by Kyle Lima
The plant had tall spikes of pinkish purple flowers, and appeared in wet areas next to the Park Loop Road in the late 1980s. Purple loosestrife had a tendency to spread, and reduce the diversity of pre-existing plants and the insects, birds, and other wildlife they supported. In 1988, National Park Service staff determined that purple loosestrife was one of 12 plants considered invasive in Acadia. As a potential source of impairment — which the agency is charged with preventing — the purple loosestrife had to go.
Crews yanked out the plants by hand, and treated the patch with herbicide.
But their job wasn’t done. Instead, it was the beginning of a long-term effort to manage an increasing number of invasive plant species, including garlic mustard, honeysuckle, giant hogweed, barberry, and glossy buckthorn. For decades, park staff continued efforts to document and manage certain problematic plants, reducing the use of chemicals over time. As a result, today invasive plants cover less than one percent of park forests and wetlands. In contrast, across 38 other eastern national parks, invasive plant cover averages just under 14 percent and is as high as 40 percent, according to the National Park Service Inventory and Monitoring Program.
As park staff began addressing invasive plants, they also recorded the location and number of species managed, the hours they spent actively managing those species, the amount of herbicide used, and which plants received which treatments. Having such detailed metrics enabled us to analyze how and why Acadia’s approach has been so effective. The findings, published in November in the Journal of Applied Ecology, document Acadia’s “unusual success.”
Compared to other parks in the region, Acadia has been more resistant to invasive plants in part because of its distance from population centers, rural surroundings, and cooler climate. All of these factors are changing as surrounding forests and fields are fragmented by roads and converted to residential and commercial development, the climate rapidly warms, and disturbances, such as from storms and insect pests, become more frequent. The need for vegetation management is expected to increase.
Some one-third of protected areas around the world have experienced an increase in invasive plants over the past 30 years. Invasive plants have numerous impacts, including reducing biodiversity, preventing forest regeneration, and affecting the ability of ecosystems to soak up floods and filter water.
We highlighted four major recommendations for successfully managing invasive plants in parks and other protected areas:
Commit to sustained investment. Consistent management, supported by five years of funding from Canon U.S.A., allowed Acadia staff to be dedicated as well as flexible and responsive, demonstrating that “an ounce of prevention is worth a pound of cure.”
Set goals. It is crucial that managers set clear and achievable management goals and establish frameworks for making decisions. Most invasive species can’t be completely eradicated as they persist just outside park property and will continue to encroach into the park. Setting a goal of eradication would not be feasible, so managers decided to manage populations to “maintenance levels” where a species is not spreading and requires minimal effort year to year to control.
Learn as you go. Before treating or removing invasive plants, Acadia staff establish monitoring plots to document the effectiveness of treatments and to identify re-invasions. This “learning while doing” approach has helped them identify successful approaches, gain support from park leadership, and prioritize funding and effort.
Don’t do it alone. Parks have limited capacity. In Acadia, partnerships with U.S. Fish and Wildlife Service, Friends of Acadia, Schoodic Institute, and Wabanaki Nations have been key to sustaining and updating invasive plant management over time.
Acadia’s vegetation crew now spends less time managing invasive species, and uses less herbicide, but their work is never finished. Their list of managed plants has grown to 25. Purple loosestrife still grows in the park, albeit at very low levels, with less than 1,750 square feet – an area smaller than a tennis court — managed each year.
“Without this long-term commitment by dedicated National Park Service staff and support from partner organizations like Friends of Acadia and the U.S. Fish and Wildlife Service, Acadia’s landscape would not only look differently but would no longer meet the primary purpose of the National Park Service—to preserve and protect natural and cultural resources for this and future generations,” said Judy Hazen Connery, retired Acadia natural resource specialist.
Read the study, “Unusual success, future uncertainty, and science needs for adaptive management of invasive plants in a US national park.”