Prairie grassland landscape areas
Description | Landscape areas
One of the last of the great glacial movements in Minnesota, the Des Moines Lobe advanced across present-day North Dakota into Minnesota and on into Wisconsin and Iowa. The level to gently rolling lake plains and ground moraines of the Prairie parklands biome are its legacy. The northern portion was primarily influenced by Glacial Lake Agassiz and its drainage. From there, the Red River flows north, and the Minnesota River, south. The southern portion features a high plateau of quartzite bedrock topped with till that defines the character of the area.
The Ecological Classification System classifies this biome on the basis of its bedrock, glacial deposits, topography, climate, and plant communities. It formed four subsections, or landscape areas, rich in its diversity of prairie communities.
Red River Prairie
This flat glacial lake plain is subtly interrupted by wetlands, meandering streams, sand dunes, and old beach ridges. Bedrock is Precambrian in the east and sedimentary in the west, where exposures near Lake Traverse are rich in fossils. Glacial Lake Agassiz deposited silt, sand, and clay, with some saline patches. Beach ridges are dry with sandy, gravelly soils. Minimal drainage has developed; rivers and streams meander extensively, few lakes occur, and flooding is common. The Red River flows north to the Hudson Bay, which is still frozen when Minnesota thaws, causing water to back up and flood the lake plain. Precipitation is even through the year, nourishing the 111- to 136-day growing season.
Tallgrass prairie and wet prairie dominated presettlement vegetation. Narrow, forested floodplains lined larger streams and rivers, in whose "fire shadows," woodland or brushland were common. Fire, drought, annual flooding, tornados, and straight-line winds were frequent hazards; even buffalo and ant activity affected plants and soils. Today, with intensive ditching, most land use is agricultural. Fragments of native prairie can be found east of the beach ridges and in the interbeach zone. Conservation concerns include preservation of prairie, wetland, and wildlife habitat, along with control of wind erosion.
Minnesota River Prairie
This gently rolling landscape of ground moraine is roughly bisected by the Minnesota River, today's incarnation of the Glacial River Warren, which partially drained Glacial Lake Agassiz. Though area bedrock is mostly shale, sandstone, and clay, River Warren scoured out granite exposures near Ortonville. Loam dominates, with local deposits of clay, sand, and gravel. The continental climate produces harsh temperature extremes but a lush growing season of 147 to 152 days. Lack of precipitation over the winter months dried woody plants, tipping the advantage to prairie grasses. Poor drainage development left many wetlands and large but shallow lakes; 150 measure more than 160 acres.
Tallgrass prairie once dominated this area, with few wet prairies and floodplain forests. Dry prairie types occurred on the Big Stone Moraine and on kames. Fire, floods, and straight-line winds disrupted woodland growth, constraining the oak openings and brush prairie. Today this area is the heart of the cornbelt, and remnants of the tallgrass prairie are rare. Water pollution and wetland destruction, both brought about by agricultural activity, and prairie protection have become the focus of conservation efforts.
Coteau is French for highland, which typifies this area sculpted of glacial till as deep as 800 feet. This landscape is made up of two related landforms, the middle coteau of rolling moraine ridges mantled with 1 to 3 feet of loess, and the outer coteau, a series of gently undulating to steeply rolling moraines. On the northeast edge, a steep escarpment, or slope, is cut by several streams in narrow ravines. The middle coteau, with its easily eroded loess, has a better developed drainage network of streams than the outer coteau of glacial till, which harbors more wetlands and lakes. Loamy, well-drained soils combine with a growing season of 145 to 150 days and ample annual precipitation to make the land an important agricultural area today.
Before settlement, tallgrass prairie covered the landscape, with wet prairie and forest found along streams. Few examples of these communities remain, since agriculture has developed. Water quality, both in shallow aquifers and surface water, and preservation of prairies and wetlands are important conservation concerns.
This "highland" or coteau is made up of moraines covered by loess ranging from 6 to 15 feet thick. Up to 800 feet below lies Sioux quartzite bedrock, visible in Rock and Pipestone counties' massive formations. The loess accounts not only for the loamy soil but also the well developed drainage network, which has left few lakes. In its 145- to 150-day growing season, the area receives only 11 to 12 inches of precipitation, not quite half of the annual total. Combined with the drying effect of the prevailing winds, this climate favored dry grassland vegetation.
Drier here than elsewhere in Minnesota, tallgrass prairie was only occasionally broken by wet prairie or floodplain forest. Few examples of these plant communities remain. Today agriculture is the most important land use, with some wind generator farms established on ridges along the coteau. Priority conservation concerns are water pollution, both in shallow aquifers and surface water, along with the loss of remaining tall and midgrass prairies and wetlands.