Science & Nature
Nearly 80% of Chicago-Area Forests Are Infested With Invasive Plants. Ecologists Urge Homeowners to Join the Fight
A volunteer helps remove buckthorn. (The Morton Arboretum)
Restoration ecologist Matt Ueltzen can remember a time not that long ago when the Lake County Forest Preserve District had to more or less “hide” some of its most vital work from the public.
Those were the days when, if people saw crews clearing invasive buckthorn, angry calls were sure to follow. Why was the forest preserves cutting down trees?
“In the past, people would think that anything that’s green is good,” said Ueltzen. “Now I think people have come to realize there are some very invasive and damaging, harmful plants out there.”
European buckthorn — an ornamental shrub that escaped cultivation — has earned a reputation as public enemy No. 1. Like most invasives, it crowds out native plants, creating a monoculture that offers few benefits to wildlife. In a dastardly twist, buckthorn also emits a toxin — emodin — that kills or stunts other flora.
“In most areas where you have very dense buckthorn thickets, it’s bare dirt,” Ueltzen said. “It’s an ecological desert really.”
The question facing land managers today is how to capitalize on the increased awareness of the threat buckthorn poses and involve more people in the fight against this formidable opponent. People who aren’t, say, professional restoration ecologists employed by forest preserve districts.
Because buckthorn doesn’t exist in a vacuum. It’s everywhere that birds drop the seeds of buckthorn berries — backyards, office parks, roadsides. Everywhere.
“It’s not just thinking about our preserves," said Ueltzen. "We all need to be in this together.”
‘If We Don’t Do Anything … It’s Just Going To Be Buckthorn’
Buckthorn is spread through the seeds of its berries, which are a common food for birds. The seeds not only contain a laxative, which ensures their dispersal, but they also remain viable for years. (Lorianne DiSabato / Flickr Creative Commons)
A 2020 census revealed that buckthorn accounts for 36% of trees in the Chicago region, which encompasses the city of Chicago and the surrounding counties of Cook, DuPage, Kane, Kendall, Lake, McHenry and Will.
That survey, led by Morton Arboretum, used sample plots to estimate total numbers. Lindsay Darling, a researcher at the arboretum who specializes in data analysis and mapping, drilled down even further.
Darling took high-resolution aerial imagery gathered by the U.S. Department of Agriculture and combined it with airborne LiDAR (a type of laser scanning technology) to map the location of buckthorn stands, as well as other shrubby invaders like honeysuckle.
The results, recently published in the journal Urban Forestry and Urban Greening, confirmed land managers’ worst fears: Shrubby invaders have infested nearly 80% of the region’s forests.
Though she wasn’t necessarily surprised by what the data showed, Darling called the findings “devastating.”
“Nothing grows under these shrubby invaders,” she said. “If you go out into one of these forests, you’ll see no wildflowers, no tree seedlings, nothing. So if we don’t do anything … it’s just going to be buckthorn. That’s all we’ll have.”
An interactive version of Darling’s map is available online. Her hope is that land managers will use it not only to identify hot spots within their preserves but also to pinpoint clusters of invasives on adjacent properties, and then use that data to encourage private landowners to tackle buckthorn.
Otherwise, ecologists are just playing Whac-a-Mole, eliminating buckthorn from their forests, only to have birds bring in seeds from the shrubs next door.
“And it becomes a problem again,” Darling said. “So trying to take care of (buckthorn) at a landscape scale is far more sustainable.”
Beyond Borders
Lindsay Darling, a researcher at Morton Arboretum, mapped the location of shrubby invaders in the Chicago region. The yellow represents stands of buckthorn as well as honeysuckle. (The Morton Arboretum)
Lake County has by far the greatest buckthorn infestation in the Chicago region. Some 52% of its trees are buckthorn, according to the 2020 census.
“That’s pretty alarming,” said Ueltzen. “We recognized that we can do a lot within our property, but if we’re not reaching out to our neighbors and trying to stop that influx of seeds and berries, we’re never going to get ahead of this.”
In 2020, the forest preserve district received a $170,000 grant from the National Fish and Wildlife Foundation to administer a pilot program that offered incentives to private landowners for buckthorn removal around Middlefork Savanna.
The Chicago Bears — whose Halas Hall headquarters abuts Middlefork — answered the call.
Ultimately the project reached some 40 property owners who paid for half the cost of buckthorn removal, with grant funds covering the rest. (None of the money came from forest preserve coffers; the district is restricted from spending taxpayer dollars on private land.)
Under the cost-share agreement, a private contractor cut down and disposed of the buckthorn and applied herbicide to the stumps, and then returned the following growing season to re-spray any emerging sprouts, Ueltzen said.
All told, 100 acres of buckthorn were eliminated before the grant expired in 2023.
“I think through that cost-share, we proved that we could be successful,” Ueltzen said. “Unfortunately the grant money only went so far. With just this one project we were able to address a good percentage of (buckthorn), although there is still quite a bit left.”
Asked what it would take, from a financial and manpower standpoint, to eradicate buckthorn, Ueltzen paused.
“I don’t know,” he said. “We had a roughly $170,000 grant — that was what it required to reach that 100 acres.”
The 2020 tree census estimates the leaf area covered by buckthorn in the seven-county region to be more than 250,000 acres.
From Knowledge to Action
Before and after images showing an area choked by invasive buckthorn (l) and then cleared. (Lake County Forest Preserves)
The scope of the problem is almost unfathomable, but “the stakes are so high that we can’t give up,” Darling said.
“We can get rid of (invasives). It’s just really expensive and time-consuming,” she said, pointing to natural areas like Morton Arboretum and the Chicago Botanic Garden, both of which are pretty much buckthorn-free.
“It’s not impossible, it’s just really hard,” said Darling.
But don’t discount what a group of volunteers armed with loppers and hand saws can accomplish. Darling has gone mano a mano against buckthorn in Cook County’s LaBagh Woods preserve.
“We have cleared a heckuva lot of buckthorn out of there. It’s been hugely beneficial,” Darling said.
Likewise, Ueltzen has seen native ecosystems bounce back once buckthorn is not present.
“As we’re clearing buckthorn, things are coming up from the seed bank but we’re also installing native seed to promote that establishment of regrowth,” he said. “And it’s exponential. In places where there was buckthorn and maybe two or three other species, now there’s literally hundreds of species.”
Plants like the purple fringed orchid have reappeared in the county’s northern flatwoods. And on the wildlife side, Ueltzen cited the rebound of red-headed woodpeckers and amphibians such as wood frogs and blue spotted salamanders.
“Our preserves are just amazing places,” he said. “They’re jewels of habitat, and the wildlife species and plant species that are in these places are just amazing. And they’re worth saving and worth fighting for.”
Which is why the Lake County Forest Preserve District has compiled a host of materials and resources for homeowners and other private landowners to help guide them through the process of eliminating buckthorn from their property. The district’s goal is to reach 50% removal countywide.
Got a homeowners’ association or community group that would like to learn more? Ueltzen will take your call.
“Pretty much if you ask for a presentation on buckthorn, we will come there and do it,” he said.
Despite the enormity of the challenge, Ueltzen said he remains hopeful that the battle against buckthorn can be won.
In the 25-plus years he’s been working in natural resource management, he’s seen the conversation shift from having to explain what buckthorn is, to now starting from a place where people have an understanding of what invasive species are and the damage they can do.
“I think our focus now is … trying to get them to do something about it, not just know what it is,” Ueltzen said. “We are moving in the right direction. I feel like we’re, in general, pulling on the rope in the same way. I think we have people at a good knowledge base now, but how do we get them to move to actually doing this work?”
Try This at Home
Battling buckthorn in a backyard isn’t a whole lot different than battling it in a forest preserve. Combat is largely hand to hand, and the weapons of choice are pruners, loppers and saws.
The first step is to identify the shrub, which can be tricky, Ueltzen said, because a lot of plant leaves look similar to buckthorn’s.
One tip, he said, is to scratch off the outer bark of a suspected branch. If it’s buckthorn, it will have an orange inner bark (or cambium layer).
“That bright orange color is a dead giveaway,” Ueltzen said. “There’s no other tree that has that.”
Buckthorn’s telltale orange color, similar to a sweet potato. (Patty Wetli / WTTW News)
If buckthorn sprouts are small enough, they can be pulled out by the roots. Larger shrubs need to be chopped down to the stump.
Then paint an herbicide onto the stump to kill the roots, Darling said.
Yes, the experts do advise using herbicide — this is the same process ecologists follow in the field — and they know it can be controversial with some homeowners.
“The most questions we have about the entire program are about herbicides, so people are curious about it and there is some mystique about it,” Ueltzen said. “We developed a resource guide about herbicides on how to apply that herbicide safely and what we recommend.”
Alternatives include suffocating stumps either by placing a bucket over them or wrapping them in black plastic to prevent photosynthesis. Plastic comes with its own issues, and Ueltzen couldn’t vouch for its effectiveness, never having tried the technique.
He did note that buckthorn infestations are rarely limited to a single stem, making buckets and baggies less practical to deploy at scale.
A third option for particularly patient people is to cut the shrub down to roughly 4 feet in the spring. And then every spring and fall for the next few years, “just keeping ripping all of the leaves off from that and it eventually will kill the plant,” Darling said.
What’s important is to take action.
“The more widespread we can do this,” Ueltzen said, “the bigger the impact we’ll have, and it’ll be exponential.”
Contact Patty Wetli: @pattywetli | (773) 509-5623 | [email protected]
