Avaliação do efeito de borda sobre a vegetação do cerrado stricto sensu inserido em matriz de pastagem / Edge effects on plant community of cerrado sensu stricto inserted into a matrix of pasture

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

From the Brazilian biomes, the Cerrado has been the most widely and rapidly converted to agribusiness in recent years. The expansion of agricultural frontier over the Cerrado domain resulted in thousands of small fragments embedded in matrices of low similarity, causing a series of negative impacts on the natural ecosystem. Habitat fragmentation is considered one of the most serious threats to the conservation of biodiversity and ecological consequences vary, being intensified in the range of transition between matrix and fragment. The edge effects are caused by biotic and physical changes in marginal areas of the islands of natural vegetation, promoting changes in microclimatic characteristics, which leads to a series of important changes in the ecosystems. The aim of this study was to investigate the existence of edge effect and their consequences on the plant community of Cerrado sensu stricto. The study was conducted in Cerrado fragment with an area of 980.8 ha, located in the municipality of Iaras, SP, whose surrounding area was occupied by pasture for about a century. Structure and floristic composition of distinct vegetation layers was assessed at different distances from the edge (0, 10, 20, 40 and 80 m). Climatic data were collected in two seasons (dry and wet), at the same distances withing the fragment and also in the matrix (10 m away from the edge). The existence of a gradient of vegetation composition or structure and the microclimatic variables related to distance from the edge was investigated. No changes in microclimate and structure or composition of the wood layers related to distance from the edge was observed. Although independent of the microclimate and therefore different from classic edge effects, invasion by the African grass Urochloa decumbens (braquiária) was detected as the only consequence of exposure of the periphery of the cerrado sensu stricto to the pressures of the matrix, causing the exclusion of native grasses and inhibiting the development of small woody plants. The absence of edge effect on other components of the vegetation suggests, at first, that this is not a major threat to the conservation of the Cerrado. However, the biological invasion by the African grass is relatively recent (it was locally introduced about three decades ago) and its consequences have not been adequately assessed. It is possible that their impacts on the upper strata of the vegetation may be observed in future, when the inhibition of regeneration of shrub and tree species jeopardize the dynamics of plant community and the replacement of adults in the populations of these species. In addition, at present the invasion has significant impacts only over 0-20 m from the edge, but it is impossible to predict whether the invasive grass will expand or not into the core area of the fragment in the future.

ASSUNTO(S)

savana fragmentation invasões biológicas fragmentação biological invasions microclima savanna microclimate

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