Urban Tree Selection in a Changing Climate

Current climate projections indicate that mean global temperatures will increase 1 to 2 °C by 2050 and an additional 1 to 3 °C by the end of the century.  Trees in urban and community forests may be especially vulnerable to climate change since general warming will be exacerbated by urban heat island effects.  The long-term goal of this project is to identify street tree cultivars that show a high potential to acclimate to potential climate change.  We are conducting the project in two phases.  In Phase 1, we conducted a greenhouse study to determine the relative ability of street tree cultivars to acclimate their physiological responses to changing temperature regimes.  Trees (5’–6’ whips) of nine shade tree (Acer rubrum 'Frank Jr.', Acer saccharum 'JFS-Caddo2', Acer truncatum x platanoides 'Warrenred', Carpinus betulus 'Fastigiata', Gleditsia triacanthos 'Skycole', Liriodendron tulipifera 'JFS-Oz', Pyrus calleryana 'Glen’s Form', Quercus bicolor, and Ulmus propinqua 'JFS-Bieberich') were grown in #10 (34 L) containers under three temperature regimes (ambient, ambient +5 °C, ambient +10 °C) in a greenhouse trial during Summer 2012.  Following two months of temperature acclimation, we developed photosynthetic temperature response curves for each species or cultivar.  Among the species and cultivars evaluated, Quercus bicolor showed the greatest temperature acclimation and maintained relatively high net assimilation rates at elevated temperatures.  In Phase 2 of the project, we planted larger (#25, 104 L) container-grown trees of the same species and cultivars on two sites with contrasting temperature profiles (urban heat island vs. park-like conditions) near downtown Detroit. Field sites were established in cooperation with the Greening of Detroit, a community based tree planting program.  We will present initial results and long-term plans for the out-planting portion of the study.