Species shifts in response to climate change: Individual or shared responses?

PUCKO, C., B. BECKAGE (Department of Plant Biology, University of Vermont, Burlington, VT 05405), T. PERKINS (Proctor Maple Research Center, University of Vermont, Underhill, VT 05490), AND W. S. KEETON (Rubenstein School of Natural Resources, University of Vermont, Burlington, VT 05405). Species shifts in response to climate change: Individual or shared responses? J. Torrey Bot. Soc. 138: 156-176. 2011.-Individual species are expected to shift their distributions in response to global climate change. Species within existing communities may respond to climate change individualistically, resulting in the formation of novel communities, or may instead shift as intact communities. We examined whether montane plant communities in the northeastern United States have shifted their elevational range as intact assemblages or individualistically in response to recent regional climatic and environmental change. We used non-metric multidimensional scaling (NMDS) to examine changes in plant community composition and species distributions using vegetation surveys repeated five times between 1964 and 2006 across an elevational gradient (549-1158 m) on Camels Hump Mountain, Vermont, USA, in conjunction with an analysis of local climate change. We found evidence that species elevational distributions and community compositions have shifted in response to a 0.49 degrees C per decade warming. These species responses were complex and largely individualistic at some elevations, while at other elevations species in a given community tended to respond similarly. The magnitude of community compositional change was largely dependent on location with respect to the ecotone between northern hardwood and boreal forests. While climate change likely contributed to the large shifts in species within NMDS space, these shifts may also be a response to invasive earthworms at low elevations and to prolonged exposure to acid deposition at high elevations. Though we found evidence of shared species responses within communities, future species responses may become increasingly divergent as the magnitude of climate change increases causing species-specific environmental thresholds to be reached and as the synergistic effects of multiple anthropogenic perturbations rise.