The Wingra Marsh: A Purple Population Problem
- To develop in students an understanding of plant/animal interactions, communities, populations, and the impact of exotic, invasive species
- To engage students in an ecological inquiry
- To engage students in using their science knowledge to make informed decisions in a real life setting
Context for Use
http://serc.carleton.edu/introgeo/icbl/size.html - Different types of objectives can be accomplished by implementing case-based learning in different sized classes.
http://serc.carleton.edu/introgeo/icbl/adapt.html- What issues need to be taken into account before introducing cases to your class?
As you enter the inland section of Wingra Marsh it is blanketed with beautiful dark pink flowers. The marsh is silent. You do not hear the familiar sound of song birds; you no longer see the muskrat family that once lived here. Deer that once frequented the marsh edge have disappeared, along with the raccoons, waterfowl, shorbirds and painted turtles that once shared this habitat.
A closer look tells you that the vegetation has changed along with the fauna. Native sedges, bulrushes, cattails and grasses are gone, as are the floating and submerged aquatic plants that once lived here. You find it difficult to reach the lakeshore as the sea of the dark pink flowering plants stop you from walking more than a few steps into the wetland.What is this plant? Where did it come from?
The plant is purple loosestrife (Lythrum salicaria), a hardy flowering plant that was introduced to the United States as a garden perennial from Europe during the 1800's. It is still promoted by some horticulturists for its beauty as a landscape plant, and by beekeepers for its nectar-producing capability. Currently, about 24 states have laws prohibiting its importation or distribution because of its aggressively invasive characteristics. It has since extended its range to include most temperate parts of the United States and Canada.
Purple loosestrife can overtake wet areas such as lake shores, streambanks, and marshes, crowding out native plants and reducing habitat diversity. It can seriously impact a wetland area in just a few seasons, as each mature plant will produce over a million seeds. In addition, the plant can resprout from a small part of a root or stem. No wildlife species are known to use this plant, and the dense thickets of dead stems deter waterfowl and other wildlife access.
Purple loosestrife is an herbaceous perennial characterized by long showy spikes of magenta flowers. Usually under 4 feet in height, the plant may reach up to 10 feet tall in nutrient-rich habitats such as a marsh. Purple loosestrife has flowers with 5 to 7 petals which occur in dense clusters on terminal spikes and which bloom from June to September. The leaves are opposite or in whorls of 3, lance-shaped, and without teeth. The plant is a member of the loosestrife family Lythraceae.
Purple loosestrife may have achieved its widespread distribution due to its lack of natural predators in North America, as well as its reproductive capabilities. A single stalk may produce as many as 300,000 seeds, and densities of up to 80,000 stalks per acre have been reported. The species also readily reproduces from stem or root segments.What can be done to save Wingra marsh?
Press Release: Manitoba, Canada, May 1999
Galerucella beetles released to Control Purple Loosestrife
A cooperative environmental project will release 1000's of purple loosestrife eating beetles into Manitoba and Saskatchewan over the next two summers. The Manitoba Purple Loosestrife Project has received a grant from Environment Canada's EcoAction 1000 Fund to set-up 5 mass-rearing satellite stations for purple loosestrife beetles, 4 in Manitoba and 1 in Saskatchewan. EcoAction 2000 funds will be matched by funding contributions from Ducks Unlimited Canada, Manitoba Natural Resources, and the City of Winnipeg. Each satellite station will start with 100 beetles inside specialized insect rearing tents and within 4 weeks 5,000 beetles will be produced per tent for release into purple loosestrife infested habitats. Rearing stations will be located in Winnipeg, Libau Marsh, Morris and Holland (Manitoba) as well as Saskatoon. The Manitoba Weed Supervisors Association will play a large role in the project by rearing insects for release in the Morris and Holland (Cypress River) areas.Press Release: Horicon, Wisconsin May 1999
Purple Loosestrife Herbicide Eradication Considered
Purple loosestrife is one tough plant. It is a deep-rooted perennial that spreads like wildfire. No magical solution for control of the exploding population is immediately available, but some practical ones are on the horizon. A variety of techniques and tools will be needed to bring this exotic pant under control. Bio-controls and herbicides are two options which hold some real promise. But the bottom line is that any control method must be environmentally acceptable.
A number of herbicides have proven effective in dry land control of loosestrife, but are still un-registered for that use. Registration procedures for these applications are underway. Initial research on herbicides now being tested in aquatic situations suggest an effective control is possible for the Horicon Marsh. However, this research is in the formative stage and it will be some time before an aquatic herbicide is registered and available.
While herbicides are used to "eradicate" weeds, biological agents are used to "control" them. Both reduce weed densities, but their impact on other species is unknown.
Is there a way to return the marsh to the natives?
Case Analysis Worksheet - A helpful aid in guiding students through the use of cases.
Teaching Notes and Tips
Preparing Students for Cases and Collaborative Learning - Hints and advice on how to introduce cases into your class.
Students will create a power point presentation to the grounds management committee including their recommendation for the control of purple loosestrife on campus. Group presentations should be assessed based on communal effort, quality and quantity of research and the learning goals for the activity.
References and Resources
Websites on Purple Loosestrife Lythrum salicaria
Ducks Unlimited Canada
Wisconsin State Herbarium's searchable database of vascular plants in Wisconsin
Spider Web Sites