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How Many Tree Species Are In Chicago? The Number Might Surprise You

By Justin Breen | April 27, 2017 5:44am
 Chicago is home to more than 200 tree species and possibly as many as 300, officials say.
Chicago trees
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DOWNTOWN — Chicago could be home to as many as 300 different tree species, and it's because of humans.

Before Chicago become a city, only 22 tree species were identified, according to Lydia Scott, director of The Morton Arboretum-based Chicago Region Trees Initiative.

Scott said Morton Arboretum now has 218 species officially recorded in Chicago city proper, and she believes that number could grow as high as 300. Many of these species are planted in residents' yards, she said.

"Residences are less hostile than along city streets, as they have less salt and better soils," Scott said. "Also, houses frequently create microcosms where it is warmer than the rest of the region. We've seen species like southern magnolia and atlas cedar grow in the city, and their northern limit is supposed to be in central Illinois."

Morton detailed the number of Chicago tree species to DNAinfo as part of its Friday event to honor Arbor Day at the Daley Plaza, where a massive coloring display highlighting trees' existence in several different environments. Friday's free event runs from 7 a.m.-6 p.m.

Officials from the Chicago Region Trees Initiative conducted a tree inventory from 2010-13 that showed Chicago's most common trees were the white ash (6.2 percent of total trees), mulberry (5.3) and green ash (4.9). But she noted that the white and green ash are likely not among the most common now due to damage from the emerald ash borer. She said Norway and silver maples now are likely the most common trees.

Scott said the vast majority of Chicago trees are on private property, and the highest density of trees are in the Cook County Forest Preserves within the city.

No one knows definitively what is Chicago's oldest tree — although there are guesses. A detailed analysis of trees in the Chicago region from the United States Department of Agriculture determined there are about 157,142,000 trees in the area.