Analyzing the Habitat Factors for Multiple Taxa Occurring on Granite Bedrock Glades and Surrounding Communities in the Huron Mountains

Using any one taxonomic group as a proxy for an entire community can result in misleading conclusions. Determining the ecological gradients that are most important in structuring the species assemblages across a variety of taxa at multiple spatial scales improves our understanding of the ecological forces which shape differences between communities. This study identified the gradients most important in structuring the vascular plant, cryptogam (lichens and bryophytes), herptile (amphibians and reptiles) and breeding bird communities between a rock outcrop community and the surrounding communities (peripheral and matrix forest) and the biotic and abiotic habitat factors associated with those gradients. We sampled 890 plots across 47 sites in the Huron Mountains, Marquette County, MI. We recorded abiotic and biotic (habitat) variables at 3 scales: 100-m transect, 1-m2 plot, and 0.4-m2 plot. We used non-metric multidimensional scaling (NMDS) to identify the ecological gradients most important for each taxonomic group, multi-response permutation procedure (MRPP) to determine if differences occurred between habitat types for all taxa, and indicator-species analysis to determine which species are significantly associated with each habitat. This study demonstrated that the same variables (percent canopy cover and amount of exposed bedrock) were most associated with the strongest gradients for all taxonomic groups evaluated. While the upland ecosystems of the northeastern US are characterized by extensive forest cover, small inclusions dominated by exposed bedrock can contribute significantly to regional biodiversity.