Differential responses of ground dwelling arthropods to ski-piste restoration by hydroseeding

The construction of ski-pistes can cause serious damage to all the components of an ecosystem and may therefore be considered as one of the main causes of human-driven environmental changes in mountain habitats. This study was aimed at assessing the responses of different ground dwelling arthropod assemblages (i.e. ground beetles, spiders and grasshoppers) to ski-piste restoration through hydroseeding with commercial seed mixtures. The soil, vegetation and arthropods of restored and un-restored ski-pistes and the adjacent grassland have been sampled at two high altitude sites in the north-western Italian Alps. The ski-piste soil was characterized by a higher skeletal content and, consequently, a lower amount of fine earth and organic matter than that of the undisturbed adjacent grassland. The plant cover of the restored ski-pistes was very low above 2,500 m a.s.l.; the vegetation cover below this threshold was higher in the study area, mainly due to the seeded species. The unrestored ski-pistes showed very large proportions of bare ground. The responses of the three ground-dwelling arthropod groups to vegetation conditions were different. GLMMs and IndVal analyses showed that all three groups avoided the unrestored ski-pistes plots, which were characterized by a very scarce vegetation cover, irrespective of the altitude. The low altitude plots of the restored ski-pistes, which were characterized by a high vegetation cover, had a significantly larger number of grasshoppers on the ski-pistes than on the adjacent grassland plots. Moreover, these restored ski-piste plots were used in equal proportion to the adjacent grassland plots by ground beetles but avoided by spiders. When ski-pistes become sufficiently revegetated by hydroseeded plants, they are colonized by grasshoppers and, to a lesser extent, by ground-beetles. Spiders, instead, do not colonize the pistes, thus demonstrating that they are the most sensitive arthropods and may therefore represent the best indicators of human-driven environmental changes in high altitude alpine habitats.