A multiscale method for selecting indicator species and priority conservation areas: A case study for broadleaved forests in Lombardy, Italy

Our purpose was to define a quantitative and expeditious method to analyze the effects of processes that influence species distribution and abundance at different organizational scales. We considered habitat loss, the breaking apart of habitat patches, and habitat structural alteration critical processes that affect species distribution and abundance. We evaluated the effects of these processes by considering the response of selected indicator species to isolation (landscape scale), patch size and edge effect (patch scale), and habitat structure (plot scale). We used broadleaf forests as our case-study ecosystem and birds as indicator species. Faunal data came from a georeferenced, long-term, breeding-bird database, and environmental data were obtained from field surveys and land-use digital cartography. Birds, grouped according to their sensitivity to patch isolation, patch size, edge effect, and habitat structure, indicated how environmental conditions affected species abundance. The most sensitive group to the above-mentioned processes included the Marsh Tit (Parus palustris), Nuthatch (Sitta europaea), and Short-toed Treecreeper (Certhia brachydactyla). We evaluated the umbrella effect of these species for the conservation of the other co-occurring birds and found that their effectiveness varied according to the criterion used to select sites for protection. Site selection based on indicator species identified forest patches with greater species abundance than an alternative criterion that chose sites based on patch isolation and size, edge effect, and forest structure. The alternative criterion, although not as efficient as indicator species, may nevertheless be useful and effective for conservation when faunal data are lacking and guidelines for habitat management or restoration are needed. Our method is applicable to other ecosystems and taxa because the processes we considered occur in many ecosystems and may have significant effects on species from all taxonomic groups.