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Oak Savanna Ecosystem

Oak Savanna
Oak Savanna
© TNC

An intact oak savanna in Ohio is a community of oaks and other less common tree species forming an incomplete canopy over an understory of prairie species, typically grasses. These plant communities are characterized by sparse (10-50%) canopies of bur oak (Quercus macrocarpa) and white oak (Quercus alba) with an herbaceous layer which includes mesic prairie species such as big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium) purple coneflower (Echinacea purpurea), prairie dock (Silphium terebinthinaceum), stiff goldenrod (Solidago rigida), gray-headed coneflower (Ratibida pinnata)and Indian grass (Sorghastrum nutans).        

Generally, these are areas with isolated groves of trees found on gently sloping to nearly flat terrain. Soils are typically moderately drained to well drained and deep. Natural processes important in the formation of Midwest oak savanna include fire, climate, topography, soil, and grazing by large herbivores. Where this occurs, oak savanna is typically viewed as a transitional community between forest and grassland.                                                                                                                                                                           
The oak savannas and open oak woodlands of the Midwest are among the world’s most threatened communities. At one time, oak savannas may have covered some 27 to 32 million acres in the Midwest. By 1985, the number of relatively high-quality stands had been reduced to about 0.02 percent of the original amount. Most are highly degraded as a result of timber harvesting, overgrazing, agricultural use, fragmentation, and fire suppression. Thousands of acres of this oak savanna ecological community originally existed in the Big Darby Creek watershed. As in other areas throughout the Midwest, oak savannas in the Darby watershed have undergone a massive decline.

Restoration of oak savanna has been successful in central Ohio and other regions. Restoration specialists have found that when savanna remnants are actively managed, dormant seed banks can assist in reestablishment of both the understory and canopy layers of this community. Management on the approximately 18 acre privately owned W. Pearl King Savanna in Madison County, has been successful in maintaining one of the few remaining natural occurrences of oak savanna in central Ohio.

The values of maintaining this ecological community in the Darby watershed are many. Most savannas are small relics and historical remnants of a once common community that evolved in association with fire and grazing in the Darby plains. As such they serve as a natural seed source and potential targets for restoration. Although each surviving grove is typically small, the total acreage in the Darby watershed, while unknown, could be considerable.

Sources: Faber-Langendoen, D. (ed.) 1999. International Classification of Ecological Communities: Terrestrial Vegetation of the Midwestern United States, Ohio Portion. The Nature Conservancy, Midwest Conservation Science Department, Minneapolis, Minnesota. 109 pp. and appendices.

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