Frank Carini: Invasive plants are winning in R.I.

Japanese barberry in Penwood State Park, in Connecticut

— Photo by Sage Ross 

From ecoRI News (ecori.org)

This intrusive plant was brought to the United States from Japan and eastern Asia in the late 1800s. The ornamental is still used in residential and commercial landscapes because of its fall coloring and deer resistance. But the prickly shrub easily spreads into woodlands, pastures and meadows, where, like many invasives imported from faraway lands, it chokes out native species.

Japanese barberry can also be popular with ticks. A multiyear study conducted in Connecticut looked at the relationship between the deciduous shrub, white-tailed deer, white-footed mice, and deer ticks, also known as black-legged ticks. It found that the larger amount of barberry in an area, the higher the prevalence of deer ticks, which can carry Lyme disease.

The hearty species, which can grow up to 6 feet tall, has denser foliage than most native species and, as a result, the invasive bush retains higher humidity levels that ticks crave, according to the study published in 2010. The shrubs also provide nesting areas for white-footed mice, which are a main source for larval ticks’ first blood meal.

Follow-up research in 2011 found that barberry-infested forests are about 12 times more likely to harbor deer ticks than forests without barberry.

This past fall Pennsylvania became the most recent state to include Japanese barberry on its list of invasive plants that can’t be legally sold or cultivated. The sale of the multi-stemmed shrub with needle-sharp spines has been banned in Massachusetts since 2009 and in New Hampshire since 2007. The sale of the plant is also prohibited in Maine and Vermont.

Connecticut recognizes it as an invasive, but nurseries there can grow and sell it. Connecticut does prohibit the sale of other plants on its invasive species list, but barberry is popular and the nursery industry lobbied against a ban. Big-box stores are still selling it, even after the Connecticut Nursery & Landscape Association agreed to phase out the most invasive barberry plants.

The sale of barberry is allowed in Rhode Island. In fact, the Ocean State is the only New England state that doesn’t have a complete list of noxious plants. While the other five states have a long list of invasive species that are banned or at least identified in Connecticut’s case, the Rhode Island Department of Environmental Management’s invasive plants webpage notes the damage inflicted by non-native species but only mentions one: phragmites, which aren’t sold at nurseries and garden centers.

“For more information and resources about invasive plant species in Rhode Island,” the state’s environmental agency directs those interested in the problem to a broken link on the website of the Rhode Island Natural History Survey, a small nonprofit that over the years, as DEM staffing and funding have been cut, has become increasingly relied on to help protect the local environment.

The organization’s executive director, David Gregg, said the Natural History Survey and others have been working since the early 2000s to get Rhode Island to at least create a list of invasive plants that should be avoided, such as burning bush, privet and Japanese barberry.

Those efforts have continually stalled, thanks in part from pushback from lobbyists representing nurseries, garden centers and growers who have developed their businesses based on consumer demand.

This snarl of oriental bittersweet has climbed into trees along a roadside in Portsmouth, R.I.

— Photo by Frank Carini/ecoRI News

Shannon Brawley, executive director of the Rhode Island Nursery & Landscape Association (RINLA), said the organization favors a list but wants the industry to have a significant say in what species are listed or banned.

“We have to make sure we’re not collapsing someone’s business by outlawing particular plants,” she said. “It takes a long time to grow them. Nurseries are growing it and then they have to tear out acres and acres of product, and it takes five to eight years to grow something else to sell. If it’s not done carefully, there’s going to be an economic impact on these businesses.”

Gregg said if that is the case then there needs to be a plan to deal with the issue of economic hardship. But maintaining the status quo, he added, can’t be an option.

Like many other non-native species, Japanese barberry can tolerate a range of site and soil conditions, which means, like multiflora rose, oriental bittersweet and autumn olive, it comes to dominate the landscape, and can change soil chemistry.

Common barberry, a European invasive first brought to this country during the 17th Century, is shade-tolerant, which allows it to easily invade woodlands. It can reach a height of 13 feet.

Barberry, like other ornamentals brought in from overseas, spreads from home and commercial gardens to open spaces and areas that have been disturbed, such as roadsides. Barberry produces a lot of seeds and has a high germination rate. Its seeds aren’t very nutritious for wildlife, but they are eaten anyway and deposited in more areas, where more of the invasive becomes established — part of a larger cycle that is crowding out native plants, destroying habitat, and starving native insects and wildlife.

Tangles of bittersweet, forests of burning bush and heaps of multiflora rose mar much of Rhode Island’s landscape.

“Invasive species are the second-greatest threat to biodiversity after development when it comes to areas of habitat they wipe out,” Gregg said, “It’s what wrecks the outdoor experience for people who want to relax in green space. There’s a crack ton of it. It’s a physiological and cultural problem, as well as an environmental and economic one.”

He noted that both sides of the East Bay Bike Path from end to end are full of invasives. “Good luck getting a view of the water. It’s like going through a tunnel of phragmites.”

Brawley noted she gets out-of-state phone calls from people looking to buy burning bush because of its intense red foliage. She provides them with native alternatives that are similar but don’t suffocate woodlands and coastal scrublands.

“I couldn’t in good conscience recommend the purchase of this plant,” said Brawley.

She said most Rhode Island nurseries and garden centers don’t sell burning bush, or if they do, it’s a sterile variety.

Burning bush was introduced to the United States in the mid-1800s as an ornamental plant for use in landscaping. The sale of it is prohibited in Massachusetts, New Hampshire and Maine, and the invasive is on watch lists in Connecticut and Vermont.

— Photo by Chris Barton/Gif absarnt

Douglas Tallamy, a University of Delaware entomologist and author of Bringing Nature Home: How You Can Sustain Wildlife with Native Plants and Nature’s Best Hope: A New Approach to Conservation That Starts in Your Yard, has been researching and writing for years about the threat invasives pose to native insects and wildlife habitat.

His work has shown that the transformation of native plant communities into landscapes dominated by imported species and lawns imperil insects, most notably caterpillars, and the birds and other animals that depend on them for survival.

A paper he co-authored in 2020 reviewed the research supporting the theory — which has had its detractors — that the widespread displacement of native plant communities by non-native species is contributing to insect decline. It found that our longtime fascination with ornamentals over native plants is degrading the local environment.

Japanese knotweed can grow 3 inches a day and reach 10 feet in height. Oriental bittersweet can climb to 60 feet, strangling host trees. Tree-of-heaven can reach a height of 80 feet and grow to be 35-50 feet wide. Glossy buckthorn can colonize without disturbance, and its dense foliage and ability to mature quickly allows it to easily outcompete native plants. Extensive stands of it can also produce conditions favored by deer ticks.

These four invasives and most others don’t have natural predators feeding on or killing them. The vast majority of native insects can’t eat or reproduce on these invaders — native plants and insects co-evolved over thousands of years — creating a food desert for invertebrates and the birds and animals that feed on them. They provide little support for pollinators.

Many of the worst invasives strangling Rhode Island, such as bittersweet, knotweed and glossy buckthorn, are no longer sold, but the lack of diversity created by the totality of the state’s invasive species problem, including the continued sale of many intrusive plants, makes the local environment much less resilient, by leaving it, for example, with fewer options when responding to the climate crisis.

The continued sale of invasives is directly tied to consumer demand and the Rhode Island landscape and nursery industry responding to those wants.

Catherine Weaver, a RINLA board member and past president who owns a North Kingstown-based landscape design studio, said her clients often request miscanthus, also known as Chinese silvergrass, a popular ornamental grass she called “a nuisance.” Hedges of invasive privet are also a high-demand request by her clients. She called privet “a nasty invasive,” and said she instead recommends the use of natives like sweet pepperbush or viburnums.

“We need to prioritize environmental integrity over aesthetics,” Weaver said, “but we’re so used to using aesthetics to judge if a plant is good. Planting something beautiful is pleasing … but we have to use other criteria when we’re making these decisions. We shouldn’t be sacrificing ecosystem function for beauty. We can have both. There are so many great native plants.”

Both Weaver and Brawley said the public needs to be better educated about the importance of native plants to create more demand. They believe progress is being made on that front, albeit slowly.

“Five clients in the past year have asked for mostly native plants,” Weaver said. “That almost never happened before.”

Not every non-native species is invasive, however. Invasives are those that, reproducing outside their native range, actively cause ecological or economic harm, according to the Invasives Species Act of 1996.

Species exchange is natural, as there has always been drift — plants moving with the tides and seeds scattered by birds and storms. Ecosystems change over time. Early humans brought hitchhikers with them as they migrated. But comparatively, today’s invasive species levels are monstrous, because of growing human globalization, including two-plus centuries of importation of ornamentals from exotic places to show off wealth and later to keep up with the Joneses.

In Rhode Island, the limited amount of attention being paid to invasive plants is largely focused on aquatic invaders, which interfere with boating, paddling, fishing and other recreational activities. More than 100 lakes and 27 river segments in Rhode Island are plagued with at least one species of invasive plant, according to DEM.

The agency’s webpage for aquatic invasives includes a list of the problem species. Many only need a couple of cells or a leaf to reproduce. They can take over a waterbody quickly.

In its 2020 fishing regulations, DEM prohibited the transport of invasive plants on any type of boat, motor, trailer or fishing gear to help prevent the inadvertent movement of aquatic invasives from one waterbody to another.

DEM also has proposed regulations to ban their sale, purchase, importation and distribution. The proposed regulations list 48 species of aquatic invasive species whose sale would be prohibited, such as Carolina fanwort, a problem species in Smithfield’s Stump Pond; American lotus, which covers 18 acres of Chapman Pond in Westerly; Brazilian waterweed, which has invaded Hundred Acre Pond in South Kingstown; and common water hyacinth, an Amazonian species now found in the Pawcatuck River.

DEM’s proposal to limit aquatic invasives is still under review, according to an agency spokesperson. Enacting the proposal doesn’t require enabling legislation.

Gregg said Rhode Island should be taking the same precautions when it comes to terrestrial invasives, as they inflict as much damage to the environment and local economy. He noted the fact Rhode Island hasn’t banned the sale of many invasives or even bothered to compile a complete list doesn’t paint the state as very neighborly.

He said it was also unfair that as taxpayers fund efforts to eradicate invasives, nonprofits create programs to battle their spread and volunteers spend their free time cutting and pulling them from the landscape, their local garden center is selling more intrusive non-natives to be unwittingly planted at homes and businesses.

“We’re spending good money and time removing invasives from the woods to maintain the status quo,” Gregg said. “It would make more sense to have a regulation that banned the sale of these plants.”

Gregg offered a solution: remove the word “aquatic” from DEM’s invasive plant proposal.

“It’s pretty clean and simple,” he said. “Delete a single word and create an invasives species list.”

A bill filed last year would have done just that, making it illegal to import, transport, disperse, distribute, introduce, sell or purchase in the state any invasive plant species.

Black swallow-wort, an invasive vine from Europe, reproduces by sprouting new stems from existing roots and by spreading seeds. Inside this seed pod are thousands of seeds that will float on the wind or hitch rides on animals to other areas. Removing and disposing of seed pods before they open is one way of slowing the spread of this invader. (ecoRI News)

Two years earlier, in 2019, the Protection From Invasive Plant Species Act would have prohibited the planting of running bamboo within 100 feet of a property line. The fast-spreading invasive can penetrate asphalt and the siding of buildings. Many homeowners, not knowing the unintended consequence, plant running bamboo as a natural barrier that offers privacy and blocks out animals such as deer. But some bamboo species can grow 40 feet high and their roots can travel 15 feet in a year.

Violators would have been liable for the cost of removing the plant from a neighbor’s property, plus any damages. Rhode Island retailers and landscapers would have been required to provide customers written notice of the risks of running bamboo.

To address other non-native invaders, the legislation would have required DEM to create a list of invasive plant species, regulate their sale and enforce compliance.

DEM, however, was opposed to the legislation. The state agency said it already regulates invaders and can assess fines of up to $500 for transporting invasive aquatic plants. It noted it doesn’t allow federally designated noxious weeds to enter the state. The U.S. Department of Agriculture list doesn’t include Japanese barberry, privet or burning bush. It doesn’t even include multiflora rose, oriental bittersweet or phragmites.

The Rhode Island Farm Bureau feared the bill would punish farmers for invasive species they didn’t actually plant. It suggested the state — that is, taxpayers — instead offer money to farmers and property owners for the removal of invasive plants, of which some were likely bought in Rhode Island and planted by the current landowner.

Like past attempts to tackle the problem of invasive plants, such as the 2021 bill that would have removed the word aquatic, the Protection From Invasive Plant Species Act didn’t go anywhere.

Since the state seems unwilling to address the problem, Gregg said the key to reducing the impact of invasives is educating the public about the environmental harm many non-native plants cause.

“It’s in the public’s interest that we grow the right plants,” he said. “The importance of native species has come a long way in the past 15 years, but we need an invasive species list so we can have conversations that educate the public and bring awareness to the problem. It’s a complex issue, but at the end of the day we’re spending money to remove stuff people are buying at garden centers.”

Frank Carini is senior reporter and co-founder of ecoRI News.