Invasive Plants

  • Norway maple
  • Tara vine, Rockland
  • Goutweed
  • Garlic Mustard, photo by Bob Moosman
  • Japanese barberry fruits
  • Japanese barberry at Wells Reserve
  • Asiatic bittersweet, Cape Elizabeth
  • Crown vetch
  • Black swallowwort flowers
  • Black swallowwort
  • Japanese knotweed flowers
  • Japanese knotweed stems
  • Himalayan balsam
  • Yellow iris
  • Invasive honeysuckle fruits
  • Invasive honeysuckle in the forest understory
  • Purple loosestrife, photo by New England Wild Flower Society
  • Eurasian milfoil, Prout's Pond
  • Japanese butterbur
  • Phragmites colony
  • Phragmites flowering tops

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Maine Invasive Plant Fact Sheets

Invasive Plant Publications

What is an invasive plant?

An invasive plant is defined as a plant that is not native to a particular ecosystem, whose introduction does or is likely to cause economic or environmental harm or harm to human health. There are currently approximately 2,100 plant species recorded from Maine. Approximately one third of those are not native. Of those plants that are not native, only a small fraction are considered invasive, but these have the potential to cause great harm to our landscape.

How do these plants reach our landscape?

In many cases, people have imported invasive species for ornamental and landscaping purposes because many of these species are very attractive. In other cases, these plant species are purposely planted because they have strong root systems and can provide soil stabilization and prevent erosion. Accidental introduction through tagging along with other plants purchased at garden shops and through soil contamination are also possible. Aquatic invasives are easily transported on boats, float planes, and their gear. Watercraft registration fees in Maine help fund the prevention and control of aquatic invasive plants and fish.

Why are invasive plants so successful on our landscape?

Invasive plant species often lack natural predators, diseases, and other pathogens that keep them in check in their native habitats. They have competitive adaptations including early leaf-out, aggressive reproductive strategies, and efficient dispersal methods. In many cases, they take advantage of disturbances, like road construction, and establish themselves before native species can get a foothold.

Why should you care?

Invasive plants are a direct threat to what we value about Maine's natural and working landscapes. The aggressive growth of invasive plants increases the costs of agriculture, can affect forest regeneration, threatens our recreational experiences, and potentially decrease property values. Species like Japanese barberry and multiflora rose can form thorny, impenetrable thickets in forests and acricultural fields. Aquatic invasives can choke waterways, making it difficult to boat or swim.

Invasive species are the second-greatest threat to global biodiversity after loss of habitat. Invading plants out compete native species by hogging sunlight, nutrients, and space. They change animal habitat by eliminating native foods, altering cover, and destroying nesting opportunities. Some invaders are so aggressive they leave no room for our natives.

What can you do to help?

Our natural landscape is precious. Its future depends on the choices we make. When buying plants or moving them from place to place consider whether the plants are likely to escape. Plants advertised as fast growing, prolific, and tolerant of many growing conditions are often the ones that become invasive. Maine just won't be Maine if the plants dominating our landscape are all from away.

  • Verify that plants you buy for your yard or garden are not invasive. Ask your local garden supplier to include more native species.
  • Replace invasive plants in your garden with non-invasive alternatives.
  • When boating, clean your boat thoroughly before transporting it to a different body of water.
  • Don't release aquarium plants, fish, live bait, or other exotic animals into the wild.
  • Volunteer at your local park, refuge, or other wildlife area to help remove invasive species. Help educate others about the problem.
  • Learn what plants are problematic in Maine and tell your state representatives that you care about the future of Maine's natural landscape.

Invasive Plant Status and Law in Maine

Maine State Law

The State of Maine enacted Title 38, Section §419-C Prevention of the spread of invasive aquatic plants in 1999. This statute provides the following prohibitions:

A person may not:

  1. Transport any aquatic plant or parts of any aquatic plant, including roots, rhizomes, stems, leaves or seeds, on the outside of a vehicle, boat, personal watercraft, boat trailer or other equipment on a public road;
  2. Possess, import, cultivate, transport or distribute any invasive aquatic plant or parts of any invasive aquatic plant, including roots, rhizomes, stems, leaves or seeds, in a manner that could cause the plant to get into any state waters; or
  3. After September 1, 2000, sell or offer for sale in this State any invasive aquatic plant.

Aquatic Invasive Plants currently found in Maine

Please visit the Maine Department of Environmental Protection-Invasive Aquatic Plants for more information about these species.

Outreach and education

The Maine Natural Areas Program (MNAP) provides outreach and education services to help spread the word about invasive plants in Maine. MNAP has worked in conjunction with the Maine Department of Environmental Protection on a rapid assessment aimed at collecting baseline information about aquatic plant species and substrate types commonly found in Maine lakes. MNAP also produced the Invasive Plant Survey Atlas of Maine in 2002 which shows the distribution of many invasive plant species known from Maine.