Abstract
Ever-increasing international trade and anthropogenic activity has led to the relocation of thousands of plant species worldwide. So far, the harsh climate of the European Alps historically has restricted the establishment of alien plants. However, new opportunities created by rising temperatures and increasing human activity might allow alien plants to spread further upwards. Here, the distribution of alien plants along an altitudinal gradient in two Austrian valleys is analyzed. Specifically, the distribution along two contrasting corridors (roads, rivers) and the spread of alien plants into adjacent habitats is examined. Following the MIREN sampling protocol, 20 transects composed of three plots along each river and main road, were established in each study region. Plant species cover and a range of site-specific factors were collected. In total, 641 plant species were recorded, of which 20 were alien. Alien species richness along roads was slightly higher compared to rivers, and the composition of the alien flora differed markedly between roads and rivers. Further, alien plant species richness decreases with distance to roads and rivers (indicating that adjacent habitats are less invaded), as well as with increasing elevation. Mowing along roadsides resulted in lower alien plant species cover, but higher alien plant species richness. Finally, compositional dissimilarity between sites showed that elevation, proximity of a plot to a river or road, and alien plant cover are important factors for higher dissimilarity. This study demonstrates that both natural (rivers) and man-made (roads) corridors play an essential role in the upward spread of different alien plants in mountains.
Highlights
Rising intensity of international trade and anthropogenic activity increases the humanmediated transport of plant species to regions beyond their native range
In Austria, where 60% of the country has an elevation above 500 m, alien species are mostly confined to the lowlands and large river valleys in the Alps (Walter et al 2005)
We selected the main rivers and roads of two mid-size Austrian valleys as study regions: the Lech valley located in the Northern Alps, and the Isel valley located in the Central Alps (Fig. 1A, B, D)
Summary
Rising intensity of international trade and anthropogenic activity increases the humanmediated transport of plant species to regions beyond their native range. Many newly introduced alien species undergo a ‘lag phase’, i.e. range expansion, that often follows with substantial delay after initial introduction (Aikio et al 2010; Rouget et al 2016; Alexander et al 2018). This implies that many alien species are still expanding, and that the equilibrium distribution of alien plant species will be considerably larger than their current one
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