Cofrin Center for Biodiversity

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Introduction

Savannas are semi-wooded grasslands that are transitional between open grasslands and woodlands. The characteristic habitat consists of scattered trees in a matrix of grasses and herbs, creating a "park-like" environment. In North America the dominant trees in many savannas are oaks, leading to the more specific term "oak savanna."

Oak Savannah Variations include "scrub savanna," which may contain dense thickets of oak sprouts, "oak openings," which occur locally within forested landscapes, and "brush prairies," where oak sprouts are often hidden by tall grasses.

At the time of European settlement in the 1800's oak savannas extended over large portions of Minnesota, Iowa, Missouri, Illinois, Wisconsin, Michigan, Indiana, and Ohio, covering approximately 11-13 million hectares (Nuzzo 1986). Today, only about 0.02% of the original area of oak savannas remains, and many of the remnants are degraded, threatened, or atypical of presettlement savannas. Chaplin et al. (1999) describe oak savannas of the Midwest as one of the world's most endangered ecosystems.

Fire has played a significant role in generating and maintaining savannas in the Northern Lake States. Bur Oak (Quercus macrocarpa), an important savanna tree in this region, is capable of regenerating from underground "grubs" after fire or severe drought. Frequent burning leads to fires of low intensity, which rarely kill canopy trees but maintain an open understory. Higher intensity fires stimulate sprouting by species like Bur Oak, leading to thickets of young woody plants among the grasses. Settlement in the 1800's was accompanied by widespread replacement of oak savannas by farmland. Cessation of fires caused a further conversion of remnant savannas to oak forests (Grimm 1984).

More photos of Oak Savannas

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