Government agencies, private organizations and volunteers have spent decades fighting the spread of invasive plant species in the tri-state area, but they continue to grapple with not having enough resources for the massive effort and the ever-increasing challenges they face.

This battle is linked with the one that similar groups have undertaken to protect and enhance native habitats, which these invasive species threaten.

“(Invasive species) can become so abundant they outcompete for sunlight or space and displace native species, changing the natural plant landscape,” said Iowa Department of Natural Resources ecologist John Pearson. “That has cascading effects.”

Wildlife, agricultural production, city planning and even access for hunters and anglers are negatively impacted when an invasive species overwhelms an area.

In response, managers of public lands have prioritized the control of invasive species more and more in recent years.

“Certainly for foresters, but others, too, it’s become a much bigger deal,” said Kelly Kearns, natural heritage conservationist for Wisconsin Department of Natural Resources. “There’s been a real awareness that these can cause problems for the mission they are trying to accomplish on their lands.”

Eagle Scout Mason Caldwell, of Dubuque’s Troop 51, is joining the effort. Rather than build bluebird houses or benches for his Eagle Scout project, Caldwell is assembling a crew to remove invasive species from an overgrown pocket of Swiss Valley Nature Center and Preserve just outside of Dubuque.

“My family goes hiking all of the time, so I’d been thinking about it,” he said. “So, I decided that we could try to help the plants that are supposed to be there grow by taking out all of the vines and lower-down invasive plants that have come in there.”

The big deal

Officials distinguish between non-native species and invasive species. An invasive species is both not native to an area and “causes or is likely to cause economic or environmental harm or harm to human health,” according to U.S. Natural Resources Conservation Service.

So, all invasive species are non-native, but not all non-native species are considered invasive.

Non-native plant species are rampant in the area. For example, in Iowa, there are about 2,000 species of plants — and more than 20% of them are non-native, according to Pearson.

“There are about 500 (non-native) species. Most of those have been introduced but haven’t really become a problem,” he said. “They don’t spread, and if they do, they don’t outcompete native species and ruin habitats for plants and animals.”

Jay Potter, conservation manager for Four Mounds Foundation, had the rare opportunity to know exactly which of Iowa’s plant species — native and invasive — are on his organization’s 100-acre site in Dubuque, thanks to a recent botanical survey.

The tally: 235 individual species — 189 native and 46 introduced.

Some of the latter are not a problem, Potter noted.

“Even in a nice prairie, you’re going to have (non-native) wild asparagus growing, for instance,” he said. “It’s never in a million years going to take over the prairie. With fire, eventually, if we manage the site, the natives will overtake the non-natives.”

But Pearson said there are a few regular offenders that can devastate a landscape.

“In the Driftless area, Japanese knotweed is a big, tall shrub that affects riparian areas, along streams,” Pearson said. “There are some places where it’s eaten up miles-long populations.”

He said Yellow River State Forest in Allamakee County, Iowa, is a severe example but not the only one.

“It’s so thick along shorelines (that) it outcompetes almost all other species,” Pearson said. “From a more practical human standpoint, it makes access to streams for fishing impossible. People can’t get to the water, or if they can, they can’t cast a pole without getting hung up.”

Pearson said other invasive plants are harmful to native insect species, either by taking up the space of food plants or by being toxic.

“Some plants are introduced here because they are ‘pest-free,’” he said. “There are a lot of native species that cannot eat that plant. So, there are then fewer insects around to be eaten by birds, so it cascades up.”

At Four Mounds, the oriental bittersweet vine can be seen choking the life out of many trees and other plants, even as Potter and contractors endeavor to return the site to historic oak savanna and preserve the rest of its forest. Honeysuckle can be found all over the property. Japanese barberry continues to wind through.


Non-native plant species, including invasives, arrived in North America at the same time as non-native colonizers did.

At Four Mounds, though, it is easy to see exactly how and when bush honeysuckle and Japanese barberry arrived on site because the foundation has the original planting plan.

“They were planted in 1908 the same way you’d go today to a nursery to buy a plant,” Potter said. “They had no idea it would take over into the property. Over time, different neighbors, different parks, different areas of town would plant other things.”

The bittersweet causing so many problems was brought in to connected properties and crept its way on.

“A lot of species were just commonly sold at home centers,” Potter said. “Some were sold by the (U.S. Department of Agriculture) or Iowa DNR to people at various times.”

As Pearson said, “Different species have different origin stories.”

“One of the worst problems we have on native prairies is leafy spurge,” he said of the perennial weed. “Range land and pastures are subject to it. It degrades the integrity of forage for wildlife and grazing livestock.”

Because there was an economic impact, Pearson said, Iowa invested in studying that invasive.

“There was probably an introduction in Fargo, N.D., coming in through wheat seed from Asia around 1900,” he said.

Pearson said other invasives, including one of the most pervasive, landed in America much farther away.

“Garlic mustard came in on the East Coast about 120 years ago, became established in the New England area and has been spreading,” he said. “Our populations in Iowa became noticeably problematic only in the last 25 years.”

There are three species of bush honeysuckle in Iowa, of which Pearson said the Amur honeysuckle is the most egregious. He said that once it arrived, it found an inviting new home.

“It grows in very similar habitats in Asia — woodland habitats,” he said. “Over there, there are a lot of insects that prey upon and eat honeysuckle. So, there are natural checks and balances. But over here, without all those indigenous pest species that limit the spread of honeysuckle in its native range, there’s nothing to stop it. It grows and spreads and takes over the whole woods.”

Other species are aided by unique features specific to certain areas, such as Cassville (Wis.) Bluffs State Natural Area. There, the natural area is separated from the Mississippi River by railroad tracks. That can help keep waterborne species from creeping up the bluff, but it has also played a role in the poison hemlock in the area.

“It is the one that killed Socrates back in the day,” said Nate Fayram, Wisconsin DNR State Natural Areas manager for the southwest region. “We don’t see that on a lot of sites. In this case, (hemlock) travels along roadsides and right-of-ways like railroads. We have to manage it every year.”

Possible solutions?

People have come up with many ways to control invasive plant species. Of those, the most effective and natural is fire.

Prescribed burns, on public lands in particular, have been an increasingly common tool for managers. The blazes remove non-native plants that are not used to it but fosters regrowth of native species, which have evolved with regular fire.

“On state natural areas, we have a crew whose job is to manage those,” Kearns said. “They have probably 120 state natural areas to manage. A lot of those need prescribed burns.”

Fayram leads those crews in Grant, Iowa and Lafayette counties in Wisconsin. He said they try to burn areas of Cassville Bluffs every couple of years.

“We go after that (sweet clover) on remnant prairies because that’s the best part of the site, ecologically,” he said. “We go after bush honeysuckle as funding allows ... especially as it is encroaching on prairie remnants.”

Kearns said different types of areas receive different treatment.

“We also have state wildlife areas, which are managed so they can be hunted and trapped,” she said. “Those are managed more than the state parks are, often because they’re being managed for a specific type of habitat.”

Other strategies simply require a lot of grunt work.

Potter said that at Four Mounds, officials see success via concentrated workdays.

“One thing we always do in the fall is get a big group of our students and staff and we’ll go out and look for bittersweet vines in the trees,” he said. “We spend a day, six or seven people. That’s more productive than just me going out and futzing around for a little bit at a time.”

Pearson said the Iowa DNR is particularly focused on aquatic nuisance species, for which there is a specialized program.

“They track five or six problematic invasive species that are fully aquatic,” he said. “They might impact fisheries in rivers and lakes.”

Pearson said other invasives become the pet project for certain managers.

“About 10 years ago, the manager of Yellow River State Forest marshaled an effort to control the (Japanese knotweed) species,” he said. “It included mowing down large strands, treating the stump with a chemical.”

Pearson said methods are changing along with scientists’ growing understanding of these species. He referenced East Coast botanist Bernd Blossey, who has studied the long-term effects of garlic mustard.

“What he’s observed is that garlic mustard populations on the East Coast have been dying out or not being the problem they once were,” Pearson said. “Over time, there’s a chemical garlic mustard secretes in the soil. Over 75 years or so, that chemical becomes self-inhibitive. In Iowa, that has not been around long enough to have an effect.”

One of the best solutions, according to Pearson, is prevention.

“In garlic mustard, if you catch it early enough and pull up all the individuals in the population, you’ll stop it getting a foothold,” he said.

And if carefully identified and safely processed, many invasive species are edible. Garlic mustard, as its name suggests, is a flavorful herb. Autumn olive produces a tasty, abundant berry. Several parts of thistles and wild parsnip are tasty and edible. White mulberry can be collected and used for pies and jams.


The biggest obstacle that managers face in controlling invasive flora is a lack of resources — both in finances and workforce.

“We could have a part-time person on our 100 acres working on just that for years,” Potter said of Four Mounds. “There’s that much to be done. I just go out and treat what I can as I can. ... The goal is to make it better, progressively.”

Pearson said that on the government front, every state park manager is well aware of the proliferation of garlic mustard on their property.

“Everybody does what they can in their jurisdiction,” he said. “But there isn’t a dedicated program. Within the manpower and budgets available to our land managers, they attack them the best they can. But that’s not the only thing they do.”

Fayram said his crew is not big enough to maintain regular invasive species management at Cassville Bluffs.

“We don’t have the time or resources to actively manage that there,” he said.

And, according to Kearns, some state properties’ most prominent uses take priority over species management.

“Wyalusing (Wis. State Park) is managed primarily for recreation,” she said. “So, they don’t have anyone on staff who is a land manager. There’s no funding specifically for doing that.”

Other challenges

The effective control of invasive species also is hampered by nature itself.

Pearson said rivers themselves can convey invasives.

“Natural seeds can also fall into a river and float some distance,” he said. “A lot can survive one day or so of floating in a river.”

In particular, Pearson said, high floods — which most experts predict will become more and more common, due to climate change — can carry even more invasives farther inland than the usual riverbank, exacerbating the problem.

Potter said Four Mounds also struggles because the property is amid a landscape of various private landowners.

“We’re doing our little pocket, but we’re surrounded by all of these plants,” he said. “You will always have that reinvasion. Birds, too, can fly miles and miles and miles.”

Also, because state governments have no robust programs, land managers both public and private are always left searching for other funding and the authority that comes with it.

For example, until three years ago, a “gigantic” elm tree grew in front of the Gray House at Four Mounds.

“When that died, it changed the whole dynamic,” Potter said. “After that died and we had to remove it, we applied to the State Historical Society (of Iowa) to restore the landscape of that area.”

But, technically speaking, the bush honeysuckle and Japanese barberry were “historic” because they had been planted when the building was built.

“We had to really sell it to the State Historical Society, restoring the landscape but for that change, removing those,” Potter said. “Tearing ‘historic material’ out of that landscape and disposing of it is not how they think. ... But the detriment these plants make when they spread into that other area justifies making that change.”

The next thing

Potter said there always is a “new” invasive species to be on the lookout for.

“We found some Japanese hops on the property next door,” he said. “I’d never known what they were until we had somebody from Iowa Natural Heritage Foundation, that has an easement on the property, was walking around and said, ‘Oh, you should take care of that before it takes over the whole place.’”

Potter said he is also busy learning about what could come to the property as human-caused climate change makes temperatures resemble those of climate zones farther south.

“In 20 years, we could have kudzu (vines) taking over like they do in the South,” he said.

So far, Pearson said Iowa is thought to be free of giant hogweed, an invasive relative of the wild parsnip with nasty phototoxins spread by touch.

But “it’s just a matter of how it gets around — typically vehicles, as a contaminant,” Pearson said.

Kearns said her team, too, is always on the lookout for “early detection species.” She recalled the emergency response removal of Japanese stiltgrass when it was found on a state property in northwest Wisconsin.

Potter said the fight is never-ending but necessary.

“Ecological restoration is something I’ll be doing until I retire,” he said. “Then, the next person will take it over.”

Recommended for you