Designing an Oak Savanna

Savanna Conservation Practice Information Sheet (IS-MO643)

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   IS-MO643: Designing an Oak Savanna  (PDF, 709 KB)

What is an Oak Savanna?

Although definitions vary, one common definition is: an oak savanna is a plant community with scattered "open-grown" fire tolerant oak trees. Other terms for these savannas are "oak openings" and "barrens". In contrast to a forest, which has a closed canopy, the oak savanna canopy ranges from about 10% to 50%. In such a habitat, the ground layer receives sun and shade, which permits growth of a wide diversity of grasses and flowering plants. There is usually enough sun to the ground to permit the growth of typical prairie species, such as big and little bluestem grass, and many goldenrods and asters.

Oak savannas have their own characteristic and complex communities of ground-layer grasses, flowering plants, and shrubs. A few examples of flowering plants of the savanna include white wild indigo (Baptisia leucantha), lead plant (Amorpha canescens), purple coneflower (Echinacea purpurea), round-headed bush clover (Lespedeza capitata) and blue aster (Aster anomalis). Common savanna shrubs are New Jersey tea (Ceonothus americanus), hazelnut (Corylus americana), and pasture rose (Rosa carolina) .

Early settlers to the Midwest described the park-like setting of oak savannas. At one time these savannas and open woodlands were common throughout the landscape of MAn oak savanna is a transitional between tall grass prairie in the west and deciduous forest in the east. Although there is a continuum from prairie to savanna to forest, oak savannas are still considered a distinct vegetation type.

An oak savanna is a fire-controlled vegetation community. With settlement, fires were eliminated and the savanna changed into denser forested landscapes, losing the characteristic open tree canopy with grass and forb understory. Grazing by bison and elk may also have helped keep the savanna open. When settlement eliminated these animals and fire from Missouri, most of the savanna acreage experienced an invasion by dense shrub and tree growth.

Oak savannas are now considered one of the most threatened plant communities in the Midwest and among the most threatened in the world. Less than 0.01% of the original savanna community remains.

What Should an Oak Savanna Look Like?

Savanna design for a new undeveloped field should take into account management objectives, topography, soils, presettlement history and cost. This practice should only be applied on fields with transitional or woodland derived soils that comprise at least 50 percent of the field primarily in upland landscapes.

Species selection for trees

A minimum of two native tree species should be used from an approved list for savanna species. Normally, bur oak should be a predominant tree species in the northern 2/3 of Missouri and post oak in the southern 1/3 of the state.

Tree density

In oak savannas, plant trees at the rate of 25 trees per planted acre at no less than 30-foot spacing. Tree cover should be at least 10 percent but no more than 50 percent cover of any field.

Tree layout

If possible plant the trees in clusters or blocks rather than evenly spaced across a field. This will allow for some parts of the savanna to be more open (greater spacing or "openings") than other parts and create a more natural appearance.

Historically trees in oak savannas were more common on south and west slopes, along ridge lines and knolls, and in protected draws or ravines. Well, drained, shallow soil sites and those with gently rolling topographies that carried fire well, characteristically had more open (wider spacing) tree cover. Tree cover was more closed (closer spacing) on moist, deep soil, highly dissected, or poorly drained sites where fire usually became a less intense or frequent factor.

Use topographic features and soil mapping units to assist in determining where tree cover would be more appropriate.

Tree Planting Stock

Tree planting stock should be at least 3 feet tall with at least ½ inch caliper. The large initial size is required to facilitate their protection from fire, and reduce competition from grass. It is recommended that container grown air root pruned stock be used because these seedlings have thick fibrous roots as opposed to a large taproot, which may be difficult to plant.

Seedlings should be planted by hand or using an auger. Soil should be firmly packed around seedling roots.

Other important criteria to consider for savanna development and design are planting stock care, planting dates and weed control.

Understory Planting

Grasses: Plant a total of 5 pounds PLS of any combination of at least 4 species (see list below). Switchgrass, big bluestem, Indian grass, and eastern gamagrass should be limited to not more than ¼ pound PLS per acre. All other grass species should be planted at not less than 1 pound PLS per acre.

No more than ¼ lb PLS/ac
Big bluestem Andropogon gerardii
Indian grass Sorghastrum nutans
Switchgrass Panicum virgatum
Eastern gamagrass Tripsacum dactyloides

No more than ¼ lb PLS/ac No less than 1 lb PLS/ac
Canada wildrye Elymus canadensis
Little bluestem Schizachyrium scoparium
Virginia wildrye Elymus virginicus
Prairie dropseed Sporobolus heterolepis
Sideoats grama Bouteloua curtipendula

Forbs (Wildflowers): A minimum of 10 forb species should be selected with the mixture being a minimum of one-half pound PLS per acre with no single species exceeding 25% by weight of the forb mixture. Some examples of suitable species are listed below.

Management

At a minimum, vegetation should be controlled in a three-foot wide band around each tree for at least three years with an approved herbicide, weed mat, or tillage.

Fire is essential for the management of savanna communities. Prescribed burning is an essential management practice, but should not be applied to the areas planted in trees until it is determined that the trees have developed sufficient fire resistance. Trees may need to reach 3 to 6 inches diameter at breast height before becoming fire resistant.

For planted habitats prescribed burning should be conducted no earlier than the beginning of the third growing season in areas devoid of trees. Burning in the late fall or winter will encourage the native forbs and reduce damage to trees.

See Printable Format PDF for a Savanna Design and Layout Example.

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