Deciduous-forest bird communities in a fragmented landscape dominated by exotic pine plantations

Impacts of habitat fragmentation on forest bird communities have often been studied in landscapes dominated by agriculture. The striking structural differences between forest fragments and the matrix have led most researchers to rely on island biogeographic theory to predict the distribution of bird species in fragmented forests. However, in some cases the vegetation surrounding fragments is not completely unsuitable for forest birds. Thus, a more general framework is needed to understand the effects of habitat fragmentation. The mosaic approach considers fragments as integrated parts of a complex landscape composed of patches of habitat of different qualities. In the coastal area of the Maule region in central Chile the remaining hualo (Nothofagus glauca) forests cover <10% of the landscape, are severely fragmented, and are imbedded in a matrix of exotic pine plantations. We compared the island and mosaic approaches as explanations for the distribution and abundance of forest birds. Variable circular plots were used to study the distribution of diurnal forest birds in hualo forest fragments and in the surrounding pine plantations. There was a negative relationship between the size of forest fragment and bird species richness per unit area. Fragmentation effects were mostly species-specific. A few large-sized bird species tended to be absent from the smaller fragments, while the presence or abundance of most birds showed no relationship with fragment size. The type of vegetation adjacent to forest fragments had a significant effect on the composition of the bird community inhabiting them. The abundance of most cavity-nesting species in pine plantations was related positively to the proximity of either the nearest native forest fragment or the nearest creek. On the other hand, the frequency of most open-nesting species in pine plantations was spatially unrelated to either forest fragments or creeks and depended mostly on the characteristics of the Vegetation in the understory. Results support the use of the mosaic approach for the study of fragmentation on birds in forest-dominated landscapes.