Northern Prairie Wildlife Research Center
DISCUSSION: Section XI gets its name from the vegetation, which is a mosaic of [trembling] aspen groves, prairies, and wetlands located between the extensive Lake Agassiz peatlands to the east and the agricultural lands of the flat clay plain to the west. This mosaic of vegetation probably occurs because drought and fire are frequent enough to prevent succession to forest but not frequent enough to eliminate trees. The section is a low-relief landscape of ground moraine further subdued from inundations by Glacial Lake Agassiz. Low dunes, beach ridges, and wet swales form the western edge and provide a barrier that reduces both fire frequency and intensity, resulting in increased dominance by shrubs, trembling aspen, and balsam poplar. Farther east, low ridges of water-reworked till are surrounded by herbaceous wetlands.
The section is transitional between flat agricultural lands to the west and extensive peatlands to the east. It is much more extensive to the north and west in the Canadian Provinces of Manitoba, Saskatchewan, and Alberta, where it is also viewed as transitional between tallgrass prairie to the south and boreal forest to the north.
Section XI has no subsections.
ELEVATION: 900 to 1,250 feet (274 to 381 m).
AREA: 4,052 square miles (10,500 sq km).
CLIMATE: Similar to that of the northern edge of Section I to the west. Total annual precipitation is 20 to 22 inches; 40 percent of this falls during the growing season (Hargrave 1992). Only 11 to 14 percent of the annual precipitation falls from November through February (estimated from Wendland et al. 1992). Annual average snowfall is 40 to 44 inches (Wendland et al. 1992). This low amount of winter precipitation, combined with extreme cold and desiccating wind, probably accounts for both increased spring fires and severe stress on most shrub and tree species, resulting in the open woodland vegetation of the section. Growing season is approximately 120 days; last spring frosts are in late May, and first fall frosts are in mid-September. Extreme minimum temperatures are -40½F to -45½F (Reinke et al. 1993) or colder. Climate within the parklands has been generally stable for the last 2,000 years (Janssen 1992).
BEDROCK GEOLOGY: Bedrock is overlain by 100 to 400 feet of calcareous glacial drift. The glacial drift is underlain by several types of bedrock; in the western portion Ordovician dolomite, sandstone, and shale are the most common, along with Cretaceous shale, sandstone, and clay; and Jurassic shale, dolomite, and gypsum (Morey et al. 1982). East of these sedimentary rocks are Precambrian undifferentiated granites and metamorphosed mafic to intermediate volcanic rocks.
LANDFORMS: The section consists of two distinct parts: the sand lake plain to the west and the water-reworked moraines to the east. Portions of the sand lake plain are level, but there are also small dunes and series of low beach ridges and swales. The beach ridges can be gravelly, and the swales often contain abundant cobbles and boulders (Cummins and Grigal 1981). The reworked moraines generally have reduced relief resulting from the reworking by wave action of Glacial Lake Agassiz; the topography is that of an undulating plain broken by large areas of marsh, wet meadow, and shrub swamp.
LAKES AND STREAMS: Few Lakes. The major river is the Roseau, which flows north into Canada (Hargrave 1992). The drainage system is poorly developed. Rivers and streams meander extensively, and flooding occurs regularly on the flat topography.
SOILS: Soils of the sand lake plain range from sands to gravels. Calcareous and saline seeps occur at the bases of sand dunes and beach ridges, often resulting in interesting vegetation communities. Soils are classified as Entisols (Psamments and Aquents), Histosols (Hemists), and Mollisols (Aquolls) (USDA Soil Conservation Service 1967, Cummins and Grigal 1981). On the reworked moraines, soils are generally loamy. The till often contains large boulders that restrict land use (Cummins and Grigal 1981). The till is partially mantled with lacustrine sands, silts, and clays.
|Figure 36.Subsection XI: Twin Lakes Wildlife Management Area, Kittson County, Minnesota. Stunted bur oak grow on a gravelly beach ridge of Glacial Lake Agassiz. Bur oak dominates the driest sites as long as fires occur frequently. Trembling aspen is more common on more mesic sites and replaces bur oak when fires are eliminated. Minnesota Department of Natural Resources photo by C.K. Converse.|
PRESETTLEMENT VEGETATION: Marschner (1974) mapped the vegetation as a mosaic of prairie, wet prairie (including marsh), brush prairie, and aspen-oak land. The prairie was generally tallgrass prairie, with mixed-grass prairie on the drier beach ridges and dunes. Wet prairie occurred in the flats and swales between the beach ridges. On the till in the eastern part of the section, much of what was mapped as wet prairie was probably rich fen, dominated by sedges rather than by prairie grasses. Bearing tree data suggest a higher proportion of the landscape was dominated by shrubs rather than trees.
At present, willows are the predominant woody species. Common shrubs include Betula glandulifera (bog birch), Potentilla fruticosa (shrubby cinquefoil), Corylus spp. (hazel), and Amelanchier spp. (Saskatoon). Prairie species are those of the tallgrass prairie, Andropogon gerardi (big bluestem), Sorghastrum nutans (Indian grass), Sporobolus heterolepis (dropseed), Calamagrostis spp. (bluejoint), and Agropyron trachycaulum (slender wheatgrass), rather than those of the mixed-grass parklands of Canada, such as Agropyron smithii (western wheatgrass), Koeleria macrantha (Junegrass), and Schizachyrium scoparium (little bluestem).
Ewing's (1924) study on succession within the brush prairie of the aspen parkland was conducted south of Section XI, as presently delineated, and may not be applicable. At Ewing's study site, brush prairie was concentrated in areas of small wetlands and irregular topography, where fire frequency and intensity, as well as desiccation by strong winds, were reduced. Ewing considered brush prairie to be a successional community tending toward trembling-aspen-dominated forest or parkland.
Aspen-oak land, typically called aspen woodland or parkland, was dominated by trembling aspen, with scattered bur oak. The woodland was also concentrated where there was increased fire protection. Stream valleys and wetlands often provided the necessary fire protection for woodland establishment. Although most of the trembling aspen is found on ground moraine, the western boundary of the aspen is found on the sandy and gravelly beach ridges of the Red River Valley part of Glacial Lake Agassiz.
NATURAL DISTURBANCE: Fire was important for maintaining the open brush prairies and aspen woodlands here, as were the desiccating winds characteristic of the prairie. Buffalo destroyed trembling aspen by breaking the stems and rubbing the bark (Bird 1961); snowshow rabbits also girdled young aspen (Moss 1932). Buffalo also exposed bare soil by overgrazing and wallowing, which allowed shrubs to establish (Bird 1961). Burrowing mammals, such as ground squirrels, pocket gophers, badgers, fox, and coyote, exposed bare soils for shrub establishment. Sharp-tailed grouse, pine grosbeak, and other birds distributed shrub seeds.
PRESENT VEGETATION AND LAND USE: In the north, large areas have been drained and farmed. Grazing, gravel mining, and agriculture are the primary land uses. The remaining unfarmed lands have become much more dominated by shrubs or trees as the result of fire suppression.
Plant communities well represented in this section include: aspen brush prairie, aspen openings, dry prairie, lowland hardwood forest, mesic brush prairie, mesic prairie, wet brush prairie, wet prairie, wet meadow, calcareous seepage fen, and rich fen.
RARE PLANT COMMUNITIES: All prairie and fen communities listed in PRESENT VEGETATION AND LAND USE.
RARE PLANTS: Androsace septentrionalis var. puberulenta (northern androsace), Astragalus neglectus (Cooper's milk-vetch), Platanthera praeclara (western prairie fringed orchid).
RARE ANIMALS: Ammodramus caudacutus (sharp-tailed sparrow), Coturnicops noveboracensis (yellow rail), Grus canadensis (sandhill crane), Limosa fedoa (marbled godwit).
NATURAL AREAS: State Natural Areas: Lake Bronson Prairie Parkland; Other: Halma Prairie, Norway Dunes.
|Figure 37.Subsection XI: The flat, poorly drained landscape of the Aspen Parkland was originally a mosaic of prairie, wet prairie, marsh, brush prairie, and aspen-oak land. Wet brush prairie dominates most of the landscape shown, with trembling aspen in the background. Willows are the dominant shrubs in the brush prairies, but bog birch, shrubby cinquefoil, hazel, and Saskatoon (Amelancier sp.) are also common. Minnesota Department of Natural Resources photo by B.C. Delaney.|
PUBLIC LAND MANAGERS: Wildlife Management Area: Beaches, Belgium, Caribou, Crane, Devil's Playground, East Park, Eckvoll, Elm Lake, Emardville, Emerson, Erskine, Espelie, Florian, Gervais, Halma Swamp, Higginbothan, Huot, Jacksnipe, Larix, Marcoux, Nereson, Oriniak, Pelan, Pembina, Polk, Polonia, Roseau River, Skull Lake, Thief Lake, Twin Lakes; State Parks: Lake Bronson, Old Mill; Other: Agassiz National Wildlife Refuge.
CONSERVATION CONCERNS: Aspen has become much more prevalent since the time of settlement; fire suppression has allowed "brush prairie" to become aspen parklands. Prescribed burns or timber harvesting may be required to reduce aspen dominance, where this is desirable.
The dynamic association of wetland and upland plant communities found on the parklands is best maintained at a landscape level. Full representation of the parkland ecosystem can only be accomplished by protecting multiple patches of each community type at a scale dictated by the patch size of the constituent communities. A recent acquisition of 6,900 acres of parkland, combined with existing wildlife management areas, provides an opportunity for long-term management of large land blocks, essential for maintaining the dynamic flux of prairie and woodland.
BOUNDARY JUSTIFICATIONS: Section I to the west is flat clay lake plain and supports more tallgrass prairie than Section XI. Subsection X.12 to the east is very poorly drained peatland. Section III to the south has more irregular topography (largely end moraines) and a warmer climate.