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Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin


SECTION VI. SOUTHERN LOWER MICHIGAN


Part of Bailey and Cushwa's (1981) Humid Temperate Domain, Humid Hot-Summer Continental Division, Eastern Deciduous Forest; Great Lakes-moderated climate (Denton 1985, Eichenlaub 1979, Eichenlaub et al. 1990); glaciated landscape of late Wisconsinan-age, underlain by Paleozoic bedrock; white oak-black oak savannas and forests, beech-sugar maple forest.
Section VI contains six subsections: Washtenaw, Kalamazoo Interlobate, Allegan, Ionia, Huron, Saginaw Lake Plain. The section and subsections are shown on the large three-State map (Plate I).
DISCUSSION: This section of rolling hills and flat lake plains has been greatly modified by agricultural and urban development. The Great Lakes have moderated the climate and provided fertile lacustrine soils along the east and west edges of the section.

ELEVATION: 572 to 1,280 feet (175 to 390 m).

AREA: 24,248 square miles (62,821 sq km).

STATES: Michigan.

CLIMATE: The climate of the section is strongly influenced by the Maritime Tropical air mass, with some lake-effect snows and moderation of temperature from Lake Michigan (Albert et al. 1986, Denton 1985, Eichenlaub 1979, Eichenlaub et al. 1990). Compared to the rest of the study area, the southern Lower Peninsula of Michigan has more warm humid air masses from the Gulf of Mexico and fewer cold dry air masses of continental origin. Winter precipitation is higher (7 to 10 inches; 23 to 26 percent of annual precipitation) and more of it falls as rain than in Wisconsin's Section V to the west or Michigan's Section VII to the north. The growing season is longer and warmer than that of Sections VII to XI and similar to that of Sections I to V.

BEDROCK GEOLOGY: Section is underlain by Paleozoic bedrock deposited in marine and near-shore environments, including sandstone, shale, limestone, and dolomite (Dorr and Eschman 1984). This Paleozoic bedrock was deposited in an intercratonic basin, known as the Michigan basin, which was occupied by marine waters from the Silurian through Pennsylvanian Periods. Mississippian and Devonian bedrocks are nearest the surface in the south and along the Great Lakes shorelines; Pennsylvanian bedrock is near the surface in the north (at the center of the Michigan basin). Bedrock exposures are few and small. At the eastern edge of the section near Lake Erie, Devonian limestone bedrock is often within 5 feet of the surface and is locally exposed along streams. Local exposures of Mississippian shale, sandstone, and limestone are near Saginaw Bay of Lake Huron, but glacial lacustrine deposits can be as deep as 300 feet on the inland portions of the lake plain.

Over the rest of the section, 100 to 400 feet of loamy glacial drift cover bedrock (Akers 1938). Very localized outcrops of Pennsylvanian sandstone occur along the Grand River and its tributaries (Dorr and Eschman 1984).

LANDFORMS: Wisconsinan-age glacial and postglacial landforms cover the entire land surface of the section. Landforms include lake plain, outwash, ground moraine (till plain), and end moraine. Broad lacustrine plains occur along all of the Great Lakes; these plains extend more than 20 miles inland along Lake Michigan and more than 50 miles inland along the Lake Huron shoreline at Saginaw Bay. Sand dunes form a 1- to 5-mile band along much of the Lake Michigan shoreline. The interior of the section consists of a relatively low plain of ground and end moraines, with narrow outwash channels throughout. A broad interlobate outwash plain occupies the southern half of the section.

SOILS: Most of the soils are calcareous and loamy, derived from underlying limestone, shale, and sandstone. Till deposits are primarily loams, silt loams, and clay loams. Lacustrine soils are silt- and clay-rich; lacustrine sands are often banded with silt or clay. The outwash plains of the interlobate are sands, often containing abundant gravel. Most of the soils are classified as Alfisols, including Aqualfs and Udalfs, but there are also Aquepts, Aquolls, and Psamments (USDA Soil Conservation Service 1967).

PRESETTLEMENT VEGETATION: Almost the entire section was forested. Oak savanna was probably the most prevalent, followed by oak-hickory forest and beech-sugar maple forest. This is the only section of Michigan that originally supported large areas of tallgrass prairie, which was concentrated in the sandy interlobate area in the southwestern part of the section. There were also large areas of wet prairie on the lake plains of Lake Erie, Lake St. Clair, and Lake Huron. Wetlands included extensive marshes, fens, and swamp forests (Comer et al. 1993a, 1993b).

NATURAL DISTURBANCE: Fire was important for maintaining oak savannas and tallgrass prairie. Large windthrows were documented in the GLO surveys of the glacial lake plains along Lake Huron and Lake St. Clair.

PRESENT VEGETATION AND LAND USE: Most of the section is farmed for row crops; it is the most heavily farmed section in Michigan. Almost all the original tallgrass and wet prairies have been converted to farmland. The oak savannas have become forests as a result of fire suppression. The heaviest urban, industrial, and residential development has occurred in this section, especially along the Great Lakes shoreline.

RARE PLANT COMMUNITIES: Savannas (oak openings), once common on rolling ground moraine and glacial lake beds, have become rare due to fire suppression. Similarly, prairies on both flat glacial lake beds and outwash plains have become rare due to agriculture. Inland salt marshes are the rarest plant community in Michigan. Coastal plain marshes, containing disjunct plants from the Atlantic Coastal Plain, are locally common in sandy depressions in outwash plains and glacial lake beds.

RARE PLANTS: See subsections.

RARE ANIMALS: See subsections.

NATURAL AREAS: See subsections.

PUBLIC LAND MANAGERS: See subsections.

CONSERVATION CONCERNS: Most of the forests and savannas have been nearly eliminated by farming or greatly altered by fire exclusion. Restoration will probably be required if large, functional examples of these are to persist. The savannas provided important habitat for several invertebrates, including the federally threatened Karner blue butterfly; restoration efforts are presently underway on State lands.

The marshes and wetlands along Great Lakes shorelines are critical for maintaining migratory waterfowl, shore birds, and the Great Lakes fisheries. Restoring and expanding these coastal wetlands are high priorities within the section and the State.

BOUNDARY JUSTIFICATIONS: Lake Michigan creates the western boundary of the section; Section V, west of Lake Michigan, has a more continental climate, with more impact from dry Maritime Polar air masses; Section VI is more greatly influenced by the Maritime Tropical air mass. The boundary between this section and Section VII to the north is based on 1) analysis of climatic data (Denton 1985), 2) the topographic boundary between a low plain to the south and a prominent upland plateau to the north (Albert et al. 1986), and 3) a long-recognized floristic boundary (Potzger 1948, McCahn 1979).


Previous Section -- Section V. Southeastern Wisconsin Savanna
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