Woodland Invasives: Doing Battle with Non-Native Plants

Woodland Invasives: Doing Battle with Non-Native Plants

David Paganelli prepares for battle.
Photo by John Douglas / Flying Squirrel

A huge mound of vines, 8 feet wide by a dozen yards long, lay baking in the August sun. The effort required to cut all those vines by hand, drag them out of the woods, and pile them up to dry suggested someone with a mission.

Walking past the mound, I left the clearing and turned down a woods trail in search of that someone. A few minutes later, I found David Paganelli at work with a chainsaw. Strewn along the slope were the felled stems and silver-bottomed leaves of another targeted plant, autumn olive (Elaeagnus umbellate). Working alongside him – wielding clippers and a yellow mustard squeeze-bottle – was his son Ryan, dragged out here during a visit home from Tufts Medical School. Father and son had spent most of that day cutting olives and applying Roundup to the stumps.

David greeted me with an easy smile and was eager to jump right into the subject at hand – invasive plants. “We’ve got quite a bouquet here,” he began. He estimates that 12 to 15 percent of his 200 woodland acres in Strafford, Vermont, had been dominated by autumn olives. After hundreds of hours of labor, there are still several acres left to clear. Shade-tolerant buckthorns – both common (Rhamnus cathartica) and glossy (Frangula alnus) – are scattered over the entire property, forming a patient and ubiquitous understory. There are also a few barberries on ledge outcrops among the larger trees and 20 to 30 Morrow’s honeysuckle (Lonicera morrowii) shrubs to deal with.

And the pile of vines in the clearing? Oriental bittersweet (Celastrus orbiculatus). Paganelli didn’t even know he had it until a year earlier. He had seen it in the woods’ edge, but noted that “it never really clicked until last fall, when I looked over and saw this bright yellow vine.” When he investigated, he found the bittersweet was so thick he couldn’t walk into it. A 25-yard-diameter area of sugar maple poles was completely covered with vines just a few inches apart, intertwined and twisted around everything. Along the edges, he was able to remove the bittersweet and save the hardwoods. But at the center of the infestation, the maple poles – bent over and broken by the weight of the vines – had to be cut down.

“One of our biggest problems,” said Paganelli, “is that even those of us who are supposed to be informed don’t know much about invasive species.” He has been a Vermont County Forester for nearly two decades. Yet, when he first walked this property and bought it five years ago, he didn’t recognize the problems he faced.

He had been generally aware of the issue: invasives are species that adversely affect ecosystems to which they are not native. They are aggressive competitors that reproduce vigorously – often producing abundant seed every year – and can choke out native plant communities. “Many of them leaf out early in the spring, ahead of native species, and drop their leaves later in the fall,” he said. “Those extra weeks are a significant advantage in a short growing season.” Outside their own native habitats, invasives are no longer held in check by the insects and diseases they evolved with, nor by their natural mammalian predators. Norway maple seedlings, for example, are mostly ignored by squirrels and deer, who much prefer to browse young sugar maples; likewise, beavers generally don’t touch buckthorn.

While nearly 5,000 non-native plant species grow wild in the U.S., only a fraction of those cause serious trouble. Nationwide, the U.S. spends $120 billion per year on controlling and mitigating the effects of those few species, and invasives have a negative impact on almost half of all species federally listed as threatened or endangered. Globally, invasive plant and animal species are a leading threat to biological diversity, second only to outright habitat loss.

“But,” said Paganelli, “I honestly thought: ‘This is somebody else’s problem.’” He had the impression that woodland invasives were only an issue farther south. This land has taught him otherwise. A nutrient-rich northern hardwood site with a south-facing slope and thin soil susceptible to over-drying, the property is 75 percent sugar maple. Just 25 years ago, it was pasture. And open land offers invasives their best opportunity to gain a foothold.

The best-laid plans

Paganelli figures that the olives he’s battling got their start when a previous owner planted seedlings purchased from the State as part of a well-intended wildlife food-plot program. “Now it’s a race to see who’s going to control this land, the invasives or me.”

The origin of Paganelli’s olives in a pro-wildlife effort is ironic, since invasive plants spell trouble for wildlife. In addition to their impacts on habitat, their dominance of a given area reduces the diversity of available food. And research suggests that the berries of many invasive species – including autumn olive – may lack the high-calorie, high-lipid nutritional value of fruits from native trees and shrubs such as dogwoods and winterberry holly.

Across New England and New York, most of the invasives that threaten woodlands were originally brought here as ornamental landscape plantings, and these introductions continue today. Others were planted as domestic crops or to benefit wildlife. Once invasive plants mature, their seeds are spread by wind, birds and other seed-eating animals, and human carriers who don’t know any better. Paganelli recalls how, years ago, he and his wife clipped some bittersweet along the Housatonic River in Connecticut and brought it home as a decoration for their front door. He hopes none of those seeds survived the compost heap, but doesn’t know for sure. Forest invasives can also spread when plant parts – or seed-laden soils – travel from one place to another on logging or construction equipment or recreational vehicles, just as aquatic invasives such as Eurasian water milfoil hitch rides on boats.

Because woodland invasives got their first footholds in human settlements, their current distribution patterns vary dramatically across the region. Ted Elliman, vegetation management coordinator for the New England Wild Flower Society, points out that the concentrations of invasives are extremely high in Massachusetts, Connecticut, and Rhode Island. With many decades to get established and only mild winters to contend with, invasives are deeply entrenched in these areas.

Likewise, last year Elliman did survey work along the east edge of Lake Champlain in Vermont. There, in a relatively mild climate near long-standing human settlements, he found a lot of invasives. “You name it, they were all there,” he said. But less than 30 miles farther east near Montgomery and Belvidere, where historical settlement and disturbances have been sparser, he found very few.

The pattern is similar in Maine, says Don Cameron, a botanist with the Department of Conservation’s Maine Natural Areas Program. The southern and coastal portions of the state have serious problems, especially with honeysuckle and barberry (Berberis vulgaris or B. thunbergii). The area immediately around Poland Spring, for example, has major infestations. On Mount Desert Island – with its long history of lavish landscaping – Cameron notes that “you can bump into some strange things in the woods.” But across much of Maine’s North Woods, far from historical settlements, he sees virtually no invasives at all. That puts Maine in a good position to prevent their spread.

Using herbicides

Photo by John Douglas / Flying Squirrel

Due to ecological concerns, some people are understandably reluctant to use herbicides. In the case of invasives, however, many experts feel that their judicious application is better than letting the plants thrive.

Ted Elliman of the New England Wild Flower Society uses herbicides in his work. “We certainly don’t discourage people from using them on their own land,” he said. “We just advise them to use the best chemicals and techniques for the application, and in the right concentrations.”

The herbicide most widely used in invasives control is glyphosate. Originally sold under the trade name Roundup, glyphosate is no longer under patent and is available in various formulations. It works by inhibiting an enzyme reaction crucial to plant survival. Although it is a full-spectrum herbicide, killing most plants, it is considered significantly less toxic than many other herbicides, including chemicals from the organochlorine family such as DDT.

Appropriate concentrations of herbicide vary depending on the application. More diluted solutions are used for spraying leaves, while higher concentrations are used for direct application to cut stumps. Cut-stump application is particularly effective in the fall, when nutrients are being moved downward into the plant’s root system for winter storage. Directly applying the herbicide to the stump also minimizes the risk of inadvertently spraying other plants and animals. (Alternatively, cut stumps of woody species can be covered with a patch of heavy duty black plastic tied around the stump to suppress re-sprouting.)

Cut-stump applications can be impractical, especially with vines that have extensive root systems. In the case of Oriental bittersweet, for example, a spray treatment of triclopyr is often recommended. This herbicide kills broadleaf weeds and woody plants without affecting grasses or sedges.

For further guidelines on herbicide use, landowners can consult conservation organizations experienced in invasive species control. If wetlands are nearby, your state environmental agency must be consulted. Local regulations may also apply.

The need for early response

David Paganelli removes a buckthorn he just cut.
Photo by John Douglas / Flying Squirrel

With woodland invasives, early detection and early response are vital. In the early “establishment phase,” when the plants are just getting started, it takes only a few minutes to pull, cut, or spray them. When that window of opportunity closes and they reach the “expansion phase,” growth and seed production shoot up exponentially. Once invasives achieve the “saturation phase” – as Paganelli’s autumn olives have done in many places – they’re much more difficult to remove. At that point, labor-intensive cutting and hand-application of herbicide to each stump is often the only solution. (Another measure in use in some areas is called “over-planting.” After invasives are removed, fast-growing trees are planted to provide shade and slow down any re-establishment of the invasive.)

To succeed in detecting invasives in the “establishment phase” at the statewide and regional scale, planners need to know what to expect. In New York, reports Paul Fuhrmann, people are just getting a handle on how to make the necessary predictions. Fuhrmann is a resource manager and restoration specialist for Ecology and Environment, Inc., based near Buffalo. He says the situation in New York is complex.

In the Adirondack region – which is comparable to Maine’s North Woods, with a relatively pristine center and invasives along the populated fringes – the focus is on mapping and monitoring the roads and other potential avenues of entry. Southeastern New York has more deep-rooted infestations. In the western portion of the state, some areas have already been devastated. In Niagara Reservation State Park, for example, Fuhrmann says much of the Niagara Gorge’s understory is dominated by bush honeysuckles (Lonicera spp.) and common buckthorn (Rhamnus cathartica). But the broader challenge is assessing the impact of the western region’s crisscrossing transportation and utility corridors. All are pathways along which invasives can move.

Because of these variations, the New York State Invasive Species Task Force has designated eight regional Partnerships for Regional Invasive Species Management (PRISM). Fuhrmann, who is acting coordinator for the Western New York PRISM, says each region needs a different management approach to deal with its particular challenges. “Eradication on a landscape scale is not feasible, but control and management within selected habitats can be a realistic goal.”

Though each battle is different, Fuhrmann notes that the first steps are always to assess the situation and then to define your goals. “What are you doing it for?” he asks. “For botanical diversity? For wildlife species of concern? For recreational uses?” These questions are often accompanied by more difficult ones: Can you achieve those goals? Are they practical and affordable? What are the costs, benefits and alternatives? Whatever your objective, you can’t expect to achieve it with any one-time solution. When it comes to invasives, commitment is crucial.

In Fuhrmann’s work, his basic goal is to reestablish more natural succession patterns. That kind of habitat modification usually involves much more than just pulling or cutting the invasive in question. “You have to replace it with native vegetation, something that’s vigorous enough to compete and maybe put some shade over the invasive,” he said.

Across New York and New England, says Fuhrmann, new soil disturbances of any kind – including those caused by removing invasives – need to be carefully considered. Unless vegetation recovery plans are thought out properly, invasives are likely to take over. Rose Paul, director of science and stewardship for The Nature Conservancy’s Vermont chapter, pointed out that it’s particularly important to remove invasives before a logging job: “If the canopy is opened up, we’re giving them a free meal ticket.”

Paul says there’s an important role for state governments to play in providing education and leadership for forest owners. She notes that people are far more aware of aquatic invasive species – such as milfoil, zebra mussels, and water chestnut – than they are of terrestrial invasives. Since all navigable waters are subject to public oversight, state environmental agencies have stepped in with species control and public education efforts. With so much land in the Northeast in private hands, there hasn’t been a comparable public effort concerning terrestrial species.

Paul is concerned because shifts appear to be occurring very rapidly. “I’m finding invasives like barberry and bittersweet in places where I didn’t see them just a few years ago,” she said. “Something is suddenly triggering them to really take off and thrive.” Maine’s North Woods or the Northeast Kingdom of Vermont might have it easy for the moment, but Paul expects that to change in the next decade. “If I was a forest owner there, I’d start watching for species like barberry now. Time spent walking and monitoring your property is the most effective effort you’ll ever spend on invasives.”

A threat on many levels

Forest owners aren’t the only folks who should be concerned. Sportsman and outdoor writer Lawrence Pyne lives in Vermont but hunts with a friend in the Taconics of southern New England. “Down there you can look at a mature hardwood ridge you’d think would have a beautiful open understory. When you get there, it’s almost impassable barberry,” said Pyne. “It’s sobering. To think of that moving our way – and we’re told it is – is alarming.”

Once, sitting down to hunt turkey on a mature hardwood side hill in the Taconics, Pyne couldn’t see more than 10 to 15 feet in any direction. The entire understory was garlic mustard (Alliaria petiolata), a species that has also established itself farther north and could seriously threaten the future of sugar maple. According to a 2006 study at Harvard, garlic mustard devastates hardwood regeneration by killing the mycorrhizal fungi that provide vital nutrient links for the trees’ root systems.

It’s this kind of impact – the interruption of natural forest succession patterns – that most bothers Paul Fuhrmann. In the case of garlic mustard, soil chemistry is literally being changed. “It’s really insidious,” said Fuhrmann. “There’s an unseen biological war going on under the forest floor. It’s tremendously damaging. It spider-webs out into incredible biotic destruction. And that’s just garlic mustard.”

Working to reclaim his Vermont woodlot, David Paganelli says that a lot of folks don’t understand the threats. Some people have told him he should just sell the land. He feels they are missing the point. “What they don’t realize is that this is just the tip of the iceberg.  It’s an invasion. I’m at one beachhead, but they’re invading the countryside and breaking through everywhere,” he said.

As Paganelli sees it, what we most need is a shift in perception. Invasive species are a big deal and all of us – foresters, landowners, loggers, state officials, and citizens-at-large – need to recognize the fact. “If a significant part of the Northeast or North America is degraded ecologically and in economic production capacity, that’s huge,” he said. Only when that reality sinks in will people be willing to invest the money, devote the state staff time, and implement the policy changes needed for an effective response. The expense and effort would, contends Paganelli, be cheap in the long run. (On his property, an essential factor in the battle has been cost-share funding from the Wildlife Habitat Incentives Program, or WHIP, administered by the USDA’s Natural Resources Conservation Service.)

He has hosted three tours of the invasive species situation on his property and, in 2007, did a presentation on invasives for the Society of American Foresters. Afterward, one forester came up and said it gave him nightmares. Those nightmares are what Paganelli hopes to avert. As we sat talking in his woods, he looked up at the 12-foot-high wall of autumn olive behind us. “This,” he said, “is what I’m afraid the future is going to look like.”

Learn More

There are extensive resources on invasive species available online, including field manuals, identification cards, and plant control recommendations. Here are some examples:

The Invasive Plant Council of New York State
The Invasive Plant Atlas of New England
The National Invasive Species Information Center
The Nature Conservancy
The New England Wild Flower Society

The Invasive Plants Field and Reference Guide: An Ecological Perspective of Plant Invaders of Forests and Woodlands, produced by the U.S. Forest Service for the Northeast, is also available online at www.treesearch.fs.fed.us/pubs/20715. Organizations such as The New England Wild Flower Society and The Nature Conservancy provide free training to volunteers interested in helping with invasive species control. Other educational opportunities are available through local nature centers, town conservation commissions, and regional natural resource conservation programs. If you have invasive landscape plantings and are interested in removing them, the websites above can help you identify alternatives. If you have more serious invasives on your land, assistance with removal costs may be available through the Landowner Incentive Program (LIP) or the Wildlife Habitat Incentives Program (WHIP), which are administered by state and federal agencies. Landowners and municipalities can also combine forces in seeking funds.

Plant by plant, Tovar Cerulli is removing invasive honeysuckle from the few acres he and his wife, Catherine, own in north-central Vermont.

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  1. Sheila O'Connor Hysick → in Syracuse, NY
    May 21, 2009

    My yard borders a small natural woodland. I’ve been busy pulling out mustard garlic and would like to identify some of the beautiful native flowers that populate the area.

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