Efeito de borda em um fragmento de floresta estacional semidecidual no interior do Estado de São Paulo

Abstract

Forest fragmentation processes have been leading to a fast degradation of Atlantic Forest Biome in Brazil, currently one of the most threatened world’s biomes. The edge effect is one of the key processes linked to habitat fragmentation, which accounts for much of ecosystem degradation. In seasonal semideciduous forest ecosystems, were the fragmentation process is older, the importance of edge effect has not been sufficiently documented. We had the objective to assess the edge effect existing in a seasonal tropical forest fragment, considering physical environment and forest structure parameters .The study was conducted in a remnant forest at Lençóis Paulista county, state of São Paulo , at the “Olavo Egydio Setubal”private reserve. The forest is surrounded by Eucalyptus sp commercial plantations and a former Pinus sp stand which had been recently harvested and shifted to Eucalyptus sp. We sampled four 200m long transects, allocated perpendicularly from the edge to the inner part of the fragment. Microclimatic variables (air temperature and relative humidity, soil moisture, light intensity and soil temperature) where collected every three months, during three consecutive days in each transect. We also sampled all individuals with height ≥1,30m in 10x10 m contiguous plots and the regenerating individuals (height ≥50 cm and < 1,30m) in one 1x10 m subplots inside each plot. Data were analyzed using descriptive statistics and analysis of variance. The main effect of distance to the edge was studied by nonlinear regression analysis (exponential model) using the package "Statistica 7.0". The results indicated a non- linear gradient in the microclimatic variables, suggesting an asymptotic edge effect after 50 m from the edge, if we consider the microclimatic variables, and the forest structure. Some species could be pointed out as forest interior indicators (Actiostemon concepciones, Metrodorea nigra, Actinostemon concepcionis, Angostura pentandra), and at least one species (Psychotria sp.) could be associated to forest edges. Based on microclimatic parameters, the affected area was estimated to be as much as 22,5% of the fragment area. Despite the narrow and elongated shape of the fragment, there is still a core area, free of edge effect, where the inner community can persist. However, the high proportion of affected area indicates the need for management looking forward to buffer the edge effect and increase the effective habitat area for more specialized species.