Missing the mammals for the trees: comparative biogeography of southern Appalachian sky island biodiversity

Sky islands are patches of relic ecosystems on mountaintops, often forest types, that were previously connected in the geological past and are now patchily distributed. Whether a particular sky island forest serves as an umbrella for conserving sky island fauna with a similar patchy distribution is an open question. To address this, we systematically delineate sky islands, identify relic spruce-fir-birch (SFB) forest patches, and map sky island mammal distributions in the southern Appalachians. Leveraging digitized museum records and vegetation maps, we compare the distribution of sky island mammals to one another as well as to the distribution of SFB forest patches. We identify 10 southern Appalachian mammals associated with high elevations, and our results show that 5 of the 10 focal species do co-occur with large SFB forest patches across sky islands. These "spruce-fir associates" all occur on 1 or more sky island lacking extensive SFB forests. Furthermore, pairwise comparisons across all 10 focal species revealed significant co-occurrence of SFB and non-SFB associates. Together, these results suggest that the presence of SFB forest is not a sufficient "umbrella" for even spruce-fir associate mammals. Conservation efforts focused exclusively on high-elevation forest types of the southern Appalachians and elsewhere may, indeed, miss the mammals for the trees.