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• • • Oak savannas are upland plant communities with 10 -70% cover by trees (of which <25% is conifer), where >30% of non -tree cover is herbaceous (prairie- dominated) and where oaks comprise >30% of the tree cover. The soil is composed of sand or gravel (sometimes with a thin organic surface layer), or any texture on steep slopes. This dry to dry -mesic community is most common in the deciduous forest - woodland zone, but also occurs sporadically throughout the prairie zone. The principal trees are bur oaks and northern pin oaks, but black oaks are also common in the southeast. Northwards, quaking aspens become more frequent in the community. The stature and spacing of trees is somewhat variable, reflecting differences in soils, topography, and climate, factors that strongly affect local droughtiness and fire frequency. Small, gnarly, open -grown trees are most common, although in moister spots, or in heavier soils, larger trees are sometimes more common. Tree spacing ranges from sparsely and evenly distributed to strongly clumped in moderately dense patches. Shrub cover is variable as well. The species composition of the shrub layer depends somewhat upon soil characteristics. Oak grubs and chokecherries are common on all soil types. On sandier soils, prairie willows (Salix humilis), New Jersey tea (Ceanothus americanus), American hazelnuts (Corylus americana), sand cherries (Prunus pumila), and juneberries (Amelanchier spp.) are usually present. Wolfberries (Symphoricarpos occidentalis) are commoner on heavier soils. Dry Oak Savanna occurs on the same kinds of landforms as Dry Prairie, except for bedrock bluffs. Correspondingly, substrates range from excessively- drained to well- drained, sand to loam soils. The presence of savanna rather than prairie indicates a lower fire frequency or intensity (or both) than in prairie. Dry Oak Savanna requires less frequent fire than Mesic Savanna for maintenance. However, in the complete absence of fire woodland will eventually replace Dry Oak Savanna. Grazing and browsing animals may also have had a role in the maintenance of Dry Oak Savanna. Because Dry Oak Savanna occurs on sites that are not as suitable for cultivation as Mesic Savanna sites, and because succession in the absence of fire is not as rapid, more examples remain of Dry Oak Savanna than of Mesic Oak Savanna. Oak Forest Oak Forest is an upland deciduous forest with >30% oaks, and is common and widespread throughout much of Minnesota. It is most common on dry to dry -mesic sites in the deciduous forest - woodland zone but also occurs occasionally in the southern and western parts of the conifer - hardwood zone, and in stream valleys in the prairie zone. At least 30% of the tree canopy in an Oak Forest is made up of oak trees. Most often aspen, paper birch, or black cherry trees make up the remainder of the canopy. The actual composition of the community, however, varies considerably in response to variation in soil moisture, soil type, fire history, and climate. The driest stands of Oak Forest are dominated by northern pin oaks and white oaks, with black oaks, shagbark hickories, and sometimes bur oaks important in southeastern Minnesota. These stands occur on nutrient -poor, well- drained sandy soils on outwash plains, river terraces, and beach ridges. They have relatively open canopies, with between 70% and 80% cover. The canopy height is usually between 13 and 17 meters. Because of the open canopy, the shrub layer is often very dense. American hazel dominates the shrub layer, which also often contains gray -bark dogwood, blueberries, and blackberries. Some of the more common ground layer species are the sedge (Carex pensylvanica), wild geranium The Preserve Conservation Development - Restoration and Management Plan 18