Distance decay of plant and fungal communities at the mesotopographical scale of the Arctic tundra

Distance decay of biological community similarity occurs at global and local scales. Although fine-scale environmental heterogeneity and stress-tolerant organisms likely promote distance decay at local scales in Arctic tundra ecosystems, these dynamics have not been fully tested. Here, community data were obtained for plants and fungi from 216 plots, including along slope gradients, at the Pond Inlet on northern Baffin Island. Beta diversity was calculated between plots resampled in systematic combinations, and variations with geographic distance and environmental heterogeneity were assessed. Our results showed that distance decay occurred at a local scale. However, the mechanisms underlying differences in distance decay varied between sites and taxa. Specifically, distance decay at the mid-slope section was caused by niche-based mechanisms underlying the increasing environmental heterogeneity with spatial extent. While the predictors of distance decay differed among taxa between the top and bottom sites, plant community composition was more strongly influenced by dispersal limitation than that of the fungal community. Moreover, the distance decay tendency disappeared for combinations of plots with different topography, suggesting that distance decay was not a dominant effect across the study area. Our results suggest that the effects of topography and distance decay on communities in the slope direction and horizontal direction, respectively, may interfere with each other, thereby making the effects less observable. The spatial dependence of community dissimilarity, even within a few meters to kilometers, should be considered when designing studies aimed at capturing the community structure in tundra ecosystems.