Steep clay bluffs border stretches of the Great Lakes shorelines and are less commonly found inland on the lower portions of streams draining into Lakes Superior and Michigan. These clay seepage bluffs are also called alkaline clay bluff. Vegetative cover can range from dense forests of red pine (Pinus resinosa), white pine (Pinus strobus), northern white-cedar (Thuja occidentalis), and paper birch (Betula papyrifera), to bare clay with only a few weedy herbs present. Buffalo-berry (Shepherdia canadensis) is a characteristic shrub, but more typically, alders (Alnus incana and A. viridis), as well as rank herbs such as Canada goldenrod (Solidago canadensis) and pearly everlasting (Anaphalis margaritacea) are dominant. Both native and exotic pioneers such as fireweed (Epilobium angustifolium) and Canada thistle (Cirsium arvense) are common, especially on the more unstable sites.
It is the semi-stabilized "weeping" bluffs that are of the greatest biological interest. Golden sedge (Carex aurea), gentians, orchids, and calciphilic fen species may colonize such sites, which can be local repositories of rare or otherwise noteworthy plant species.
Henry Chandler Cowles, regarded as the founder of plant ecology, studied this bluff environment at the end of the 19th century. He noted "there can be almost no other habitat in our climate which imposes such severe conditions upon vegetation as an eroding clay bluff." Temperature extremes, sun and wind exposure, and the variable consistency of clay soils (from mush to concrete as they dry) severely inhibit establishment by pioneer plants. During periods of erosion, Cowles felt "all vegetation is impossible."
