Avaliação de variações ambientais na expressão de um mosaico florestal

Abstract

The present study aimed to analyze the temporal changes in the structure of a semideciduous seasonal forest and its relationships with different types of soils and with variations in precipitation during 15 years of monitoring (2000-2015). The study was carried out in 25 plots of 20 x 20 m, allocated in the period between 1999 and 2000, when were measured the trees with CAP ≥ 15.7 cm. In 2005, 2009 and 2015, these plots were reinventoried with the surviving individuals, being remeasured the deaths recorded and recruits incorporated. Temporal alterations of the tree community were evaluated, from the abundance of individuals and the basal area, obtained in the surveys of the tree community, which were used to obtaining the dynamics rates. Dynamic rates were calculated for the total area and for each soil class. The tree community showed an ecological behavior characterized by a tendency to increase the basal area and reduction the density of individuals. The pattern observed in the community is a result of the combination of mortality rates higher than those of recruitment and of rates of gain higher than losses. This imbalance between dynamics rates indicates that changes in forest structure may, in function of the rhythmic cycles of forests, have been influenced by the advanced stage of forest succession, by climatic variations and by natural events. The temporal behavior similar to the tree community, present in the soil classes, resulted in few differences in the structural and dynamic parameters between the environments. With this result it was demonstrated that the edaphic variability of the fragment may not be pronounced enough to express variations in forest dynamics. However the demographic and structural changes did not occur in the same way in all diametric classes. The abundance was higher among the small individuals, contributing to a disproportional mortality among the diameter classes, whereas the growth was more accelerated among the large trees, resulting in an increase of the basal area accumulation in the larger diameter classes. These changes suggest an advance in the forest maturation process over the monitoring period, influenced by climatic variations and by competition among individuals.