Abstract ID: 3.12250 | Not reviewed | Requested as: Talk | TBA | TBA

Mountain ecosystems are increasingly affected by plant invasions, with non-native species spreading to high elevations. The biotic resistance hypothesis suggests that diverse native communities may limit invasions, yet numerous studies have reported conflicting results. While previous studies attempted to explain these contradictory results using spatial scale, in this study we focused on how environmental gradients and human disturbance associated with mountain roads influence the relationship between native and non-native diversity. To accomplish this, we used a global dataset of standardized vegetation surveys from 15 mountain regions along elevation gradients to analyze at the community level the effects of native species richness and native functional diversity on the number of non-native species.

Our findings revealed a moderation of the biotic resistance hypothesis: at high elevations, we found no evidence of biotic resistance, as non-native species richness was positively associated with native diversity in both natural and roadside habitats. However, at low elevations, communities with high native functional diversity exhibited stronger resistance to invasions, but only in natural habitats. We also found that the ratio of non-native species in natural habitats compared to roadside habitats was high at both low and high elevations, with a drop at mid elevations. This indicates that areas with high non-native richness and introduction rates, like those at low elevations, are more likely to see percolation of non-natives into natural habitats. Additionally, at high elevations, species capable of reaching these more remote environments could have traits associated with spread, and could therefore more readily shift from roadside to natural habitats.

These findings suggest that as climate change weakens environmental barriers and increasing traffic transports more propagules to high elevations, plant invasions into mountain ecosystems will likely accelerate. We conclude that once non-native species reach high elevations, which typically takes place along dispersal pathways such as roads, native plant diversity might not be able to resist their spread into natural plant communities. Therefore, monitoring and management strategies should focus on reducing propagule pressure and minimizing disturbance in vulnerable high-elevation ecosystems to mitigate future invasions.