Winners and losers from climate change: An analysis of climate thresholds for tree growth and survival for ~150 species across the contiguous U.S.
Christopher M. Clark1, *, Justin G. Coughlin2, Jennifer Phelan3, Gray Martin3, Kemen Austin3, Marwa Salem3, Robert Sabo1, Kevin Horn4, †, R. Quinn Thomas4, and Rebecca Dalton1
Changes in temperature and precipitation are already influencing U.S. forests and that will continue in the future even as we mitigate climate change. Using spatial gradients in mean annual temperature (MAT) and mean annual precipitation (MAP), we used simulated annealing to estimate critical thresholds for changes in the growth and survival of roughly 150 tree species across the conterminous U.S. (CONUS). We found that growth of nearly one third of tree species assessed (44 spp.) decreased with any increase in MAT (42-49 species), whereas fewer responded negatively to projected regional trends in MAP (<20 species each in the east and west). Hypothetical increases in temperature (+1°C, +2°C) increased average growth in the east and Pacific Northwest and decreases it in parts of the Rockies and Southeast, while survival generally decreased. Average growth and survival generally decreased with wetter conditions (-25%) in the east and with drier conditions (-25%) in the west. Beyond these averages, there were species that benefitted and those that were harmed nearly everywhere across the CONUS. We identified only eight species out of ~150 assessed that were resilient (no negative effect on growth and survival) to increases in temperature, and 24 species in the east and seven 7 in the west displaying resilience to regional trends in precipitation (increases in the east and decreases in the west). We also identified "tipping points" where several species shifted from positive to negative relationships. Average confidence in the relationships was generally high, though there were species and metrics with low confidence especially for survival. These findings have significant implications for the future national forest carbon sink and for conservation efforts in the face of climate change.
1 U.S. Environmental Protection Agency, Office of Research and Development, Center for Public Health and Environmental Assessment, Washington, DC
2 USDA Forest Service, Pacific Northwest Region, Portland, OR
3 RTI International, RTP, NC
4 Department of Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University, Blacksburg VA
5 U.S. Environmental Protection Agency, Office of Research and Development, Center for Public Health and Environmental Assessment, Durham, NC
† Currently with Freedom Consulting Group, Columbia, MD
* Corresponding Author: clark.christopher@epa.gov