A study of the floristic and structural variations of a tree community was carried out in a tropical semideciduous forest fragment, located on the margins of the Capivari river, in Lavras, Minas Gerais, Brazil, to analyze the correlations between environmental variables (related to soil, topography and fragment shape) and the distribution of tree species. The study also aimed to increase the understanding on the floristic composition and phytosociological structure of tree communities in the upper Rio Grande region. Tree species were sampled in extensive collecting excursions as well as through 28 sample plots of 20 <FONT FACE=Symbol>´</FONT> 20 m, where all individuals with dbh > 5 cm were registered. The plots were distributed into five transects placed parallel to the predominant slope of each site. The environmental variables were obtained through a topographic survey of the fragment and chemical and textural analyses of soil samples. The correlations between the distribution of species abundance and environmental variables in the plots were assessed by canonical correspondence analysis (CCA). The floristic checklist contained 166 species, out of which 140 were found inside the sample plots. The tree community produced a high Shannon diversity index (H' = 4.258 nats/individual), correlated to low ecological dominance (high Pielou evenness, J' = 0.862), and possibly to high local environmental heterogeneity. The CCA showed that the environmental heterogeneity of the fragment is characterized mainly by the steep topography and by the variations in soil fertility, texture and ground water regime. The latter is most strongly correlated with the distribution of the tree species. The analysis indicated that many tree species in the fragment show preference for either of the following two habitats: the lower slope, with moister and more fertile soils; and the upper slope, with less moist and fertile soils, and more liable to edge effects.
Tropical seasonal forest; multivariate analysis; species-environment relationship; tree community and species diversity
