An oak savanna
is a type of savanna
, or lightly-forested grassland, with oaks
as the dominant tree species.
California oak savannas
Edwards Plateau savanna
The Edwards Plateau
of central Texas is distinguished by juniper
-oak savannas, underlain by medium and short grasslands.
Midwestern oak savannas
The oak savannas of the Midwestern United States form a transition zone between the Great Plains
to the west and the broadleaf and mixed forests
to the east (the location of the precolumbian eastern savannas
). Oak savannas are found in a wide belt from northern Minnesota
, down through Iowa
, northern and central Missouri
, eastern Kansas
, and central Oklahoma
to north-central Texas
, with isolated pockets further east around the Great Lakes
. The World Wildlife Fund
divides the oak savannas into two ecoregions
, the Upper Midwest forest-savanna transition
and the Central forest-grasslands transition
, distinguished by the predominant of tree species.
The dominant tree is usually the black oak (Quercus velutina), although in some areas the bur oak (Quercus macrocarpa) or chinquapin oak (Quercus muhlenbergii) predominate. The dominant grass species is typically the little bluestem (Schizachyrium scoparium).
Before European settlement, the oak savanna ecosystem was part of a fire ecology
. Fires, set by lightning or Native Americans, ensured that the savanna areas did not turn into forests
. Only trees with a high tolerance for fire, principaly certain oak species, were able to survive. On sandy soils, black oak (Quercus velutina)
predominated. On rich soils bur oak (Quercus macrocarpa)
was the major tree in central North America. These savanna areas provided habitat for a many grazing animals, including bison, elk and deer.
European settlers cleared much of the savanna for agricultural use. In addition, they suppressed the fire cycle. Thus surviving pockets of savanna typically became less like savannas and more like forests or thickets. Many oak savanna plant and animal species became extinct or rare.
In the 1970s, conservationist began to try to restore and preserve these surviving pockets of savanna.
Surviving pockets of oak savanna can be found throughout the historical range of this ecosystem. Many are protected and maintained by government bodies or non-profit
organizations such as The Nature Conservancy
. Examples include the Neal Smith Wildlife Refuge
in Prairie City, Iowa
, the Indiana Dunes National Lakeshore
, and in Ontario
, Pinery Provincial Park
on Lake Huron
. The University of Wisconsin-Madison Arboretum
is also restoring two oak savanna areas.
Oregon oak savanna