SAVANNA

Dry-Mesic Savanna

Oak savannas were prominent among the natural landscapes of the Upper Midwest, occupying a broad transitional zone between two major biomes: the Eastern Deciduous Forest and the Tallgrass Prairie. The Midwest oak savanna can be characterized as an ecosystem where the most conspicuous plants are trees, but the most important species are the grasses. (“Mesic” is a term that means that the area occupies the middle portion of the hydrological range, i.e., neither very dry nor very wet.)

For thousands of years, landscape-scale fires favored the growth of plant species adapted to a regimen of routine burns; as a result, trees in a savanna are widely spaced, generally producing a canopy cover of about 10 to 50 percent. Savannas are, therefore, places of relatively abundant sunshine. Most of our savanna areas were quickly settled (and thereby altered) when European settlers arrived in this area during the early nineteenth century. In the absence of frequent fire, many savannas have closed in, becoming shadier and more humid over time.