Alien roadside species more easily invade alpine than lowland plant communities in a subarctic mountain ecosystem
Effects of roads on plant communities and alien plant invasions are not well known in cold-climate mountain ecosystems, where road building and development are expected to increase in future decades. Knowledge of the sensitivity of mountain plant communities to disturbance by roads is however important for future conservation purposes.
We examined whether mountain roads promote the introduction and invasion of alien plant species from the lowlands to the alpine zone, along three elevational gradients in a subarctic mountain ecosystem in the Norwegian mountains. We also investigated the effects of roads on species richness and composition, including the search for the plant strategies that are most affected by the disturbance. Observations of plant community composition were made together with the recording of abiotic, biotic and anthropogenic factors in 60 T-shaped transects on an elevational gradient from lowlands to the alpine zone.
Alpine plant communities reacted differently to road disturbances than their lowland counterparts. The roadside species composition was more similar to that of the local natural communities on high compared to low elevations, and the difference in species richness was smaller. Less competitive and ruderal species were present in alpine than in lowland roadsides, highlighting the different conditions in mountain versus lowlands.
While the effects of roads thus seem to be mitigated in the alpine environment for plant species in general, mountain plant communities are more invasible than lowland communities. More precisely, relatively more alien species present in the roadside were found to invade into the surrounding natural community at high compared to low elevations, due to a lower resistance of the alpine vegetation against invasion. We conclude that effects of roads and introduction of alien species in lowlands cannot simply be extrapolated to the alpine and subarctic environment and that higher vulnerability for future invasion can be expected on high elevations.