Oak savanna

An oak savanna is a type of savanna, or lightly forested grassland, where oaks (Quercus spp.) are the dominant trees. These savannas were maintained historically through wildfires set by lightning or humans, grazing, low precipitation, and/or poor soil.

Although there are pockets of oak savanna almost anywhere in North America where oaks are present, there are three major oak savanna areas: 1) California, Washington and Oregon in the west; 2) Southwestern United States and Mexico; and 3) the prairie/forest border of the Midwest. There are also small areas of oak savannas in other parts of the world. (See also Eastern savannas of the United States for information on pine savannas of the U.S. South.)

The oak savannas of the Midwestern United States form a transition zone between the arid Great Plains to the west and the moist broadleaf and mixed forests to the east. Oak savannas are found in a wide belt from northern Minnesota and southern Wisconsin, down through Iowa, Illinois, northern and central Missouri, eastern Kansas, and central Oklahoma to north-central Texas, with isolated pockets further east around the Great Lakes including Ontario. The bur oak (Quercus macrocarpa) is the dominant species in northern oak savannas, although black oak (Quercus velutina), white oak (Quercus alba), and Hill's oak (Quercus ellipsoidalis)are sometimes present. The dominant tree in the south is usually the black oak (Quercus velutina), although the chinquapin oak (Quercus muhlenbergii), post oak (Quercus stellata), and black-jack oak (Quercus marilandica) are also common. The flora of the herbaceous layer generally consists of species associated with tallgrass prairies, both grasses and flowering plants, although some woodland species may be present. There are also a few species that are unique to oak savannas. Oak savannas, because of their mixture of grassland, woodland, and unique savanna species, typically have a higher plant diversity than grasslands and woodlands combined.

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