Abstract:
Environmental gradients are caused by gradual changes in abiotic factors, which affect
species abundances and distributions, and are important for the spatial distribution
of biodiversity. One prominent environmental gradient is the altitude gradient.
Understanding ecological processes associated with altitude gradients may help us to
understand the possible effects climate change could have on species communities.
We quantified vegetation cover, species richness, species evenness, beta diversity,
and spatial patterns of community structure of vascular plants along altitude gradients
in a subarctic mountain tundra in northern Sweden. Vascular plant cover and
plant species richness showed unimodal relationships with altitude. However, species
evenness did not change with altitude, suggesting that no individual species became
dominant when species richness declined. Beta diversity also showed a unimodal
relationship with altitude, but only for an intermediate spatial scale of 1 km. A lack of
relationships with altitude for either patch or landscape scales suggests that any altitude
effects on plant spatial heterogeneity occurred on scales larger than individual
patches but were not effective across the whole landscape. We observed both
nested and modular patterns of community structures, but only the modular patterns
corresponded with altitude. Our observations point to biotic regulations of plant
communities at high altitudes, but we found both scale dependencies and inconsistent
magnitude of the effects of altitude on different diversity components. We urge
for further studies evaluating how different factors influence plant communities in
high altitude and high latitude environments, as well as studies identifying scale and
context dependencies in any such influences.
