Ecotone Might Provide Key Refugium for Sky Island Mammals in the Southern Appalachian Mountains

Sky islands, ecosystems found on geographically isolated mountain peaks, are among the most biodiverse ecosystems in the world but face a disproportionately high threat from climate change. High-elevation, montane ecosystems, which are already at their upper altitudinal limits, are predicted to severely contract in response to climate change. The identification and conservation of refugia is an increasingly important approach for protecting biodiversity associated with imperiled ecosystems. We explored the spruce-fir-northern hardwood ecotone as a possible refugium for mammals in the Southern Appalachian red spruce (<i>Picea rubens</i>)-Fraser fir (<i>Abies fraseri</i>) sky islands. We conducted livetrapping, camera trapping, and ultrasonic acoustic surveys to characterize mammal diversity across the spruce-fir-northern hardwood forest gradient on Grandfather Mountain and Roan Mountain Highlands in western North Carolina, USA. We detected four out of the five spruce-fir-associated small mammal species in both spruce-fir and ecotone habitats. Mammal species richness, alpha diversity, and bat activity tended to be higher in the ecotone than in the other forest types on both mountains. Next, the abundance of small mammals associated with spruce-fir was higher in the spruce-fir and ecotone forests for one of the three species we were able to estimate. Together, our results suggest that the spruce-fir-northern hardwood ecotone might serve as refugium for mammal species that are associated with spruce-fir sky islands in the Southern Appalachian Mountains and mammalian conservation efforts in this biodiversity hotspot should consider focusing on the ecotone in addition to the adjacent spruce-fir ecosystem.