintenance of regional species diversity in fragmen ted landscapes.