Northern Prairie Wildlife Research Center
DISCUSSION: Section I, once dominated by tallgrass prairie, is concentrated in western Minnesota, but continues into adjacent North Dakota and South Dakota. Like other prairie areas of the U.S., this section is characterized by geomorphic features of low relief, which allow the spread of fires over long distances (Rumney 1968, Gleason 1913). The fertile soils of the section have been intensively farmed mostly for grains, potatoes, and sugar beets, almost completely eliminating the original prairie vegetation.
ELEVATION: 825 to 1,150 feet (252 to 351 m).
AREA: 7,096 square miles (18,378 sq km).
CLIMATE: Continental, with great differences between winter and summer temperature. The section is strongly influenced by the Maritime Polar (dry, mild) air mass, but is also influenced by Maritime Tropical (moist, warm) and Continental Polar (dry, cold) air masses. Polar air masses have more regular impact upon this section than does the Gulf air mass (Critchfield 1974).
Growing season ranges from 111 days in the north to 151 days in the south. Annual snowfall averages 40 inches; total precipitation ranges from 20 to 23 inches, with roughly 40 percent occurring during the growing season (Wendland et al. 1992, Hargrave 1992). Although the total precipitation is not significantly less than that in parts of the forested sections to the east, the timing of precipitation is probably an important influence on the vegetation; only 11 percent of the annual precipitation arrives during November through February (based on Wendland et al. 1992). In contrast, savanna-dominated Section III receives 16 to 23 percent of its precipitation in this same period, and conifer-dominated Section X receives 14 to 29 percent. The combination of low levels of winter precipitation and strong desiccating winds increases the potential for spring fires. Drought conditions also occur relatively often during the growing season (Weaver 1954, Weaver and Albertson 1956). Tree growth is limited under these climatic conditions.
BEDROCK GEOLOGY: Bedrock of the entire section is overlain by 200 to 400 feet of glacial drift (Olsen and Mossler 1982). Glacial drift in the eastern part is underlain by Precambrian bedrock, including middle to late Archean and early Proterozoic gneiss, amphibolite, undifferentiated granite, and metamorphosed mafic to intermediate volcanic and sedimentary rocks. The western portion is underlain by Cretaceous marine shale, sandstone, and variegated shale; Ordovician carbonates, sandstone, siltstone, and shale; and Jurassic dolomitic shale, cherty dolomite, and gypsum (Morey et al. 1982).
LANDFORMS: Glacial lake plain, beach ridges, sand dunes, water-reworked till, and small areas of ground moraine. The section is a lowland with clay- and silt-rich soils deposited in Glacial Lake Agassiz (Wright 1972, Kratz and Jensen 1983). Wheeler et al. (1992a) describe it as a nearly featureless plain except to the east, in the interbeach zone, where there is a series of narrow beach ridges and wavecut scarps. Flat topography and clay soils combine to create poorly drained soils. As the lake levels of Glacial Lake Agassiz fell, ridges of sand and gravel formed along the shoreline; these are concentrated along the eastern edge of the lake plain and are known as the Lake Agassiz interbeach zone. Included within Section I is a large area of ground moraine, part of the Erskine moraine of the Des Moines lobe (Hobbs and Goebel 1982). The sediments of this lobe are also fine textured, and the topography is flat.
|Figure 7.Section I: Twin Valley Prairie Scientific and Natural Area, Norman County, Minnesota. Only small remnants remain of the once vast prairies of the flat clay plain of Glacial Lake Agassiz. Mesic tallgrass prairie, seen in the foreground, was much less extensive than wet prairie on the poorly drained clay plain. Drainage has allowed most of this landscape to be converted to agriculture. Minnesota Department of Natural Resources photo by D.S. Wovcha.|
LAKES AND STREAMS: A few shallow lakes (Hargrave 1992). Drainage is to the north via the Red River and its tributaries. The larger tributaries, the Buffalo, Marsh, Ottertail, and Wild Rice Rivers, originate on the upland moraines to the east and flow across the lake plain as winding, sluggish streams (Wheeler et al. 1992a).
SOILS: Poorly drained lacustrine clays, sands, and gravels, primarily Mollisols. Cummins and Grigal (1981) map most of these soils as Aquolls, and Borolls are also common. Almost all clay- or silt-rich soils have been ditched and plowed for agricultural use. Saline soils are locally present.
PRESETTLEMENT VEGETATION: At the time of settlement, almost the entire section was tall-grass prairie. Marschner (1974) indicates two vegetation types: upland prairie (primarily tallgrass prairie) and prairie wetland (wet prairie). Narrow, forested floodplains were originally present along larger streams. Broader zones of woodland or brushland often occurred along "fire shadows" of streams; size and configuration depended on prevailing wind and stream alignment.
The vegetation zone just to the west of Section I's tallgrass prairie (and outside the area of this study)the short grass prairie or steppeoccupies a long, narrow, north-south trending zone almost completely within the rainshadow of the Rocky Mountains (Rumney 1968, Küchler 1964). These shortgrass prairies, also called the transitional grassland zone (wheatgrass-bluestem-needlegrass) by Küchler (1964), occur less than 30 miles to the west of Section I at the western margin of the Glacial Lake Agassiz basin (Barker and Whitman 1988, as cited in Wheeler et al. 1992a).
Recent botanical studies have broken the prairies of the section into three major types: tallgrass prairie, wet prairie, gravel prairie. Calcareous fens occur along the slopes of beach ridges or some of the moraines at the eastern margin of the lake plain (Wheeler et al. 1992a); these artesian seepages occur along the downslope sides (west) of the shorelines.
The Minnesota Natural Heritage Program (1993) states that wet prairie was especially common on broad, poorly drained flats of the Agassiz lake plain; locally, high salt concentrations (sulfates of calcium and magnesium) influence the species composition of the wet prairie community.
The more northern fescue prairie begins just north of Minnesota in the Canadian Province of Manitoba (Wright and Bailey 1980; Küchler 1964; Bird 1961; Coupland 1950, 1961; Moss 1932).
NATURAL DISTURBANCE: Fire, drought, and annual inundation were important. Bison grazing and ant activity caused important fauna modifications of the vegetation and soils, respectively.
PRESENT VEGETATION AND LAND USE: The lake plain has been intensively ditched for agriculture. Native flora persists in fragments (though some of moderate size) east of the beach ridges and in the interbeach zone.
The interbeach zone of Glacial Lake Agassiz contains some of the largest remaining tracts of native prairie vegetation, primarily due to a combination of locally steep dunes, gravelly beach ridges, and poorly drained interbeach areas. The vegetation of the interbeach zone changes to aspen or oak woodlands. West of the interbeach zone, virtually no native vegetation remains, except on railroad and highway rights of way. Wheeler et al. (1992b) found upland prairie species to be common in parts of the section (based on herbarium records).
The interbeach zone of Glacial Lake Agassiz supports wet prairie in the interbeach areas, with bands of drier "gravel prairie" along the beach ridges and dunes. Gravel prairie, which is drier than tallgrass prairie, is dominated by Schizachyrium scoparius (little bluestem), Koeleria macrantha (June grass), Sporobolus heterolepis (prairie dropseed), and several other short grasses. The drier prairies are similar to those found further to the west in the Dakotas.
|Figure 8.Section I: Agassiz Dunes Scientific and Natural Area, Norman County, Minnesota. Sand dune formed in deltaic deposits at the margin of Glacial Lake Agassiz. Stunted bur oak and mixed grass prairie are characteristic vegetation on this landscape of small sand dunes. Minnesota Department of Natural Resources photo by D.S. Wovcha.|
RARE PLANT COMMUNITIES: Although once dominant in the section, all prairie types are now rare. Rare prairie and wetland communities include dry prairie, glacial till hill prairie, mesic prairie, wet prairie, and calcareous seepage fen (Minnesota Natural Heritage Program 1993).
RARE PLANTS: Almost all rare plants in the section are considered prairie plants (Coffin and Pfannmuller 1988). Androsace septentrionalis var. puberulenta (northern androsace), Antennaria aprica (small-leaved pussytoes), Astragalus neglectus (Cooper's milk-vetch), Botrychium gallicomontanum (prairie moonwort), Carex garberi (Garber's sedge), Carex hallii (Hall's sedge), Carex obtusata (blunt sedge), Carex scirpiformis (sedge), Carex sterilis (sterile sedge), Carex xerantica (dry sedge), Chamaerhodos nuttallii (Nuttall's ground-rose), Cladium mariscoides (twig-rush), Cypripedium candidum (small white lady's-slipper), Eleocharis pauciflora (few-flowered spike rush), Gentiana affinis (northern gentian), Helianthus nuttallii (Nuttall's sunflower), Lygodesmia rostrata (annual skeleton-weed), Orobanche fasciculata (clustered broom-rape), Orobanche ludoviciana (Louisiana broom-rape), Platanthera praeclara (western prairie fringed orchid), Rhynchospora capillacea (hair-like beak-rush), Salicornia rubra (red saltwort), Spartina gracilis (alkali cord-grass), Stellaria longipes (long-stalked chickweed), Tofieldia glutinosa (false asphodel), Triglochin palustris (marsh arrow-grass).
RARE ANIMALS: Most of the rare fauna is strongly associated with prairies. Mammals: Bison bison (bison), Canis lupis (gray wolf (plains subspecies)), Cervus elaphus (elk), Felis concolor (mountain lion), Microtus ochragaster (prairie vole), Thomomys talpoides (northern pocket gopher); Birds: Ammodramus bairdii (Baird's sparrow), Ammodramus caudacutus (sharp-tailed sparrow), Anthus spragueii (Sprague's pipit), Athene cunicularia (burrowing owl), Asio flammeus (short-eared owl), Bartramia longicauda (upland sandpiper), Calcarius ornatus (chestnut-collared longspur), Coturnicops noveboracensis (yellow rail), Grus canadensis (sandhill crane), Lanius ludovicianus (loggerhead shrike), Limosa fedoa (marbled godwit), Phalaropus tricolor (Wilson's phalarope), Tympanuchus cupido (greater prairie-chicken); Reptiles: Heterodon nasicus (western hognose snake); Insects: Cicindela limbata nympha (tiger beetle), Cicindela scutellaris criddlei (tiger beetle), Hesperia assiniboia (Assiniboia skipper), Hesperia dacotae (Dakota skipper), Oarisma poweshiek (Poweshiek skipper), Oeneis uhleri varuna (Uhler's arctic).
NATURAL AREAS: State Natural Areas: Bicentennial Prairie, Bluestem Prairie, Felton Prairie, Frenchman's Bluff, Malmberg Prairie, Ottertail Prairie, Pembina Trail Preserve, Prairie Smoke Dunes, Richard M. and Mathilde Rice Elliot Prairie, Sandpiper Prairie, Santee Prairie, Twin Valley Prairie, Verlyn Marth Memorial Prairie, Western Prairie South; The Nature Conservancy Preserves: Felton Prairie Complex (Bluestem Prairie and Blazing Star Prairie), Western Prairie North, Malmberg Prairie; Others: Anna Gronseth Prairie, Audubon Prairie, Bluestem Prairie, Foxhome Prairie, Kettledrummer Prairie, Miller Prairie East, Pankratz Prairie North, Pankratz Prairie South, Town Hall Prairie.
PUBLIC LAND MANAGERS: Wildlife Management Areas: Agassiz-Nelson, Agassiz-Olson, Alberta, Andrea, Atherton, Bejou, Belgium, Bjorson, Burnham, Chicog, Clay County, Cromwell, Cupido, Dalby, Dittmer, Dugdale, Faith, Felton, Gruhl, Highland Grove, Hitterdal, Janssen, Jeral, Joe River, Kertsonville, Kube-Swift, Lake Ida, Liberty, Magnusson, Maple Meadows, Marcoux, Moccasin, Neal, Ogema Springs, Onstad, Orwell, Rothsay, Rush Lake, Shypoke, Spring Creek, Stipa, Syre, Tilden, Trail, Twin Valley, Tympanuchus, Ulen, Vangsness, Wambach, Waubun; Waterfowl Production Areas: Agassiz Beachline, Bellmore, Brown, Buchl, Chief Lake, Damaree, Eide, Flickertail Prairie, Foss South, Fuglie, Geyer, Haggman, Hanneman, Haugrud-Sillerud, Hellickson, Hoykens, Kloos, Lofgren, Marks, Melvin Slough, Nelson Prairie, Pepperton, Ruona, Squirrel Lake, Swede Grove Lake, Wildung; Others: Buffalo River State Park.
CONSERVATION CONCERNS: Some of the major resource management issues are (1) gravel mining and its destruction of prairie, (2) degradation of prairies, including rare prairie bird habitat, by present grazing practices, (3) loss of wet prairies of the interbeach zone due to invasion by woodlands of trembling aspen as a result of fire suppression (Wheeler et al. 1992a), and (4) the conversion of prairie to crop land and the impacts of altered water regime on fens at the base of beach ridges. The cumulative effects of increased timber harvesting activities upon forest biodiversity within this section are being evaluated by the Minnesota Department of Natural Resources.
Privately owned prairies are being managed as part of the Prairie Bank program. Some prairie lands are under county management, but many of these have no formal protection.
Virtually nothing remains of the extensive landscape of tallgrass prairie and wet prairie that occupied this section before settlement. Prairie preserves, as seen at Malmberg Prairie, are threatened by the effects of surrounding agriculture, notably by the accumulation of soil blowing from fields and being caught by vegetation, thus stimulating invasion by exotic plant species.
BOUNDARIES: I chose to take this section to the southern limit of the reworked till instead of stopping at the boundary between reworked till and clay lake plain. This is an arbitrary decision because the clay lake plain and reworked till both supported extensive areas of wet prairie. The prairies on the reworked till have been reported to be more similar floristically to prairies further to the south in Subsection II.1 (Upper Minnesota River Country). Although rainfall and minimum temperatures differ significantly from the southern to northern edges of the section, investigations of the prairie flora in Minnesota and adjacent eastern North Dakota have not noted any major floristic changes to justify further subdivision of the section from north to south (Wright and Bailey 1980, Redmann 1972, Cosby 1965, Küchler 1964, Buell and Facey 1960, Rudd 1951).