Non-native plants in mountain ecosystems. An exploration of plant diversity and its response to road disturbance and alien invasion.

Abstract: Understanding patterns of invasive plants becomes ever more important as anthropogenic presence continues to facilitate their spread. In mountainous landscapes, cases of establishment by nonnative species have become frequent, despite the environmentally unfavorable conditions for plants less adapted to the harsh climate. This development can be attributed much to the construction of mountain roads at high elevations, as they provide both a means of seed transport and the disturbance in the vegetation cover needed for germination. Along with an increased presence of non-native species comes the inquiry of threat to biodiversity: Are these supposed invaders reducing the richness of native plants? This study examines the relationship between elevation, road proximity and presence of non-native plants as factors affecting species richness, a simple measure of biodiversity. The analysis uses data gathered following a standardized protocol provided by the MIREN research organization, sampled in Norwegian mountains. Results show that non-native species richness decreased with elevation and were highest in abundance near the low-lands. Richness was on average 14.1 species higher in roadside than natural vegetation. The relationship between non-native and native richness was positive (1.57 increase per unit), showing no sign of negative biotic interactions. An interaction between non-native species richness and road proximity was not found. The results support previous studies, giving strength to the conclusion that human activity is changing the distributional patterns and diversity of plants in mountain landscapes. It also implicates that close attention to new arrivals and preventative measures are important tools for managing potentially invasive species.