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• • • The soils within the community are mainly mollisols (aquolls). They range in texture from silty clays to fine sands and are somewhat poorly drained to very poorly drained. Impermeable subsurface layers impede soil drainage on some sites, and a thin layer of muck may be present at the ground surface on Wet Prairies in seepage areas. Most soils are calcareous. Salt concentrations (sulfates of calcium and magnesium) high enough to influence the species composition of the community are present in the soils of Wet Prairies along the western edge of Minnesota, primarily in the Agassiz Lacustrine Plain. On drier sites Wet Prairie often grades into wet -mesic stands of Mesic Prairie; on wet sites it often grades into Wet Meadow. Mesic Prairie, Wet Prairie, and Wet Meadow do not have well - defined floristic boundaries, and sometimes are difficult to separate from one - another in the field when they occur together. Shrub cover increases in Wet Prairie northward, and in the northern part of the community's range Wet Prairie often grades into Wet Brush- Prairie. Wet Prairie in southeastern Minnesota is distinctive from that elsewhere in the state, containing several species with restricted distribution. Floristic diversity is low in Wet Prairies in western Minnesota, but distinctive species assemblages occur there in association with saline sites. Dry Prairie /Oak Savanna Dry Prairies are upland grasslands dominated by prairie species, with <10% tree cover and <50% shrub cover, where the substrate is composed of sand or gravel (sometimes with a thin organic surface layer), or any texture on steep slopes. (Some examples may occur on sandy soils in temporarily flooded areas). Dry Prairie is a type of Upland Prairie, which occurs primarily in the prairie zone, with scattered occurrences in the deciduous forest - woodland zone. These communities are dominated by grasses. The tall grasses, big bluestem (Andropogon gerardii) and Indiangrass (Sorghastrum nutans), are the major dominants on moist sites. Prairie dropseed (Sporobolus heterolepis) is common on both dry and moist sites. Forbs typically are abundant (but subdominant to the grasses) and may have high local diversity. Forb species composition varies with site moisture, although some forb species occur on almost all sites, moist or dry. Several low shrub or sub -shrub species are common on Upland Prairie; the most characteristic is leadplant (Amorpha canescens). Taller brush and trees are absent or scattered, however brush or woodland areas may be interspersed with prairie, usually in association with topographic and aquatic features that provide protection from fire. The most important cause of variation in species composition in prairie communities is variation in soil moisture. The local soil moisture regime is determined by slope, aspect, proximity to the water table, and soil texture. On a regional scale, variation in species composition is primarily caused by climatic variation (i.e., the westward decline in precipitation and northward decline in temperature in Minnesota). Upland Prairies occur on a range of landforms in the prairie zone, from nearly flat glacial lakeplains to steep morainic slopes. In the deciduous forest - woodland zone, prairies occur on droughty, level outwash areas and steep south- and west - facing slopes. The pre- European settlement distribution of prairie was related to the interaction of local fire frequency with growth rates of woody species: where conditions were favorable for rapid growth, more frequent fires were necessary to maintain prairie over savanna, woodland, or forest. Fragmentation of Upland Prairie since European settlement has reduced fire frequency throughout the prairie and deciduous forest - woodland zones, and most prairie remnants have more brush and trees than were present in the past. The Preserve Conservation Development - Restoration and Management Plan 16