Nature & Science
In a global context, northeast Minnesota is in the southern edge of the boreal forest biome. The boreal biome is the largest biome in the world, crossing northern Asia, Europe, and North America.
The National Hierarchical Framework of Ecosystem Units classifies and maps ecological units based on associations of different factors. These factors include climate, topography, soils, water, and potential natural communities.
In the national ecological framework, Minnesota is at the western edge of the eastern block of Humid Temperate Domain. Minnesota is unique because it has three different ecological Divisions, meaning the State supports a diversity of natural communities. These ecological Divisions are Warm Continental, Hot Continental, and Prairie. The Superior NF is in the Warm Continental Division.
Short, warm summers and long, cold winters define the climate of northern Minnesota. Average range of summer temperature is from 55°F to 78°F in July and average range of winter temperatures is from –11°F to 12°F in January.
On the Superior National Forest (NF), precipitation is 26 to 29 inches annually.
Most of the Laurentian Mixed Forest Province has little relief with rolling hills. However, the highest point in Minnesota, Eagle Mountain, is on the Superior NF and is 2,301 feet high. The lowest point is approximately 600 feet on the shore of Lake Superior.
Early in the Earth’s history, the bedrock underlying the Superior NF was deposited during the Early, Middle, and Late Precambrian ages. Early Precambrian rocks have been a valuable source of iron ore and have yielded small quantities of gold. The present day Mesabi Range has been producing high quality iron ore from Middle Precambrian sedimentary rocks for over 100 years. The most important mineral deposits of the Late Precambrian age are the copper-nickel deposits that occur along the base (northwest margin) of the Duluth complex.
The formation of the Superior NF’s soils is directly related to glaciation. As the glaciers advanced and retreated, different textured soils were deposited. Mixed, poorly sorted depositions called glacial till dominate the surface soils on the Forest. These deposits vary from large, extensive ground moraines to localized drumlins. Outwash deposits, which tend to be more sorted and stratified than till, are limited on the Forest and occur primarily in small outwash plains and eskers.
The Superior NF contains over 445,000 acres of surface water, or about 12 percent of the Forest area. There are almost 2,000 lakes at least 10 acres in size; over 1,300 miles of major streams supporting cold water fisheries; and over 950 miles of major streams supporting warm water fisheries. The quality of the water in lakes and steams is good to excellent.
Although many lakes and streams do not support a diversity of aquatic organisms, they are still an important fisheries resource. The quality of water in most lakes is good, with only a few classified as either very degraded or very pure. On a national, scale these lakes rank in the upper 50 percentile for water conditions; and on the average the lakes are in the upper 20 percentile.
The Superior NF lies within the transition zone between the boreal forests to the north and the broadleaf deciduous forests to the south.
The forested region of northern Minnesota is a mosaic of forest communities ranging from relatively pure standsof hardwoods (mainly birch, maple, and basswood) in areas with relatively nutrient-rich soils to relatively pure stands of conifers (mainly pine) in areas with relatively nutrient-poor soils. Between these two extremes are a variety soil types and habitats, which produce mixed stands of conifers and hardwoods. The dominant landscape forest communities include:
• Jack pine
• Red pine
• Red and white pine
• Mixed boreal hardwoods and conifers
• Northern hardwoods
• Aspen, birch, and spruce-fir
• Conifer bogs composed of black spruce, tamarack, or white cedar
Embedded within these forested landscapes are smaller-scale native plant communities, such as black ash swamps, riparian forests, forested bogs and fens, barrens, shrub swamps, and sedge meadows.
The patterns of dominant forest communities in northern Minnesota are largely a product of climate, geology, soils, topography, and a variety of disturbance factors. Historically, fire and wind have been the primary natural disturbance factors shaping forest vegetation patterns in this area. Floods, insects, and disease also influenced forest vegetation.
The compositional and structural characteristics of forest vegetation at both the landscape and stand levels shift through time in response to both natural and human-induced disturbances. For instance, the size, amount, and spatial arrangement of dominant forest vegetation types, early successional vegetation, and old-growth forest at the landscape-scale changed from decade to decade. These shifts in landscape patterns are primarily in response to stand-replacement disturbance events.
Similarly, the composition and structure of the understory, midstory, and overstory of individual stands are shaped by more local, less severe disturbance events. Less intense, more localized disturbance events, such as low intensity ground fires, small-scale wind events, and localized insect and disease outbreaks, influence individual stand characteristics, such as crown closure, canopy gap creation, understory and midstory development, and the availability of snags and downed woody material.
The Superior NF provides abundant and diverse habitat for thousands of breeding, wintering, and migratory species of terrestrial and aquatic wildlife.
These include: over 350 species of birds,mammals, reptiles, amphibians; 50 species of fish; and thousands of species of invertebrates, plants, lichens, fungi, and other organisms.
All these species provide for a wide array of crucial ecological benefits as well as social and economic benefits and uses, from big game hunting and fishing to wildlife watching and research.
The rich diversity, abundance, and distribution of species are largely a function of the biological and physical settings and environmental conditions of the Superior National Forest. The most important factors include:
• Diversity of lake and stream types
• Wide variety of vegetation communities in different successional stages
• Natural disturbances and other ecosystem processes (such as nutrient cycling, fire, wind, and flooding)
• Interrelationships among species
Species have also been affected by humans’ past and present use of forests through such activities as settlement, agriculture, logging, recreation, introduction of nonnative species, hunting, and fishing. Human influences far from the National Forests such as airborne pollutants and climate change also affect wildlife diversity. All these factors result in a continuously changing mosaic of environmental conditions and, in response; wildlife habitats and populations also continuously fluctuate in numbers, extent, quality, and location across the landscape and over time.
The Superior NF has over 100 species of migratory breeding birds in a zone that has the greatest diversity in North America of songbirds, including forest-dependent warblers; among the largest populations outside Alaska of gray wolves, common loons, and moose; popular game species such as walleye, trout, deer, ruffed grouse, fisher, and beaver; and numerous rare species such as great gray owl, black-backed woodpecker, ram’s-head ladyslipper and other orchids, and lake sturgeon.
The Superior NF has a great abundance and diversity of species common to the true boreal forest biome to the north, such as three-toed woodpecker, boreal owl, boreal chickadee, lynx, moose, and grizzled skipper butterfly.