Mill River group attacks invasive plants

The Mill River and its 52-square mile watershed have been occupied by various groups of people who have impacted or altered the nearby landscape through settlements, farming, logging, building mills and dams and purposefully or inadvertently introducing plants from other parts of the world into the local ecosystem.

Now, a significant number of invasive species are negatively impacting the plant communities along the river, and one local organization is developing a strategy to reverse that.

The Mill River Greenway Initiative is distributing a new action guide to educate people on how to identify and remove several invasive plants species commonly found along the river.

The initiative is a volunteer organization that works with private individuals, professionals, organizations and communities to restore ecosystems, conserve natural resources, preserve cultural heritage and document unique historic sites within the Mill River watershed.

“This is a pocket guide that shows people exactly what things like bittersweet and Japanese knotweed look like, and how you go about combating these plants,” said Gaby Immerman, co-founder of the initiative, and a Smith College laboratory instructor who teaches horticulture.

The guide “Making Room for Native Plants and Wildlife along the Mill River” was written by the New England Wild Flower Society for the Mill River Greenway Initiative, with financial support from Smith College.

The full-color 28-page manual identifies 18 invasive plants commonly found in the region and also provides advice on how and when to remove them and what to plant in their place.

Some of the 18 invasives described are Japanese knotweed, Oriental bittersweet, multiflora rose, Amur cork tree, black locust and burning bush.

The guide also lists 15 additional invasive plants to watch out for, with information on how to report such findings.

The goal of the publication is to raise awareness about invasive species and give people an easy-to-use tool to help combat them.

John Sinton, also a co-founder of the initiative and a retired professor of environmental studies and landscape history at the University of Massachusetts Amherst, said he hopes the guide will be used by a variety of groups as part of organized action plans to tackle particular sections of the river.

Sinton said that the initiative will host informational events this summer.

“We’re planning to organize a series of educational and stewardship events along the river,” he said.

While the guide is the product of the New England Wild Flower Society and the Mill River Greenway Initiative, part of its inspiration and support grew out of Smith College’s Mill River Invasive Species Management Project, which began in 2010.

That project was part of an agreement with the Department of Environmental Protection regarding the impact caused by the installation of a synthetic turf field at the college in 2010. The field was within the Mill River riparian area close to the margins and banks of the river.

The college agreed to remove 75 percent of the invasive plants species in areas adjacent to the river every year in perpetuity.

As part of the project, Smith students interning with Immerman at the Botanic Garden spent hundreds of hours painstakingly locating, identifying and removing nine invasive species, and gathering data along a one-mile stretch of the river that runs through the campus.

Immerman knew that while the endeavor was providing an exceptional learning opportunity for students, the specific problem of invasives would likely go unresolved if it was not addressed on a larger scale.

“There is really a ceiling on the efficacy of individual efforts. We can pull knotweed all day long and just be spinning our wheels,” Immerman said. “We can’t just pull invasives, we have to plug the gaps and replace them with natives species. Restorative species.”

Immerman’s students are now propagating areas of native plants, and “they have made progress in all four installed test plots to see if we can get a sufficient plot of natives established,” she said.

Still, to effectively address the problem of invasive plant species, Immerman knew that the strategy would have to be more comprehensive and encompass a much broader scope.

“I like to think on a regional level, think like a watershed and act on a watershed scale,” Immerman said.

In 2015, an Invasive Plant Management Plan prepared for Smith by the New England Wild Flower Society agreed with Immerman. It reported that in order to get rid of invasive plants on campus it was important to address “invasive species onsite in a holistic manner with a comprehensive approach” in order to “mitigate impacts of current invasions and improve ecosystem function.”

The report suggested that collaboration with organizations like the greenway initiative would benefit the process.

It stated that “locally based partnerships such as this have the power to influence a wider array of partners, leverage funding and more effectively implement ecosystem-based management restoration.”

Immerman said that with the initiative’s new guide, river stewardship can now be extended well beyond the campus.

“What is in this guide is what everybody should be doing about invasives,” Immerman said.

There are tangible repercussions to the local ecosystem when native plants that have co-evolved with other plants, insects, fish and wildlife are replaced by invasives that do not provide the same resources to the system.

According to the Massachusetts Audubon Society, invasive plants can outcompete, crowd out, and overtake native plants, as well as eliminate or diminish resources such as food and cover for wildlife. Invasive species can also disrupt pollination, change the flora gene pool through hybridization and alter the soil chemistry, making it more difficult for native plant species to flourish.

Local naturalist Laurie Sanders said that native plant succession has been disrupted along the Mill River. Seedlings for trees such as sugar maple, hickory and white pine are being suppressed because there is little opportunity for them to establish in areas where Japanese knotweed covers the banks and floodplain.

Sanders said that Japanese knotweed is almost completely valueless for wildlife because it does not provide food, shelter or nesting places, and “from a geomorphology perspective, the growth of Japanese knotweed has also changed the way sands and sediments are eroded and deposited along the river.”

In addition, Sanders said that there are also implications to human health with the spread of invasive plants like Japanese barberry, as more incidents of Lyme disease are found in areas highly infested with it.

“Barberry alters the humidity regime, making it more suitable for deer ticks and the spines on the barberry provide protection for the mice (deer tick host) from predators like foxes,” Sanders said.

With its headwaters at Upper Highland Lake in Goshen, the Mill River is about 15 miles long, flowing down through Williamsburg and ending in Hulberts Pond in Northampton.

Immerman said that because the river is relatively small, there is a good chance that a large-scale, organized and concerted effort to remove invasives and replace them with native plants, could actually make a significant difference.

“You can’t say that about bigger rivers. Maybe, we could actually clean up our river from the DAR to Arcadia. Then we could say, someday, that we have a healthy flourishing ecosystem,” Immerman said.

“Making Room for Native Plants and Wildlife along the Mill River” is available to download for free from the initiative’s website at millrivergreenway.org. A printed, bound version is also available for $15 by emailing info@millrivergreenway.org.