Consequences of pastoral abandonment for the structure and diversity of the alpine avifauna.
There is a long-term trend of depopulation of rural areas and pasture abandonment throughout the Alps. This trend peaked after the Second World War and is now omnipresent. Its ecological consequences are evident mostly below the timberline, where grassland gradually turns into shrub and, ultimately, to forest. This study addresses the consequences of land abandonment and the decline of pastoral practices on the diversity and structure of the bird communities of the Italian Alps. The breeding birds of Gran Paradiso Natural Park in north-western Italy were surveyed, and bird diversity, abundance of grassland, ecotone, woodland and shrub species were analysed using regression in relation to a set of explanatory variables including elevation, local habitat variables, landscape variables and grazing intensity. Avian diversity increased in abandoned pastures as higher numbers of shrub species followed tree and shrub encroachment. Conversely, open habitat species that benefited from grazing were mostly confined to pure grasslands and high altitudes. The effects of grazing were more evident in the montane belt. Grazing maintained open habitats by limiting tree and scrub encroachment, thereby favouring grassland bird species. At higher altitudes, however, grazing had little effect on typical open habitat alpine species (choughs Pyrrhocorax spp., water pipit Anthus spinoletta, alpine accentor Prunella collaris, wheatear Oenanthe oenanthe, snow finch Montifringilla nivalis, rock thrush Monticola saxatilis) and only skylark Alauda arvensis and linnet Carduelis cannabina preferred grazed meadows. Synthesis and applications. This study shows that the abandonment of grazing in the Alps has significant effects on bird species diversity and abundance, especially below the timberline where pastoral decline leads to significant changes in vegetation structure. However, grazing importance differs markedly depending on whether the focus is avian α-diversity or grassland bird abundance. Pastoral abandonment leads to an overall increase in avian diversity, but most species invading abandoned pastures are already common, whereas several grassland bird species that are dependent upon grazed pastures have an unfavourable conservation status. Overall, in terms of bird conservation objectives, large-scale abandonment of long-established pastoral habitats and their complete replacement with scrub, or even forest, is likely to be detrimental.