Are Non-native Plant Species a Threat to the Alps? Insights and Perspectives

Mountain systems throughout the world are recognized as important biodiversity hot spots with rich and distinct flora, compared to the surrounding lowland regions and provide ecosystem services that are important for agriculture and forestry, for touristic, recreational and cultural activities. For these reasons the spread of invasive non-native species can be a threat to the mountains, increasing direct and indirect costs or decreasing the income of the inhabitants. Several studies have been carried out in the Alps, in order to highlight the distribution of alien species and to elucidate the factors that influence their occurrence, considering climate, disturbance and, in particular, human impact and introduction pathways as extrinsic factors while the plant traits of alien species, propagule pressure, and the invasibility of habitats have been considered as intrinsic factors driving the arrival and success of the new comers. All results highlight that the invasion process in the Alps is at the beginning and it is still possible to limit its impacts, since the invasions at high elevations will occur over long periods of time so that researchers and managers have the opportunity of responding in time to the threat. In this work results that have been obtained from research carried out in the Western Italian Alps are analyzed and discussed considering similar results obtained in other mountain regions. The following topics are discussed: (a) the distribution of alien species along the elevation gradient; (b) the influence of climatic factors on the distribution; (c) species invasive capacity; (d) habitat invasibility; (e) distribution models.