Relationship between the density of birds and the availability of resources in Nothofagus antarctica (Nothofagaceae) forests under silvopastoral systems in Tierra del Fuego, Argentina

BLAZINA ANA PAULA; SOLER ROSINA; BENITEZ JULIETA; LENCINAS MARÍA VANESSA

Mariano Roque Alonso

Congreso; X Congreso Internacional de Sistemas Silvopastoriles; 2019

Instituto Forestal Nacional de Paraguay

The Nothofagus antarctica forests in Tierra del Fuego mainly occupy the central zone of the island and currently, sustainable management proposals for them are silvopastoral systems. In this province, birds are the most abundant and diverse vertebrate group in terrestrial environments. Because availability of resources, as well as the characteristics of the forest regarding its forest structure, are determining factors of the density of bird populations, the objective of the study was to determine how forest structure, understory vegetation and arthropods influence in bird density of N. antarctica forest under silvopastoral handling in Tierra del Fuego (Argentina). We selected 32 patches with livestock and different forest structure (distributed in Ea Los Cerros and Ea. Rolito). Three bird censuses were carried out monthly (January and February of two consecutive years) in each patch, where we characterized: forest structure, by a plot of variable radius in the center of the patch; understory vegetation, by visual estimation of plant species cover consumed by birds; and arthropod assemblage, with 3 pitfall traps during those sampling months. The data were evaluated by a canonical correspondence analysis-CCA, using a density matrix of 15 species x 120 samples (922 registered individuals, omitting the carnivorous). This was contrasted against several variables: 3 of forest structure (basal area-AB, canopy cover-CC and growth phase), 5 of understory (total richness, and shrub, grasses, dicots and total cover) and 9 of arthropods (order richness, and abundance of Coleoptera. Diptera, Hymenoptera, Araneae, Acarina, Homoptera and total). Initially all the explanatory variables were considered, but CC and the growth phase have too much strong influence; therefore, we considered them as covariables looking to evaluate the influence of the other variables. The maximum variation explained with two axes was 75% and grouping of the species was observed according to their trophic level. The more correlated variable with axis 1 was the shrub cover, while Coleoptera and Diptera abundance correlated with axis 2 in opposite directions. In the ordination diagram, there was a differentiation between excavator insectivorous bird species, as Campephilus magellanicus, that was associated with Coleoptera abundance, while omnivorous birds as Curaeus curaeus and Xolmis pyrope were more associated with Diptera abundance and shrub cover, respectively. Therefore, regardless forest structure, the density of the bird species would be associated with the abundance of its main source of food, especially certain groups such as excavator insectivorous bird species. The conservation of bird communities in N. antarctica forests under silvopastoral systems could be improved by maintaining structures or conditions that promote the presence of their food sources (e.g. decomposing trunk that favor the presence of Coleoptera).