We have defined an oak savanna as "a plant community with scattered 'open-grown' oaks." Other terms sometimes used are "oak opening" and "oak barren." In contrast to an oak forest, which has a closed canopy (approaching 100%), the savanna canopy ranges from about 10% to 60%. Although at one time oak savanna was one of the most common vegetation types in southern Wisconsin and throughout the Midwest, today it is exceedingly rare. One estimate by researchers at the Wisconsin Department of Natural Resources is that only about 0.01% of the original oak savanna still remains.

Redrawn here is part of a map of the original vegetation of Dane County constructed by Robert Ellarson from the records of the original land surveyors. As seen, the dominant vegetation of western Dane County, the Driftless area of the county, was oak savanna. The most common oaks recorded by the surveyors were bur and white oak, with small amounts of red oak. In sandy areas, black oak was present, and in wetter areas swamp white oak

Open-grown oaks A characteristic of the savanna is the presence of trees that have grown in the open, away from other trees. Trees that have developed in an oak woods generally lack lower branches, a growth form that indicates development in lower light regimes. In contrast, savanna oaks have large lower branches, an indication that they have developed without competition from nearby trees. The presence in the habitat of open-grown oaks is a good indication of a savanna. Even if the habitat was later heavily invaded by other trees, the open-grown characteristic of the oaks stands out. Large areas of oak savannas shown on Ellarson's map still exist, especially on the south-facing slopes and ridge tops. The existence of these open-grown oaks at Pleasant Valley Conservancy was a principal reason why restoration work was undertaken.

A principal activity in oak savanna restoration is the "daylighting" of oaks, removing trees that are crowding out the oaks. The bur oak in the above photo is a good example. This oak, whose age is estimated at about 200 years, was virtually invisible when restoration work began, being completed crowded with elm, cherry, and buckthorn. Once daylighted, the lower branches could thrive again, and the tree has been saved for posterity. Note also the other open-grown oaks farther up the hill. The open-grown oak is a handsome specimen which has often survived from the period before European settlement.

The Importance of Fire Probably the most common reason why the oak savanna has disappeared is because of lack of fire. This is a fire-controlled vegetation. The oaks themselves are fire-resistant, whereas weedy trees such as walnut, elm, maple, and ash are not. Protection from fire became an established practice of the U.S. Forest Service, as well as the Wisconsin Conservation Commission (the forerunner of the Department of Natural Resources). Although fire is a real danger in the coniferous forests of northern Wisconsin, not so for southern oaks. We know now that it was wrong to prevent fires in the southern oaks. Oaks do not suffer from the disastrous crown fires that rage through the coniferous forest. Except under unusual circumstances, fire in an oak woods is confined to the ground, to the leaf litter. Oak leaves are unusually susceptible to fire. When they burn, weedy woody vegetation such as prickly ash, buckthorn, and honeysuckle is killed, thus keeping the woods open. An open woods encourages the growth of grasses and flowering plants, which are the glories of an oak savanna.

Ideas have changed completely about fire in the woods. Without fire, restoration of an oak savanna is difficult, expensive, and generally unsuccessful. Research in Wisconsin, Illinois, Minnesota, Missouri, and Iowa has shown clearly that fire is not the enemy of the oak forest, but its friend.

Photo gallery of some typical savanna plants

Principles of Oak Savanna Restoration

Although material on oak savanna restoration is found in many places in this web site, an overview of how this sort of restoration work should be accomplished is covered on this link. The history of oak savanna restoration at Pleasant Valley Conservancy is given at this link. As discussed briefly there, the cost of oak savanna restoration is substantial, much higher than the cost of prairie restoration. Although some government agencies provide support to private landowners for savanna restoration, the amount per acre provided by their grants is much lower than the actual cost. Thus, withouth private funds, significant savanna restoration is difficult to carry out.

Oak Savanna Locations at Pleasant Valley Conservancy The savanna habitats at Pleasant Valley are in the areas where fire would have been most common. These include the south-facing slope and the part of the ridge top that is nearest to the south slope. Because the south-facing slope receives intense sunlight, it is much drier (more xeric) than the north-facing slope. Historically, the whole south slope was prairie, and fire would have spread quickly up into the savannas. The graph below shows data from a transect that was run from Pleasant Valley Road on the south side uphill to the ridge top and down the north side to County Highway F. Digital photos taken with a fish-eye lens were used to measure the openness of the canopy. The principal savanna area was is on the upper south slope and the ridge top, where many large open-grown bur oaks are present. In the savanna zone, the canopy ranges from about 25 to 70% cover. The oak woods, where there are no open-grown oaks, has canopy cover around 90%.

	Some Plant Species in Oak Savanna Areas at Pleasant Valley Conservancy. This represents aggregate data from the years 2002-2007. Not all species were in every savanna unit.
At Pleasant Valley Conservancy, we have oak savannas of two types, bur oak and white oak. The bur oak savanna is predominantly on the top of the ridge, on the dolomite cap. The white oak savanna is mainly on the Jordan sandstone just below the dolomite. As a result of restoration, the full magnificence of the oak savanna can be appreciated. A hike along the upper ridge trail takes one through the heart of our oak savanna. Because the open canopy means that light can get to the forest floor, the oak savanna has a wide diversity of grasses and other flowering plants. Because the habitat is so variable, there is more diversity in savanna than there is in prairie. In 2004, 184 species of flowering plants were identified in the oak savanna areas of Pleasant Valley Conservancy. The list to the right, an aggregate of years 2002 to 2007, has 275 species. However, not all species were present in all savanna areas. For photos of many of the species listed, go to the species checklist. Important savanna grasses include silky rye (Elymus villosus), bottle brush grass (Elymus hystrix), ear-leaved brome (Bromus latiglumis), and riverbank or woodland rye (Elymus riparius). Pennsylvania sedge (Carex pensylvanica) is very characteristic of oak savanna. The most interesting flowering plant in our savanna is purple milkweed (Asclepias purpurascens), a state endangered species which only appeared after restoration and controlled burning had begun. Other flowering plants include yellow giant hyssop (Agastache nepetoides), a plant of special concern in Wisconsin; shooting star (Dodecatheon meadii); upland boneset (Eupatorium sessilifolium), a plant considered threatened in Wisconsin; purple (or woodland) joe pye weed (Eupatorium purpureum); Lion's foot (Prenanthes alba); elm-leaved goldenrod (Solidago ulmifolia); and yellow pimpernel (Taenidia integerrima). A number of the listed species are found only rarely or not at all in prairie or in oak woods. They seem to thrive in the savanna habitat. Follow this link for a a list which shows which savanna species are also present in prairies, woodlands, or wetlands. Click to download a paper we gave at the 2004 North American Prairie Conference on Oak Savanna Restoration (pdf).	Latin name Common name Achillea millefolium Yarrow Actaea alba White baneberry Actaea rubra Red baneberry Agastache nepetoides Yellow giant hyssop Agastache scrophulariaefolia Purple giant hyssop Agrimonia gryposepala Tall agrimony Allium canadense Wild onion Allium cernuum Nodding wild onion Ambrosia artemisiifolia Common ragweed Ambrosia trifida Giant ragweed Amelanchier arborea Juneberry Amorpha canescens Lead-plant Amphicarpaea bracteata Hog peanut Anaphalis margaritacea Pearly everlasting Andropogon gerardii Big bluestem Anemone canadensis Meadow anemone Anemone cylindrica Thimbleweed Anemone quinquefolia Wood anemone Anemone virginiana Tall anemone Antennaria neglecta Field pussytoes Antennaria plantaginifolia Plantain-leaved pussytoes Apocynum sibiricum Clasping dogbane Aquilegia canadensis Wild columbine Arabis canadensis Sickle pod Arabis divaricarpa Rock cress Aralia racemosa Spikenard Arctium minus Common burdock Arenaria stricta Sandwort Arnoglossum atriplicifolia Pale Indian plantain Asclepias exaltata Poke milkweed Asclepias purpurascens Purple milkweed Asclepias syriaca Common milkweed Asclepias verticillata Whorled milkweed Asparagus officinalis Asparagus Aster ericoides Heath aster Aster laevis Smooth blue aster Aster lateriflorus Calico aster Aster novae-angliae New England aster Aster oolentangiensis Sky-blue aster Aster pilosus Hairy aster Aster prenanthoides Crooked aster Aster sagittifolius Arrow-leaved aster Aster sericeus Silky aster Astragalus canadensis Canadian milkvetch Aureolaria grandiflora Yellow false foxglove Baptisia lactea White wild indigo Berberis vulgaris European barberry Bidens sp. Beggar's tick Bouteloua curtipendula Side oats grama Brassica sp Mustard Bromus inermis Smooth brome Bromus kalmii Prairie brome Bromus latiglumis Ear-leaved brome Calamagrostis canadensis Blue-joint grass Campanula americana Tall bellflower Campanula rapunculoides European bellflower Campanula rotundifolia Harebell Carex blanda Common wood sedge Carex eburnii Bristle-leaf sedge Carex pensylvanica Pennsylvania sedge Carya ovata Shagbark hickory Ceanothus americanus New Jersey tea Celtis occidentalis Hackberry Circaea lutetiana canadensis Enchanter's nightshade Cirsium altissimum Woodland thistle Cirsium arvense Canada thistle Cirsium discolor Pasture thistle Cirsium vulgare Bull thistle Clematis virginiana Virgins bower Coeloglossum viride Frog orchid Convolvulus arvensis Field bindweed Conyza canadensis Horseweed Coreopsis palmata Prairie tickseed Cornus racemosa Gray dogwood Corylus americana American hazelnut Crepis tectorum Hawk's beard Cryptotaenia canadensis Honewort Cuscuta cuspidata Dodder Cypripedium calceolus pubescens Large yellow lady-slipper Dactylis glomerata Orchard grass Dalea purpureum Purple prairie clover Daucus carota Queen Anne's lace Desmodium canadense Showy tick-trefoil Desmodium glutinosum Pointed tick-trefoil Desmodium illinoense Illinois tick-trefoil Dodecatheon meadia Shooting star Echinacea pallida Pale purple coneflower Echinocystis lobata Wild cucumber Elaeagnus umbellata Autumn olive Elymus canadensis Canada wild rye Elymus hystrix Bottlebrush grass Elymus riparius Riverbank wild rye Elymus villosus Silky wild rye Elymus virginicus Virginia wild rye Erechtites hieracifolia Burnweed Erechtites hieracifolia Fireweed Erigeron philadelphicus Marsh fleabane Erigeron pulchellus Robin's plantain Erigeron strigosus Daisy fleabane Eryngium yuccifolium Rattlesnake master Erysimum cheiranthoides Wormseed-mustard Eupatorium altissimum Tall boneset Eupatorium maculatum Spotted joe-pye weed Eupatorium perfoliatum Common boneset Eupatorium purpureum Purple joe-pye weed Eupatorium rugosum White snakeroot Eupatorium sessilifolium Upland boneset Euphorbia corollata Flowering spurge Festuca subverticillata Nodding fescue Fragaria virginiana Wild strawberry Galearis spectabilis Showy orchis Galium aparine Annual bedstraw Galium boreale Northern bedstraw Galium concinnum Shining bedstraw Galium lanceolatum Lance-leaved bedstraw Galium tinctorium Stiff bedstraw Galium triflorum Sweet-scented bedstraw Gentiana alba Cream gentian Gentianella quinquefolia Stiff gentian Geranium maculatum Wild geranium Geum canadense White avens Geum triflorum Prairie smoke Hackelia virginiana Stickseed Hasteola suaveolens Sweet Indian plantain Helenium autumnale Sneezeweed Helianthemum canadense Common rockrose Helianthus decapetalus Pale sunflower Helianthus divaricatus Woodland sunflower Helianthus grosseserratus Saw-tooth sunflower Helianthus strumosus Pale-leaved woodland sunflower Helianthus tuberosus Jerusalem artichoke Heliopsis helianthoides Ox-eye sunflower Heuchera richardsonii Prairie alum-root Hieracium aurantiacum Orange hawkweed Hieracium kalmii Canada hawkweed Hieracium longipilum Prairie hawkweed Hippuris vulgaris Mare's tail Hypericum perforatum Common St. John's-wort Hypericum punctatum Dotted St. John's wort Hypoxis hirsuta Yellow star-grass Kuhnia eupatorioides False boneset Lactuca biennis Tall blue lettuce Lactuca canadensis Tall lettuce Leonurus cardiaca Motherwort Lespedeza capitata Round-headed bush clover Leucanthemum vulgare Ox-eye daisy Liatris aspera Rough blazing star Liatris cylindracea Dwarf blazing star Lobelia cardinalis Cardinal flower Lobelia inflata Indian tobacco Lobelia siphilitica Great blue lobelia Lobelia spicata Pale spiked lobelia Lotus corniculata Birdsfoot trefoil Lupinus perennis Wild lupine Lysimachia ciliata Fringed loosestrife Lysimachia quadrifolia Whorled loosestrife Medicago lupulina Black medick Melilotus alba White sweet clover Melilotus officinalis Yellow sweet clover Monarda fistulosa Wild bergamot Muhlenbergia spp Muhly grass Nepeta cataria Catnip Oenothera biennis Common evening-primrose Orobanche uniflora Cancer root Osmorhiza claytoni Hairy sweet cicely Osmorhiza longistylis Smooth sweet cicely Oxalis stricta Yellow wood-sorrel Oxalis violacea Violet wood-sorrel Panicum latifolium Broad-leaved panic-grass Panicum oligosanthes Small-seed panic grass Panicum virgatum Switch grass Parthenium integrifolium Wild quinine Parthenocissus quinquefolia Virginia creeper Pastinaca sativa Wild parsnip Penstemon digitalis Penstemon Phalaris arundinacea Reed canary-grass Phryma leptostachya Lopseed Poa spp Blue-grass Podophyllum peltatum May-apple Polemonium reptans Jacob's ladder Polygala sanguinea Field milkwort Polygala senega Seneca snakeroot Polygonatum biflorum Smooth Solomon's seal Potentilla argentea Silvery cinquefoil Potentilla arguta Prairie cinquefoil Potentilla norvegica Rough cinquefoil Potentilla recta Sulfur cinquefoil Potentilla simplex Old-field cinquefoil Prenanthes alba Lion's foot Prunella sp. Self-heal Prunus americana Wild plum Prunus serotina Wild black cherry Prunus virginiana Choke cherry Pyrus malus Apple Quercus alba White oak Quercus macrocarpa Bur oak Quercus velutina Black oak Ranunculus abortivus Small-flowered buttercup Ranunculus acris Tall buttercup Ranunculus fascicularis Early buttercup Ranunculus recurvatus Hooked buttercup Ratibida pinnata Yellow coneflower Rhus glabra Smooth sumac Ribes americanum Black currant Ribes spp Gooseberry Rosa sp. Rose Rudbeckia hirta Black-eyed Susan Rudbeckia triloba Brown-eyed Susan Sambucus canadensis Elderberry Sanguinaria canadensis Bloodroot Sanicula gregaria Black snakeroot Saponaria officinalis Bouncing bet Schizachyrium scoparium Little bluestem Scirpus cyperinus Wool-grass Scrophularia lanceolata Early figwort Scrophularia marilandica Late figwort Scutellaria parvula Small skullcap Senecio pauperculus Balsam ragwort Senecio plattensis Prairie ragwort Setaria faberi Giant foxtail Silene spp. Campion Silene vulgaris Bladder campion Silphium integrifolium Rosinweed Silphium laciniatum Compass plant Silphium perfoliatum Cup plant Sisyrinchium campestre Blue-eyed grass Smilacina racemosa False Solomon's seal Smilax herbacea Carrion flower Solanum carolinense Horse nettle Solanum dulcamara Deadly nightshade Solidago canadensis Common goldenrod Solidago flexicaulis Zig-zag goldenrod Solidago gigantea Giant goldenrod Solidago juncea Early goldenrod Solidago missouriensis Missouri goldenrod Solidago nemoralis Gray goldenrod Solidago ptarmicoides Stiff aster Solidago rigida Stiff goldenrod Solidago speciosa Showy goldenrod Solidago ulmifolia Elm-leaved goldenrod Sonchus spp Sow thistle Sorghastrum nutans Indian grass Sporobolus heterolepis Prairie dropseed Stachys palustris Hedge-nettle Stellaria media Common chickweed Taenidia integerrima Yellow pimpernel Taraxacum officinale Common dandelion Teucrium canadense Germander Thalictrum dasycarpum Purple meadow-rue Thalictrum dioicum Early meadow-rue Thlaspi arvense Penny cress Torilis japonica Hedge parsley Toxicodendron radicans Poison ivy Tradescantia ohiensis Common spiderwort Tragopogon porrifolius Salsify Trifolium pratense Red clover Trifolium repens White clover Trillium grandiflorum Large-flowered trillium Triodanis perfoliata Venus looking glass Triosteum perfoliatum Tinker's weed Urtica sp. Nettle Uvularia grandiflora Bellwort Verbascum thapsus Mullein Verbena hastata Blue vervain Verbena stricta Hoary vervain Verbena urticifolia White vervain Veronicastrum virginicum Culver's root Viburnum lentago Nannyberry Viola canadensis Tall white violet Viola pedata Bird's foot violet Viola pedatifida Prairie violet Viola soraria Door-yard violet Vitis sp. Wild grape Zanthoxylum americanum Prickly ash Zizia aurea Golden Alexander
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