Limited influence from edges and topography on vegetation structure and diversity in Atlantic Forest

Abstract

Although Atlantic Forest is diverse and heavily fragmented, little is known about the impact of edges created from fragmentation on forest structure and plant diversity. Our investigation of vegetation at agricultural edges aimed to determine edge width, to compare effects of edge influence and topography and to assess patterns of diversity. We collected data on forest structure, plant groups, plant families, and vertical vegetation structure in 2 × 2 m contiguous plots along 250 m transects across the edges of 24 fragments approx. 70 km west of São Paulo, Brazil. We used randomization tests to estimate the magnitude and distance of edge influence, generalized linear mixed models to assess the effect of topography, and wavelet analysis to evaluate spatial patterns. Although there was evidence of edge degradation (lower diversity and cover of most plant groups compared to interior forest) and edge sealing (abrupt changes at the edge particularly for leafy vertical diversity), edge influence did not extend very far with a distance of edge influence of 20 m or less for most variables. Less extensive edge influence compared to other tropical forests was not explained by topography (slope) but could be due to more extensive fragmentation and land use history. The use of multiple approaches to studying forest edges provided complementary information to improve our understanding of the structure of anthropogenic edges in Atlantic Forest. Signs of edge degradation suggest that edge influence should be considered in conservation planning even though edges are narrow.