In the heart of Northbrook, sunlight streamed through the trees of Chipilly Woods, illuminating vibrant patches of native witch hazel and bottlebrush grass as ecologist Anna Braum explored the area.
Just two years prior, this forest preserve was overwhelmed by invasive buckthorn shrubs, described by Braum as a substantial ‘wall’ of invasive vegetation.
With the invasive buckthorn trees cleared during winter last year, new waist-high shoots have since sprouted, necessitating further action.
Recognizing this persistent challenge, forest preserve workers treated the shoots with herbicide last month as part of their ongoing battle against invasive species, a task exemplified by a recent study revealing that nearly 80 percent of forests in and around Chicago are infested with unwanted invasive shrubs.
“Removing all the invasives doesn’t mean the work is done,” Braum emphasized. “It requires ongoing maintenance.”
Thanks to a growing volunteer network and funding secured through a 2022 referendum, the Forest Preserves of Cook County has ramped up its efforts to eliminate invasive species in recent years.
Each year, restoration crews employ a strategic blend of fire, brush mowers, hand saws, herbicides, and the reintroduction of native plants in their campaigns against invasive flora.
A team of researchers from Purdue University and the Morton Arboretum published a study this spring intending to raise awareness among landowners about the invasive plants threatening Chicagoland.
Their work produced an interactive map filled with yellow splotches representing shrubby invasives, a strong visual indication of the problem.
Lindsay Darling, who recently obtained her PhD in forestry and natural resources from Purdue, has devoted years to mapping invasive species in the Chicago area.
While contracted with the Morton Arboretum, she utilized LiDAR technology—laser scanning—and developed 3D maps depicting forest conditions across multiple counties including Cook, DuPage, Kane, Kendall, Lake, McHenry, and Will.
The study found that approximately 77 percent of Chicago-area forests suffer from invasive shrub infestations, with McHenry County leading at a staggering 90 percent and Cook County following closely at over 77 percent.
Darling described the findings as “devastating,” yet she expressed hope that they could inspire action.
Among the most prevalent invasive shrubs in the region are European buckthorn and Tatarian honeysuckle.
Buckthorn, introduced as an ornamental hedge plant in the 1800s, proliferates rapidly, aided by birds consuming its berries.
Due to the diuretic properties of the berries, the seeds are dispersed widely through the birds’ waste.
The dense thickets of buckthorn cast shadows over the forest understory, inhibiting native plant growth and releasing a toxin called emodin, which can kill surrounding flora.
This takeover limits ecosystem diversity by creating monocultures that diminish insect and animal populations, according to Braum.
The effort to clear buckthorn from Chipilly Woods has created more light within the forest, allowing for the flourishing of wildflowers and other native plants.
Braum noted that the removal of buckthorn has unearthed the landscape’s subtle hills and streams, leading to a rediscovery of the natural beauty in the area.
“When buckthorn dominated, visibility was reduced to a few feet. Now, we have reconnected with the broader landscape,” she shared.
Kimosky Kalosky, an assistant resource project manager with the Forest Preserves, remarked that removing buckthorn also enhances visitor experiences, as the open spaces harbor more light and wildlife, contributing to a more vibrant environment.
Despite the daunting statistic that 77 percent of forests are infected with invasive species, the situation has shown improvement over the years.
Reflecting on the intensive restoration work began in 1987 by Jim Vanderpoel and local volunteers at Barrington’s Grigsby Prairie, the community witnessed dramatic advancements.
Initial efforts involved clearing invasive shrubs, followed by a practice Vanderpoel refers to as “plant rescues.”
Using the land adjacent to the North Western Railway tracks—maintained by the railroad through regular prescribed burns—the Vanderpoels would salvage native plants for transplanting into the former hay farm, gradually transforming it into a thriving prairie.
Today, Grigsby Prairie has become a source for collecting native seeds utilized in restoration projects throughout Cook County.
In a parallel effort, conservationist Stephen Packard along with volunteers from the North Branch Restoration Project began cultivating native seeds along the North Branch of the Chicago River in the late 1970s.
Historically, awareness of invasive species was minimal, as noted by Benjamin Cox, Executive Director of Friends of the Forest Preserves.
Many residents opposed invasive removal, misunderstanding it as deforestation—leading to a moratorium on restoration work in 1996.
Though the ban was partially lifted the following year, it persisted on the Far Northwest Side of Chicago until 2006.
“Let nature take its course was a common refrain,” Cox recounted. “But we, as humans, are part of nature, and our involvement is crucial.”
A study by Friends of the Forest Preserves and Friends of the Parks in 2002 highlighted the declining state of the land; 68 percent of Cook County Forest Preserves were rated as poor quality, with the most common tree species being buckthorn.
“That study painted a gloomy picture, reinforcing the urgent need for action,” it concluded.
In 1998, the Friends of the Forest Preserves was established to confront the invasive issue.
Now, thousands of volunteers participate annually in efforts to restore these vital ecosystems.
As the Forest Preserves of Cook County created its own volunteer resources division in the early 2000s, formalized training and certification began to play an important role in these initiatives.
Director of Volunteer Resources Kris DePra shared that between 4,000 and 5,000 individuals volunteer each year, showcasing a growing commitment to restoration.
“This concept of utilizing volunteers for restoration is rooted here in Cook County,” Cox noted. “We have witnessed significant changes, turning former weed patches into recognized Illinois Nature Preserves.”
Darling’s LiDAR mapping indicated promising outcomes in regions with sustained removal efforts against invasives.
However, challenges remain as buckthorn can easily propagate from adjacent properties.
“All it takes is one bird, consuming one seed,” she cautioned. “Birds disregard property lines and county borders.”
Darling expressed hope that the map could enlighten landowners regarding the invasive plants present on their properties.
The Morton Arboretum aims to assist with resources guiding identification and removal of invasive species, and the Illinois Department of Natural Resources offers tax incentives to promote large-scale invasive removal.
Long Grove resident Jeanette Burger has found fulfillment in volunteer restoration work since 2011, although she began with little knowledge of invasive species.
Over eight years, her understanding and ability to manage the buckthorn on her own property have greatly improved through her volunteer experience.
The Forest Preserves of Cook County set an ambitious restoration target in 2014, aiming to rehabilitate 30,000 acres of land to good or excellent condition by 2039.
Currently, nearly 17,000 acres are actively undergoing restoration efforts, and while there is much work left to do, Cox remains optimistic.
“We have a comprehensive plan and are earnestly working towards it,” he stated. “Engaging everyone is vital because these forest preserves belong to us all.”
For those interested in volunteering, more information is available through the Forest Preserves of Cook County and Friends of the Forest Preserves.
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