Diversity may be evaluated by adopting different hierarchical approaches. In this study, we analyzed the breeding bird communities of five habitats spatially distributed along a gradient of landscape vegetation in central Italy. We highlighted their structural differences at three hierarchical diversity metrics (α-, β- and γ-diversity). The beech forest showed the highest averaged values in terms of both abundance and species richness (α–diversity), as well as in terms of Shannon index, while chestnut and oak woods showed the lowest values. Along the vegetation gradient we observed an inverse pattern of spatial diversity from the Mediterranean sclerophilic wood to the temperate and mesophilic beech forest. The beech forest was very rich at the point count scale (higher α-diversity) but had the lower value both in β- and γ-diversity; in contrast, the sclerophilic wood had a low α-diversity (point-scale) and the higher β- and γ-diversity values. The beech forest showed a low β-diversity (low habitat heterogeneity at the vegetation patch level), but due to the higher tree diameter and the related niche availability, it showed a high α-diversity (at point-scale). The sclerophilic wood, which was more simply structured, had a low α-diversity at point-scale, but a high β-diversity at the vegetation patch level, due to a high heterogeneity. This study demonstrates that patterns of diversity may be complex at different hierarchic levels. If conservation and landscape planning strategies are promoted at landscape scale, objectives should be carefully specified in terms of component of species diversity (α-, β-, γ-level).

Peer reviewed