When buckthorn moves in to the ecosystem, it dominates.
Imagine a friend invites you to a dinner party, promising a delicious spread of food and libations. You arrive, excited and hungry, only to find nothing but raw kale, brought by an uninvited guest. Regardless of your feelings about kale, this would be pretty underwhelming. The other guests are obviously disappointed about the monotonous spread. Most people leave, and because most people aren’t eating the kale, the kale continues to dominate the party. Even if someone brought in better foods that more people enjoy, there is no room on the tables. The kale is everywhere!
While not a perfect analogy, this anecdote relays the reasons why buckthorn invasion is detrimental to forest ecosystems. The dinner guests are like the other plants and animals that usually live in the woods. They have certain dietary needs, and if those needs cannot be met, they will have to leave and find another place to live. The more one species dominates (kale, or in many local forests, buckthorn) the fewer species can live there, leading to the ecological equivalent of a party that ends at 8:30, just as everyone was arriving. While it may be true that one person at the party really likes kale, it’s hardly fair for the preferences of that person to supersede everyone else’s needs. In the case of buckthorn, many have opposed its removal because that denies robins a berry that they enjoy. However, keeping the buckthorn (which doesn’t belong there in the first place) is like keeping all of the kale on the tables and not allowing for other foods to be served just for that one person. Even more frustrating, the person that likes kale has plenty of other dietary options. Kale isn’t even their favorite food!
To many people, the idea of cutting down trees to help forests grow stronger is counterintuitive. But buckthorn is no ordinary tree. It is an invasive species, meaning that it doesn’t belong in Chicago area forests, and it steals resources from the plants that are supposed to live here. So remember, when you hear people talking about cutting down buckthorn, they are actually doing it to make the habitat healthier and more inclusive in the long term. They are working to replace the kale at the party with better food and drinks, ensuring that all the guests that were invited can have a good time, staying up until sunrise.
Bob Sherman is an undergraduate studying environmental science at Northwestern University. His research interests include prairie restoration and how abiotic factors impact prairie and forest ecosystems. He hopes that his research will have a positive impact on ecosystem restoration and management.
Tranquil, peaceful, and serene are words often associated with the McDonald Woods, which wrap around the northeastern edge of the Chicago Botanic Garden. But to Jim Steffen, senior ecologist at the Garden, the oak woodland is a bustling center for natural processes and species, and may hold answers to unsolved scientific questions.
“Nothing out there exists by itself. It’s all a network,” said Steffen. Since he arrived at the Garden 25 years ago, he has used his powers of observation to document, study, and breathe life into the systems that sustain a healthy woodland.
In the late 1800s, most area native oaks were cleared for settlement, leaving behind a fragmented and altered landscape. Invasive plants, including buckthorn and nonnative critters, such as all of our present-day earthworms, moved in. The climate began to change. While many may have thrown up their hands and walked away from this complex puzzle, Steffen saw a treasure.
At age 15, he began to explore the natural world in earnest and to grow the insight that guides him today. After taking a course in his community, he was federally licensed to band birds for research, a pursuit he followed for another 40 years. As he searched for hawks, owls, and other birds of prey, Steffen couldn’t help but notice the activity beneath his feet. Among the fallen leaves were scuttling rodents, insects, and blooming plants. He realized their presence was integral to the entire community of life in the woods.
“I started getting more into how those things are related rather than just narrowly focusing on the birds or the plants,” he said.
Steffen developed a broad ecological background as he pursued his education and worked toward a career in conservation science. He was hired to manage 11 acres of woods alongside a nature trail at the Garden. Now, that management responsibility includes more than 100 acres.
Although he does not expect to recreate the exact natural community of the past, Steffen does aim to grow an oak woodland of today. “My goal is to increase the native species diversity and improve the ecological functioning that is going on in the Woods,” he said.
Early in his career, he successfully advocated to expand the managed area to include adjacent acres. His management activities and detailed inventory work has grown the number of species there from 223 to 405. Of those species, 345 are native to the region.
The leaf canopy of the second-growth woodland was nearly 100 percent sealed when he arrived. It is now more open, allowing sunlight to punctuate the ground—encouraging the reproduction of oak species and promoting the flowering and seed-set of the native grasses, sedges, and wildflowers. The rewards of his work? Less carbon being released from the soil, improved water retention and nutrient cycling, and a place to bolster native species of plants and animals.
Each season brings new challenges. This winter, Steffen, his crew, and hired contractors carefully removed nearly 600 ash trees killed by emerald ash borers, cleared three acres of mature buckthorn, and conducted a six- to seven-acre controlled burn.
“It’s a difficult thing to do,” he said of oak woodland management. Steffen is grateful for each helping hand. “I’d say I’d be about ten years behind if it hadn’t been for my dedicated volunteers who help with the physically demanding work.”
Springing Into Action
This spring, Steffen and his team will begin to collect seed from more than 120 native plants they nurture in the Garden nursery and from dozens more in the woodland.
The process continues through November. It includes plants like the cardinal flower (Lobeliacardinalis), which was once common in Glencoe’s natural areas.
Steffen also collects seed from external natural areas, bringing new genetic diversity into the Woods to strengthen existing plant populations. (This is an increasingly challenging task, as 50 percent of his collection sites has been lost.) Collected seeds are scattered in prepared areas of McDonald Woods, either in the spring or fall, or sometimes in the middle of winter on top of the snow.
“Everything you see growing, walking, or flying in the woodland is just 10 percent of the picture. In any native ecosystem, probably 90 percent of the diversity is at and below the soil surface,” he said. An entire network of plants and other living organisms exist and interact there, helping to sustain what grows above them. Oak trees and most other native plants rely on entrenched fungi, for example, to deliver nutrients and water or protect them from herbivores and disease.
Microarthropods living in the leaf litter and soil, such as tiny springtails and mites, and larger organisms including spiders, also play important roles. Together with a volunteer, Steffen has dedicated 14 years of work to better understanding those interactions. They have found several species never found before in Illinois and some that even appear to be new to science. “We are still identifying some of the things we collected ten years ago,” Steffen said. And similar, rarely studied subcommunities exist higher up in the trees. “That’s another hint as to how complex the system is and how much we don’t know about it,” he added.
Some things are clear. A pioneer of oak woodland restoration, Steffen was among the first to notice that the natural layer of decomposing oak leaves and plant material was vanishing from the ground in the McDonald Woods and most other woodlands in the region. He attributes the effect to higher levels of nitrogen from the decomposing leaves of nonnative plants, and the presence of exotic, invasive earthworms. “Because so many organisms live in that layer and depend on it for survival, they are disappearing,” he cautioned.
But first, it is time to take in the rewards of winter. May is peak season for migrating birds in the Woods, including warblers and flycatchers. Sedges will bloom, along with spring ephemerals such as trillium.
Activity is everywhere, and it is a welcome sign of progress for Steffen. “It’s much healthier now than it was when I started,” he said. “All this diversity is able to function more easily now.”
The McDonald Woods are also an educational resource. Steffen will lead a rare off-trail hike there this year, and teach classes in bird watching and sedges through the Garden’s Adult Education programs.
Learn more about Jim Steffen and watch a video about his work.
Before our might, the foliaged foe fell along a stretch of the Green Bay Trail near the Braeside Metra station.
That’s where a group of 50 of us gathered to vanquish thickets of invasive buckthorn (Rhamnus sp.) on Wednesday, June 19. The removal was initiated by the City of Highland Park and the Park District of Highland Park in partnership with the Chicago Botanic Garden. Ravinia Festival also provided volunteers and space for parking and picnicking afterward.
“This was an ideal place to demonstrate what buckthorn control could accomplish through taking back our beautiful natural surroundings, even in very busy settings,” said Rebecca Grill, natural areas manager for the Park District. The area links two major cultural institutions serving the community, the Garden and Ravinia. It is also near a planned bike path for cyclists and pedestrians that eventually will extend to the Garden, connecting the North Branch and Green Bay Trails.
From 9 to 11 a.m. we sawed, chopped, cut, tugged, pulled, dragged, and stacked so much buckthorn that by the time a break was called, some piles were as high as me (5 feet), extending in an impressive line down the trail. Joggers, walkers, and cyclists made their way past the activity, occasionally cheering on the workers, including Garden President and CEO Sophia Siskel and her sons.
Why has buckthorn become such a problem in the Midwest? It’s the story of a plant species imported for perceived benefits that runs amok, crowding out less aggressive native plants and altering the landscape. Buckthorn arrived in the United States in the mid-1800s, brought from Europe as an ornamental plant admired for its thick, long-lasting foliage and fast growth. Native birds relished the fruits of the tall shrub and helped to disperse them. Once scattered, the seeds could remain dormant for as long as six years. In contrast to native plants, buckthorn supports almost no native invertebrates, like butterflies and moths, many of which are either food for native animals or serve as important pollinators. Soon buckthorn expanded far beyond its original boundaries of home landscapes and farms—where it was used as a windscreen—crowding out native plants, changing nutrients in the soil, and threatening native habitats.
How much buckthorn did we eliminate? Rebecca estimated that our group cleared 1,500 feet of trail—more than a quarter-mile. At 2:30 p.m., she and her crew were still feeding the cut plants into a wood chipper, making sure the chances of reseeding are minimal. They also selectively applied herbicide to the remaining stumps. In the future, they plan to monitor the area for the return of native wildflowers, seeding if necessary.
I live near the trail and run along it often. Already I have enjoyed seeing how the sunlight filters into this new clearing, reaching areas that will soon flourish with returning “natives.”
Learn more about invasive species on the Garden’s website. For information about future buckthorn workdays, contact Liz Ettelson at the Park District of Highland Park (firstname.lastname@example.org).