Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin
SUBSECTION VI.6. Saginaw Bay Lake Plain
DISCUSSION: Subsection VI.6 consists primarily of flat glacial lake plain. The clay plain is broken by several extensive sand channels. One of the State's largest pineries occurred here on the somewhat poorly to poorly drained sands and clays. Agricultural development has been intensive as a result of the lake-moderated climate and the rich, loamy soils.
ELEVATION: 572 to 800 feet (174 to 244 m).
AREA: 2,390 square miles (6,190 sq km).
STATES: Michigan.
CLIMATE: Growing season is nearly as long (150 to 160 days) as in subsections at the southern boundary of the State. This long growing season differentiates this subsection from the Sandusky Lake Plain sub-subsection (VI.5.1). Extreme minimum temperature is -24½F to 28½F. Average annual precipitation is 28 to 30 inches, with 40 inches of snowfall. Both annual precipitation and snowfall are among the lightest in the State, but not low enough to deter agricultural land use. Toward the northern end of the subsection, there is a sharp climatic gradient due to characteristic positions of air masses. The Arenac subsection (VII.1) to the north is separated from the Saginaw Bay Lake Plain subsection (VI.6) on the basis of this gradient; the latter is notably warmer.
BEDROCK GEOLOGY: Bedrock is only locally exposed, with surface glacial lacustrine deposits as thick as 300 feet. Underlying Paleozoic bedrock was important in the economic development of this portion of the Saginaw basin. The subsection is underlain primarily by Paleozoic bedrock, primarily Pennsylvanian sandstone, shale, coal, and limestone (Dorr and Eschman 1984). At the western edge of the subsection, there are scattered occurrences of Mesozoic bedrock; these Jurassic red beds consist mainly of sandstone, shale, and clay, with minor beds of limestone and gypsum. Beneath the Pennsylvanian and Mississippian bedrocks are extensive deposits of Devonian and Silurian shallow marine deposits, which have yielded evaporites and brines important to the chemical industry in Midland and Saginaw. Important oil and gas fields are also associated with marine deposits underlying this sub-subsection.
LANDFORMS: Relatively flat plain of glacial lacustrine origin. The lacustrine deposits, which consist of sands and clays, are thickest along the farthest inland edge of the lake plain (up to 300 feet thick) and thinnest along the present shorelines of Lake Huron, where they are generally 50 feet thick or less along Saginaw Bay.
Clay sediments are generally quite thick on the lake plain, but several broad sand channels were created by glacial meltwater streams that deposited sand into the shallow proglacial lakes. Many of these sand channels are several miles wide, but the sand in them is generally only 5 to 10 feet thick.
LAKES AND STREAMS: No natural lakes. There are several large rivers, which were important for floating white pine timber to mills along Saginaw Bay. These include the Tittabawassee, Shiawassee, Saginaw, Pine, Flint, and Chippewa. Most of the rivers flow through broad sand plains.
SOILS: Poorly drained mineral soils characterize the clay plain. The sand-channel deposits were reworked by wave action when the Great Lakes were at higher levels, creating small sand dunes and spits and intervening depressions. The resulting features are typically higher and have steeper slopes than any found on the clay lake plain. The soils of the dunes and spits are often excessively well drained; those in the swales are poorly or very poorly drained. Soils of the lake plain are classified as Haplaquents, with some Haplaquods (USDA Soil Conservation Service 1967).
PRESETTLEMENT VEGETATION: Extensive Great Lakes marshes occurred along Saginaw Bay. The marshes, which extended into water 4 to 5 feet deep, were 1 to 2 miles wide in places and extended for miles up major rivers such as the Quanicassee and Saginaw (Comer et al. 1993a, b). Along the western shore of Saginaw Bay, the marshes were generally one-eighth to one-half mile wide, much narrower than along the southern edge of the bay.
Shoreward of the marshes were extensive wet and wet-mesic prairies. These prairies extended several miles inland along the Quanicassee and Saginaw Rivers. The wet prairies are probably quite variable in plant composition, ranging from true prairie grasses, such as big blue stem, Indian grass, and cord grass, to blue joint grass and sedges closer to the marsh edges and in wetter depressions. They also contain other aquatic vegetation, including rushes, bulrushes, cattails, reed grass, and willow or other shrubs.
Within the coastal marshes and wet prairies were low beach ridges and sand spits that supported scattered white oak and black oak. Local areas of trembling aspen and other lowland hardwoods were also within the wet prairies.
Inland of the coastal marshes and prairies, there was typically a broad band of lowland forest. Lowland hardwoods were prevalent, with black ash, [American] elm, and [red] maple as common dominants, and often with tamarack, eastern hemlock, and alder present.
Lowland conifer swamps, dominated by tamarack often occurred in broad depressions within the sand lake plain, especially where these depressions were located 1 or more miles inland from the present shoreline.
Flat, inland expanses of sand lake plain supported eastern hemlock, with some white pine as well as black ash, elm, and other hardwoods. There were also hemlock-dominated areas described by the GLO surveyors as swamp. On the flat sand lake plain, a few inches of elevation often results in changes of drainage class, making it difficult to determine whether an area should be called upland or wetland. Flooding is common in both spring and autumn.
On the better drained portions of the clay plain at the southern end of Saginaw Bay, forests were dominated by beech and sugar maple. Many of the upland forests on clay plain were probably fairly moist, as indicated by the abundance of [American] elm, basswood, and black ash. These three lowland hardwood species dominated large expanses of the clay plain, but tamarack and northern white-cedar were also present in the swamps. The flat conditions of the clay lake plain resulted in an intergrading of upland and wetland hardwoods on the landscape. Forests on fine-textured till plain were similar to those found on the clay lake plain.
In the north, forests dominated by hemlock were common on the clay lake plain. These forests also contained hardwood species; beech was often the most common hardwood species, but black ash and [American] elm were sometimes equally common. North of the Saginaw River, balsam fir and white birch became more common.
Swamp dominated by tamarack occurred on the flat, poorly drained clay plain near the boundary with sand lake plain. This was most common near the Quanicassee River, but also occurred elsewhere.
Fine-textured end moraines generally have slopes greater than 2 percent, resulting in better drainage conditions than typically found on clay lake plain. As a result, forests dominated by beech and sugar maple were common. Associated trees included white oak, [American] elm, basswood, and birch. Hemlock and black ash were generally much less common here than on the upland clay lake plain. At the northern edge, hemlock became increasingly common, even on these well-drained moraine ridges.
NATURAL DISTURBANCE: Although extensive areas of windthrown forest are generally common near the Great Lakes shorelines, GLO surveyors did not note any such areas here, possibly because the location at the southern and western edge of Saginaw Bay provided protection from the prevailing winds. Water level fluctuations of 2 to 3 feet are common along Saginaw Bay shorelines, causing tree mortality, shoreline erosion, and major alteration in species composition of marshes and wet prairies. The surveyors noted such water-level fluctuations near the east edge of the subsection.
PRESENT VEGETATION AND LAND USE: Before European settlement, Native American settlements were common along the shorelines of the Great Lakes. Oak savannas were probably maintained on beach ridges near the shoreline of Saginaw Bay by Indian land management with fire.
Some of the earliest intensive development in the State took place in this part of the Saginaw basin. Billions of board feet of white pine were logged between the 1830's and 1870's. Simultaneously, the salt industry and the Saginaw Bay fishery were developing, resulting in the harvest of oak and ash for barrels to store and ship these valuable commodities. Following logging, drainage began for agricultural use of the clay plain. By 1900, the chemical industry was well developed.
Most of the clay lands have been ditched and tiled, and they are among the most valued agricultural lands in the State. Parts of the sand plain were also ditched for agriculture, but the wettest areas remain, either as swamp forest, wet prairie, or marsh. Diking and pumping have allowed vast expanses of wet prairie and some areas of marsh to be farmed, especially along Saginaw Bay. Organic soils were burned to improve their suitability for agriculture (Wonser 1934, Deeter and Matthews 1931, Moon 1938).
RARE PLANT COMMUNITIES: Wet and wet-mesic prairies were originally extensive, along with oak savannas or "openings," but these now remain only as small remnants, primarily on State-owned lands. Prairies and savannas on the lake plain are called lakeplain prairie or oak opening because of the distinctive flora and fauna. The white pine and hemlock forests of the lake plain have been virtually eliminated.
RARE PLANTS: Most of the species in this subsection are associated with either Great Lakes marshes or lakeplain prairies. Aristida longispica (three-awned grass), Asclepias hirtella (tall green milkweed), Asclepias sullivantii (Sullivant's milkweed), Cacalia plantaginea (prairie Indian-plantain), Juncus brachycarpus (short-fruited rush), Juncus biflorus (two-flowered rush), Platanthera leucophaea (prairie fringed orchid), Scirpus clintonii (Clinton's bulrush).
RARE ANIMALS: Asio flammeus (short-eared owl), Chlidonias niger (black tern), Dysnomia triquetra (snuffbox), Elaphe vulpina gloydi (eastern fox snake), Rallus elegans (king rail), Sterna caspia (Caspian tern), Sterna forsteri (Forster's tern), Sterna hirundo (common tern).
NATURAL AREAS: None to date.
PUBLIC LAND MANAGERS: State Game Areas: Crow Island, Gratiot-Saginaw, Tobico Marsh, Shiawassee River (and Shiawassee National Wildlife Refuge); State Wildlife Areas: Nayanquing Point, Quanicassee, Wigwam Bay; State Parks: Bay City; State Forests: Au Sable; Environmental Areas: Coryeon Point, Quanicassee, Pinconning, Nayanquing, Oil Fields.
CONSERVATION CONCERNS: Efforts have begun along Saginaw Bay to restore coastal marshes and prairies, which are important for several rare plant and animal species, as well as for waterfowl, wading birds, and the Lake Huron fishery.
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