Geographical variation in the contribution of planted and natural pine forests to the conservation of bird diversity

Aim: Tree plantations can have beneficial or detrimental effects on regional biodiversity. Here, we focus on how the contribution of pine plantations to the maintenance of regional bird diversity varies geographically compared to natural pine forests, after controlling for the effects of other factors that are known to influence the regional richness of pine forest dwelling birds. Location: Spain. Methods: We combined large-scale datasets from diverse sources (i.e. the Spanish Breeding Bird Atlas, the Third Spanish Forest Inventory, land use and forest distribution maps) to analyse the geographical variation of the contribution of pine plantations in relation to their natural counterparts to the maintenance of the regional species richness of pine forest dwelling birds. To do so, we also controlled for the main environmental, land use and forest structure factors using GLM models. Results: Differences in bird diversity among planted and natural pine forests varied along latitudinal and longitudinal gradients after accounting for altitude, climate, land uses and vegetation structure of pine forests. Planted pine forests in the north-west of the Iberian Peninsula have the lowest bird species richness as compared to natural pine forests, and that difference decreased following a north-west-south-east gradient. Differences also varied among pine species; they were larger for the species with a higher productive vocation (Pinus sylvestris, Pinus nigra and Pinus pinaster) and not significantly different from zero for species with low commercial interest and mainly used for the restoration of tree cover (i.e. Pinus halepensis). Main conclusions: The potential of plantations or natural pine forests to enhance biodiversity is highly dependent on both the pine species and the geographical location. On this basis, we identify the geographical areas (and pine species) where a major naturalization effort of plantations would be needed to increase bird diversity.