Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin
SUBSECTION X.10. Border Lakes
DISCUSSION: Subsection X.10 is characterized by shallow soils upon granitic bedrock. Lakes occupy the glacially scoured depressions in the bedrock. Differential erosion of bedrock has produced the pattern of lakes and ridges (Wright 1972). Soil development is minimal, and bedrock outcrops are common (Kratz and Jensen 1983).
SUB-SUBSECTIONS: None.
ELEVATION: 1,250 to 2,301 feet (381 to 701 m).
AREA: 4,530 square miles (11,740 sq km).
STATES: Minnesota.
CLIMATE: Cool continental climate, with short warm summers and long winters (Heinselman 1973). Annual precipitation averages 28 inches, and the mean annual temperature is 36½F. Annual snowfall ranges from 52 inches in the west to 64 inches farther east (Wendland et al. 1992). Growing season ranges from 108 to 123 days (University of Minnesota et al. 1981b). Extreme minimum temperatures are -35½F to -45½F (Reinke et al. 1993) or colder, with lowest temperatures in the west. Heinselman (1973) considers the area to be transitional between the Great Lakes-St. Lawrence and boreal forest regions due to the presence of white pine and red pine along with boreal tree species.
BEDROCK GEOLOGY: Thin glacial drift covers much of the subsection, and bedrock exposures are common (University of Minnesota et al. 1981b). The subsection has Precambrian-age (late Archean and early Proterozoic) bedrock, including gneiss, undifferentiated granite, and metamorphosed mafic to intermediate volcanic and sedimentary rocks (Sims et al. 1970, Morey 1976, Day et al. 1990). There are also iron formation and metasediments. Middle Proterozoic bedrock includes basalt, rhyolite, gabbro, diabase, anorthosite, granite, sandstone, and shale.
Fire causes exfoliation of granite boulders and outcrops, as noted in the Little Sioux fire of 1971 in northern Minnesota (Wright and Heinselman 1973).
LANDFORMS: The subsection, corresponding to a physiographic unit described by Wright (1972), consists of scoured bedrock uplands or shallow soils on bedrock, with many lakes. Several outwash plains also occur in the area; the largest of these is the Sawbill outwash plain.
LAKES AND STREAMS: More than 300 lakes are larger than 160 acres; these cover about 13 percent of the subsection's surface (University of Minnesota et al. 1981b).
SOILS: Soils are derived from a mantle of acid, cobbly and gravelly glacial till of variable depth. Sandy loam is the predominant soil texture, along with loamy sands. Soils of the outwash plains are sand. The soils are classified as Ochrepts, with localized Aquents (Anderson and Grigal 1984).
PRESETTLEMENT VEGETATION: Heinselman (1973) describes the vegetation as dominated by jack pine forest, white pine-red pine forest, and hardwood-conifer forest dominated by balsam fir, white spruce, paper birch, and trembling aspen. Fire dependence characterizes all these forest types. Sugar maple was not found growing in the subsection, but there were scattered red oak (in stunted stands on rock outcrops), yellow birch, and basswood.
Jack pine is most prevalent in the two areas where the landscape is least dissected by small lakes, north of Vermilion Lake and within and north of the Sawbill outwash plain. White pine-red pine forests are most common in areas most dissected by lakes, probably as a result of partial fire protection.
NATURAL DISTURBANCE: The average interval between significant fire years was about 4 years in presettlement times, and a natural fire rotation of about 100 years was characteristic of the area (Heinselman 1973). The rotation was shortest (about 50 years) in jack pine and aspen-paper birch forests, and 150 to 350 years in red pine-white pine forests. Lightning caused many fires; the importance of Native American fire management in the area has not been established. Heinselman's work indicated that major fires occurred during drought years. Major drought years occurred two to three times per century. The timing of the fire, spring or fall, determined how severely soils burned and what tree species regenerated. Pollen records indicate that the fire history has not changed substantially for several thousand years.
Windthrows occurred on the thin soils, providing additional fuel for fires (Heinselman 1973). Similarly, insect infestations, especially by spruce budworm, resulted in cyclic heavy balsam fir, white spruce, and black spruce mortality, which added to the fuel load.
PRESENT VEGETATION AND LAND USE: Most of the subsection remains forested; most forest types persist with stand composition and structure similar to those present originally. Logging occurred within the subsection, but large areas remain unlogged. Heinselman (1973) maintained that this was because of the relatively sparse densities of forest stands, particularly white and red pines. However, it has also been maintained that the lack of logging was the result of two other factors; inaccessibility and the public sentiment for preservation when these forests were beginning to be exploited.
High-quality examples of the following plant communities are well represented in this subsection: red pine forest and white pine forest. Inventory is insufficient on many plant communities here.
RARE PLANT COMMUNITIES: None identified to date.
RARE PLANTS: Most of the rare plants known from the subsection are northern species at the extreme southern edge of their range. Agrostis geminata (twin bentgrass), Arenaria macrophylla (large-leaved sandwort), Asplenium trichomanes (maidenhair spleenwort), Caltha natans (floating marsh marigold), Carex katahdinensis (Mount Katahdin sedge), Carex praticola (prairie sedge), Carex supina (sedge), Cypripedium arietinum (ram's-head lady's-slipper), Geocaulon lividum (northern comandra), Littorella americana (American shore-plantain), Osmorhiza obtusa (blunt-fruited sweet cicely), Phacelia franklinii (wild heliotrope), Potamogeton vaseyi (Vasey's pondweed), Rubus chamaemorus (cloudberry), Saxifraga aizoon (encrusted saxifrage), Saxifraga cernua (nodding saxifrage), Subularia aquatica ssp. americana (awlwort), Tillaea aquatica (pigmyweed), Viola novae-angliae (New England violet), Woodsia scopularia (Rocky Mountain woodsia).
RARE ANIMALS: Mammals: Microtus chrotorrhinus (rock vole); Birds: Haliaeetus leucocephalus (bald eagle), Pandion haliaetus (osprey); Insects: Erebia disa mancinus (Disa alpine, butterfly), Cicindela denikei (tiger beetle).
NATURAL AREAS: State Natural Areas: Burntside Islands, Eagles Nest Island #4, Hovland Woods, Purvis Lake-Ober Foundation; Research Natural Areas: Keeley Creek, Lac La Croix; Other: Lost Lake Peatland Scientific and Natural Area, South Fowl Lake Cliff Natural Heritage Registry site.
PUBLIC LAND MANAGERS: National Forests: Superior; Wilderness Areas: Boundary Waters Canoe Area (Superior NF); State Forests: Bear Island, Burntside, Grand Portage, Kabetogama, Pat Bayle; State Parks: Bear Head Lake, Soudan Underground Mine.
CONSERVATION CONCERNS: Voyageurs National Park and the Boundary Waters Canoe Area were both identified as critical landscapes for biodiversity protection by the Minnesota Heritage Program. There is inadequate protection of significant natural areas outside the BWCA wilderness.
BOUNDARIES: The western boundary of the subsection forms at the boundary with the portion of the Erskine moraine (Des Moines lobe) located between Kabetogama Lake and Nett Lake. This part of the Erskine moraine is treated as Subsection X.11, the Little Fork-Vermilion Uplands.
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| Figure 33.—Subsection X.10: Lac La Croix Research and Natural Area, Boundary Waters Canoe Area, St. Louis County, Minnesota. Upland conifers grow on the thin soils of this subsection; boulders and bedrock are exposed beneath this old-growth stand of red pine and white pine. Fire dependence characterizes the forests of this subsection; the bark of the large red pine to the left is charred from a recent fire. Minnesota Department of Natural Resources photo by K.A. Rusterholz. |
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| Figure 34.—Subsection X.10: Boundary Waters Canoe Area, Cook County, Minnesota. Small northern conifers, including tamarack, black spruce, and balsam fir, and lichens cover the granitic bedrock along one of the hundreds of small bedrock lakes of the subsection. Minnesota Department of Natural Resources photo by D.S. Wovcha. |
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