University of Minnesota
University of Minnesota
College of Biological Sciences
Oak savanna.Pulsatilla nuttaliana blooming amid red oak leaves.Prairie grasses against a blue sky.

Sand prairie and savanna

Some of the best remnants of Sand Savanna found in Minnesota occur at Cedar Creek and vicinity. They are found on old dune topography which was historically considered unfit for farming. The gently rolling topography of dry crests and moist swales contains an abundance of native grasses and forbs. They have never been plowed, but some pasturing has occurred in the past. Many of the tracts south of Fish Lake have been part of an experimental Burn Program since 1964. Additional Burn Units at the south end of North South Lab Road (NSLR) were added in the 1980s. Helen Allison Savanna is a beautiful 80 acre tract of sand savanna situated off the SE corner of Cedar Creek. It is owned by The Nature Conservancy (TNC) and administered by the Minnesota DNR as a Scientific and Natural Area (SNA). The gently rolling landscape contains scattered open grown Bur Oaks (Quercus macrocarpa) within a diverse matrix of native prairie grasses and forbs. It has never been plowed, only lightly pastured, and since 1964 has received periodic burns.

Unburned Plots in Cedar Creek burn areas illustrate the impact of fire on savanna communities. In them one finds open-grown bur oak with wide-spreading, lichen-covered limbs (evidence of a more open community in the past); but the open canopy and the absence of fire has allowed these compartments to ‘brush up’ with hazel, sumac, blackberry, and pin oak saplings eliminating most reminders of their savanna past. These patches of Overgrown Savanna can be contrasted with the Scrub Oak Woodland found in Burn Units that have been subjected to infrequent but intense burns. (See section on Upland Woods for more detailed descriptions of these two community types.)

More than 100 fields have been abandoned from agricultural use and a few of the oldest are now respectable Sand Prairie with a rather impressive prairie flora. Those that are part of the Burn Program are rather xeric in appearance with bare soil and cryptogams (mosses, lichens, fungi) between the native bunchgrasses. The best examples of sand prairie are found in the southern half of Cedar Creek, and especially in the Burn Units. Unburned fields, even if having a respectable prairie component, have a more continuous cover of Poa pratensis (Kentucky Bluegrass). Several of the older fields in the North Section of Cedar Creek are dominated by Schizachyrium scoparium (Little Bluestem) but are not as rich floristically as those in the south. There simply is not the prairie seed inocula from surrounding savannas. (See section on Old Fields & Disturbed Land.)


While Quercus macrocarpa (Bur Oak) is the dominant and characteristic tree of sand savanna, Quercus ellipsoidalis (Northern Pin Oak) also figures prominently. Both trees have fire tolerant properties. Bur Oak has a thick corky bark protecting its cambium layer, and Northern Pin Oak, though thin-barked, resprouts vigorously after being burned. An occasional Fraxinus pennsylvanica (Green Ash) survives if established in a particularly sandy area, but few other species of trees are found. The Prunus (Cherry) and Amelanchier (Juneberry) species common in Dry Oak Woodland are lost after the first few burns. Photo Gallery of Hardwood Trees

Woody shrubs

Corylus americana (Hazelnut) is the most common woody shrub in savanna and Dry Oak Woodland. Although frequently top-killed during spring burns, this clonal species vigorously resprouts and is very difficult to eradicate. Rhus glabra (Smooth Sumac) is another fairly common shrub of savanna and field edges that is difficult to eliminate by burning. Rosa arkansana (Prairie Rose), Amorpha canescens (Leadplant), Salix humilis (Prairie Willow), and Prunus pumila (Sand Cherry) are less common but characteristic low-growing woody perennials of sand prairie and savanna. Photo Gallery of Upland Shrubs

Native prairie grasses

Savanna openings and sand prairie groundlayer are dominated by native perennial grasses. Most common are Schizachyrium scoparium (Little Bluestem), Andropogon gerardii (Big Bluestem) and Sorghastrum nutans (Indian Grass). Koeleria macrantha (June Grass), Sporobolus cryptandrus (Sand Dropseed), Stipa spartea (Porcupine Grass), and Aristida tuberculosa (Sea Beach Triple-awn Grass; an annual) are common on xeric upland sites. Leptoloma cognatum (False Witch Grass) became established in the 1980s, and this aggressive native tumble-grass is becoming increasingly abundant. Common short-statured grasses include Eragrostis spectabilis (Purple Love Grass) and the Panic Grasses (Panicum oligosanthes, P. praecocius, P. perlongum). Grasses of lesser prominence include Panicum virgatum (Switch Grass), Elymus canadensis (Nodding Wild Rye), and Bouteloua hirsuta (Hairy Grama). Poa pratensis (Kentucky Bluegrass), an introduced perennial, and Carex foenea are always present but only of significance in unburned grasslands. Photo Gallery of Prairie Grasses

Prairie forbs

It’s impossible to provide anywhere near a complete listing of prairie forbs, suffice it to mention here some of the more characteristic species. Among the first species to flower in the spring are Pulsatilla nuttalliana (Pasque Flower), Viola pedatifida (Prairie Violet), Ranunculus rhomboideus (Early Buttercup), Lithospermum caroliniense (Hairy Puccoon), and L. canescens (Hoary Puccoon). The early summer show begins with the flowering of Penstemon grandiflora (Large-flowered Beardtongue), Tradescantia occidentalis (Spiderwort), Delphinium virescens (Prairie Larkspur), Geum triflorum (Prairie Smoke), and Rosa arkansana (Prairie Rose). Perhaps, the most spectacular mid-summer species is Asclepias tuberosa (Butterfly Weed). The showy orange flowers of this milkweed attracts thousands of Hairstreak Butterflies (Satyrium edwardsii). Late summer species include Helianthus rigidus (Red-stem Sunflower), Liatris aspera (Rough Blazing Star) and representatives of the large genera Aster (Asters), and Solidago (Goldenrods). During August migratory Monarch Butterflies fill the air with orange and black as they search for lavendar blazing stars on which to nectar in preparation for their long flight south. Some prairie legumes and other prairie forbs are imaged here. Photo Gallery of Prairie Forbs

Special features of sand prairie and savanna

Prairie Swales

A striking feature of the savanna and prairie region of Cedar Creek is the number and quality of small wet swales found there. Several good examples occur on Helen Allison Savanna and in the Burn Units south of Fish Lake. Among the forbs occurring here one may find the orchids Calopogon tuberosus, Pogonia ophioglossoides, Platanthera lacera, P. hyperborea, and Malaxis unifolia. Though these species do not appear every year. More regular in occurrence are Krigia biflora, Lobelia spicata, Hypoxis hirsuta, Polygala sanguinea, Polygala cruciata, Cicuta maculata, Pedicularis canadensis, Viola sagittata, Viola lanceolata, and Castilleja coccinea. Characteristic graminoids of many of these swales are Carex haydenii and Carex buxbaumii. Spartina pectinata (Prairie Cord Grass) is found in a couple of swales. Swale rims are frequently bounded by the common Calamagrostis canadensis (Canada Blue Joint), but these may hide the uncommon sedge Scleria triglomerata. Such prairie swales are probably one of the most endangered plant communities in Minnesota, and every effort should be made to protect those few remaining. (See section on Wet Meadows.) Photo Gallery of Prairie Swales


Several natural occurring blowouts are present in the sand prairies and savannas of Cedar Creek. Calamovilfa longifolia (Sand Reed Grass) is a dune-stabilizing tall grass found atop sandy ridges at the perimeter of blowouts. Aristida tuberculosa and Panicum commonsianum are two prominent graminoids. Hudsonia tomentosa (False Heather), Petalostemum villosum (Hairy Prairie Clover), and Polygonella articulata (Coast Jointweed) are three noteworthy forbs. Geaster sp (Earthstars) are a conspicuous puffball fungus. Blowouts are also an excellent arena for observing the behavior of various insects. One sees Tiger Beetles (Cicindelidae), Spider Wasps (Pompilidae), and Velvet Ants (Mutillidae) scurrying about searching for prey or nesting sites. Digger Wasps (Sphecidae) commonly use blowouts for digging burrows to provision with prey. Photo Gallery of Blowouts

Noteworthy reptiles of sand prairie

No poisonous snakes occur at Cedar Creek. However, a first encounter with a bullsnake in sand prairie may generate second thoughts. This snake sometimes reaches 2 meters in length and is mottled in ‘coffee and cream’. It may coil up and shake its tail in the dry grass raising the specter of an impending rattlesnake strike. Equally interesting, but not nearly as threatening, is an encounter with a hognose snake. Both eastern and western species occur here. When startled, this snake flares its neck cobra-like. If this bluff doesn’t work, it will roll over on its back and play dead. If you turn the snake upright, it reportedly turns over again, insisting that it is dead.