U.S. Fish and Wildlife Service
Savanna ecosystems refer to a variety of related plant communities consisting of open-grown trees found scattered or in small groves, with a grassy understory. Savanna ecosystems are typically transitional communities found between forests and a grasslands. The term savanna is used in the Midwest to describe an ecosystem bordered by the prairies of the west and the deciduous forest of the east, a mosaic maintained by frequent fires and possibly by large ungulates. Botanists typically use tree density to distinguish between prairie ecosystems, savanna ecosystems, and forest ecosystems. Commonly occurring plants within Midwestern savannas include little blue stem, coreopsis, and wild lupine. Natural processes important in the formation and maintenance of Midwestern savannas include: fire, climate, topography, soil, and large herbivores.
Midwest oak savannas are among the world's most threatened communities (Anderson, et al. 1993). Prior to European settlement, oak savanna covered approximately 2732 million acres of the Midwest (Nuzzo 1985). This same author indicates that in 1985, only 113 sites (2,607 acres) of high-quality oak savanna remained. Nationwide, over 99 percent of the original savanna has been lost to agriculture, fire suppression, and over grazing (Nuzzo 1986), and Midwest oak savannas are among the rarest and most endangered ecosystems in the Nation (Noss et al. 1995). Development has destroyed, fragmented, and disrupted natural processes needed to maintain quality savanna ecosystems.
To learn more about Midwest savannas, visit:
Oak Savanna Communities (Adobe pdf document, 596 KB)
In the Midwest, the term savanna has a relatively narrow definition. Here it is generally used to describe an ecosystem that was historically part of a larger complex bordered by the prairies of the west and the deciduous forests of the east. This complex was a mosaic of plant community types that represented a continuum from prairie to forest. Savannas were the communities in the middle of this continuum. The mosaic was maintained by frequent fires and possibly by large ungulates such as bison and elk. Oaks were the dominant trees, hence the term oak savanna.
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