Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin
SUBSECTION IX.6. Bergland
DISCUSSION: The subsection is divided into three sub-subsections on the basis of landform and bedrock.
SUB-SUBSECTION: The Gogebic-Penokee Iron Range sub-subsection (IX.6.1) consists of steep ridges of volcanic bedrock; the Ewen sub-subsection (IX.6.2) is a highly dissected clay lake plain; and the Baraga sub-subsection (IX.6.3) is primarily broad ridges of rocky, sandy till derived from underlying sandstone. (See figures 4 and 6.)
ELEVATION: 900 to 1,890 feet (275 to 576 m).
AREA: 2,426 square miles (6,286 sq km).
STATES: Michigan and Wisconsin.
CLIMATE: Annual precipitation averages 32 to 36 inches. Annual snowfall is 100 to 180 inches; snowfall is greatest at the northern edge of the subsection in Michigan, on high elevation areas near Lake Superior (Eichenlaub et al. 1990, Wisconsin Statistical Reporting Service 1967). Growing season ranges from 100 to 130 days, longest near the Lake Superior shoreline and rapidly shortening inland. Extreme minimum temperature ranges from -40½F to -50½F, with coldest temperatures inland.
BEDROCK GEOLOGY: The entire subsection is underlain by Precambrian bedrock, primarily Keweenawan basalts and conglomerates; it also includes iron-rich marine sandstones and dolomites of Huronian age (the Gogebic-Penokee Range) and Archean bedrock (Dorr and Eschman 1984, Morey et al. 1982). There are localized to extensive bedrock exposures throughout, except in Sub-subsection IX.6.2. Bedrock is diverse and includes Jacobsville sandstone (feldspathic to quartzose sandstone and shale), granitic rock, mafic volcanic rock, quartzite, basalt, and other minor sedimentary bedrock types (Morey et al. 1982).
LANDFORMS: Sub-subsections IX.6.1 and IX.6.3 consist primarily of ground moraine; Sub-subsection IX.6.2 consists of highly dissected lacustrine deposits (Farrand et al. 1984, Goebel et al. 1983, Clayton 1984). Much of Sub-subsection IX.6.1 is mapped as thin till over bedrock, with discontinuous deposits of till separated by numerous or extensive bedrock outcrops.
LAKES AND STREAMS: The only large lake here is Lake Gogebic in Michigan. Several streams flow north across the subsection and drain into Lake Superior. Many of these streams originate near the southern edge of the subsection. Small waterfalls are common, and many of the streams have steep, bedrock ravines. In Sub-subsection IX.6.2, the streams have formed deep ravines in the clay soils.
SOILS: Soils are classified as Haplorthods and Fragiorthods on the ground moraine and Eutroboralfs and Haplaquepts on the clay lake plain (USDA Soil Conservation Service 1967). In Sub-subsection IX.6.1, soils are red loams and sandy loams, derived from the iron formations eroded and abraided by the glaciers (Hole 1976). On the lake plain of Sub-subsection IX.6.2, soils are red, silty, acidic clays. On the ground moraines of Sub-subsection IX.6.3, soils are rocky, loamy sands and sandy loams, not generally as red as those in Sub-subsection IX.6.1. These soils are classified as Orthods and Inceptisols (Hole 1976).
PRESETTLEMENT VEGETATION: Northern hardwood forests of sugar maple, hemlock, basswood, and yellow birch occupied most of the well-drained soils. On the dissected clay plain, diverse swamp forests of hardwoods and conifers were common on poorly drained sites; common species included balsam fir, white spruce, northern white-cedar, trembling aspen, and paper birch (Albert 1990). White pine occurred locally as pure stands on the lake plain.
NATURAL DISTURBANCE: Windthrows occurred frequently on the steep bedrock-cored ridges, as noted by GLO surveyors (Albert 1990, Albert et al. 1986).
PRESENT VEGETATION AND LAND USE: Northern hardwoods continue to dominate the well-drained moraine ridges, but the hardwood-conifer swamps of the lake plain have become largely dominated by hardwoods after logging. Iron mining was an important industry, but most mines here have been abandoned. Much of the timber from early logging operations was used for construction of mine shafts and buildings within the mining towns.
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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