Beyond the trailside

It is a question not too often asked: what is the impact of hiking trails on the vegetation they cross? In a series of observational studies in mountain regions across the globe with the Mountain Invasion Research Network, we are trying to tease these impacts apart.

Part of the MIREN team in Mendoza surveying the dry steppe vegetation

In a recent study, led by the MIREN team from Mendoza, we show what these trails do with the surrounding vegetation in the dry Argentinean Andes. As so often, we found a positive effect of trails on non-native species presence, although surprisingly little impact on richness and cover was found. In contrast, the presence of livestock – assessed simply by counting their dung – had a positive effect on non-native presence, richness, ánd cover.

Lead author Lisi monitoring vegetation on a breathtaking mountain backdrop

Additionally, the typical decline of non-native species with elevation was observed: the higher one goes into the mountains, the fewer non-natives are found. Nevertheless, even the highest elevations were not entirely free of non-native species, with the omnipresent Cerastium arvense and Taraxacum officinale occurring all the way up to 3500 m a.s.l.

The native vegetation of the dry Argentinian Andes includes this fabulous ‘mandala-shaped’ Viola species

The conclusion here is rather worrying: the dry Andes vegetation – with its patches of bare soil under protective shrub canopies that facilitate establishment – are relatively vulnerable for non-native plant species expansion away from the trail into the natural vegetation. This effect is strengthened by the intensive use of the landscape by livestock, which rarely sticks to the trail and might spread non-natives even more rapidly away from the trails. With the more than 40 non-native plant species identified in the system, it is clear that the effect of trails here reaches significantly further into the mountain vegetation than the mere imprint of footsteps.

Touristic activities such as horseback riding can mean a significant boost for the spread of non-native plant species in the region

Reference: Alvarez, M. A., Barros, A. A., Vázquez, D. P., Bonjour, L. D. J., Lembrechts, J. J., Wedegärtner, R. E., & Aschero, V. (2022). Hiking and livestock favor non-native plants in the high Andes. Biological Invasions, 1-14.

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