Trampling to save mountain plant diversity?

Posted on June 13, 2022 by lembrechtsjonas

By Ronja Wedegärtner and Jonas Lembrechts

What do you think about when you follow a hiking path up to the nearest mountain peak? When not thinking about the next chocolate break or the view, I spend my time thinking about ways that the trail that I am walking along might change the vegetation.

As I walk up I am passing through different vegetation types. First, the last meters of mountain forest before entering a zone of willow shrubs, followed by a mosaic of low dwarf shrub tundra and alpine meadows. Up on the peak, the vegetation is sparse and close to the ground.

The fact that trail hiking locally affects mountain vegetation is rather obvious. How exactly the vegetation reacts to this persistent trampling, that has up till now however been surprisingly unknown.

Climate is considered the most important driver of where species grow at broader scales. How could those distribution patterns be changed by trails? Well, seeds can stick to boots and clothes and trampling on and along the trail can create gaps in the vegetation that might allow seeds to grow and establish. Alpine plants are considered especially vulnerable to new neighbor plants that might be moved in by hikers from the vegetation at lower zones. On the other hand, alpine species CAN grow in lower elevation zones – just think about those alpine plants thriving in lowland rock gardens. The climate is suitable for them, but the neighboring lowland plants are most often what hampers their lowland success: When they have to compete with faster growing lowland plants for light and nutrients, alpine species are usually outcompeted. When we remove those neighbors along trails by trampling on them, this could potentially improve alpine species chances in such locations?

With this in mind we surveyed almost 200 transects along 16 hiking trails in two popular hiking areas (Dovrefjell in Norway and Abisko, Sweden) and compared which species we found in trailsides and which in the vegetation away from trails. We identified all plant species and measured how disturbed the plots were.

We surveyed the vegetation along 16 hiking trails in the Scandinavian mountains of Abisko (Sweden) and Dovrefjell (Norway) to pinpoint the effects of hiking trails on the unique vegetation of those systems. The study is now published in the journal *Diversity and Distributions.*

Interestingly, we found a median of 4 plant species more in trailside plots than in those away from the trails, an average increase in diversity of 24%.

A simple figure but with important implications: trails have a higher plant species richness than the adjacent interior vegetation. A positive effect of disturbance on vegetation, perhaps a bit counter-intuitive to most?

Based on our more than 11000 species observations and a unique high-resolution climate data, we examined in which climate we found species along trails and away from them (their realized climatic niches) and checked if these niches had shifted along the trails.

*Lead author Ronja immersed in dense willow shrubs along a mountain trail. Picture: I. Janssens.*

We found that alpine species’ distributions shifted towards warmer locations along trails and that more species’ niches overlapped in trailsides – creating greater richness. As such, trails seemed to create interesting opportunities for range expansion for a variety of species.

Importantly, trampling can create space for alpine plants and may help them persist in a changing climate. But we need to consider trails in context: disturbances may also destroy rare communities or rare and trampling-sensitive species.

So, think where you walk when you are next hiking in the mountains and maybe have a little look around for yourself – do you see more or different species along the trail than away from it?

Reference:

Wedegärtner, R. E., Lembrechts, J. J., van der Wal, R., Barros, A., Chauvin, A., Janssens, I., & Graae, B. J. (2022). Hiking trails shift plant species’ realized climatic niches and locally increase species richness. Diversity and Distributions. https://doi.org/10.1111/ddi.13552