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Climate Change Threatens Nearly 1 In 5 Of Chicago's Tree Species: Report

By Alex Nitkin | May 22, 2017 5:39am | Updated on May 23, 2017 11:32am
 Hotter and wetter conditions could make it harder for many of the city's native tree species to survive, according to researchers with the U.S. Forest Service.
Hotter and wetter conditions could make it harder for many of the city's native tree species to survive, according to researchers with the U.S. Forest Service.
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DNAinfo/Alex Nitkin

CHICAGO — Nearly one in five trees native to the Chicago area faces a serious threat from climate change, according to a report published by the U.S. Forest Service.

The study, commissioned by foresters from the U.S. Department of Agriculture in collaboration with nearly 100 local naturalist groups, found that a hotter and wetter climate could decimate the city's tree population if officials don't find new ways to stay ahead of the changing landscape.

The report zoomed out to 7 million-acre region stretching from Milwaukee all the way to southwestern Michigan, detailing the potential impact of climate change on trees native to the region. But it also zeroed in on the Chicago Park District, ticking off the unique challenges urban planters will face — and the strategies they can harness to save the city's tree canopy.

Researchers found that the average temperature in the region has climbed by about 1 degree Fahrenheit in the past 100 years, already leading to a "significant increase" in rain, especially during the summer. Depending on how quickly greenhouse gas emissions are curtailed, they projected the average temperature to rise another 2.3 to 8.2 degrees before the end of the 21st century.

That will likely mean both more intense storms, which could "increase runoff and local flooding," and "extreme and exceptional droughts," according to the report. Both would put pressure on the hundreds of tree species found in and around Chicago.

Of the 179 native tree species studied by the Forest Service, about 17 percent were rated with "moderate-high or high vulnerability" to climate change, thanks to creeping dangers like wind damage, air pollution, heat stress and storm runoff.

Combined, they threaten a punishing blow to the kinds of pine and spruce trees more often found in Wisconsin and southern Canada, according to Leslie Brandt, a Forest Service researcher who co-authored the study.

"There are a lot of native species at the southern edge of their range that just aren't going to be able to tolerate the hotter summers and milder winters that we expect to be having," Brandt said. "They might be more vulnerable to certain insect attacks and diseases, which we've already been seeing."

Further muddying the future of the region's trees, foresters expect to see new visitors migrate from the south just as more cold-resistant species start to die off, the report concluded.

These "invasive species," most notably European Buckthorn trees in Chicago, promise greater resilience to the changing climate — but they also threaten to throw the city's already tenuous ecosystem off balance, Brandt said.

"Invasive species have a number of adaptations that allow them to be invasive, and that can make them better able to withstand a lot of the stressors that climate change may bring," she said. "And a lot of these species haven't co-evolved with the wildlife that's already there, meaning that they won't provide the same benefits."

But the city's park district is uniquely prepared for the environmental stressors coming its way, researchers said. They listed trees in the city's parks at "low-to-moderate" risk for climate change-induced degradation, citing the district's "large, trained staff and engaged public," according to the report.

Chicago parks face a special challenge amid a sea of steel and concrete, with city air pollutants and "urban heat island effect" make it less hospitable to older plants. But park officials keep a long planting list replete with "a large number of trees and a mix of both young and mature individuals," the report noted.

As Chicago keeps trending warmer and wetter over the coming decades, district staffers will have to keep up a planting regimen that's aggressive and versatile enough to keep the tree canopies intact — even if that means changing them from previous years, Brandt said.

"Chicago has been looking at a planting list and thought about replacing some species that are vulnerable, with others that are more climate-resistant," she said. "You'll have to be thinking not just about what [trees] belong there historically, but what might belong there in the future."