Non-native species distribution along the elevation gradient in the western Italian Alps

Abstract

In this work the occurrence of non-native species was recorded along the elevation gradient in the Alps, in order to establish their distribution pattern, their current altitudinal limits and to elucidate which species are presumably adapted to higher elevations. Plots were located along the course of rivers in five valleys from 100 to 2100 m a.s.l. Sixty-eight non-natives were recorded in the study area. The proportion of invasives was found to be much higher in the study area then in the whole administrative region. The number of non-natives per plot decreased strongly with increasing elevation. The great majority (94%) of the non-native species grows at the lowest elevations, while only 6% survive up to 1500 m and none was found above this limit. Results were interpreted considering the factors driving the invasion process (disturbance, the native communities' resistance to invasion, propagule pressure, climatic conditions) and plant traits with particular respect to pre-adaptation to the harsh climate, which increases progressively with elevation. Results confirm that the Alps are not immune from invasion, at least up to medium elevation.

Keywords:

• Alps
• elevation gradient
• non-native species
• plant invasion
• rivers

Acknowledgments

This 3-year research (2006–2008) was supported by funds from Regione Piemonte, Assessorato Ambiente, Settore Pianificazione Aree Protette, under the direction of Dr. Ermanno De Biaggi. The authors express their gratitude to Daniela Bouvet for all geographical and mapping support, to Alessio Tisi, Chiara Minuzzo, Giampaolo Bruno, Simone Falzoi and Lucia Sitzia for their work in the field.