Edge effects in savanna fragments: a case study in the cerrado

Background: Although impacts of edge effects on forest ecosystems are well known, their consequences on savannas have rarely been explored.Aims: To investigate the influence of edge effects on the plant community and microclimate of a cerrado fragment in south-eastern Brazil.Methods: Several plant community variables (density, basal area, richness and cover by each vegetation layer) and microclimatic variables (light, air temperature and humidity), were measured in 10 transects across a savanna fragment surrounded by exotic grasses, and were used to fit semi-parametric models relating these variables with the distance from the habitat edge.Results: Differences in microclimate and tree communities were poorly related to distance from the edge. On the other hand, there were detectable edge effects on the ground layer community (i.e. plants less than 50cm in height). Edges had a negative effect on native plants of this layer (density and richness of all species and cover of native grasses), while favouring invasive grasses.Conclusions: Unlike reports for edge effects in forest ecosystems, microclimate does not explain changes in this cerrado fragment. The most significant edge effect threatening the conservation of cerrado vegetation is the widespread invasion by African grasses. Starting from the fragment borders, this invasion causes changes in the structure and composition of the native plant community, thus jeopardising the population dynamics and persistence of native species.