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Urban tree study published

September 25, 2013

The Morton Arboretum, in cooperation with the U.S. Forest Service, has today released the results of their “Urban Trees and Forests of the Chicago Region” study of trees in the seven-county Chicago region.

The study provides the most comprehensive look ever at the structure of the Chicago region urban forest – defined as trees in Cook, DuPage, Kane, Kendall, Lake, McHenry and Will counties – as well as the environmental and economic value of those trees, based on widely used mathematical models. Results from the study will provide a basis for further research on the need for maintaining and improving the tree canopy in our region. The study is now available for download at http://www.nrs.fs.fed.us/pubs/44566.

Key highlights from the Tree Census:

  • The Chicago region has an estimated 157,142,000 trees.
  • The most prevalent species in the area are European buckthorn, green ash, box elder, black cherry and American elm.
  • An estimated 24,170 tons of pollution are removed each year by Chicago region trees and shrubs, an associated value of $183 million a year.
  • The region’s trees remove an estimated 11,976 tons of VOC emissions each year.
  • The region’s trees reduce energy costs from residential buildings by an estimated $44 million annually.

Overall, the region’s trees are estimated to provide services worth $51.2 billion each year.

“Our goal at The Morton Arboretum is to continue to improve our trees and forests, which we know will result in improved air quality, energy savings and a greater well-being,” said Dr. Gary Watson, Head of Research at The Morton Arboretum and one of the authors of the study. “This new research will be critical in helping us develop strategies to ensure the future of our trees.”

Added David Nowak, a Project Leader and research forester with the U.S. Forest Service’s Northern Research Station and the study’s lead author: “This study is one of the most comprehensive metropolitan tree and forest assessments ever conducted and provides essential information to guide forest management in the coming years.”

The Region’s Ash Trees
According to the study, it’s likely that the most profound change in the Chicago regional forest over the next 10 years will be the loss of nearly all of the region’s 13 million ash trees to the emerald ash borer (EAB). Ash is a significant tree in the Chicago region and makes up 18 percent of the Chicago region street trees, second only to maple, as well as a substantial portion of trees in natural areas and on private property. The expected loss of ash trees to EAB will have a significant impact on the entire region, but will be especially noticeable in some residential areas and along transportation routes where ash trees are prominent.

“Prior to the arrival of EAB in 2005, ash trees were an extremely popular choice for planting – they’re hardy, they’re adaptable and provide nice fall color – which is why we have so many in the area,” said Dr. Nicole Cavender, Vice President of Science & Conservation at The Morton Arboretum. “But the devastation of the emerald ash borer, as well as Dutch elm disease before it, revealed that planting too many trees of the same kind leaves them vulnerable to pests and diseases.” Cavender adds, “We’ve learned that one of the best ways to ensure a healthy tree canopy for generations to come is to plant a genetically diverse selection of trees. Put simply, if you like your neighbor’s tree, plant a different one.”

What is an “Urban Forest?”
The urban forest of our cities and suburbs is comprised of all trees, including those in boulevards, parks and private property, and trees that naturally occur in public spaces. Until now, relatively little was known about how many trees there are, what kind and what size they are, and what they collectively contribute to the environment and people’s quality of life. The value of trees’ contributions are posed to increase in the future, but at the same time mounting threats from insects, disease, invasive species, climate change, development and changing infrastructure could limit these contributions.