Influences of forest type and forest structure on bird communities in oak and pine woodlands in Spain

Abstract

Complex vegetation structure and floristic composition heterogeneity increase niche diversity, which is thought to also increase avian diversity. Woodland avifauna from the Sierra de Guadarrama, Madrid, was studied during spring 2003 to test whether floristic composition and structure of mixed oak-pine forests provided a suitable environment to sustain a specialized avian community that differed in species composition from those of pure pinewoods and oak woodlands. Habitat selection patterns of each species, as well as the intensity with which they selected their preferred habitat were also studied. Bird species richness was significantly higher in mixed oak-pine forests than in pinewoods, whereas differences in avian abundance among the three forest types were not clear. No species preferred or exclusively used mixed transitions. Therefore, slight increases in avian abundance and species richness within mixed forests were explained through the assemblage of both typical oakwood and pinewood avifauna. The results are discussed in the context of the general impoverishment of Nearctic-Palaearctic bird species in the southwestern Palaearctic margin, and the high spatiotemporal fluctuations that mixed transitions have suffered since the Quaternary period. The results highlighted the importance of forest maturity, low altitudinal position of forests and, diversity and development (cover and height) of the shrub layer for forest birds in the region.