Effects of forest composition and structure on bird species richness in a Mediterranean context: Implications for forest ecosystem management

There is a growing need to manage forest ecosystems for biodiversity conservation. However, there is still a lack of knowledge on which forest characteristics have a greater influence on biological diversity, particularly in Mediterranean forests. To provide further insights in this respect, we analyzed how different characteristics related to forest composition and structure (forest area, canopy cover, canopy cover diversity, development stage, development stage diversity, coniferous species percentage, tree species diversity, and mono-specific forest percentage) influence the richness of forest breeding bird species (considering 22 specialist and 31 generalist species) in a large dataset comprising 2923 UTM 1 km × 1 km cells in Catalonia (NE Spain). Bird species richness was estimated through presence/absence data obtained from surveys conducted within the framework of the Catalan Breeding Bird Atlas (1999–2002). Forest characteristics were obtained from the Spanish Forest Map (scale 1:50,000), which was developed within the Third Spanish National Forest Inventory. Best regression models for forest specialists accounted for up to 53% of the variability in species richness, while models for generalist and total species richness accounted for 34% and 49% of total variability, respectively. Species richness was favoured by more developed forest stages and by tree species diversity, but very dense, closed forest canopies (>70%) decreased species richness for both groups. For specialist species richness the percentage of coniferous forest cover had a slightly negative influence, while generalists were favoured by more diverse canopy closure. We discuss the implications of these results for Mediterranean forest management considering the current situation of Catalan forests.