10 tree species native to Illinois are at risk of extinction, study finds: How you can help

Ten Illinois species of a plant that happens to do $4 billion worth of work in the Chicago region to stop greenhouse gases are under threat of extinction: trees.

Of the nearly 900 native tree species in the contiguous 48 US states, up to 16% of them are threatened with extinction — including 10 tree species native to Illinois. That’s what recent results of a joint study by the Morton Arboretum, the United States Botanic Garden and others show.

The report, the result of five years of research, is the first comprehensive threat assessment of its kind. It will serve as a critical guide for future tree conservation efforts, researchers said, including the growing restoration initiatives across the Chicago area.

Primary threats to US tree species are invasive pests and diseases, wildfires, urban development and climate change, according to the study. In Illinois, the driving threat is invasive species, said Murphy Westwood, the vice president of science and conservation at the Morton Arboretum and senior author of the report.

“What we are looking at in our region are things like ash and elm and butternut, and even historically American Chestnut, that are native to the state or to our region, which are all threatened by invasive pests and diseases,” Westwood said. “These are keystone species in our forests that were historically widespread and are either already completely decimated or kind of on their way to becoming that way.”

Emerald ash borer

In one particularly widespread example, all ash species in the region are either endangered or critically endangered because of a small, shiny green beetle from Asia: the emerald ash borer.


The insect arrived in the 1990s, emerging in Detroit. It likely traveled to the US via shipping pallets. Since then, it has rapidly spread, decimating ash tree populations in the Eastern half of the United States.

Westwood said native ash trees have “essentially zero resistance” to the insect, which lays its eggs on the bark of the tree. Its larvae eventually burrow inside and feed on the tree’s tissue.

Within about five years of a new infestation, more than 99% of a forest’s ash trees will be dead.

Because of the severity, Westwood said it is not a viable option to treat and save wild ash trees. Instead, the tree will likely live on solely as residential street trees and in botanical collections where they can be treated, and the current focus is to prevent any further spread of the emerald ash borer.

“This is what the impact of invasive species can do. It can basically eliminate something from the (ecological) web,” Westwood said. “We can do things to try to prevent more invasions, like have better detection, have better policies, have better regulations at our borders and that kind of thing. But we live in an increasingly globalized world, and invasive species will continue to be a big challenge that we have to stay vigilant for.”

Oaks and buckthorn

One keystone group of Illinois tree species that doesn’t currently qualify as at risk of extinction — but that is deteriorating — is native oak trees.

Oaks are currently under threat from the European shrub buckthorn. The plant, which outnumbers trees in the region, creates a dense thicket close to the forest floor, blocking sunlight from reaching the oak’s acorns on the ground and preventing new trees from growing.

It’s not just trees that suffer in the shade of the buckthorn but all native plants, Westwood said.

What trees, we can do

The solution at both the community and individual level is prioritizing a diversity of native plants in forest preserves, natural areas and even backyard gardens.

“I would love for people to understand that it’s not just about that one individual tree. It has to exist in a healthy habitat and in a healthy ecosystem. That includes things like pollinators and seed dispersers and soil decomposers,” she said. “That’s why things like having healthy soils and healthy native plants can all contribute to ecosystems that are supportive to our native trees.”

Trees serve as a framework for our ecological system, Westwood said. They provide a long list of benefits that include mitigating stormwater, cooling houses and boosting moods.

They also represent a vital nature-based solution to climate change: Trees take in carbon dioxide and store it in their tissues as they grow, reducing the amount of greenhouse gases released into the atmosphere.

The region’s trees currently store 21 million tons of carbon, and an additional 542,600 tons are sequestered each year. The plants’ collective carbon capture services are valued at more than $4 billion, according to the Morton Arboretum’s 2020 Tree Census.

Ongoing initiatives to support native trees in the region include a Cook County project to restore 30,000 acres of forest preserve over the next two decades, said John McCabe, director of resource management at the Forest Preserves of Cook County.

Restoration efforts include brush removal, prescribed burning and clearing out invasive plants. Currently, 15,000 acres are undergoing restoration.

Radhika Miraglia, the program director at Friends of the Forest Preserves, said the volunteer-based nonprofit works closely with Cook County to contribute to conservation projects.

Miraglia said volunteers have been working in the preserves for over 40 years and have amassed invaluable knowledge.

“We think a really important piece to solving the problems is this local knowledge and local engagement,” she said. “We feel like that is by far the most sustainable way to make change and to bring back health to our natural areas, is to include as many people as possible.”

• Jenny Whidden is a Report For America corps member covering climate change and the environment for the Daily Herald. To help support her work with a tax-deductible donation, see https://www.reportforamerica.org/newsrooms/the-daily-herald-2/


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