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Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin


SECTION X. NORTHERN MINNESOTA


Part of Bailey and Cushwa's (1981) Humid Temperate Domain, Humid Warm-Summer Continental Division, Laurentian Mixed Forest Province; drought prone with low winter precipitation; Precambrian Shield bedrock, late Wisconsinan-age glaciated landscape; upland conifer forests, extensive paludified peatlands and conifer swamps.
Section X contains twelve subsections: Bayfield Barrens, Mille Lacs Uplands, Laurentian Highlands, Tamarack Lowlands, Pine Moraines and Outwash Plains, Chippewa Plains, St. Louis Moraines, Nashwauk Uplands, North Shore (Lake Superior) Highlands, Border Lakes, Littlefork-Vermilion Uplands, Agassiz Lowlands.
DISCUSSION: Section X is characterized by rolling to steep ground- and end-moraine ridges, low bedrock knobs, and vast peatlands on glacial lake plains. Topographically it is similar to Section VI to the east. However, from near the Wisconsin-Minnesota border, there is a major shift in upland vegetation from northern hardwoods in Section IX to fire-dependent pines and hardwoods to the west in Section X.

Ecoclimatic regions have been defined on the basis of forest vegetation by several authors. In Canada, Rowe (1972) treats the forests along the U.S.-Canadian border as the Great Lakes-St. Lawrence Forest Region, which contains sugar maple, yellow birch, white pine, and red pine. Bailey and Cushwa (1981) include Rowe's Great Lakes-St. Lawrence Forest Region and this section as the Laurentian Mixed Forest Province.

In an alternative treatment, The Ecoclimatic Regions of Canada (Ecoregions Working Group 1989) shows boreal forest extending into Minnesota in the Border Lakes (Boundary Waters), Lake Superior Highland, and Agassiz Peatlands subsections, thus subdividing the Great Lakes-St. Lawrence Forest Region or Laurentian Mixed Forest Province on the basis of climate. The Canadian climatic units, LBst (Subhumid Transitional Low Boreal Ecoclimatic Region) and LBx (Moist Low Boreal Ecoclimatic Region), are based on conifer dominance in both the uplands and lowlands. LBx, described as containing sugar maple and yellow birch, is shown as extending into the Border Lakes, but that subsection does not include either species in any number.

In this study, I use Bailey and Cushwa's and Rowe's treatments, with the realization that the northernmost subsections (Border Lakes, Agassiz Peatlands, and portions of the North Shore Highlands) may be transitional to the boreal forest. However, the presence of large areas of bedrock in the Border Lakes subsection and broad, poorly drained landscapes ideal for peatland development may also contribute to the greater conifer dominance, in addition to the more severe northerly (boreal) climatic conditions. Analysis of climatic data, now being conducted, should help resolve this question.

ELEVATION: 602 to 2,301 feet (184 to 701 m).

AREA: 40,108 square miles (103,903 sq km).

STATES: Minnesota and Wisconsin.

CLIMATE: Annual precipitation is slightly higher than in Sections I, II, and XI to the west, and lower than in Section IX to the southeast (especially where Section IX's topographic relief causes increased precipitation along the southern shore of Lake Superior). Average and extreme winter temperatures are lower than in Section IX, but similar to temperatures in the northern part of Section I, and in Section XI.

An important climatic factor influencing the vegetation is probably the low amounts of winter precipitation. Of the annual precipitation, 15 to 19 percent falls between November and February (interpolated from Wendland et al. 1992). Winter snowfall increases relatively sharply to the east in Section IX, partially as a result of increased snowfall near the Lake Superior shoreline. Light winter precipitation increases the potential for spring fires. Heinselman (1973) discusses the importance of spring fires for maintaining the conifer-dominated forests of parts of this section.

Heinselman (1973) and Frissel (1973) demonstrate the recurring pattern of severe droughts that occur in the section as often as two to three times a century. Major fires are associated with these periods of drought.

BEDROCK GEOLOGY: Precambrian igneous and metamorphic bedrock underlies the entire section (Morey 1976, Ostrom 1981). Thick glacial drift up to 600 feet deep blankets much of the section (Olsen and Mossler 1982), but abundant Precambrian bedrock exposures occur along the Lake Superior shoreline and in the Border Lakes area (Morey 1981, Olsen and Mossler 1982). Small bedrock exposures occur throughout the entire eastern half of the section.

Iron mining in Minnesota has been concentrated within the Mesabi Range in this section. Early mining here was concentrated in local pockets of "soft" iron ore, but recent mining has been in unaltered iron formation, called taconite (Wright 1972). Mining has diminished greatly in recent years (Hargrave 1992).

The greatest amount of exposed bedrock occurs in the Border Lakes subsection, where several types of Precambrian bedrock are exposed, including slate, diabase, gabbro, and granite (Wright 1972). Each of these bedrock types is reflected in distinct patterns of lakes and drainages.

From Duluth to the Canadian border, the North Shore (Lake Superior) Highlands subsection is underlain by Keweenawan basalt and diabase, which dips sharply to the southeast. These volcanic bedrocks, part of the Lake Superior syncline, dip below Lake Superior and are exposed along the southeastern edge of the syncline from the Keweenaw Peninsula in Michigan to south of the Porcupine Mountains in northern Wisconsin. On the Highland Flutes of the Superior Highlands, bedrock is exposed on approximately 30 percent of the land surface (Hargrave 1992).

Even though most of the section is underlain by Precambrian bedrock, there are also Cambrian sandstone, shale, and dolomite at the extreme southeastern edge and Cretaceous shale, sandstone, and clay near the southwestern edge (Morey 1976).

LANDFORMS: The entire section is characterized by Wisconsinan-age glacial drift and landforms. The largest glacial feature within the section is a large part of Glacial Lake Agassiz; most of the Beltrami arm of Lake Agassiz (Wright 1972) is within the section. The fine-textured lacustrine sediments of the peatland are 100 to 200 feet thick along the western margin of the lake plain, but much shallower at the eastern edge, where there are local exposures of bedrock (Olsen and Mossler 1982). Smaller glacial lacustrine features are Glacial Lakes Upham and Aitkin.

Glacial erosion of bedrock, with only minimal deposition of till on the bedrock, characterizes the Border Lakes subsection of northeastern Minnesota (Wright 1972). Similar bedrock abrasion features are common in the Superior Highlands and locally within the eastern half of the section.

Ground- and end-moraine ridges cover large areas. The moraine features range from ice stagnation moraines with many lakes to distinct end- and ground-moraine ridges with few lakes. The till of these moraines is also quite variable, depending on the source material. Tills from the Des Moines lobe are typically calcareous and fine-textured; Wadena lobe tills are also calcareous, but often course-textured; Rainy lobe tills are non-calcareous and coarse-textured; and Superior lobe tills are non-calcareous and fine-textured. Stoniness of the till from the lobes is variable.

Sandy outwash plains and channels occur throughout. The Pine Moraines (Subsection X.5) contains several large outwash plains. Pitted outwash, with many small lakes and wetlands, is common in this subsection, as well as throughout the remainder of the section. Narrow outwash channels, often as wide as 2 to 3 miles, are also widespread.

SOILS: The soils are both upland and wetland forest soils developed under either conifers, hardwoods, or a mix of hardwood and conifers. The soils are developed on either glacial drift or bedrock. There are four major glacial lobes within the section, each with somewhat distinctive till, as well as lacustrine and fluvial deposits. As a result, the soils are quite variable in texture, chemistry, stoniness, and drainage conditions. Soils are classified as Alfisols (Boralfs), Entisols (Psamments and Orthents), and Histisols (Hemists), with some Borolls, Orthods, and Ochrepts (USDA Soil Conservation Service 1967, Anderson and Grigal 1984). See subsections and sub-subsections.

PRESETTLEMENT VEGETATION: Conifers dominated both upland and lowland forests, but forests of northern hardwoods were also present. The prevalence of conifers on relatively mesic, upland soils distinguished the forests of the section from those of Section VI to the east, where hardwood dominance was more typical on mesic soils. Preliminary analyses showed northern hardwood dominance on only 10 to 25 percent of the mesic sites of the section, as opposed to 75 percent or more of the mesic sites of Section VI. Sugar maple and other northern hardwoods were nearly absent from the northern and northwestern portions of Section X, probably because of frequent and intense fires, late spring frosts, and poor drainage conditions in the peatlands. In the north, northern hardwoods persist on ridgetops and near large lakes, or on highly irregular, steep topography protected from both fire and frost.

On the uplands, jack pine dominated the droughty, fire-prone outwash plains, beach ridges, and thin soils on bedrock. White pine and red pine dominated pitted outwash and sandy moraines that burned less frequently and less intensely than the outwash plains. Marschner also mapped many areas of aspen-birch forest, a type he considered successional to red pine, white pine, white spruce, balsam fir, and paper birch. Aspen-birch occurred on a broad range of upland soils and landforms (Grigal and Kernik 1980).

The Agassiz, Upham, and Aitkin glacial lake plains all supported extensive areas of swamp and peatland. The extensive peatlands of Glacial Lake Agassiz supported swamp forests dominated by black spruce and tamarack, along with some northern white-cedar, balsam poplar, paper birch, and trembling aspen. Open bog and patterned peatlands were also extensive, as were numerous other wetland communities related to water flow and water chemistry (Heinselman 1963, 1970; Glaser et al. 1981; Glaser 1983).

Fairly extensive areas of northern hardwoods were in the southern half of the section, especially in Aitkin, Pine, and Mille Lacs Counties.

NATURAL DISTURBANCE: Fire was the most important form of natural disturbance, occurring in both uplands and wetlands. Fires occurred as frequently as every 10 years on many sites (Frissel 1973). Insect mortality was also important and partially responsible for the frequency and intensity of fires; spruce budworm was the most important cause of mortality for white and black spruce and balsam fir (Heinselman 1973).

PRESENT VEGETATION AND LAND USE: Red and white pine forests were heavily logged at the beginning of the 20th century, resulting in major changes in forest composition; on many lands, aspen increased greatly in dominance. Jack pine and red pine plantations are also quite extensive in some subsections. Many of the other forest types have not changed greatly in composition from those of the original forest.

Iron mining, although now reduced, continues to be an important industry in the Mesabi Range.

RARE PLANT COMMUNITIES: See subsections and sub-subsections.

RARE PLANTS: See subsections and sub-subsections.

RARE ANIMALS: See subsections and sub-subsections.

NATURAL AREAS: See subsections and sub-subsections.

PUBLIC LAND MANAGERS: Minnesota: National Forests: Chippewa and Superior; Wilderness Areas: Boundary Waters Canoe Area (Superior NF); National Parks: Voyageurs; National Wildlife Refuges: Rice Lake; State Forests: St. Croix, Snake River, Rum River, Savanna, Solana, Smokey Hills, White Earth, Huntersville, Crow Wing, Badoura, Foothills, Lyons, Paul Bunyan, Hill River, Land O'Lakes, Black Duck, Big Forks, Finland, Cloquet Valley, George Washington, and Nemadji; Wildlife Management Area: Mille Lacs; State Parks: Mille Lacs, Katheo, Jay Cooke, Savanna Portage, St. Croix, St. Croix Wild River. Wisconsin: National Forests: Chequamegon; State Forests: Brule River, Governor Knowles; National Scenic Rivers: St. Croix-Namekagon; County Forests: Douglas, Bayfield, Burnett, and Washburn Counties.

CONSERVATION CONCERNS: The Minnesota Environmental Quality Board is producing a Generic Environmental Impact study of the cumulative effects of increased timber harvesting activities, with forest biodiversity a major issue.

BOUNDARY JUSTIFICATIONS: Section X has lower annual precipitation and more severe summer droughts than Section IX to the east. Compared to Section III, it has lower temperatures and more soils derived from igneous and metamorphic Precambrian bedrock. The boundary between Section XI and Section X may be the product of more extreme drought conditions in the aspen parkland and prairie of Sections XI and I to the west. Even though the prairie-forest ecotone has been related to mid-tropospheric flow patterns during the summer (Harman and Braud 1975, Harrington and Harman 1985), aspen woodland and brush prairie dominance in Section XI is at least partially the result of more irregular topography and increased areas of wetland rather than a sharp climatic transition.


Previous Section -- Section IX. Northern Continental Michigan, Wisconsin, and Minnesota
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Next Section -- Section XI. Aspen Parkland

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