Estrutura da comunidade de plantas lenhosas em fragmentos de cerrado: rela？？o com o tamanho do fragmento e seu nível de perturba？？o

in this study we analyzed the structure of the woody plant community in 11 cerrado (savanna) fragments located in the triangulo mineiro region, brazil. we evaluated whether vegetation density, diversity and/or composition were related to fragment area or its level of disturbance (cover of exotic grasses and the historical occurrence of cattle and fire). in each fragment (7 to 509 ha in size) 50 plots of 10 x 10 m were established in order to survey all trees with a circumference at breast height (cbh) > 15 cm. tree saplings and shrubs (cbh < 15 cm) were sampled in sub-plots of 5 x 10 m. larger fragments had more individuals (of saplings and shrubs), more species (of trees, saplings and shrubs), and more diversity (of trees) than the smaller fragments. fragment area also explained part of the variation in the species composition of saplings and shrubs. with the exception of a negative relationship between the cover of exotic grasses and the density of saplings and shrubs, we did not find any correlation between the level of disturbance and the structure of the vegetation. however, it was not possible to disentangle size effects from the effects of disturbance as the smaller fragments also presented a higher degree of disturbance, particularly a greater cover of exotic grasses. these results indicate that smaller cerrado fragments are not only more vulnerable to effects resulting from habitat fragmentation, but also to the effects of invasive grasses and disturbance by fire and cattle.