Pitcher’s thistle (Cirsium pitcheri) is a native of the shorelines of the western Great Lakes, one of the upper Midwest’s most extensive linear ecosystems and an important landmark for founding the concept of succession and the science of ecology (e.g. Cowles, 1899). In the early 20th century, Pitcher’s thistle was found along the entire coast of Lake Michigan.
Currently, it is extinct in Illinois, except for an experimental reintroduced population. Ninety percent of the remaining populations are found in Michigan. Its preferred habitat is the upper beaches, foredunes and blowouts maintained by cyclic natural disturbance processes (Loveless, 1984; McEachern et al., 1994).
Succession or disturbance eventually eliminates populations; thus persistence is through colonization. As a result, this species serves as an important bioindicator of natural shoreline processes that maintain dynamic sand dune ecosystems.
Historically, the factors that have contributed the most to endangerment of C. pitcheri are habitat loss through development and recreational beach use and human-caused shoreline erosion that prevents the natural disturbances associated with sand dunes, thereby eliminating C. pitcheri’s preferred habitat.
Emerging threats include climate change and predation by weevils used as biocontrol agents for Canada and musk thistles. Pitcher’s thistle was listed as a federally threatened species under the U.S. Endangered Species Act in July of 1981.
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