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Southeastern Wisconsin Savannah and Till Plain

↑About the Southeastern Wisconsin Savannah and Till Plain

The Southeastern Wisconsin Savannah and Till Plain is a large region in southeastern Wisconsin; the city of Madison is located towards the southwest of this region. This region was originally transitional between sugar maple-basswood-oak forest in the east, and oak savanna in the west. It is now heavily used for agriculture, and only small, fragmented wild areas remain. The Rock River originates in the north of this region and is the largest river in this region, except in the northwest where the Wisconsin river briefly flows through this region.

The terrain here is flat on a large scale, but locally irregular, with a high density of glacial features including till plains, terminal moraines, kettles, and drumlins. Large areas of drumlins mostly trend in the northeast-southwest direction, becoming north-south in the east of the region. There are also numerous wetlands and small lakes, particularly near the ridges formed by terminal moraines. This region is underlain mostly by dolomite, with some limestone, sandstone, and shale, but this is covered by glacial drift, mostly less than 50 feet deep, but becoming as deep as 100-200 feet in the east. Surface soils tend to be silt loams, with subsoils of calcareous loams, or in a few places, calcareous sands or gravels. These soils are ideal for Western agriculture. Most sites are well-drained but good at retaining water, but there are some areas of poorly-drained depressions, as well as some droughty, excessively-drained terminal moraines.

The region has a humid continental climate with hot summers and very cold winters, and highly variable weather in general. Precipitation is higher in summer and lower in winter, mostly following trends of temperature and thus yielding similar relative humidity year-round, although spring averages slightly drier than fall. Weather patterns vary both month-to-month and year-to-year, and long periods of dry or wet weather, or hot or cold spells, deviating significantly from averages, can occur.

The original vegetation cover here was transitional between sugar maple (Acer saccharum), American basswood (Tilia americana), and oak in the east, to, in the west, savannas of white oak (Quercus alba), black oak (Quercus velutina), and bur oak (Quercus macrocarpa), and sedge meadows. Fire and the drought-prone nature of soils tended to dictate this transition: this region tended to experience more fire than the moister, clayey areas to the east and north, but less fire than areas to the west. Native Americans, in this region the Ho-Chunk or Winnebago people, probably increased the frequency of low-intensity fires through controlled burns, and thus increased the portion of oak savanna here.

Nowadays, this region is largely used for agriculture, with only small amounts of woodland and wild areas remaining. The agriculture here mostly produces forage crops to support the dairy industry, but there are also a large number of truck crops and other specialty crops. Most of the region is rural and sparsely populated, but Madison, Wisconsin is located here, and is surrounded by significant suburban development. The rest of the region also has numerous small towns throughout. Remaining forest is mostly concentrated either on swampy ground, or the excessively-drained terminal moraines. There are small, highly fragmented woodlots throughout, and even these are disproportionately located on steeper terrain of glacial origins.

This region is bordered to the north by the Lake Michigan Lacustrine Clay Plain, which has finer-textured soils less prone to drought and fire. To the east it is bordered by the Kettle Moraines, a region with more areas of hillier terrain and forest cover, and more poorly-drained soils. To the south, this region is bordered by the Rock River Drift Plain, which has thinner glacial drift, more leached surface soils, and more soil diversity. To the west, this region borders the Driftless Area, a hillier area that escaped glaciation; most of the region borders the Blufflands and Coulees, but there is a small border to the southwest with the Savanna Section. This region also borders the Central Sand Ridges to the northwest, a region with sandy soils and abundant lakes.

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