Invasive Plants on Door County’s Shorelines

Invasive species are exotic plants and animals that have been introduced to our area and are likely to have lasting impacts on our environment, economy or health. They are often characterized by their ability to out-compete our native species and reproduce successfully in their new environment. Invasive plants occur in all types of ecosystems, but their encroachment into our coastal habitats can inflict a unique suite of effects that includes:

  • alteration of water and soil chemistry
  • lower aesthetic values and resulting impacts on tourism
  • increased costs associated with equipment and marina maintenance
  • damage to fish habitat and impediment of fish migration
  • lower species diversity and limited critical habitat for rare and endangered species

In our global society, the topic of invasive plant and animal species is broad and continually evolving and, locally, recent low-water levels have only complicated the issue for natural resource professionals and land managers. Everyday citizens can help in the fight against invasive species by learning to identify common invaders in their area – like the following six species – and working to prevent their spread.

Common Reed Grass (Phragmites australis)

Often referred to as Phragmites, this perennial grass is found in large colonies ranging in height from 6’ to 13’. The brown, dead stems persist through the winter and aid in identification during this time of year. The low water levels have created vast expanses of new habitat for Phragmites – during the growing season keep an eye out for long stolons (above ground, horizontal shoots) growing up to 60’ away from the other plants and across newly exposed lakebed.

Reed Canary Grass (Phalaris arundinacea)

This large, coarse grass reaches 2’ to 6’ in height and forms dense stands that displace other native plant species. Flowering occurs in May to mid-June and flowers initially appear purple to green before changing to beige. Reed canary grass is a very common wetland invader in Door County, but it is also often found on our shorelines where low water levels have expanded available habitat.

Hound’s Tongue (Cynoglossum officinale)

This emerging invasive plant in Door County is being found in woodlands and meadows, and more commonly along shoreline and riparian areas. A biennial, hound’s tongue can grow from 1’ to 4’ tall. Its reddish-purple, 5-petaled flowers bloom during June and July and its wide, hairy leaves are distinctive. Hound’s tongue can be toxic to livestock and other animals if consumed.

Purple Loosestrife (Lythrum salicaria)

Photo by Elizabeth J. Czarapata, courtesy of WI DNR.

This recognizable wetland perennial grows 2’ to 7’ tall. It forms dense stands in wet soils and has little value for wildlife. The stem is stiff and usually 4-sided (square in cross-section) while the leaves are whorled and flat. Flowers have five or six rose-purple petals that form a spike.

European Marsh Thistle (Cirsium palustre)

Photo by Elizabeth J. Czarapata, courtesy of WI DNR.

This somewhat shade-tolerant thistle has been recently spotted in coastal wetlands and cedar swamps along Door County’s shorelines. Once introduced, it can aggressively colonize natural areas and may become more common with fluctuating water levels. In its second year of growth, European marsh thistle will have a 4’ to 5’ tall, thick flowering stem that branches near the top. This stem will be bristling with spiny wings making it distinct from our native marsh thistle. Clusters of 12 or more purple flower-heads will bloom in June and July.

Narrow-leaved Cattail (Typha angustifolia)

Photo by Richard Bauer, courtesy of WI DNR.

This cattail species can be found invading marshes, wet meadows, roadsides, shallow ponds, streams, and shorelines. While it may serve as a source of food and shelter, large monotypic stands exclude less common wildlife and bird species. Low water levels have created new and expanded habitat. Complicating invasions is the fact that narrow-leaved cattail hybridizes with our native broad-leaved cattail, making identification difficult in some situations.

If you’re a shoreline property owner who has any of these species on their property, help is available. Contact the Door County Invasive Species Team for more information on what you can do to control invasive plants.

Photo by Elizabeth J. Czarapata, courtesy of WI DNR.

Don’t have invasive species on your property? You can still practice good shoreline stewardship – prevent erosion, manage runoff, and protect native plants to keep our waters healthy and resilient.

The Door County Invasive Species Team

Photo by Steve Garske, cortesy of WI DNR.

Message Line: 920-746-5955

Email: [email protected]

Photo by Elizabeth J. Czarspata, cortesy of WI DNR.