Forest remnants in the Atlantic Forest domain consist mainly of secondary forests at different successional stages. Studies of succession dynamics of this vegetation are important to provide guidelines for its management. The dynamic of floristic composition and of horizontal tree vegetation structure of a secondary semideciduous seasonal forest fragment was evaluated during a nine- year period in the county of Viçosa, State of Minas Gerais, southeastern Brazil. Diameter at breast height (DBH) and height of trees with a DBH greater than or equal to 5 cm were measured in 1992, 1995, 1998, and 2001, at ten sites with different aspect, slope and degree of anthropogenic disturbance. The Shannon-Weaver index and importance value (IV) were
obtained for each sampling date, and the mean annual mortality and ingrowth rates were determined for the period studied. A total of 161 species, 114 genera, and 48 families were sampled in the nine-year study period. Leguminosae, Lauraceae, Euphorbiaceae, Myrtaceae, Flacourtiaceae and Meliacae families presented the greatest abundance of species. Leguminosae has the highest number of species, possibly due to their life strategy. The initial secondary species constituted the largest ecological group, indicating that the studied forest fragment is at an intermediate stage of succession. The diversity index of the
entire forest did not vary significantly during the nine-year period, increasing slightly from 4.18 to 4.22. Sites 1, 2, and 9 presented the lowest diversity indices due to the intensive anthropogenic interference in these areas. The importance values of species changed with time due to their ingrowth and mortality balance and to the variation in species composition. The following species presented importance values above 10% in at least one site: Piptadenia gonoacantha, Zeyheria tuberculosa, Anadenanthera peregrina, Villaresia megaphylla, Pseudobombax longiflorum, Dalbergia nigra, Vernonia diffusa, Apuleia leiocarpa, and Myrcia fallax. An increased importance value of Siparuna guianensis at most studied sites indicates the remarkable plasticity of this species. The variability of floristic composition, species importance value, mortality and ingrowth rates, and ecological group stribution is the result of anthropogenic interference, in addition to variation in physiographic conditions, especially aspect and slope of terrain.
