There are a lot of threats to Maine forests — fragmentation, poor forestry practices, development, imported and native pests and diseases . . . and invasive plants.
Plants like “burning bush,” famous for its red color. Or the distinctive “Crimson King” Norway maple. Or the common privet. Plants that have graced Maine lawns and gardens for decades because they were attractive, hardy and readily available.
Now the state is taking a step to slow the spread of these invaders, banning — beginning this month — the sale and importation of 33 plant species, including many that long ago slipped their leashes and began roaming the countryside.
The threat the banned plants pose to forests — those existing and the forests of the future — is real and serious, said Gary Fish, the Maine state horticulturist.
“Forests are very vulnerable” to invasives like Japanese barberry and glossy buckthorn, which can take over the understory and elbow aside native species, said Fish, who is a forester himself.
They can also make forest management more difficult: “Sometimes it’s so bad that they prevent regeneration of the forest. I’m not being extreme here. I’ve seen it in many places. People have done a cutting with a certain rotation in mind and they get nothing back. You end up with this new dominant understory that takes over the site. It’s also impacting forests as far as their wood product value and their habitat value.”
Some of these species simply outcompete similar native species. Norway maple, long a popular yard tree, has supplanted sugar maple in some areas. Along the banks of the Kennebec River, off the Rail Trail in Augusta, for instance, Norway maple grows thick. “Is Norway maple providing the same type of habitat as sugar maple or red maple? Not at all,” said Fish.
Fish has seen forests in southern Maine where the understory is so dense with Japanese barberry or glossy buckthorn that you couldn’t walk through it without a kevlar bodysuit.
He’s seen acres of pines engulfed by asiatic bittersweet vines.
He’s looked into the woods in the fall to see the understory blazing with the distinctive orange-red of winged euonymus, also known as burning bush, a shrub native to China, Japan and Korea and long prized in North America for its distinctive autumn foliage.
The new banned plants list includes 15 invasive species, 12 species that are likely invasive and six that are potentially invasive. All are sold commercially, though many nurseries began phasing out their sales years ago. A few aren’t really sold, as such, but are “hitchhikers” found as weeds growing in nursery stock. Those stowaways include Japanese stilt grass, garlic mustard and mile-a-minute weed.
Others of the 33 most unwanted: Amur maple, tree of heaven, black locust,, purple loosestrife, Japanese knotweed, Paulownia, Bishop’s weed, yellow iris, multiflora rose, common barberry and white cottonwood. You can access the full list as well as much more information at maine.gov/invasives.
Given that most of these plants have been sold as landscaping plants for decades, and some have virtually become naturalized — black locust, anyone? — isn’t it a case of shutting the barn door after the horse is already gone?
Well, yes, said Fish. But it’s not an empty gesture. He believes that banning the sale of these plants will at least slow their spread.
“I think it’s a fairly important action,” he said, especially as people build homes and vacation cottages in formerly remote areas — importing their favored landscape plants to make themselves feel at home, they “pose a much greater threat.”
“If we stop selling them now they’re less likely to get into northern or western Maine, or areas where there haven’t been a lot of formal landscapes in the past so there isn’t as big a problem,” Fish said.
The list only includes terrestrial plants. Invasive aquatic plants are regulated by the Maine Department of Environmental Protection, which bans several aquatic invaders. Trained volunteers inspect boats at landings in an effort to stop them from making it into new waterways and water bodies.
The origin of the terrestrial banned plants list dates back to the middle of the 1990s, when some experts began raising concerns about the invasiveness of commonly planted trees and shrubs like Norway maple, burning bush and Japanese barberry.
Fast forward to 2016: a terrestrial invasive plants working group finished its review of 38 species to see if they qualified as invasive. They judged the 38 candidates on whether they are non-native species: whether they have spread or could spread into surrounding habitats; and whether they have already, or could, develop self-sustaining populations that could cause economic harm or disrupt natural ecosystems.
The panel found that 33 did. The rule banning them was adopted last year, with a one-year delay in implementation to allow nurseries to sell existing inventory. They had to do that by the end of last year.
Fish said the ban only applies to sales and propagation. It doesn’t prevent people from moving beloved specimens or force them to destroy the plants in their yards. The department just doesn’t have the resources to do that, he said.
To see what a monumental effort that would be, consider the decades-long expensive war against gooseberries and currants — hosts of white pine blister rust — and multiply by, well 33. By the way, Maine still bans the sale of Gooseberries and currants. Some states that relaxed or removed their bans on those plants have seen a resurgence in blister rust.
If homeowners want to grub out their burning bushes or chainsaw down their Norway maples, however, the Maine Department of Agriculture, Conservation and Forestry has recommendations on more accommodating, and benign, alternatives to replace them.
Some land trusts, Acadia National Park, and woodlot owners are actively engaged in trying to oust these invaders from unique or highly valued ecosystems, but, absent a large-scale campaign, it’s a difficult, even never-ending, battle. Plants don’t recognize boundary lines.
Meanwhile, the scrutiny of terrestrial plants continues, said Fish, with a larger committee looking at the issue. That panel will consider future additions to the list. Plants that narrowly missed being banned last time may be added, he said.
The five that were considered for, but didn’t get on the current list, were rugosa rose, hardy kiwi, common valerian, Bradford pear and western lupine. Most of those were not included because there wasn’t enough evidence to show that they jump from one habitat to another.
Rugosa rose, for instance, stays in sandy soils, said Fish. But there’s a lot of pressure to ban it because it’s extremely common in trade. Bradford pear, also known as callery pear, is, however, “incredibly invasive. It goes everywhere,” said Fish. So far it hasn’t been widely planted in Maine. Other states, have banned its sale, he added.
The Department of Agriculture, Conservation and Forestry has waged a months-long information campaign to alert nurseries and other licensed sellers of plants about the sales ban.
The biggest challenge now will be online sales, though it helps that the same plants on the Maine list are banned in many other states as well. It also helps that the larger online retailers keep abreast of such bans and which states they can and can’t ship certain species to, said Fish.
As this ban takes effect, one question that remains is, did we act soon enough? Another is, what more should be done? It might be years before we get answers. But at least it’s a start.
Joe Rankin writes on forestry, nature and sustainability. He lives in New Sharon.