Habitat structure influences the diversity, richness and composition of bird assemblages in successional Atlantic rain forests

This study evaluated the influence of vegetation structure on bird diversity, guilds, and the richness and composition of species in different successional stages of the subtropical Atlantic rain forest. Much of the land that was formerly agricultural in the Brazilian Atlantic rain forest region is now given over to secondary forests. The habitat structure of these successional forests vary and are influenced by time, historical use and local variables, all of which affect bird assemblies. Sampling of bird species was carried out through audio-visual point counts conducted in forests varying from six years after abandonment to old-growth areas. Forests in which the point counts were conducted were further classified into initial, intermediate and advanced stages according to 11 vegetation structural variables, through cluster analyses. The study found that bird richness and diversity were similar between initial and intermediate stages, but higher in advanced areas. Bird species composition differed between the initial and advanced stages, whereas the guild composition of initial forests differed in both intermediate and advanced stages. Late successional forests had more heterogeneous habitats, and some species and guilds were found only in this stage. However, bird diversity and species and guild composition were similar in intermediate and advanced forests, emphasizing the importance of successional forests for conservation efforts, especially when they are located near old-growth forests and conservation units. The recovery patterns of the successional forests studied indicate a great potential for the natural regeneration of the Atlantic rain forest, at least in areas where slash-and-burn agriculture was the previous landuse.