Washington State faces climate change impacts that include sea level rise, temperature increases, and changes in precipitation. The conservation and restoration of our valuable urban forests becomes increasingly important in addressing these changes by mitigating storm water impacts from increased precipitation, reducing temperatures, and sequestering carbon. Limited information has been available to guide decisions on species selection for urban forest restoration, seed source selection and other management practices. The Green City Partnerships, with support from the US Forest Service, partnered with the University of Washington’s College of the Environment to evaluate climate change impacts on habitat suitability of native tree species that are commonly used for restoration of urban forests in the Puget Sound region. Climate change impacts were assessed using climate envelope modeling and seed transfer zones as well as through creation of future plant hardiness zone maps.
This research, led by Dr. Soo-Hyung Kim of the UW’s School of Environmental and Forest Sciences, suggests clear impacts from climate change on three native tree species. Climate conditions that make up the current seed transfer zones of western redcedar, western hemlock and Douglas-fir are likely to change radically within western Washington or, in some cases, nearly disappear towards the end of the century. In addition, the research team found that plant hardiness zones are likely to rise by a half zone in the Puget Sound area. This means that the Puget Sound area is projected to experience an increase of 5 to 6 degrees F in annual minimum temperatures. This implies that less hardy species may be able to grow in the region and could alter ecological dynamics in urban forests. These findings have implications for how we choose current and future planting materials for urban forest restoration sites.
We hope this research fuels further discussion and research into restoration strategies to mitigate climate change impacts to Puget Sound’s urban forests. To find research summaries on Seed Transfer Zones, Plant Hardiness Zone Maps, or to view the full report, go to the Green Cities research webpage: http://www.forterra.org/what_we_do/build_community/green_cities/green_cities_research