A site analysis of purple loosestrife (Lythrum salicaria) invasion in northern Michigan.

Abstract

Purple Loosestrife (Lythrum salicaria) is an exotic perennial aquatic plant, native to Eurasia that now thrives in many mid-latitude North American wetlands. It was most likely introduced to North American habitats by ship ballast, livestock feed, or bedding (Haber, 1997). L. salicaria forms dense monospecific stands that can result in the loss of wetland habitat and the demise of native wetland species. This, in turn, affects animal, fish, and bird communities; about 50 percent of endangered species listed in 1986 depend on wetlands for survival (Mitsch and Gosselink, 1993). In addition, there are economic consequences when plants clog irrigation ditches and cause the loss of forage value of lowland pastures (Haber, 1997). L. salicaria spreads both sexually and vegetatively. A single L. salicaria plant produces an enormous number of seeds in one year, and it has the ability to produce lateral buds via adventitious roots. In addition, it has several adaptations allowing it to survive and multiply in a wide range of environmental conditions. L. salicaria is still cultivated and sold in wildflower mixtures or as individual plants for horticultural use. It was thought that these plants are sterile, however, they can produce fertile seeds when cross-pollinated by wild plants (Haber, 1997). Once established, L. salicaria is very difficult and expensive to eradicate. Possible methods include repeated clipping, targeted herbicide application, or, more recently, the use of biocontrol. The advantages and drawbacks of each of these methods need to be evaluated carefully before action is taken. L. salicaria invasion is occurring in Michigan at an alarming rate. This infiltration is of recent concern to The Nature Conservancy staff in Cedarville, Michigan, where L. salicaria has recently been spotted in isolated patches on roadsides and private properties (Hadley, personal communication, 8/2000). Due to the overwhelming effects of L. salicaria on wetland vegetation, The Nature Conservancy has been actively working to educate the community and prevent further invasion. A property owner on the shore of Cedarville Bay became concerned about the presence L. salicaria on her property and contacted The Nature Conservancy for information and assistance in weed removal. In an effort to assist The Nature Conservancy, we looked at the abundance, density, and concentration patterns on the property with the goal of drafting a suitable eradication plan for this and other, similar properties.