Distance decay of plant and fungal communities depends on microtopography in the Arctic tundra

Distance decay of biological community similarity exists at global and local scales. Although fine-scale environmental heterogeneity and stress-tolerant organisms of the Arctic likely promote distance decay at local scales in tundra ecosystems, these dynamics have not been fully tested. Here, we got community data of plant and fungi in 216 plots including along slope gradients, at the Pond Inlet on northern Baffin Island. Community similarity was calculated between plots sampled in random combinations, and variations in this similarity with geographic distance and environmental variables were assessed. Our results show that distance decay occurred at a habitat scale. However, the mechanisms underlying differences in distance decay varied between habitats and taxa. Specifically, distance decay in the middle of the slope was caused by increasing environmental heterogeneity with spatial extent. The predictive factors for distance decay in the top and bottom habitats differed among taxa. The distance decay tendency disappeared when a combination of plots that presented variations in topography were sampled, suggesting that distance decay was not a dominant effect across the study area. However, our results also suggest that the effect of topography on communities in the slope direction and the effect of distance decay on communities in the horizontal direction may interfere with each other, making the respective effects less observable. The spatial dependence of community similarity, even within a few meters to kilometers, should be considered when designing studies aimed at capturing the community structure in tundra ecosystems.