Bird beta-diversity of tree plantations and natural forests immersed within a grassy landscape in southern Brazil

The conversion of natural grasslands into tree plantations has reduced the extent of natural habitats in southern Brazil, altering bird composition due to local species extinction and colonization. Tree plantations represent a new land use in the region and are within a mosaic of altered and native vegetation. We investigated whether bird composition of tree plantations immersed within a grassy landscape consists of a nested subset of species from adjacent riparian forests. We sampled birds in riparian forests and in eucalyptus plantations at two stages of development using the point count method. We partitioned beta-diversity into nestedness and turnover components to detect the strength of local extinction and colonization processes, respectively, in determining variation in composition among native forests and intermediate and old-aged plantations considering all birds together and only forest-specialist birds. We then used linear models to test the effect of land use on the pairwise turnover and nestedness that each plantation presents relative to native forests. We recorded 72 bird species, of which 62, 25, and 22 species were found in riparian forests, intermediate, and old-aged plantations, respectively. Turnover predominated in beta-diversity partitioning-whether all birds or just forest-specialist birds were analyzed-showing that the bird composition of tree plantations might not depend on adjacent forests, but instead on sparse resource availability within tree plantations. Finally, we found lower bird turnover for plantations relative to native forests with increasing cover of tree plantations in the landscape. Large extents of tree plantations in the landscape, therefore, homogenize bird composition across sites.