Succession and community gradients of arctic macrolichens and their relation to substrate, topography, and rockiness

Abstract

We describe lichen community structure and its relation to environment in the Bering Land Bridge National Preserve in northwestern Alaska. We used a stratified random sample to estimate macrolichen abundance and several environmental variables from 78 0.38-ha plots within lichen-dominated areas of the Preserve. We found a total of 140 macrolichen taxa. Two primary gradients in lichen species composition were related to habitat rockiness and a substrate-topographic gradient. The strongest gradient, rockiness, correlates with lichen succession. Rocky habitats have less competition from vascular plants and may be more resistant to soil disturbance. The substrate-topography gradient is largely driven by the presence of Sphagnum moss contrasting with calcareous parent rock material. To uncover additional underlying patterns in lichen community composition, we deleted rocky and calcareous plots and strictly saxicolous species from the analyses. Although we found similar patterns from the original analysis in this subset, diversity and community composition also varied with differing microtopography. These gradients of lichen community composition can also be divided into three major groups; rocky non-calcareous sites, calcareous areas, and the remaining plots form the alluvial lowland communities. We used two-way cluster analysis which combines independent clustering of sample units and species into a single diagram. This technique linked individual species and species assemblages with these major trends.