Diversity-Elevation Relationships of Vascular Plants in Austral Temperate Ecosystems Are Strata Dependent

Using elevational gradients as natural laboratories to examine patterns and drivers of biodiversity has a long history in biogeography and ecology. Across mountain ecosystems globally, diversity commonly decreases with increasing elevation. However, anthropogenic disturbances-particularly those at lower elevations-may alter the diversity-elevation relationship. Here, we examined elevational diversity patterns, community composition, and the effect of disturbances on the diversity-elevation relationship of vascular plants in Hornopirén (Chile). Using a total of 44 plots along two transects, we assessed species diversity in undisturbed habitats (800-1500 m) and in undisturbed and disturbed habitats (300-1500 m) for overstorey and understorey vegetation. We found that species richness of overstorey and understorey vegetation decreased monotonically with elevation, but that of understorey vegetation responded less markedly to elevation. While the Simpson diversity-elevation relationship for understorey vegetation showed a hump-shaped relationship, that of overstorey vegetation decreased monotonically with elevation. Our results are consistent with the idea that decreasing temperature along the elevation gradient likely operated as an environmental filter on overstorey diversity, whereas understorey vegetation was more decoupled from temperature in forested habitats. In the alpine scrub (> 1300 m), variation in Simpson diversity, species evenness, and species composition suggests that biotic interactions potentially shape plant community structure to a greater extent than abiotic conditions. Our results also indicate that the shifted shape of the diversity-elevation relationships and altered species composition when including both undisturbed and disturbed habitats might be associated with anthropogenic disturbances. This suggests that human disturbances fundamentally alter natural processes generating diversity-elevation relationships. We emphasize the importance of assessing biodiversity inside and outside protected areas to detect potential shifts in local biodiversity patterns associated with anthropogenic land use and argue that sustainable management and conservation strategies are essential for mitigating further human impacts on these unique ecosystems.