Effects of habitat fragmentation on plant guild structure in the montane Atlantic forest of southeastern Brazil

Habitat fragmentation is a major cause of biodiversity erosion in tropical forests. The Brazilian Atlantic forest has both high species richness and a long history of anthropogenic disturbance, beginning with colonial agricul ture in the sixteenth century. Here we examine the species composition and guild structure of woody plants within five montane Atlantic forest fragmen ts of the Tiet River basin, State of Sao Paulo, southeastern Brazil, rangin g from 5 to 7900 ha in area. We found a negative relationship between fragm ent size and the relative importance of tree and shrub species that (1) dep end on abiotic modes of seed dispersal, (2) are shade-intolerant, and (3) o ccupy the forest canopy. As fragment size decreased, there was a marked ris e in the relative importance of ruderal species, primarily in the Composita e, Euphorbiaceae, Solanaceae, and Leguminosae. There also was a 9% average decline in smaller fragments in relative importance of Myrtaceae, Lauraceae , Sapotaceae, and Rubiaceae, which are the main sources of fleshy fruits fo r vertebrate frugivores in these forests. Our results suggest that predicta ble shifts in plant guild structure occur as tropical forest fragments are reduced in size, and that small fragments may become dominated by edges and the surrounding habitat matrix. We suggest that small forest fragments wil l be unlikely to preserve intact plant and animal assemblages of Brazil's A tlantic coastal forest (C) 1999 Elsevier Science Ltd. All rights reserved.