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<br />aspect, proximity to the water table, and soil texture. On a regional scale, variation in <br />species composition is primarily caused by climatic variation (i.e., the westward <br />decline in precipitation and northward decline in temperature in Minnesota). <br /> <br />Upland prairies occur on a range of landforms in the prairie zone, from nearly flat <br />glacial lake plains to steep morainal slopes. In the deciduous forest-woodland zone, <br />prairies occur on droughty, level outwash areas and steep south- and west-facing <br />slopes. The pre-European settlement distribution of prairie was related to the <br />interaction of local fire frequency with growth rates of woody species: where conditions <br />were favorable for rapid growth, more frequent fires were necessary to maintain prairie <br />over savanna, woodland, or forest. Fragmentation of upland prairie since European <br />settlement has reduced fire frequency throughout the prairie and deciduous forest- <br />woodland zones, and most prairie remnants have more brush and trees than were <br />present in the past. The introduced grass Kentucky bluegrass (Poa pratensis) is <br />present at most sites; it is a function of the site's disturbance history. <br /> <br />Forbs are abundant (but usually subdominant to grasses) and have high local <br />diversity. Forb species-composition also varies locally with soil moisture. There is <br />greater regional variation among forbs than among grasses. Common forb species <br />include purple prairie-clover (Da/ea purpureum), white prairie-clover (P. candidum), <br />ground-plum (Astragalus crassicarpus), prairie-turnip (Psoralea esculenta), rough <br />blazing-star (Liatris aspera), Canada goldenrod (Solidago canadensis), stiff goldenrod <br />(S. rigida), Missouri goldenrod (S. missouriensis), prairie thistle (Cirsium fIodmanii), <br />smooth aster (Aster laevis), stiff sunflower (Helianthus rigidus), Maximilian sunflower <br />(H. maximiliani), smooth rattlesnake-root (Prenanthes racemosa), white sage <br />(Artemisia ludoviciana), wood lily (Lilium philadelphicum), white camas (Zigadenus <br />elegans), heart-leaved alexanders (Zizia aptera), prairie larkspur (Delphinium <br />virescens), downy phlox (Phlox pilosa), hoary puccoon (Lithospermum canescens), tall <br />cinquefoil (Potentilla arguta), alum-root (Heuchera richardsonii), wood-betony <br />(Pedicularis canadensis), northern bedstraw (Galium boreale), prairie bird-foot violet <br />(Viola pedatifida), oval-leaved milkweed (Asclepias ovalifolia), and showy milkweed (A. <br />speciosa). Purple coneflower (Echinacea angustifolia) is common on drier sites in the <br />western part of the community's range. Leadplant, prairie rose, sand cherry, wolfberry, <br />and prairie willow are common low-shrub or sub-shrub species. Fragrant false indigo <br />is common on moister sites. Trees and taller brush often occur along the margins of <br />wetlands adjacent to mesic prairies <br /> <br />City of Elk River, MN - Natural Resouce Inventory <br />Bonestroo Natural Resources, September 2004 <br /> <br />35 <br />