Invasive plant species are threatening the forests of Maine.

When she makes this statement, Amanda Devine, a biologist and regional stewardship manager for the Maine Coast Heritage Trust, isn’t talking about the forests that exist now.

She is talking about forest that should exist 100 years from now, when climate change makes Maine too warm for the trees and other plants that now grow here.

“A hundred years from now, the forests of Maine should look more like the forests of the Virginia mountains look now,” she said, meaning they’ll be comprised of plants native to the Eastern United States that are now too tender to survive Maine’s winters.

Ideally, those Virginia mountain trees and perennials would drop their seeds. Winds and wildlife would move the seeds north bit by bit until they’d slowly make their way up the East Coast to reach what will be a warmer and more welcoming Maine climate.

What will likely prevent this transition is that the understory of the forests from Virginia all the way up to Maine is already made up of non-native, invasive species that will prevent the less aggressive native Eastern plant seeds from reaching the soil or, if they do reach it, from sprouting and thriving. The native species from the Eastern Seaboard states to our south cannot compete. Devine singled out invasive Japanese barberry as particularly intractable.

Berberis thunbergii, or Japanese barberry, in autumn. The shrub, which was introduced, is “severely invasive” in Maine, according to the Maine Department of Agriculture, Conservation & Forestry. Shutterstock/Oleg2KV

Five years ago, the state of Maine banned the sale at nurseries of 33 invasive species. Beginning in January 2024, the sale of 30 more will be banned. Are these bans helping? I asked Devine.

“Nope,” Devine responded. “The horse is out of the barn on that one.”

She isn’t suggesting that Maine should allow sales of invasive plants that were once thought to be harmless ornamentals. Rather, she says banning such sales won’t get rid of the species that have escaped gardens and already threaten Maine’s forests and fields.

Devine keeps a list of 17 plants that she considers the worst of the invasive plants. In the case of two of them, black swallowwort (which was never sold commercially) and Japanese knotweed, after mentioning them, she added, “It’s no longer a fight. They’ve already won.”

Devine described invasive species as the second largest threat to global biodiversity. Human disruption of the natural environment – buildings, roads, parking lots, commercial farms and more – is the largest threat, she said.

Can we do anything to stop these invasives?

The solution sounds simple, but is difficult in practice: Remove the invasive species from any plot of land over which you have control. Devine compared such an effort to Douglas Tallamy’s new project, Homegrown National Park, in which he asks citizens and homeowners to plant native species and remove invasive ones from their yards and communities. If enough small property owners in the right places get rid of the invasive species, maybe the southern native species have a chance of reaching Maine when the climate gets warm enough.

“Go visit your neighbor, and ask them if you can get rid of their buckthorn,” she said.

For small properties, manually removing the invasive species could work, but Devine supports using herbicides – meaning glysophate, which is sold under the commercial name Roundup. To do so, homeowners would need to cut the invasive species’ stem close to the ground and paint the cuts with glysophate.

State Horticulturist Gary Fish also supported this method in a recent talk at Maine Audubon Society. The herbicide is controversial, but it kills the invasive plant with no damage to surrounding plants that you want to keep. Retired Maine Cooperative Extension horticulturist Lois Berg Stack has said that autumn is the ideal time to use this method, and my wife and I have used it on our property.

“It’s not a silver bullet,” Devine said, “but it saves a lot of pain and the use of an awful lot of fossil fuels to bring in heavy equipment to remove the invasive plants by their roots.”

A land trust or group of neighbors who want to eradicate a large area of invasives can hire a commercial firm. She noted that the Cape Elizabeth Land Trust used a Massachusetts firm that specializes in such work.

Flowers of the Eastern Redbud, or Cercis canadensis. Biologist Amanda Devine likes the tree and says it may live in a warmer Maine a century from now. Shutterstock/gg-foto

The question I had – even though I won’t be around to see it – is, what will the Maine forest look like 100 years from now, assuming we get rid of enough invasive species?

Devine mentioned the trees and shrubs that could grow here then: The loblolly pine, a Southern species of yellow pine, as well as the tulip poplar; Cornus Florida, a large native dogwood; and Rhododendron maximum, which can be grown as an ornamental along the Maine coast but does not grow in the wild here.

One species Devine hopes shows up is the redbud tree, Cercis canadensis.

“I drive down to visit my parents (in New Jersey), and they are in bloom everywhere. They are wonderful and I want some,” Devine said. “I contacted Jake Pierson (of Pierson’s Nurseries in Dayton) to see if I could get one I could grow in Freeport. He said, ‘Not yet.’”

But probably in a few years.

Tom Atwell is a freelance writer gardening in Cape Elizabeth. He can be contacted at: tomatwell@me.com.