The impact of high-altitude ski-runs on alpine grassland bird communities.
Treeless mountainous areas at high altitudes have increased in value as wildlife habitat, but they are affected and increasingly threatened by ski-resort developments, in particular by the construction and enlargement of ski-pistes. To assess the extent of this threat, we compared bird diversity and community composition in circular plots centred on (i) ski-runs of recent construction, (ii) grassland habitats adjacent to ski-runs and (iii) natural grassland habitats far from the ski-runs. The study was carried out in the grasslands of the western Italian Alps, located at the top end of Susa Valley (Piedmont) and around the Monte Bianco and Monte Rosa massifs (Aosta Valley). Plots located in natural grasslands supported the greatest bird species richness and diversity and the greatest grassland species density, whereas those set in ski-pistes presented the lowest values. Plots located beside ski-runs did not support smaller numbers of bird species and diversity than plots of natural areas, but they supported a significantly lower bird density. This suggests that ski-pistes, besides exerting a negative direct effect on the structure of local bird communities, may also exert an indirect, detrimental effect on bird density in nearby patches. Generalized linear models showed that species richness and diversity, and abundance of grassland species were best modelled by combinations of factors, including habitat type (the three categories defined above) and altitude. The category ski-run, in particular, was negatively correlated with species richness, diversity and abundance, and altitude was negatively associated with richness and diversity. Richness and abundance of arthropods were significantly lower in ski-pistes than in the other plot types. Given that many invertebrates were preyed upon by birds, low food availability on ski-runs may be one of the factors reducing the attractiveness of these patches to birds. Retaining the avifauna around ski-resorts is likely to involve developing new, environmentally friendly ways of constructing pistes, such as only removing rocks and/or levelling the roughest ground surfaces, to preserve as much soil and natural vegetation as possible. Restoration of ski-pistes should promote the recovery and maintenance of local vegetation to enhance invertebrate and bird assemblages. In order to not compromise the safety of the ski-runs, it may be necessary to control encroaching shrubs through pruning and/or cattle grazing.