Invasive Species

Why control invasives?

Invasive plants impact our existing ecosystems resulting in habitat loss and reduction of native plant and animal diversity. Invasive plants have aggressive growth behavior that leads to fast colonization of the undesirable plants. This impacts town citizens by degrading agricultural lands, reducing forest growth, restricting recreational activities, and eventually impacting property values.

Habitat Loss

Aggressive growth can affect native herb, shrub, and tree growth. They crowd out desired plants, even impacting forest regeneration. Invasive plants are out of step with the natural community of insects, birds, fish and mammals living in our town, impacting habitat and food resources.

Most invasives are a poor quality food source for native wildlife. For instance, the berries of burning bush have little nutrition and are unwittingly eaten by birds who need better food to survive seasonal migration and overwintering. Others like Purple loosestrife, Japanese barberry, and multiflora rose are avoided by insects, birds and waterfowl, leading to nutritional brownfields. While our native plants provide a wide variety of foods for animals, either directly through leaf and berry browsing or indirectly by acting as host species for native caterpillars and other insects needed by our fauna, the non-native invasive plants do not provide the rich abundance needed by our ecosystem either in our short burst of summer or through the calendar full year.

Tree growth

Invasives inhibit the growth of trees by preventing seedlings from become established. Asiatic Bittersweet vines, for example, choke trees causing girdling, breaking of limbs, or snapping off the entire seedling top, causing them to die.


Invasives increase the cost of agriculture by requiring more effort to control. Unattended farmland may become so overgrown that eradication is not feasible resulting in permanent loss. Undesired plant species impacts the quality of hay, out-competes planted crops, and adds to a farmer’s already demanding task of managing the land.


Here are key identifying characteristics of some key species found in Topsham. Click image for more information about the species like habitat and methods of control. Click the titles for additional identification pages.

Oriental Bittersweet

asiatic bittersweet

Japanese Knotweed


Japanese Barberry


Asian Bush Honysuckles


Burning Bush

Burning Bush

Multiflora Rose

Multiflora Rose

Autumn Olive

Autumn Olive


Removal of invasive plants is seldom a once and done operation. It often takes repeated effort over several years. Removal of whole plants including roots can be effective when the infestation is small. Repeated cutting of some like japanese knotweed and asian bush honeysuckle will exhaust the root and seed bank. For established infestations, cutting and applying herbicide to the cut stem is the best approach. The best time for removal is before the seeds start forming.

There will be a separate area at the Solid Waste Facility for disposing of invasive species. Please use it to help avoid spreading them in our compost.

Further Resources

Maine Invasive Species Network