BY SHANNON BRYAN

Invasive plants can spread quickly, elbowing out native plants like hangry party crashers at a tapas table. They can reemerge, year after year, despite being cut, dug up, or treated with herbicide. Their persistence would be admirable, were they not so detrimental to the ecosystems they overtake.

As it happens, Acadia National Park’s Invasive Plant Management Team – comprised of a cadre of biologists, researchers, and technicians from the park and Schoodic Institute – are decidedly tenacious, too.

Their collective dedication over the last 35-plus years to early detection and rapid response, as well as science-based experimentation, has resulted in tangible success. Their ongoing work is made possible by sustained funding from partners like Friends of Acadia.

The history of that work, and the integral partnerships that enable the program’s continued development, are outlined in an article published in the Journal of Applied Ecology (JAE) in November 2024.

Co-authored by Kyle Lima, data analyst at Schoodic Institute; Jesse Wheeler, Acadia’s vegetation program manager and biologist; Judith Hazen Connery, who started and managed the invasive plant management program in Acadia National Park for many years until retiring in 2019; Abe Miller-Rushing, science coordinator for Acadia National Park; and Nicholas Fisichelli, president & CEO at Schoodic Institute, the article offers lessons learned and recommendations to resource managers worldwide.

It also shares successes earned over decades of forward-thinking management that may help ecosystems retain resiliency in the face of future change.

Acadia National Park’s invasive plant management team – comprised of a cadre of biologists, researchers, and technicians from the park and Schoodic Institute – work to remove invasive plants from the park. (Photo by Will Greene/Friends of Acadia)

Of Acadia’s more than 800 vascular plants (think flowering plants, ferns, grasses, trees, and shrubs) almost a quarter are non-native, meaning they don’t occur naturally in the park or its coastal waters, but were introduced either deliberately (perhaps planted in a garden) or accidentally (hitching a ride in the treads of a truck tire or adhered to the hull of a boat).

Some, like domestic apple trees and lilacs, don’t directly threaten native plants or wildlife, so they aren’t considered invasive. But there are two dozen or so species that pose real threats to the park’s natural environments. Purple loosestrife, for example, grows in Acadia’s wetlands, choking out native vegetation like cattails.

But it’s not just the loss of native plants; a host of insects, mammals, birds, and fish depend on the vegetation that purple loosestrife pushes out.

In short: Invasive plants are a pressing issue at Acadia, and managing them requires substantial financial and staff resources.

“It’s the park’s biggest natural resource effort,” Wheeler said.

Olivia Zukas (right) and Emma Lanning, both Acadia National Park Biological Science Technicians, chop down invasive Canada thistle plants in the meadowlands of Baker Island. (Photo by Sam Mallon/Friends of Acadia)

In Acadia, the presence of invasive plants is relatively low compared to other protected areas in the northeast. That’s partly a perk of Acadia’s geography—cold Maine winters and the benefits of being on parcels of earth largely bordered by ocean.

Additionally, more than 35 years of collaboration and continuous effort have made a sizeable difference. It also puts Acadia in a unique position.

“A lot of other parks don’t have an embedded team like Acadia National Park does,” said Wheeler. “They rely on regional teams that do initial suppression efforts and sometimes follow-ups.”

The longer-term success of those efforts is contingent on that park being responsible for maintenance and reinvasion, “which is a challenge for many smaller parks that don’t have the staffing or capacity,” Wheeler said. But thanks to park partners, Acadia does.

Continuous invasive plant management in Acadia began in 1988. Purple loosestrife was then identified as the most threatening species, so it became the priority. Resource managers developed a plan with management goals, plans of action, and monitoring. And they kept at it.

A decade later, the JAE article notes, an assessment of their work confirmed their efforts had held back purple loosestrife from invading additional wetlands, and that existing patches were managed down to maintenance levels. Complete eradication is always a goal but challenging to accomplish.

As funding and staff allowed, more invasive plants were targeted in the early 2000s.

The (a) number of species and (b) number of sites managed, (c) hours of work, and (d) herbicide concentrate used during invasive plant management have increased overtime. More recently, however, time spent managing invasive species has decreased as populations are being maintained at low densities, as has the amount of herbicide concentrate used. Hours of work were not recorded in 1988. (Graphics replicated from JAE article)

In 2009, a pivotal partnership between the National Park Service, U.S. Fish and Wildlife Service, Friends of Acadia, and other partners to provide multi-year funding further advanced the work. Within a couple years, Acadia was managing 20 invasive species, including infestations of glossy buckthorn, Japanese barberry, Asiatic
bittersweet, and Japanese knotweed.

Among the successes referenced in the JAE article is the reduction of invasive honeysuckle on Bar Island from 7.6% cover down to 0.2% between 2015 and 2017. With monitoring and maintenance, those numbers have held to <1% cover.

“Because of partnerships and the funding and support for the program, managers were able to take on more and more problematic species,” said Kyle Lima, data analyst at Schoodic Institute and lead author of the JAE article. “At the same time, the amount of staff time needed and the amount of herbicide used also decreased.”

“That sustained support allows us to have the crews we need. We can do early detection and rapid response,” said Wheeler. They’ve also been able to experiment and adjust their methods over time to work more effectively.

Today, Acadia’s Invasive Plant Management Team manages 29 invasive plant species.

“Most of our larger-scale sites are at maintenance levels,” said Wheeler. “Which allows our teams to respond to new sites.” Bass Harbor Marsh and Great Meadow, for example, are significant focus areas where science-based experimentation is taking place.

Getting to this point is the result of decades of dedicated funding and staff efforts.

“That’s why sustaining this work is so important,” Lima said.

National Park Service vegetation program biology technician Jim Burka enters data while managing glossy buckthorn on Cadillac mountain in Acadia National Park. (Photo by Will Newton/Friends of Acadia)

“Climate change is always a challenge,” said Wheeler. But with resources and experimentation, the team can continue to develop approaches that may prove valuable as the climate continues to change and adds pressure to native species.

“A lot of Acadia’s spruce forests are pretty non-invaded right now. But what if our spruce forests and other forest types have less suitable growing conditions? What if they’re stressed by invasive insects? Windstorms? You name it,” said Wheeler.

“On the other hand, I see the work we’ve done with invasive plant suppression as a climate-adapted model of management. Because of the work we’ve done, we’re in a pretty good place,” he said. “And we’re continuing to evolve. We’re still so early with considering new methods, learning from Indigenous partners, utilizing native shrubs for competition.”

“We look at this as being sustainable, but is it forever? We don’t know,” Wheeler said. “Even if you’re not able to eradicate something, you can do a lot to keep landscapes together, more diverse, healthier, and more resilient.”

Olivia Zukas, Acadia National Park biological science technician, removes invasive glossy buckthorn off the Jesup Path near Hemlock Road. (Photo by Ashley L. Conti/Friends of Acadia)

Read the full article, “Unusual success, future uncertainty, and science needs for adaptive management of invasive plants in a US national park,” in the Journal of Applied Ecology at besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2664.14835

SHANNON BRYAN is Friends of Acadia’s Content and Website Manager.