natural chicago
NEW TREE CENSUS REVEALS WAYS TO
Protect Region’s Urban Forest by Sheryl DeVore
Photo by Steve D. Bailey.
I
40
Chicago
NAChicago.com
n the past decade, millions of ash trees have died in the Chicago region, with more likely to die in another 10 years. Meanwhile, the percentage of invasive species continues to rise, causing harm to the region’s ecosystems. Trees continue to provide numerous benefits for humans and wildlife, and there’s much individuals can do to improve and maintain a healthy urban forest. The results of a Morton Arboretum (MortonArb.org) 2020 census of trees in the Chicago region, which includes Cook, DuPage, Kane, Kendall, Lake, McHenry and Will counties, have spawned the new Plant Trees Campaign, which asks each of the 340 communities within the region to plant one new tree (ChicagoRTI.org/TreesforCommunities). “The campaign draws attention to value of trees,” says Lydia Scott, director of the Chicago Region Trees Initiative, which started the new program. “Trees provide oxygen for us, they cool our air, they reduce our flooding and they improve our health,” she explains. The 2020 census followed a 2010 tree census that was done on randomly selected plots by the U.S. Forest Service with the Morton Arboretum. In 2020, the Morton Arboretum re-measured trees in the same plots to gain a comparative snapshot of the regional forest and the benefits it provides. The snapshot showed red oak, on the list of 10 most common tree species in the region in 2010, has fallen off the list in 2020. In addition, there’s a greater percentage of invasive trees in the mix compared with a decade ago. The census also revealed the functional value of trees, considering how they remove pollution, store carbon, reduce
flooding and save energy. If all the trees were gone, they would cost $45 billion to replace and $416 million annually to reduce the ensuing flooding. Chai-Shian Kua, Ph.D., urban tree science leader at the Morton Arboretum, led the 2020 census. The project team measured the diameter at breast height of each tree located within the randomly selected plots. They identified the species, assessed its condition and the canopy cover. “We also measured if the tree is next to a building, measured the distance next to a building and estimated energy-saving benefits provide by trees,” Kua says. The trees were measured in residential areas, open spaces such as forest preserves, corporate and transportation areas, and agricultural lands. “In 2010, when the first study was conducted, the emerald ash borers were already here,” Kua says. “We expected to lose a lot of ash trees in 2020 due to the introduced pest, and we did.” The emerald ash borer, introduced from Asia to the U.S. likely via wood packing materials, has destroyed tens of millions of native ash trees in 30 states, according to the U.S. Department of Agriculture. “In 2010, we estimated 13 million ash trees in the region,” Kua says. “In 2020, there were 7 million. But out of this 7 million, about 4 million are dead and still standing or in decline. So, we think there are about 3 million ash trees left.” One of the biggest lessons from the 2020 tree census is, “We should plant more diversity,” says Kua. “We should also plant the right tree in the right place and give it the right care.” Greg Spyreas, a botanist with the Illinois Natural History Survey (inhs.Illinois.
Trees throughout the Chicago region including in forest preserves, such as Ryerson Woods in Lake County pictured here, were censused in 2020 by the Morton Arboretum.
