Contrasting altitudinal variation of alpine plant communities along the Swedish mountains

Changes in abiotic factors along altitudinal and latitudinal gradients
cause powerful environmental gradients. The topography of alpine areas
generates environmental gradients over short distances, and alpine areas
are expected to experience greater temperature increase compared to the
global average. In this study, we investigate alpha, beta and gamma
diversity, as well as community structure, of vascular plant communities
along altitudinal gradients at three latitudes in the Swedish mountains.
Species richness and evenness decreased with altitude but the patterns
within the altitudinal gradient varied between sites, including a sudden
decrease at high altitude, a monotonic decrease as well as a unimodal
pattern. However, we did not observe a decline in beta diversity with
altitude at all sites, and plant communities at all sites were spatially
nested according to some other factors than altitude, such as the
availability of water or micro topographic position. Moreover, the
observed diversity patterns did not follow the latitudinal gradient. We
observed a spatial modularity according to altitude, which was consistent
across sites. Our results suggest strong influences of site specific
factors on plant community composition, and that such factors partly may
override effects from altitudinal and latitudinal environmental variation.
Spatial variation of the observed vascular plant communities appear to
have been caused by a combination of processes at multiple spatial scales.