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Soils

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Purpose:

Soils of the northern Lake States

Soil is a basic resource; together with climate, its qualities affect the spatial distribution of vegetation and wildlife habitat, and key processes including plant growth, reproduction, and mortality. Soils develop in parent materials on the mantles of landform, and are strongly influenced by external (exogenous) conditions of climate, relief, and hydrology, and exogenous processes such as water or wind erosion and deposition, flooding, and fire. Soil development is also strongly influenced by internal (endogenous) conditions including soil texture, mineralogy, and microclimate, and processes or interactions among living plant roots, soil microbes, decaying leaves and litter, and inorganic soil materials. Soil development proceeds with the accretion and cycling of organic matter and nutrients, leaching and sub-soil deposition of chemical compounds, and resulting formation of distinct soil horizons. At the interface of the living and non-living domains of ecosystems, soils are both influenced by and have an influence on ecosystem development processes. Soils are thus a key component of our ecosystems, affecting human land uses, interactions of living and physical systems, and the well-being of our cultural and natural worlds.

The soils of the northern Lake States were largely formed by the Wisconsinan glaciation during the late Pleistocene, from 9,000 to 12,000 years ago. Patterns of soil types and land uses correspond strongly with glacial features. Northern Minnesota, Wisconsin, and western Upper Michigan are underlain by hard bedrock of volcanic and metamorphic origin that was somewhat resistant to glacial abrasion. Glacial till soils of fine and loamy textures dominate in these areas, and rock outcrops are common. Agricultural activities since European settlement have been limited due to the short growing season and uneven topography, and so much of the area remains forested.

In eastern Upper Michigan and northern Lower Michigan, the bedrock is made up of softer sedimentary rocks, including shales, sandstones, and limestones, which were susceptible to glacial downcutting. Because these rock formations were the source material for glacial grinding and mixing, the soils of these areas are dominantly sandy. These soil textures, along with the adverse climate, again limited agriculture and led to the dominance of forests in northern Michigan.

Glacial moraines, which were formed under an ice sheet, generally have loamy textured soils which are relatively rich in nutrients and hold water more effectively than sands. These soils often support northern hardwood forests, or aspen forests during early succession. Some of these lands have been converted to agriculture, as they are among the most productive soils in the northern Lake States.

Glacial outwash sands, deposited by glacial meltwater, as well as sands deposited from glacial lakes, formed large flat plains. These areas tend to be nutrient-poor and droughty, and are dominated by conifer forests, or oak-conifer forests in northern Lower Michigan.

Ice-contact features are sandy hills that were deposited by glacial meltwater at the edge of a moraine. They are intermediate in nutrient and moisture status, and were dominated by white pine forests prior to European settlement. Today, they support mixed forests of oak, aspen, red maple, and pines.

Topographic differences, along with subsurface bedrock or clay layers, contribute to the presence of water tables near the Earth’s surface in some areas. These locations support wetlands, some forested and some open (bogs, marshes, and fens), with deep organic soils. Wetlands are dominant in parts of Minnesota and eastern Upper Michigan, and are commonly interspersed with uplands in other parts of the northern Lake States.

There are several forest management concerns associated with soils in the northern Lake States. Soil erosion and sediment inputs to streams and rivers can occur during road construction and maintenance, and as an ongoing process from unpaved roads. Soil compaction may occur during the first few passes of heavy logging equipment, particularly if soils are moist. Compaction reduces moisture infiltration and restricts root expansion, which can lead to reductions in forest growth. Operating equipment while soils are frozen or adequately dry, minimizing areas traversed by equipment, and use of specialized equipment and tires are examples of management practices designed to reduce soil compaction.

Sandy outwash and lake plain areas are sometimes susceptible to localized blowouts or wind displacement of soils. Nutrient removal from these sandy sites during harvesting, particularly whole-tree harvesting, has also been a concern of forest soil scientists. While results of one recent study indicated compaction due to equipment operation increased soil moisture retention in sandy soils, whole-tree harvesting of aspen decreased soil nutrient pools and reduced growth of regenerating clones (Stone et al. 1999). These findings raise questions regarding the sustainable management of aspen on sandy soils. Nutrient depletion (nitrogen volatilization) and combustion of soil carbon through excessively hot ground fires is an additional concern in all soil types. Conserving our soil resource is critical from both ecological and socioeconomic viewpoints.

Analysis Team:

USDA Forest Service--North Central Research Station, Rhinelander, WI
dot.gif (71 bytes)David Cleland, Ecologist

North Central Research Station, Houghton, MI
dot.gif (71 bytes)Maureen Mislivets, Landscape Ecologist

Michigan Technological University, Houghton, MI
dot.gif (71 bytes)Sari Saunders, Landscape Ecologist

Available GIS Maps: