European settlers arriving in southeastern Minnesota in mid-19th century carved their homesteads out of a unique landscape of tallgrass prairie, oak woodland, and Big Woods.  The fertile and treeless prairies, which at the time existed east, south, and west of the Big Woods, attracted an increasingly large number of homesteaders hoping for a successful new life on the land. These newcomers had no idea that the fertile prairie, which they quickly plowed under, existed only as the result of numerous changes in the area over time.  The vast prairie land of southeastern Minnesota in the mid-19th Century is a product of the area's dynamic history before European settlement.

The tallgrass prairie as seen in southeastern Minnesota roughly 150 years ago, dominated by grasses such as big bluestem and Indiangrass, had up to four times as much plant material belowground as aboveground (Risser 1981).  The fertility of the soil was a function of the chemical composition of the parent materials, most of which had been transported by glacial forces.  Weathering allowed the minerals from these materials to be released into the available nutrient pool.  Biotic components of the prairie also contribute to the fertility of prairie soils.  Microorganisms and soil fauna convert waste into dark colored organic matte, which makes up from 2.4% to 90% of prairie soils (Risser 1981).  The prairie soil reflects vegetation past and present and began as crude glacial deposits over 10,000 years ago.

The soils blanketing southeastern Minnesota and supporting the prairies of the 1850’s were created by massive forces in times before.  According to Minnesota’s geological history, the state experienced times of volcanoes, mountains, seas, and then ice. Giant glaciers scraped across the land, removing and depositing rock and soil as they went.  In last 20,000 years, two different glaciers covered the land.  The Superior Lobe came first, creating the St. Croix Moraine with sediment from the Lake Superior region, followed by the Des Moines Lobe.  Southeastern Minnesota’s present physical landscape emerged as the result of The Des Moines Lobe’s retreat, only 13,000 years ago.  This last glacier made Minnesota a penneplain, removing weathered rock, detritus, and further leveling the land by filling in low areas with glacial deposits.  The Des Moines Lobe also distributed limestone and shale-rich drift across the state (Ojakangas and Matsch 1982).  Such glacial deposits made an excellent base for future environments, like the prairie, to develop.

Soil texture and drainage are closely related to the physical geography and the vegetative cover of the land.  After the retreat of the ice, mollisoils and alfisoils began to form under the growing prairie and forestland respectively (Grimm 1984).  Mollisoils are dark and form from nutrient rich parent material; Alfisoils are mineral soils with clay and nutrient-rich subsoil (USDA 2002).  These soils form a continuum across the area, constituting prairie, prairie-woodland, and woodland soils. According to radio-carbon dated pollen samples, expansion of the woodlands in the area began about 5000 years ago and lasted up until 24000 years ago. In the mid-Holocene, much of the 1850’s prairie was Big Woods, dominated by elm, basswood, sugar maple, and hop hornbeam and much of the 1850’s Big Woods was tallgrass prairie.  Environmental conditions over the last 5000 years have favored the persistence of woodland however woody species have a difficult time invading prairie areas because of a prairies’ susceptibility to fire (Grimm 1984).  The prairie areas of the mid 19th Century began as glacial deposits and cycled to prairie only very recently in geological terms.  This prairie area formed because of dramatic past events.

Before settlement, very large areas of the prairie burned every year. We know the frequency of prairie fires was high because explorers and settlers coming in the area expressed great concern for the fires that might consume their property. Lightening strikes and Native Americans, who wanted to improve their chances for hunting, started the fires that prevented the invasion of woody species on the prairies and maintained a prairie-forest border (Risser 1981).  Fires also affected the non-woody components of the prairies, depending on season.  Burns in the mid- to late-spring increased the overall productivity of the tallgrass prairie and especially increased the abundance of forbs.  Late summer burns occurred most frequently before the arrival of settlers and caused the most damage to warm season plant species (Bragg 1995).  Fire alters the amount and kinds of soil resources, therefore altering the distribution and abundance of plants.  By reducing the number of species able to dominate the landscape, fires caused the prairie to become more uniform in species composition. This, in turn, affects habitat structures for the animals living on the prairie. Without fires, the prairie appears more “patchy” because a greater number of plant species invades the homogeneous landscape (Collins and Glenn 1995).

Studies show that the changes from prairie to woodland to Big Woods involved reductions in fire frequency caused by decreased temperatures and increased precipitation (Grimm 1983).  With 10 years of fire suppression comes a noticeable increase of woody species that, once established, can easily re-sprout and eliminate prairie plants (Bragg 1995).  The vegetation correlated with “fire probability pattern” in the area, which was a result of biotic and abiotic factors.  Biotic factors included flammability and pattern of vegetation and abiotic factors included macroclimate, physical firebreaks, and soil texture. Course textured soils hold less water than fine-textured soils and are more damaging to woody species because they heat up more. Vegetation type also correlated with the fire-probability pattern. (Grimm 1984).  Fire in combination with these factors allowed changes in the landscape that ultimately resulted in the prairie areas seen by settlers in the 1850’s.
As one can infer from southeastern Minnesota’s dynamic history of change, the prairie areas are anything but static.  More and more European settlers migrated to the area in the 19th Century and the prairie began to change rapidly.  Settlers suppressed fire and created new firebreaks with their roads and plows, which eradicated grassland environments directly and indirectly.  Human landscape alteration and less frequent and extensive fires allowed woody species to thrive and eventually overcome much of the prairie land; the prairie-forest border continued to flux.  Early glacial activity followed by soil buildup and frequent fires built southeastern Minnesota’s prairies of the mid-19th Century.  These prairies, very much a product of past events, had a unique history and boundary determined by various factors.
 
 
 
 
 
 
 
 
 
 
 

References Cited

Risser PG, Birney ED, Blocker HD. May SW, Parton WJ, Wiens JA.  1981. The True Prairie Ecosystem.  Stroudsburg, PA: Hutchinson Ross Publishing Company.557p.

Ojakangas RW, Matsch CL. 1982.  Minnesota’s Geology. Minneapolis, MN:  University of Minnesota Press. 255p.

Grimm EC. 1984.  Chronology and dynamics of vegetation change in the prairie woodland region of southern Minnesota, USA.  New Phytologist 93 (2):  311-330.

United States Department of Agriculutre: Natural Resource Conservation Service.  Updated Feb. 7, 2002.  Soil and Soil Types.  http://www.nhq.nrcs.usda.gov/land/index/soils.html

Bragg TB. 1995. The Physical Environment of Great Plains Grasslands.  In: Joern A, Keeler K, editors. The Changing Prairie: North American Grasslands. New York:  Oxford University Press.  p49-81.

Collins SL, Glenn SM.  1995. Grassland Ecosystem and Landscape Dynamics.  In: Joern A, Keeler K, editors. The Changing Prairie: North American Grasslands. New York:  Oxford University Press.  p49-81.

Grimm EC.  1983.  Fire and other factors controlling the Big Woods vegetation of Minnesota in the mid 19th century.  Ecological Monographs 54(3):  291-311.