Alpine and subalpine areas in the mountainous region of Switzerland have long been inhab- ited by humans and used for grazing by cows or sheep and represent a living cultural land- scape. Abandonment and forestation are leading to a decline in these alpine meadows and pastures, which represent a third of all agricultural land in Switzerland. In addition, the brisk construction activity of recent years is exerting additional pressure on the agricultural land, especially in areas used for recreation and tourism. Since the 1990s, the number of transport infrastructure (in particular drag lifts, number of cable cars remained stable) in the mountains has decreased slightly (status 2020: 2,433 installations), but the extent of snow making infrastructure has increased substantially. Of the 22,500 ha of pistes in Switzerland, 11,975 ha now have artificial snow (in 2020: 53 %). Typically, these structural interventions (e.g. pipe trenches) and anthropogenic soil movements affect easily accessible subalpine and alpine nutrient-poor grassland, which have very slow regeneration times due to temperature and the short vegetation period. Today, the high-altitude revegetation shows a pleasing success with regard to the important erosion protection and the achieved coverage of the vascular plants. From a phytosociological perspective however, it represents insufficient restoration, which contradicts the conservation of alpine biodiversity in Switzerland. Therefore, several success controls of high-altitude revegetation have already been carried out in recent years. However, with the advent of genetic analyses for species identification, revegetation can now be evaluated not only on the surface, but statements can be made about the entire biocenosis. The present work on the differences in disturbed and undisturbed alpine pastures is a start by applying these same methods on a small geographical scale to the well-studied species group of soil bacteria, combined with phytosociological surveys and soil chemical analyses.
Vegetation surveys and soil samples were taken within two former construction sites and near them in undisturbed areas at 2500 m a. s. l., above the tree line in circular 10 m2 plots at the Curtinella ski lift on the Corvatsch mountain range (Canton Graubünden, Switzerland) in 2021. The construction sites were re-vegetated in 2017 (seeding and turf) and 2020 (turf). The areas from 2017 are used as ski slopes with artificial snow. The vegetation cover of the species was recorded, the soil cover (stones, gravel, fine soil) estimated and the soil depth, pH and electrical conductivity measured. The nutrient content (C, H, N) as well as the con- tent of active microorganisms of the soil samples were analysed. In addition, the bacterial community was analysed via 16S rRNA-sequencing. The Shannon index was used as a measure of Biodiversity of species community, which was compared in pairs between the different types of sites investigated.
The plots of the sown construction site from 2017 show a decrease in the number of species and Shannon index compared to the undisturbed plots, the plots of the construction site with turf from 2020 show a decrease in the vegetation cover and Shannon index. Soil chemical and biological parameters correlated strongly with soil depth and the proportion of gravel fraction of the topsoil as well as the cover of the herb layer. Both former construction sites show a significant decrease in soil depth and nutrients and an increase of pH. In addition, a significant decrease in soil microbial activity could be detected, as well as a general decrease in bacterial abundance. The Shannon index of the bacterial communities, however, was higher in the disturbed areas. In general, the composition of the bacteria differed and the undisturbed areas could be clearly distinguished. This resulted in eight common taxa of bacteria at the genus level, which in turn will serve as indicators for undisturbed alpine soils in the study area.
Despite the rather successful revegetation for this altitude, the results of this small-scale study in construction sites after one to four years, show a considerable loss of plant species diversity and topsoil quantity, which has a direct impact on the nutrients available in the soil as well as on the bacterial abundance and its composition. With the claim of maintaining biodiversity in high elevation revegetation, this methodology can be applied in a larger scale study to include additional species groups and describe a more holistic biocenosis. Given the slow regeneration time of soils and habitats at this altitude as well as the current high soil losses worldwide, the results speak also for a considerate approach to future construction sites in alpine regions.
Restoration, alpine, vegetation, soils, microorganisms, bacteria