Designing an Oak Savanna
Designing an Oak Savanna
Savanna Conservation Practice Information
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IS-MO643: Designing an Oak Savanna
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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
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
Suggested Tree Species:
||Swamp white oak
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.
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
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
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.
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
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.
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.