Cofrin Center for Biodiversity

oak savanna

Ecology

The dominant plant species of oak savannas vary with gradients of soil moisture and disturbance. Drier sites tend to be dominated by black oak (Quercus velutina), Pennsylvania sedge (Carex pensylvanica), Hill's oak (Q. ellipsoidalis), hazelnut (Corylus sp.) and other types of oaks (Haney and Apfelbaum 1994). Savannas on more mesic sites are characterized by bur oak (Q. macrocarpa), white oak (Q. alba), and perhaps northern red oak (Q. rubra) or swamp white oak (Q. bicolor). Well-drained sandy soils deposited by glacial outwash or beach formations are typical of sand savannas in northwestern Indiana, northern Illinois, southwestern Michigan, northern Wisconsin, northern Michigan, and central Minnesota (Nuzzo 1986, Haney and Apfelbaum 1994). Fires apparently were frequent in these dry sand savannas, because canopy cover will approach 100% in the absence of fire for about 50 years (Haney and Apfelbaum 1994). Jack pine (Pinus banksiana) often is a major component of northern sand savannas.

In places where fires were frequent, small oaks were inhibited from reaching tree size, so shrub communities predominated. Nitrogen limitation in sand savanna soils limits tree growth and is also is believed to be important in maintianing the the open park-like environment (Tilman 1984).

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