Introduction

Eastern Prairie–Forest Transition

Midwestern savannas occupied a transitional area between eastern deciduous forest and tallgrass prairie. These savannas were part of the eastern prairie–forest transition (Curtis 1959; Anderson 1983; Nuzzo 1986) that extended as a broad arc along the eastern edge of the northern mixed and tallgrass prairies from the Canadian provinces of Alberta, Saskatchewan, and Manitoba southward into Texas (Figure 9.1). We discuss deep-soil savannas (also called black soil, mesic, and tallgrass savannas and barrens) that occurred in the glaciated landscapes of Minnesota, southern Michigan and Wisconsin, Ohio, Indiana, and Illinois. These deep-soil savannas occurred on sites with fine-textured soils, where growth of trees was not severely limited by edaphic factors. Savannas with shallow soil profiles over bedrock, and those with sandy soil with low fertility and water-holding capacity, are considered in other chapters (see Chapters 8 and 21). Essentially all of the original Midwest, mesic, deep-soil savanna vegetation was lost to fire protection and agricultural activities, including overgrazing (Curtis 1959; Nuzzo 1986). These savannas are among the rarest natural vegetation types in the world.

Savannas of the Midwest occupied the eastern edge of a large, triangular-shaped grassland that extended from the Rocky Mountains into the Midwest (Risser et al. 1981; Anderson 1990). The grassland narrowed eastward, producing the well-known prairie peninsula (Transeau 1935).