Dinâmica da regeneração natural de espécies arbóreas e arbustivas no sub-bosque de povoamento de Mimosa scabriella Bentham, em área minerada, em Poços de Caldas-MG

Abstract

In 1982/1983 as part of its mine rehabilitation strategy, ALCOA Alumínio S.A. hydroseeded herbaceous species and planted tree seedlings of Mimosa scabrella Bentham in Retiro-Branco bauxite mining site. In 1997, 19 sample plots of 50m2 were implanted in this area for initial characterization of natural regeneration process. Sampling sufficiency and ideal size of sample plots were tested. In 2000, a second inventory was performed in these sample plots, to characterize natural regeneration dynamics. Dynamics of natural regeneration process were characterized by means of quantitative and qualitative analyses of floristic composition, horizontal and vertical structure and diameter distribution. Environmental gradients in relation to soil properties and canopy gap were also considered. These studies demonstrated that using continuous forest inventory with a sample plot grid is a viable tool for evaluating natural regeneration dynamics. The stratification process for natural regeneration was characterized. Pioneer and climax species are the main components of the inferior stratum and secondary ones the main component of the superior stratum. The forest succession of Retiro-Branco was found to be undergoing intense structuring activity, characterizing initial stage of succession. The decline of pure stand of Mimosa escabrella is modifying the sucessional order that previously occurred in this area, provoking modification in site conditions. Occupation of these sites occurs by ecological groups, pioneer species being favored in the process. Secondary species, especially Miconia sellowiana, are the most dominant in classes with greatest height and diameter, being the most responsible for construction of the superior stratum. The species which presented best performance in colonization and structuring of natural regeneration at Retiro-Branco for both inventories were Miconia sellowiana, Psychotria sessilis, Leandra melastomoides, Clethra scabra, Myrsine umbellata, Miconia pepericarpa, Tibouchina candolleana, Cordia suberba, Cestrum amictum, Alchornea triplinervia, Casearia sylvestris, Blepharocalyx salicifolius, Myrcia x rostrata and Schinus terebinthifolius. These are indicated as promising species for rehabilitation programs of mined areas in similar conditions of sucessional strategy. The prediction of diameter distributions using a transition matrix proved to be a simple way for foreseeing both the succession process of natural regeneration and future ecological groupings of species, increasing understanding of mechanisms that rule internal succession behavior. The combined use of analysis of floristic composition as to vertical and horizontal structure and distribution diameter plus correlation with environmental variables proved to be efficient for understanding the sucessional process at the level of species and ecological groups. This is useful for the selection of species and for making other strategic decisions for rehabilitation of degraded areas.