Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin
SUBSECTION VII.1. Arenac
DISCUSSION: Sub-subsection VII.1.1 is the Standish lake plain, and Sub-subsection VII.1.2 is the Wiggins Lake fine-textured end and ground moraine. The climate and slope class of these sub-subsections differentiate them from the adjacent Highplains subsection (VII.2), which has steeper topography and a colder, more continental climate. Most of the soils of Subsection VII.2 are droughty outwash sands, as opposed to the more poorly drained soils of the lake plain and ground moraine of Subsection VII.1.
ELEVATION: 572 to 1,050 feet (174 to 320 m).
AREA: 1,470 square miles (3,810 sq km).
STATES: Michigan.
CLIMATE: Growing season ranges from approximately 120 days at the inland edge of the subsection to 140 days along the Saginaw Bay shoreline (Eichenlaub et al. 1990). Frequently the subsection is exposed to cool northern air at the same time the remainder of Saginaw Bay to the south is under an air mass of southern origin (Albert et al. 1986); as a result, this subsection's growing season can be up to 20 days shorter and much cooler. In contrast, its growing season can be 20 days longer than that of the Highplains subsection to the west. Average annual precipitation is 28 to 30 inches, and annual snowfall is 40 to 60 inches, increasing at the inland margin of the subsection. Extreme minimum temperature ranges from -26½F to -40½F, with coldest values along the inland margin.
BEDROCK GEOLOGY: Subsection VII.1 is underlain by Mesozoic (Jurassic) and Paleozoic (Pennsylvanian and Mississippian) bedrock (Dorr and Eschman 1984, Milstein 1987). Jurassic red beds, consisting mainly of sandstone, shale, and clay, with minor beds of limestone and gypsum, are located beneath the inland margin of the Standish sub-subsection (VII.1.1) and all of the Wiggins Lake sub-subsection (VII.1.2). Pennsylvanian bedrock consists of sandstone, shale, coal, and limestone. Mississippian bedrock is primarily limestone and gypsum.
LANDFORMS: Lake plain characterizes Sub-subsection VII.1.1. A major delta is located at the mouth of the Au Sable River. Sub-subsection VII.1.2 is primarily ground moraine and end moraine. See sub-subsections.
LAKES AND STREAMS: Most of the few lakes in the subsection are concentrated within small areas of end moraine and ice-contact topography. Several large rivers are concentrated on the sand lake plain. See sub-subsections.
SOILS: Soils of the subsection are classified as gently sloping Haplaquepts plus Haplaquods on the lake plain of Sub-subsection VII.1.2 and as gently sloping Glossoboralfs plus Eutroboralfs on the moraines of Sub-subsection VII.1.2 (USDA Soil Conservation Service 1967).
PRESETTLEMENT VEGETATION: See sub-subsections.
NATURAL DISTURBANCE: See sub-subsections.
PRESENT VEGETATION AND LAND USE: See sub-subsections.
RARE PLANT COMMUNITIES: See sub-subsections.
RARE PLANTS: See sub-subsections.
RARE ANIMALS: See sub-subsections.
NATURAL AREAS: See sub-subsections.
PUBLIC LAND MANAGERS: See sub-subsections.
CONSERVATION CONCERNS: See sub-subsections.
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