Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin
SUBSECTION IX.8. Lake Superior Lake Plain
DISCUSSION: Subsection IX.8 is a relatively narrow band of lacustrine clays and clayey till reworked by water, ranging from 1 to 24 miles wide, located along the south and west shore of Lake Superior. It consists of nearly 200 miles of Lake Superior shoreline in Michigan, Minnesota, and Wisconsin. It is widest in Minnesota. Most of the subsection was part of proglacial Lake Superior.
ELEVATION: 602 to 1,280 feet (184 to 390 m).
AREA: 2,167 square miles (5,612 sq km).
STATES: Minnesota, Wisconsin, Michigan.
CLIMATE: Growing season ranges from 110 to 140 days; with the shortest growing season at the western edge of the subsection (Eichenlaub et al. 1990, University of Minnesota et al. 1977). Annual snowfall is heavy in Michigan, where lake-effect snows range from 120 to 160 inches. Annual snowfall decreases rapidly to the west, from about 100 inches at the Wisconsin-Michigan border to less than 60 inches at the western edge in Minnesota (Wendland et al. 1992). Total annual precipitation is 29 to 34 inches. Extreme minimum temperature ranges from -30½F to -40½F.
BEDROCK GEOLOGY: Bedrock is not exposed at the surface except in localized outcrops along streams and at isolated parts of the shoreline. Bedrock consists of Precambrian (middle Proterozoic) sedimentary bedrock, primarily feldspathic to quartzose sandstone and shale, and including lithic sandstone and siltstone (Morey et al. 1982). The shale is locally copper-rich (Dorr and Eschman 1984).
LANDFORMS: Glacial lake plain and water-reworked moraine cover almost all the subsection. Parts of this subsection are relatively flat east of the Porcupine Mountains in Michigan and along most of the Wisconsin shoreline. In these stretches, the lake plain and water-reworked moraine are dissected by numerous small rivers with straight, shallow valleys. Between the Porcupine Mountains and the Wisconsin border, the subsection is narrow and steeply sloping, with deeply eroded streams, often with waterfalls. At the west end in Minnesota, the broad lake plain is deeply dissected by the St. Louis and Nemadji Rivers and several smaller tributaries.
LAKES AND STREAMS: No lakes; many streams. See LANDFORMS.
SOILS: Leached calcareous red loams and clays as well as pink sands that are podsolized. Most of the soils are moderately well drained, but peat is extensive in some wetlands in Wisconsin (Hole and Germain 1994). Wetland soils are not extensive in either Michigan or Minnesota. Soils are derived from local, ironrich, volcanic bedrock and shale. They are classified as Aquepts and Boralfs (USDA Soil Conservation Service 1967).
PRESETTLEMENT VEGETATION: The conifer- and hardwood-conifer-dominated vegetation of both the flat uplands and the steep ravines has been called boreal forest in Wisconsin. In Michigan, common dominants included hemlock, northern white-cedar, balsam fir, white spruce, black ash, basswood, American elm, balsam poplar, and trembling aspen (Albert 1990, Comer et al. 1993a). In Wisconsin, balsam fir and white spruce were dominant and persist in parts of the Apostle Islands National Lakeshore. In Minnesota, eastern hemlock, spruce, northern white-cedar, and white pine were noted as present; this is the western extent of hemlock. Sugar maple and other northern hardwoods were dominant on only local better drained sites.
NATURAL DISTURBANCE: In Michigan, no large disturbances were mapped by the original surveyors (Albert 1990, Comer et al. 1993a). Along all other Great Lakes shorelines in Michigan, the surveyors noted small areas of windthrow; it is assumed that such windthrows were also relatively common along Lake Superior. Fluctuating levels of Lake Superior are critical natural disturbances that influence coastal wetlands.
PRESENT VEGETATION AND LAND USE: Following logging, trembling aspen is a common dominant throughout the subsection. In Minnesota, yellow birch is more common here than elsewhere in the State. In Michigan, mining for copper occurred into the early 20th century, and white pine was extensively cut for the mining industry and local construction. A small percent of the land near Lake Superior is used for pasture, but most of the land remains forested. Many rivers were diverted for mining/logging. Large tailings ponds are located here.
Species composition in forests has changed since the logging era; white pine and hemlock have become much less abundant. Urban development along the shoreline has eliminated or altered some coastal wetlands.
RARE PLANT COMMUNITIES: Spruce-fir or boreal forest is found throughout. Several rare plants grow on cliffs, where sandstone (Orienta formations) is exposed along the shoreline of the mainland and on Devil's Island. Sand dunes occur in Wisconsin, as does a large Great Lakes estuary.
RARE PLANTS: Michigan only: Mimulus guttatus (western monkey-flower). Minnesota: Tsuga canadensis (eastern hemlock), Viola novae-angliae (New England violet). Wisconsin only: Listera auriculata (auricled twayblade), Listera convallarioides (broad-leaved twayblade), Lycopodium selago (fir clubmoss), Osmorhiza chilensis (Chilean sweet cicely), Trisetum spicatum (spike trisetum), Pinguicula vulgaris (butterwort), Senecio indecorus (plains ragwort).
RARE ANIMALS: Catharus ustulatus (Swainson's thrush), Dendroica tigrina (Cape May warbler), Dendroica fusca (Blackburnian warbler), Empidonax flaviventris (yellow-bellied flycatcher), Sterna hirundo (common tern), Charadrius melodus (piping plover).
NATURAL AREAS: Michigan: National Forests: Ottawa, Black River (old-growth white pine and hemlock forest); State Parks: Porcupine Mountains Wilderness State Park (largest protected areas of northern hardwoods in Midwest). Minnesota: Hemlock Ravine State Natural Area. Wisconsin: National Lakeshore: Apostle Islands; State Natural Areas: Bark Bay Sloughs, Port Wing Boreal Forest, Big Bay Sand Spit and Bog, Apostle Islands Maritime Forest, Apostle Islands Maritime Cliffs, Apostle Islands Sandscape, Apostle Islands Critical Species Sites, Lost Creek Bog, Bibon Marsh.
PUBLIC LAND MANAGERS: Michigan: National Forests: Ottawa; State Forests: Copper Country. Minnesota: State Parks: Jay Cooke; State Forests: Nemadji; Municipal Forests: Magney-Snivley. Wisconsin: National Forests: Chequamegon; National Park Service: Apostle Islands.
CONSERVATION CONCERNS: The Kakagon-Bad River Sloughs, a huge wetland complex, occurs in the subsection and is owned by the Bad River Band of the Lake Superior Chippewa. The Bad River Band should be included in future efforts to assess and protect biodiversity.
BOUNDARIES: Both the Ottawa and Chequamegon National Forests have done more detailed ECS mapping of this subsection.
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| Figure 28.—Subsection IX.8: Kakagon Sloughs, Ashland County, Wisconsin. The sloughs are the largest intact wetland of their kind along Lake Superior. The sloughs support numerous wetland plant communities, including extensive beds of wild rice. A coastal sand spit separates the wetlands from Lake Superior. Most of the uplands surrounding the sloughs have red clay soils derived from the local iron-rich bedrock. The forests of the uplands were dominated primarily by a mix of both upland and wetland conifers, with paper birch, trembling aspen, and balsam poplar; northern hardwoods were restricted to well-drained sites. Photo by T. Cline, Photair Inc. |
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