Variações na composição e estrutura da comunidade arborea de um fragmento de floresta semidecidual em Bauru (SP), relacionadas a diferentes historicos de perturbações antropicas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

The present study describes and compares the floristic composition and physiognomic structure of the arboreal and sub-arboreal strata among secondary and preserved sectors of a fragment of tropical seasonal semideciduous forest with well-known and documented history of man-made disturbance. The study was carried out in the Ecological Station Sebastião Aleixo da Silva, municipality of Bauru, São Paulo state, Brazil, with the purpose of assessing the consequences of man-made disturbance and cattle trampling on forest regeneration. The secondary sectors corresponded to forest tracts that were felled and occupied by crops and pastures in the past and then abandoned to forest regeneration ca. 40 years before this sturdy. The preserved sectors corresponded to areas of the fragment where the forest have been maintained although with minor human impacts. The arboreal vegetation (diameter at breast height or dbh _ 5cm) was sampled in 20 plots with 40 x 40 m of dimensions, and the sub-arboreal vegetation (diameter at the base of the stem or dbs <5 cm and height _ 0,5 m) in sub-plots with 40 x 2 m. The total sample included 3903 and 2239 arboreal and sub-arboreal individuals, respectively, which were all distributed into 139 species and 44 families. A physiognomic assessment of the vegetation, as abundance of lianas and climbers and area of canopy gaps, was made through visual estimation. Soil bulk samples were collected for chemical and textural analyses. The expected effects of cattle trampling on the vegetation were not detected by the methods adopted in this study. The secondary sectors showed similar values to those of the preserved sectors for some characteristics related to the physiognomic structure (number of individuals, basal area and mean diameter of the arboreal stratum), species diversity (values equivalent to or higher than those of preserved sectors), and part of the floristic composition, suggesting that 40 years were enough to restore some aspects of the vegetation of these sectors. Nevertheless, the relative abundance of the species, the composition of species regeneration guilds, as well as soil properties were remarkably different among the sectors. The preserved sectors were characterized mainly by shade-tolerant species, which were notably more abundant than in the secondary sectors, which, in turn, showed higher concentrations of pioneer species. The soils of the secondary sectors showed higher proportions of sand and lower levels of mineral nutrients than the preserved sectors, probably because of higher losses by leaching and erosion. The results suggest that differences still observed on the distribution of abundances among species as well as differences in soil properties among the forest sectors are related to the different intensities of past man-made disturbances

ASSUNTO(S)

florestas - avaliação regeneração (biologia) reflorestamento

ACESSO AO ARTIGO

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