Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin
SUBSECTION VIII.1. Niagaran Escarpment and Lake Plain
DISCUSSION: Various landforms of glacial lacustrine origin characterize the subsection, including flat lake bed, deltaic deposits of sand, parabolic dune fields, and shallow embayments containing transverse dunes. Ground moraine is locally present. Exposures of limestone and dolomite bedrock occur along the shorelines of both Lakes Michigan and Huron, and locally several miles inland.
SUB-SUBSECTIONS: St. Ignace (VIII.1.1), limestone bedrock and sand lake plain along northern Lake Michigan; Rudyard (VIII.1.2), clay lake plain in eastern Upper Michigan; Escanaba/Door Peninsula (VIII.1.3), limestone bedrock and sand lake plain along Lake Michigan, with a more moderate climate than Sub-subsection VIII.1.1; and Green Bay Till Plain and Lake Plain (VIII.1.4), silt- and clay-rich tills and lacustrine deposits along the western Lake Michigan shoreline in Wisconsin. (See figures 4 and 6.)
ELEVATION: 580 to 1,040 feet (177 to 317 m).
AREA: 5,356 square miles (13,883 sq km).
STATES: Michigan and Wisconsin.
CLIMATE: With a climate typified by lake-effect moderation, this is the warmest subsection in Upper Michigan and northern Wisconsin. Growing season ranges from 128 days in the north to 175 days along the southern boundary (Eichenlaub et al. 1990, Wisconsin Agricultural Statistics Service 1987). Extreme minimum temperature ranges from -28½F in the southwest along Lake Michigan to -46½F at the inland edge of the subsection in Upper Michigan. Average annual precipitation ranges from 28 to 34 inches. Average annual snowfall ranges from less than 50 inches in Wisconsin (Wisconsin Agricultural Statistics Service 1989) to 120 inches near Sault Ste. Marie, Michigan, at the extreme northeastern edge.
BEDROCK GEOLOGY: The entire subsection is underlain by Silurian and Ordovician sedimentary bedrock, principally limestone and dolomite, but also including less resistant shale and gypsum (Dorr and Eschman 1984). The resistant Niagaran series dolomite and limestone of Silurian age form the Niagaran Escarpment, which is locally exposed as cliffs and limestone pavement (alvar) along the Lake Michigan and Lake Huron shorelines from the Door Peninsula in northeastern Wisconsin, to Drummond Island at the far eastern edge of the Upper Peninsula of Michigan, and eastward to Cockburn Island, Manitoulan Island, and the Bruce Peninsula of Ontario. Little Bay de Noc and Big Bay de Noc, Michigan (Sinclair 1960), and Green Bay, Wisconsin, occupy depressions where soft gypsum and shales were eroded, probably by both glacial and lacustrine erosional processes. The underlying bedrock is typically less than 50 feet below the surface of the glacial drift in Michigan (Vanlier and Deutsch 1958; Sinclair 1959, 1960; Vanlier 1963b). It is exposed or near the surface on the Door Peninsula, but is more deeply buried inland (Hole 1976).
LANDFORMS: Most of the subsection consists of lacustrine sand or clay deposits that have flat to gently undulating surfaces. On this topography, only a few inches of elevation change can greatly alter drainage conditions.
Along the shoreline and several miles inland in Sub-subsections VIII.1.1 and VIII.1.3, either bedrock or sand is at the surface. Local landforms on the sand plain include transverse and parabolic dunes, deltas, and beach ridges and swales. See sub-subsections.
At the northeastern edge of the subsection in Michigan and at the southwestern edge in Wisconsin (Sub-subsections VIII.1.2 and VIII.1.4), there are broad clay plains consisting of lacustrine deposits and water-reworked till.
LAKES AND STREAMS: Large lakes are not common, but those that occur (Indian Lake and the Manistique Lakes in Michigan) are near the junction between Ordovician and Silurian marine bedrock. They may be the result of chemical or physical erosion of less resistant bedrock. Streams are numerous on the flat lake plain. See sub-subsections.
SOILS: Soils on the lake plain itself are generally lacustrine sands or lacustrine clays. Most of the clay soils were calcareous and either somewhat poorly drained or poorly drained. The sandy soils ranged from very poorly drained to excessively drained, depending on slope and depth to underlying bedrock or fine-textured soils. Many of the sands are calcareous, but often deeply leached. Thin soils over bedrock are common throughout Sub-subsections VIII.1.1 and VIII.1.3, especially near the Lake Michigan or Lake Huron shoreline.
Calcareous sandy and sandy loam tills are locally common, often immediately adjacent to bedrock.
PRESETTLEMENT VEGETATION: The original vegetation of the subsection was diverse, reflecting the local diversity of landforms, soil texture, and drainage class on the lake plain (Comer et al. 1994). See sub-subsections.
Conifer swamps were extensive throughout. On the clay plain, a diverse forest of swamp hardwoods and conifers was found. Northern white-cedar dominated wetlands over limestone; tamarack and black spruce were common dominants on sandy soils. Near the shores of the Great Lakes were extensive marshes and wet meadows where there was adequate protection from wave action.
Northern hardwoods, including sugar maple, beech, American elm, basswood, and yellow birch, were locally common on better drained sites. White pine and red pine were locally common on sand dunes and beach ridges; white pine also occurred within the swamp forests.
NATURAL DISTURBANCE: Winds off Lakes Michigan and Huron resulted in many small areas of windthrown trees, most concentrated within a mile or two of the shoreline (Comer et al. 1993a). Such a localized storm along the north shore of Lake Michigan was observed in the summer of 1995, destroying large numbers of white and red pine. Poorly drained soils and the resulting shallow rooting increase the number of windthrown trees.
Water levels of the Great Lakes regularly fluctuated 2 to 3 feet over a period of 7 to 8 years, with a longer cycle of even more extreme fluctuation (Thompson 1992), resulting in dynamic vegetation conditions within a mile of the shoreline. Beaver ponds and resulting tree mortality are common in this flat, poorly drained landscape.
Fire, caused by lightning, has destroyed large areas of conifer forest. Conifer forests are also regularly affected by insect vectors, including jack pine budworm, spruce budworm, and larch sawfly.
PRESENT VEGETATION AND LAND USE: The clay lake plains (Sub-subsections VIII.1.2 and VIII.1.4) have been converted to crop or pasture land. Pasture is prevalent in Sub-subsection VIII.1.2, where the growing season averages only 125 days (Denton 1985); and crop land is prevalent in Sub-subsection VIII.1.4, where the growing season can be up to 160 days long (Hole 1976, Hole and Germain 1993). On most of these flat, lacustrine landscapes, some form of drainage is necessary for agriculture. Ditches 6 to 8 feet deep are common on the clay plain. In Michigan, much of this pasture has been abandoned and is slowly reverting to forest. Most of the remaining sandy lake plain is forested, and large portions are publicly owned. The Lake Michigan and Lake Huron shorelines are also popular for recreational use and for vacation homes. Limestone and dolomite are quarried locally.
Excellent examples of numerous types of wetlands occur along the shoreline. The Great Lakes marshes of the subsection are large and of high quality. The importance of these marshes for habitat of water fowl, wading birds, small mammals, and fish cannot be overstated.
RARE PLANT COMMUNITIES: Alvar, grassland on thin soils over dolomite or other marine bedrock, is a globally rare plant community. In Michigan, alvar is found only in this subsection. Although alvar is well represented in adjacent Ontario, many of these grasslands in Michigan are of extremely high quality. Calcareous fens are probably best represented along the shorelines within this subsection (Subsection VII.6 also has excellent examples), where they can extend several miles inland on Nipissing-age clay lake beds.
RARE PLANTS: See sub-subsections.
RARE ANIMALS: See sub-subsections.
NATURAL AREAS: See sub-subsections.
PUBLIC LAND MANAGERS: See sub-subsections.
CONSERVATION CONCERNS: The primary areas of concern within the subsection are the sensitive Great Lakes shorelines, both the wetlands and dunes, and alvar (grassland on limestone bedrock). All are extremely sensitive to damage by off-road vehicles. Remaining private areas of shoreline are rapidly being developed for retirement homes and second homes. Degradation of shorelines by off-road vehicles almost always follows soon after home development.
Subsection VIII.1 contains high-quality habitat for several threatened and endangered plants and animals, most of which are associated with Great Lakes shorelines. These include the following federally threatened: Pitcher's thistle, dwarf lake iris, Houghton's goldenrod, and Michigan monkey-flower. It also contains high-quality examples of many ecosystems associated with either present or past shorelines of the Great Lakes.
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