OAK SAVANNA
WHAT IS AN OAK SAVANNNA?
Oak savannas are described as having less than 50% canopy cover from Burr and White oak, with a wide variety of grasses and wildflowers growing underneath. Under and between the oaks grow a mixture of sun-loving woodland plants, and true savanna plants that prefer dappled sunlight.
The openness of the oak savanna is usually maintained by fire, and of the major tree species in the Midwest the oaks are uniquely fire resistant. Over time, these scattered oaks develop into large trees and each open-grown tree receives maximum sunlight and there is little competition between individuals. Oak savannas generally develop in drier areas, on south- or southwest-facing slopes or other areas where many other tree species are unable to compete.
The oak savanna was once one of the most common vegetation types in the Midwest but is today highly endangered. Intact oak savannas are now one of the rarest plant communities on earth. However, many degraded oak savannas still remain and can be restored. The detailed information in this web site shows the way.
Savanna Oak Foundation, Inc.
For more in-depth information about oak savannas check out the Savanna Oak Foundation, Inc., website. A nonprofit foundation dedicated to the oak savanna community. The Foundation was established by Tom and Kathie Brock of Madison, Wisconsin, who manage Pleasant Valley Conservancy, a Wisconsin State Natural Area, which has extensive restored oak savannas.
WHAT TO LOOK FOR
Oak savannas can be identified by their scattered open-grown oak trees with an open understory. The oak trees have a large, full canopy with many strong lower limbs that stretch outward rather than upward, and often short, stocky trunks. Oak trees alone do not make oak savanna ecosystems, though the trees themselves are historic. Some open-grown oak trees have been dated back to 1780! An oak savanna ecosystem will also have wildflowers such as Yellow Pimpernel, Elm leaved Goldenrod, Horse Gentian, and Woodland Boneset to name a few.
Savanna Indicator Species
The list in the table below was developed by a group of experts; Brian Bader, Ted Cochrane, Eric Epstein, Rich Henderson, Randy Hoffman, and Mark Leach for the 1995 Midwest Oak Savanna Conference and was collated by Brian Pruka, an ecologist at the University of Wisconsin-Madison.
Some of these unique savanna species have been called “savanna indicator species.” The presence of these light-dependent under-story species indicates a recent closure of the canopy. Wooded sites containing sufficient populations of these species, therefore, have the highest potential for recovery if properly managed through the use of prescribed burns, mechanical canopy thinning, and other techniques.
In his review of oak savanna communities of Wisconsin, Richard Henderson presented a smaller of characteristic savanna specialists for Wisconsin, some of which are also listed above.
These lists, should be useful to preservationists in southern Wisconsin, and in the neighboring regions.
Oak Savanna Indicator Species by Rich Henderson
Oak Savanna Indicator Species by Brian Pruka
WHERE TO LOOK
Historically oak savannas were found on upland soils in areas subjected to frequent fires. Today, seek out wide spreading oaks in lightly grazed pastures and look for native grasses and wildflowers, or look for wide spreading oak trees. Oak savannas are commonly choked with Prickly Ash, brambles, and invasive species such as Honeysuckle and Common Buckthorn. These can hide the open growth character of the oak trees.
WHAT HAPPENED TO THE OAK SAVANNAS?
Prior to European settlement, WI had an estimated 5.5 million acres of oak savanna. Today less than 1% remain, and those that do represent one of the most threatened ecosystems on Earth. Many oak savannas were lost to land conversion for row crops, logging of trees for timber, and development.
With the suppression of regular fire, invasive species such as buckthorn, honeysuckle, and garlic mustard have invaded acres of savanna habitat, and heavy grazing and conversion to pasture has led to the loss of the native diversity associated with a healthy oak savanna.
CONSERVATION NEEDS
Rare plants and species of greatest conservation need found in oak savannas.
Birds: Red headed Woodpecker, Brown thrasher, Field sparrow
Mammals: Woodland vole, Franklin’s ground squirrel
Reptiles and Amphibians: Blanding’s turtle, Prairie racerunner
Plants: Purple milkweed, Wild Hyacinth
HOW TO MANAGE
A comprehensive look into oak cover type from the WI Department of Natural Resources Silviculture Handbook.