Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin
SUBSECTION III.3. Anoka Sand Plain
DISCUSSION: Subsection consists of flat, sandy lake plain and outwash plain along the Mississippi River. Recent mapping suggests that much of the sand plain, once thought to be fluvial, is probably lacustrine in origin (Meyer et al. 1993, Meyer 1993, Meyer and Hobbs 1993).
SUB-SUBSECTIONS: None.
ELEVATION: 750 to 1,050 feet (229 to 320 m).
AREA: 1,960 square miles (5,079 sq km).
STATES: Minnesota.
CLIMATE: Total annual precipitation ranges from 27 inches in the west to 29 inches in the east; growing-season precipitation ranges from 12 to 13 inches (Hargrave 1992). Annual average snowfall is 48 to 52 inches (Wendland et al. 1992). Growing season length ranges from approximately 136 to 156 days; the longest growing season is in the south. Extreme minimum temperature is approximately -40½F (Reinke et al. 1993).
BEDROCK GEOLOGY: Bedrock is locally exposed in the St. Cloud area and in the St. Croix River Valley. Surface glacial deposits are usually less than 200 feet thick (Olsen and Mossler 1982). The subsection is underlain by Cambrian and Ordovician dolomite, sandstone, and shale (Morey 1976).
LANDFORMS: The major landform is a broad outwash plain, which contains small dunes, kettle lakes, and tunnel valleys, but there are small inclusions of ground moraine (Wright 1972). Parts of the sand plain are considered to be a lake plain, known as Glacial Lake Ann (Keen and Shane 1990). Low moraines are locally exposed above the outwash, and there are small dune features (Wright 1972). Ice-block depressions and southwest-trending tunnel valleys also occur on the plain.
LAKES AND STREAMS: There are 38 lakes larger than 160 acres; approximately 3 percent of the subsection's surface is covered by water. Peatlands occupy the linear depressions of many tunnel valleys.
SOILS: Soils are derived primarily from the fine sands of the outwash plain; most of these sandy soils are droughty, upland soils (Psamments), but there are organic soils (Hemists) in the ice block depressions and tunnel valleys as well as poorly drained prairie soils (Aquolls) along the Mississippi River (Cummins and Grigal 1981). About 70 to 80 percent of the soils are well drained or excessively well drained sands, and another 20 percent are very poorly drained (University of Minnesota et al. 1980b).
PRESETTLEMENT VEGETATION: The predominant vegetation on the droughty uplands was oak barrens and openings; characteristic trees included small and poorly formed bur oak and northern pin oak (Kratz and Jensen 1983). Jack pine was only locally present along the northern edge of the subsection. Brushland characterized large areas of the sand plain. Upland prairie formed a narrow band along the Mississippi River, as did areas of flood-plain forest (Marschner 1974). Bogs, wet prairies, and swamp forest occupied depressions in the sand plain. The largest area of wet prairie occurred in eastern Anoka County, along several strings of ice-block depressions and tunnel valleys. Small patches of maple-basswood forest also occurred on fire-protected sites.
NATURAL DISTURBANCE: Both fire and drought were probably important influences on the vegetation of the sand plain. Drought was found to cause mortality for two of the dominant species of the oak barrens and savannas, northern pin oak and bur oak, with northern pin oak appearing to be more susceptible (Faber-Langendoen and Tester 1993). During severe periods of drought, vegetation cover was greatly reduced on parts of the sand plain, resulting in eolian erosion and sand dune movement; this was documented for the Lake Ann portion of the Anoka Sand Plain ca. 7,400, 5,800, and 4,900 years B.P. (Keen and Shane 1990).
PRESENT VEGETATION AND LAND USE: Sod and vegetable crops are grown extensively on drained peat and muck areas (University of Minnesota et al. 1980). Urban development is expanding rapidly into the subsection. Wheeler et al. (1992b) found species associated with oak openings and oak barrens to be abundant in the sand plain.
RARE PLANT COMMUNITIES: Dry oak savanna, dry prairie, and dry oak forest originally covered much of this landscape; high-quality remnants of these plant communities persist, along with high-quality examples of rich fens, wet meadows, flood-plain forest, emergent marsh, mixed hardwood swamps, tamarack swamps, shrub swamps, and some upland maple-basswood forests.
RARE PLANTS: Aristida tuberculosa (sea-beach needlegrass), Besseya bullii (kitten-tails), Parthenium integrifolium (wild quinine), Polygala cruciata (cross milkwort), Rotala ramosior (tooth-cup), Scleria triglomerata (tall nut-rush), Xyris torta (twisted yellow-eyed grass).
RARE ANIMALS: Grus canadensis (sandhill crane), Emydoidea blandingii (Blanding's turtle).
NATURAL AREAS: State Natural Areas: Black Dog Preserve, Boot Lake, Clear Lake, Helen Allison Savanna; Other: Cedar Creek Natural History Area, Anoka Sandplain (both identified as critical landscapes for biodiversity protection), MacDougall Homestead, Poplar Lake Open Space, Sandhill Crane Meadows, Springbrook Nature Center, Talahi Park; The Nature Conservancy Preserves: Cold Spring Heron Colony Preserve, Helen Allison Savanna.
PUBLIC LAND MANAGERS: Wildlife Management Areas: Athens, Bethel, Carlos Avery, Crane Meadow, Crooked Road, Fremont, Kunkel, Lamprey Pass, Marget Lake, Michaelson Farm, Mountain, Rice Area Sportsmen Club, Rice-Skunk, Sand Prairie, Santiago, Spectacle Lake, Suconnix; State Parks: Fort Snelling, Lake Maria; State Forests: Sand Dunes; Regional Parks: Anoka County Riverfront, Bunker Hills, Coon Rapids Dam, Crow Hassan, Elm Creek, Grass-Vadnais (Snail Lake), Hidden Falls-Crosby, Long Lake, Martin-Island-Linwood Lake, Minnehaha, Mississippi Gorge, Rum River Central; Park Reserves: Diamond Lake, Lake Hiawatha, Lyndon-Cedarglade, Powderhorn Lake; County Parks: Goose Lake County Wetlands, Ham Lake, Neds Lake; Municipal Parks: Girard Lake, Minnehaha; Other: Fort Snelling Military Reservation, John Anderson Memorial Park, Minnesota Valley National Wildlife Refuge, Mississippi National River and Recreation Area, Sherburne National Wildlife Refuge.
CONSERVATION CONCERNS: Suburban sprawl along the Twin Cities-St. Cloud corridor is resulting in major loss of remaining forests, prairies, and wetlands. Planned development is needed.
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| Figure 13.—Subsection III.3: Helen Allison Savanna Scientific and Natural Area, Anoka County, Minnesota. Allison Savanna is in one of numerous areas of dunes scattered within the Anoka sand plain. Savannas of bur and northern pin oak grow on the droughty outwash and lacustrine sands of the plain. Blowouts and other openings on the sand soils support prairie grasses and other pioneer plant species. Minnesota Department of Natural Resources photo by B.C. Delaney. |
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