Deciduous woods landscape areas
Deciduous woods:
Description | Landscape areas
The deciduous woods biome is made up of lake and outwash plains, moraines, and drumlin fields. Topography ranges from relatively level plains, to very steep gradients in southeastern Minnesota along the edge of the Paleozoic Plateau. Containing a mixture of grassland and deciduous woodlands, it forms a transition between the Prairie Grasslands and Coniferous Forest.
The Ecological Classification System classifies this biome on the basis of its bedrock, glacial deposits, topography, climate, and plant communities. It identifies eight subsections, or landscape areas, described in the following paragraphs.
Aspen parklands
Clusters of willow and aspen dot this low, flat to gently rolling prairie landscape, formerly the lake bottom of Glacial Lake Agassiz. Coarse glacial till slows the absorption of water and acts in tandem with topography, weather, and fire, to create the patchy landscape. Low snowfall, extreme cold, and drying winds increase incidence of fire and stress on trees and shrubs, creating woodland openings.
Aspen Parkand is a transition from the tallgrass prairie lying just beyond the western border, to the forested peatlands to the east. In the western part, till deposits of 100 to 400 feet cover Ordovician dolomite, sandstone, and shale bedrock, formed from glacial lake sedimentation. Low dunes, beach ridges, and wet swales mark soil variations from loam to silt, sand, and gravel. To the east, granite and volcanic bedrock lie under a plain of till and loam, its low ridges surrounded by shrubby wetlands. Rivers meander broadly over the flatness; lakes are rare, and drainage, not well developed. Flooding is an important problem, often effectively shortening the 120-day growing season.
Presettlement communities were of aspen savanna, tallgrass prairie, wet prairie, and dry gravel prairie on beach ridges. Floodplain forests of silver maple, elm, cottonwood, and ash lined the rivers. Beach ridges up to 25 feet high "lapped" northward along the old shoreline, supporting strings of oak savanna and dry prairie, as well as trails for bison, pre-Europeans, and fur traders with ox carts. With settlement, fire suppression has allowed oak openings and brushland to become wooded. Today's parkland is a mosaic of groves of trembling aspen and balsam poplar, with prairies and sedge fens stippled with willow and bog birch. This is moose country, shared with sharp-tailed grouse, yellow rail, and other waterfowl. Agriculture dominates in the south today, and conservation efforts attempt to balance agricultural development with wetland and prairie preservation and restoration.
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Hardwood hills
Steep slopes, high hills, kettle lakes on glacial moraines, and outwash plains characterize this landscape area. The Alexandria Moraine, one of the highest in the state, contains a broad belt of lakes and also headwaters for a number of rivers. The Continental Divide sends waters north to the Hudson Bay or south into the Mississippi River. Over 400 area lakes, most on end moraines and pitted outwash plains, measure over 160 acres in size. From 100 to 500 feet of drift covers the bedrock of granite, shale, sandstone, clay, and gneiss. The soil is basically loam, mixed locally with sand or clay.
Before settlement the hilly terrain and numerous lakes and wetlands protected the area from fire, resulting in woodland or mixed hardwood forest of oak, sugar maple, basswood, and others. Along the more level western edge grew a mosaic of tallgrass prairie, aspen-oak land, and oak savanna. While agriculture is the primary land use today, the many upland forests, lakes, and wetlands make recreation and tourism also significant. Conservation concerns focus on wetlands, especially for waterfowl habitat, and also lakeshore development and water quality.
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Anoka sand plain
This flat, sandy plain is subtly relieved by low moraines, small dunes, ice block depressions, tunnel valleys, and terraces along the Mississippi and its tributaries. Bedrock of dolomite, sandstone, and shale is covered with up to 200 feet of drift, with granite outcrops near St. Cloud. Soils are sandy; more organic matter occurs in ice block depressions, tunnel valleys, and along the Mississippi. Tunnel valleys formed when glacial meltwater drained beneath heavy glaciers in long, straight pathways through drift and bed rock. These valleys are now occupied by rivers, streams, lakes, and even peatlands, but their drainage is not well networked. About 38 lakes measure over 160 acres in area. The area receives an even share of the annual precipitation throughout its 136- to 156-day growing season.
Before settlement, sandy, droughty soils supported oak barrens, jack pine, and large areas of brushland. Fire and drought had significant impact, often causing wind erosion and movement of sand dunes, even eliminating some oak species from oak barrens and savanna. A narrow band of upland prairie and floodplain forest lined the Mississippi. Today sod and vegetable crops are grown on drained peaty areas, while urban development encroaches rapidly. Conservation issues focus on urban development, wetland conservation, and protection of remaining natural areas.
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Big woods
The gently to moderately rolling terrain of this landscape area was once covered with red oak, sugar maple, basswood, and American elm, causing settlers to call this the Big Woods. Circular, level-topped hills slope smoothly to a broad lower level, pocked with lakes and peat bogs. Bedrock 100 to 400 feet below consists of sandstone, shale, and dolomite, with clay increasing to the north. Loamy soils, a growing season of 145 to 150 days, and even precipitation made this ideal for agriculture, which is its most common use today.
Only about 10 to 15 percent of presettlement vegetation remains as upland forest or wetland. Most of the area is used as cropland or pasture. Conservation concerns focus on water quality along the Minnesota River area, where agriculture pollutants become concentrated. Preservation of wetlands, Big Woods and other natural landscapes are also of concern.
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St. Croix moraines & outwash plains
Two primary types of glacial features characterize this landscape. Steep, short slopes of the large St. Croix Moraine in the north are rolling to hummocky, and strewn with lakes, while outwash areas further south are level to rolling. Limestone, sandstone, and shale bedrock, usually beneath 100 feet of drift, are often exposed along highly eroded stream valleys in the east. These formations bear fossil beds, particularly along St. Paul's river bluffs. Precambrian bedrock underlying these rocks is also exposed in the St. Croix valley. The Mississippi and St. Croix Rivers drain the center and the eastern edge, and a floodplain borders the Mississippi.
This area once supported a mosaic of vegetation. Oak and aspen savanna grew on moraine ridges in the west and in the eastern ravines. Also common were tallgrass prairie on the level to gently rolling plains, and maple-basswood forest in the steep ravines and along streams, which lent fire protection. Fire, tornados, and high winds were the chief hazards, with some periodic flooding as well. Land use today is urban, occupied by St. Paul and its suburbs. Preservation of green space and wetlands are of particular concern, with associated issues of water quality, flood control, and pollution.
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Oak savanna
This rolling plain of moraines and outwash gives way in the southwest to steep-sloped stagnation moraines. Bedrock of limestone, sandstone, and shale can be seen in the stream valleys along the eastern edge, as well as in localized outcrops. Glacial drift is generally less than 100 feet deep. Loess-a fine, wind-blown, glacial silt rich with calcareous and fossilized matter?mantles the bedrock and till across much of this area. Drainage through this easily penetrable soil is fairly well developed, with only a few lakes in the western moraines.
Presettlement vegetation ranged from the abundant bur oak savanna, to maple-basswood forest and upland, tallgrass prairies. Today agriculture has claimed much of this landscape, with urban development encroaching from the north. Wetland preservation and restoration and protection of natural areas of high quality have become critical conservation issues.
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Rochester plateau
Loess covers this old bedrock plateau along the eastern portion of this area, and also much of the gently rolling glacial till plain in the west. Cushioned only thinly with till, the bedrock of dolomite, limestone, sandstone, and shale is exposed along the valley walls of the Mississippi River. This limestone matrix, which has undergone dissolution for thousands of years in the southwestern corner, is responsible for the distinctive landscape of sinkholes (depressions in the ground usually filled with clumps of trees), caves, and underground drainage that we call karst. The drainage network is well developed over this landscape, which was "driftless" and untouched by the latest glacial activity. Few lakes occur, but the headwaters of several major rivers are found here. Coldwater trout streams are a prime feature of the eastern portion.
Tallgrass prairie and bur oak savanna grew here before settlement, amidst the hazards of fire, high winds, and ice storms. Today, the rich soils are used for farming, with 80 percent in crops, 10 percent pasture, and only 5 to 10 percent remaining in woodland. Groundwater quality, now influenced by agricultural activity, and loss of forest communities are primary conservation issues.
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Blufflands
The old plateau in this landscape gives way to deeply eroded river valleys along the Mississippi. There the tributaries, loaded with accumulated water and sediment, tumble down the 600-foot relief to the Mississippi River, eroding rugged sedimentary outcrops along the steep ravines. Karst topography is common in the southern part of this area. Toward the west, the layers of till and loess thicken to 50 feet. The drainage network of streams is well developed, and coldwater trout streams are numerous. No lakes occur.
Presettlement vegetation varied with topography. Tallgrass prairie and bur oak savanna grew along ridge tops and dry upper slopes, where fire occurred. Slopes and protected valleys, with more moisture, supported forests of red oak, basswood, and other tree types. Windstorms and ice storms also shaped these communities. Today about half of this landscape is farmed, while the other half remains woodland, due primarily to the steep relief. Conservation issues today focus on groundwater quality as influenced by agricultural activity, retention of forest communities and trout streams, and soil erosion.
