Spatial patterns of structural diversity across the boreal forest-tundra ecotone in Churchill, Canada

Vegetation structural diversity, also called structural complexity, has great effects on biodiversity and ecological processes, with higher biodiversity often observed in areas with higher structural diversity. As for other ecological variables, structural diversity is spatially heterogeneous. Thus, quantifying its spatial heterogeneity may provide clues to the spatial variation in ecological processes. We studied the spatial patterns of structural diversity in two different environments, tundra and forest-tundra ecotone, near Churchill, MB, Canada. We sampled vegetation and quantified five types of structural diversity (ground cover, herbaceous plants, woody plants, all live plants, and deadwood) along five transects, with lengths of 81-227 m, and used wavelet analysis to assess the scales of spatial pattern. We also assessed the effects of soil pH, microtopography, elevation, and distance from lakes on structural diversity. In general, structural diversity was spatially structured on a variety of scales, from 2 to 55 m, with larger scales being observed in the tundra than in the ecotone transects. In addition, structural diversity in the tundra was generally higher near lakes and in areas with a higher pH, whereas in the ecotone it increased mostly with increasing pH and microtopographic variation. Spatial heterogeneity is an important characteristic of the forest-tundra ecotone and even tundra areas that appear homogeneous are structurally diverse at a variety of scales.