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Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin


SECTION V. SOUTHEASTERN WISCONSIN SAVANNA


Part of Bailey and Cushwa's (1981) Humid Temperate Domain, Humid Hot-Summer Continental Division, Eastern Deciduous Forest Province; glaciated landscape of late Wisconsinan age; savanna (most common), tallgrass prairie, deciduous forest.
Section V contains four subsections: Central Wisconsin Sand Plain, Southeastern Wisconsin Till Plain, Lake Winnebago Clay Plain, Rock River Hill Country. The section and subsections are shown on the large three-State map (Plate I).
DISCUSSION: A large part of Section V is characterized by gently sloping ground moraine and end moraine ridges, with calcareous soils. There are also areas of lacustrine sand and clay in the north. The relatively long growing season, coupled with fertile soils, has resulted in heavy agricultural use of the land.

ELEVATION: 580 to 1,535 feet (177 to 468 m).

AREA: 13,544 square miles (35,089 sq km).

STATES: Wisconsin.

CLIMATE: Continental, with great differences between summer and winter temperatures. Section V is influenced by three air masses: the Maritime Polar (dry, mild), Maritime Tropical (moist, warm), and Continental Polar (dry, cold). Total annual precipitation, which ranges from 28 to 33 inches across the section, is intermediate between that of Section IV to the west and Section VI to the east; precipitation increases from west to east (Wisconsin Statistical Reporting Service 1967). About 23 percent of precipitation falls during winter; this relatively low amount may partially account for stress on many tree species and may increase the potential for spring fires, which are important for maintaining prairie and savanna conditions.

BEDROCK GEOLOGY: Cambrian, Ordovician, and Silurian sedimentary rocks underlie most of the section; Silurian and Devonian marine sedimentary rocks are exposed along sections of the Lake Michigan shoreline (Ostrom 1981, Morey et al. 1982). At the northern edge of the section, Cambrian sandstone is locally exposed as buttes (Martin 1932, Hole 1968, Germain and Hole 1994). Precambrian-age (Archean) gneiss and amphibolite also occur at the northern edge (Morey et al. 1982). Granitic rock of the Wolf River batholith (Precambrian age) occurs in the northeast.

Underlying bedrock is responsible for general topographic relief in this section. For example, several of the broad plains here are underlain by resistant limestone or dolomite cuestas, such as the Niagaran upland along Lake Michigan and the Prairie du Chien cuestas farther to the west (Hole 1976, Martin 1965).

LANDFORMS: Section has surface sediments and landforms from the most recent Wisconsin Glaciation. End moraine, ground moraine, and outwash are the most common landforms; a loess cap (wind-deposited silt) covers much of the section.

SOILS: Soils are generally fine textured, either derived from glacial till or aeolian silt (loess) deposits. Loess deposits are up to 16 feet deep (Hole 1976). Soils are primarily Alfisols (Udalfs) and Mollisols (USDA Soil Conservation Service 1967). The soils of the Central Wisconsin Sand Plain (Subsection V.1) are sands.

PRESETTLEMENT VEGETATION: Bur oak savannas (openings) and oak forest can be considered the characteristic vegetation of flatter portions of the section. Tallgrass prairie occupied the least dissected, rolling parts of the section; prairie grasses dominated the groundcover of the open savannas, which often occupied slightly more irregular, rolling to moderately hilly topography. Sugar maple-basswood forest occupied the steepest most fire-protected sites, as well as those areas protected from fire by either wetlands or lakes.

NATURAL DISTURBANCE: Fire occurred regularly in the savannas and prairies. Fire frequency was largely controlled by climatic fluctuations (Kline and Cottam 1979). Windthrow was not commonly referenced, but was probably important in the forests.

PRESENT VEGETATION AND LAND USE: Most of the level to hilly topography is farmed, except for parts of the Central Wisconsin Sand Plain and major river corridors. Primarily the steep, dissected topography and the large wetlands remain in natural vegetation.

RARE PLANT COMMUNITIES: Both tallgrass prairie and oak savanna, originally the dominant vegetation, have became rare because of fire exclusion and agricultural development.

RARE PLANTS: See subsections and sub-subsections.

RARE ANIMALS: See subsections and sub-subsections.

NATURAL AREAS: See subsections and sub-subsections.

PUBLIC LAND MANAGERS: See subsections and sub-subsections.

CONSERVATION CONCERNS:

BOUNDARY JUSTIFICATION: The boundary between Section IV, the Driftless Area, and Section V is based on differences in topography, with steeper slopes and more dissected topography in the Driftless Area. Lake Michigan forms the eastern boundary of Section V. Section VI begins along the eastern shore of Lake Michigan (in Michigan); it is characterized by moister, cooler summers and warmer winters (less continental conditions) than Section V because of winds off Lake Michigan. Sections VIII and IX have cooler temperatures than Section V because of higher latitude and prevailing winds from the northwest.


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