Functional attributes change but functional richness is unchanged after fragmentation of Brazilian Atlantic forests

Fragmentation of tropical forests is one of the greatest threats to global biodiversity. Understanding how biological and functional attributes of communities respond to fragmentation and, in turn, whether ecosystem functioning is impacted upon are critical steps for assessing the long-term effects and conservation values of forest fragments. Ecosystem functioning can be inferred through functional diversity metrics, including functional richness, evenness and divergence, which collectively quantify the range, distribution and uniqueness of functional traits within a community. Our study was carried out in forest remnants of the Brazilian Atlantic rain forest, which is a global hotspot of threatened biodiversity that has undergone massive deforestation and fragmentation. We focus on trees, which play critical functional roles in forest structure, food provisioning and carbon storage, to examine community organization and functional diversity across a gradient of fragmentation, from small to large fragments and at edge versus interior habitats. The interiors of small fragments have marginally higher species richness, but similar community structures, to the interiors of bigger fragments. In contrast, fragment edges suffered significant losses of species and changes in community structure, relative to fragment interiors. Despite shifts in community organization, functional richness was not impacted by fragmentation, with the same number of functions provided independent of fragment size or proximity to edge. However, functional evenness and functional divergence both increased with decreasing fragment size, while fragment edges had lower functional evenness than interiors did, indicating that the abundance and dominance of functional traits has changed, with negative implications for functional redundancy and ecosystem resilience. At fragment edges, large-fruited trees, critical as resources for fauna, were replaced by early successional, small-seeded species. The influence of fragment size was smaller, with a reduction in very large-fruited trees in small fragments counterbalanced by increased numbers of fleshy- and medium-fruited trees. Wood density was not impacted by fragmentation. Synthesis. These results suggest that the interiors of even small fragments can contain important biodiversity, ecosystem functions and carbon stores, offering potential opportunities for cobenefits under existing carbon markets. Retaining forest fragments is an important conservation strategy within the highly threatened Brazilian Atlantic forest biome. What are the impacts of forest fragmentation on the functioning of tree communities within Tropical Atlantic Forest? We show that at fragment edges there is severe change in the tree community and resulting degradation of the ecosystem functions played by trees compared to fragment interiors. However, the interiors of even small fragments can contain important biodiversity, ecosystem functions, and carbon stores, offering potential opportunities for carbon and biodiversity co-benefits by protecting fragments under global carbon markets. © 2013 British Ecological Society.