Birds of Aleppo pine plantations in south-east Spain in relation to vegetation composition and structure.
The forested habitats in a large part of the Mediterranean semiarid climates of Spain are dominated by Aleppo pine (Pinus halepensis) forests, most of which are managed plantations. Despite this, the effects of changes in the structure and composition of vegetation on birds are unknown. The work reported here was an attempt to detect the relationships between vegetation characteristics and the bird species that inhabit these forests. The point-count method was used to estimate the presence of bird species and their abundance in Aleppo pine plantations in winter and spring. Four perpendicular 15-m transects were traced in each counting station to estimate the size and density of pines, the cover of the main species in understorey vegetation and its height. Correspondence analysis was used to find the most important variables in the composition of bird communities, as well as in understorey composition and vertical structure. The composition of bird communities at forest sites was better explained by understorey characteristics than by tree-layer variables. Bird species composition was related to understorey composition in both seasons. A significant linear regression model was found relating bird species richness during the breeding season to understorey composition, in particular variation in Quercus ilex and Q. coccifera cover. No significant model could be found for bird species richness in winter. The probability of finding a bird species at a given site within pine plantations was modelled using logistic regression. It is concluded that maintenance or introduction of Q. ilex in the understorey of Aleppo pine plantations would increase the diversity of breeding bird communities and would also improve habitat quality for forest bird species with limited distribution in semi-arid climates. On the other hand, a reduction in pine density would have little effect on these bird communities provided that an appropriate understorey was conserved.