Submitted by Lacey S. Brown, Urban Forester, Openlands What if the weather in Oak Park became so hot and humid that you could not survive outside? This could be an imminent reality for 18,000 residents of Oak Park: the public trees of our urban forest. Trees that are given proper care can live one hundred years or more. But trees that are suited to Oak Park’s climate in 2011 may not be able to survive in the Oak Park of even 50 years from now.
When the USDA issued its hardiness zone map in 2006, updated from its previous 1990 map, many states had shifted one hardiness zone warmer in just 15 years. Hardiness zones refer to the geographic area in which a given species of plant can survive the area’s lowest temperatures. As illustrated in the May New York Times article A City Prepares for a Warm Long-Term Forecast by Leslie Kaufman, the City of Chicago is already preparing for a climate similar to that of Baton Rouge, Louisiana. The City has removed six tree species from its planting list, including the white oak, and has added several species more common to Southern planting zones.
While the city of Chicago is to be commended for their proactive planning, some wonder if changing the tree species list is the right thing to do. Kathryn Jonas, a certified arborist, member of the Oak Park Forestry Commission and Openlands Treekeeper comments, “I do think [the article] created a stir without a lot of research. There are many tree species that are suffering from all kinds of problems now and climate change is likely one of them. But I do not think [species such as] the white oaks warrant being singled out at this point.”
While which species deserve to stay or go from municipal planting lists may be in debate, researchers in the field recognize that the makeup of regional forests is indeed shifting over time and are putting forth models that can be of use in planting plans. The USDA Forest Service has created a Climate Change Tree Atlas based on the work of Dr. Louis Iverson and Anantha Prasad which predicts how species ranges will change according to three different climate change modeling scenarios. Some overall nation-wide conclusions that they have drawn from this modeling is that there is high probability for substantial loss of spruce-fir, maple-beech-birch, and aspen-birch habitat, while habitat for the oak-hickory and oak-pine types would increase substantially.
While not the silver bullet to making planting plan decisions, municipalities can look to tree species with a wide hardiness range, that tolerate both current conditions with below freezing temperatures in the winter and possible future conditions of considerably hotter and more humid weather, when creating current planting plans. TreeLink provides a comprehensive list of tree species in each hardiness zone across the United States. Favorites like the Lace Bark Elm, Hackberry, Hophornbeam and Redbud are rated for hardiness zones from Northern Illinois to Southern Louisiana.
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