Weeds Gone Wild


Asiatic Bittersweet

By Judith Stanton

The Harpswell Invasive Plants Partnership has declared all systems go in the launch of its survey and mapping project. A group made up of representatives from Harpswell Heritage Land Trust, Conservation Commission, Town Lands Committee, Mitchell Field Committee and others interested in stewardship of our natural community, has spent the past 14 months researching and planning a program to identify, locate, document and eventually control aggressive non-native plants.

Our coastal town is a reluctant host to invaders of all kinds: green crabs wreak havoc on clam beds, while winter moths strip valued trees of their leafy canopies. Great numbers of terrestrial invasive plants are also steadily establishing new territory. With their ability to grow quickly and aggressively, they outcompete native flora for resources, reduce wildlife habitat and alter the natural landscape. The Maine Natural Areas Program (MNAP) currently estimates that one third of all plant species in the state are not native.

With the help of MNAP, the Partnership has drawn up a list of species currently considered the biggest threats to local ecosystems. Many are familiar and attractive plants, such as Purple Loosestrife, Bittersweet, Japanese Barberry, Multiflora Rose, Yellow Iris and Honeysuckle.

Invasive Public Enemy No. 1 in much of the eastern United States, Asiatic Bittersweet’s bright red-orange berries are dispersed via animal ingestion and by humans who like to make wreaths with them. They can easily end up miles from the parent plant, which alone can produce 2,000 high-germinating seeds. Neighboring plants become rapidly enveloped by the vines, which strangle stems and engulf vegetation. Smaller trees may even be uprooted due to the weight of the bittersweet growth.

Another robust invasive often sighted along the verges of Harpswell roads is Japanese Knotweed, aka American or Mexican Bamboo. It spreads underground, forming tall, dense thickets that crowd out other plants and block sunlight required for photosynthesis. The root system has enough strength to force its way up through paving and concrete foundations.

Initially the Partnership intends to focus its survey on public lands owned by the town or HHLT, including Mitchell Field, Houghton Graves Park, McIntosh Lot Preserve, Johnson Field Preserve and Mackerel Cove Town Lot, and major public roadsides in Harpswell (Route 123, Route 24, Mountain Road, and Cundy’s Harbor Road).

A corps of volunteers will be needed to track and record invasive plants from late spring through summer, presenting a great opportunity for those interested in becoming citizen scientists. Workshops will be held in April and July to teach identification of target herbaceous and woody plants.

Those who are tech-savvy will also have the option of learning how to use an on-line mapping program called iMapInvasives. The software allows an exchange of invasive species data locally and on a state-wide level. Leading the training session will be invasive plant biologist Nancy Olmstead from the Maine Natural Areas Program.

Click here for more information about HIPP.

January 2015