Impact of different anthropogenic disturbances on bird communities of Nothofagus antarctica forests and shrublands in NW Patagonia

Abstract

To be able to plan productive uses of the land compatible with the conservation of the biodiversity, it is essential to evaluate the changes that they cause. The Andean patagonic forests undergo different anthropogenic disturbances, like fires, grazing, wood extraction and substitution by exotic coniferous plantations. These activities cause changes on the vegetation and animal communities, and could be affecting the functioning of the forest ecosystems. In Argentine Patagonia, there is a growing opposition to productive activities, particularly to pine plantations, because of its supposed negative ecological consequences, however their impacts are unknown. The aim of this study was to evaluate in which measure different uses of the vegetation of the basin of Foyel river (NO Argentine Patagonia) cause changes on bird communities, especially on the functionally important and the endangered species. Birds counts were conducted from November 2004 to March 2005 (summer) using the variable circular-plot method, in twenty four sites of Nothofagus antarctica native forests and scrubs with different levels of grazing and wood extraction (closed, semiopened, opened), and in eight exotic plantations of Pseudotsuga menziesii and Pinus spp. Although, the vegetation structure of each site was characterized, to identify structural elements of the forests that could be important for bird habitat. Population densities of birds did not differ between vegetation types (25.4 ± 8.4 individuals/ha) associated to different disturbances. Bird richness and diversity (Shannon Index), however, were different among the vegetation types, in forestations both were similar to the undisturbed vegetation types, whereas they increased in vegetations with a medium intensity of wood extraction and grazing, and were highest in those sites whit a high intensity of wood extraction and grazing. A Canonical Correspondence Analysis and an analysis of species composition similarity showed that there are two differentiated communities: those of the more altered N. antarctica forests (by grazing and wood extraction), dominated by birds of opened areas; and another community in the rest of the vegetation types, dominated by species characteristic of forests. Among the key species for the Andean patagonic forests processes, foliage insectivores (Elaenia albiceps and Aphrastura spinicauda) were not seriously affected by any of the anthropogenic disturbances; ground insectivores (Scelorchilus rubecula and Pteroptochos tarnii) used the coniferous plantations, but not the areas opened by intense wood extraction and grazing; whereas the wood insectivore species (Campephilus magellanicus) was rare in all types of vegetation. Our results suggest that the structure and composition of the forest bird communities is mainly determined by changes in the structure of the vegetation, and not by changes in the floristic composition. The bird community of the coniferous plantations is similar to the community of the original systems. Intensive wood extraction and grazing, however, cause great changes, incorporating some species to the area, but eliminating others that are forest dependent.