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For information on Wisconsin's natural communities, contact:
Ryan O'Connor
Natural Heritage Inventory Ecologist

Barrens and Savannas communities of Wisconsin

Both barrens and savannas are plant communities that have a partial tree canopy and open areas dominated by herbaceous vegetation, with barrens tending to occur in drier, sandier landscapes. Both types of communities are dependent on fire for their formation and maintenance.

Fires have burned on Wisconsin barrens and savannas for thousands of years. Prior to Euro-American settlement, some fires were caused by lightning. Others were set by Native Americans to maintain game habitat, drive game, and enhance fruit and berry crops. Historically, behavior of fire was greatly influenced by topography and soil factors. Natural wildfires usually produce a complex mosaic of burned and unburned patches depending on fire intensity, topography, soil moisture and local weather.

In the absence of fire, barrens and savannas proceed through successional stages from more open to closed-canopy forests. While barrens range from open to moderately closed, the open condition is now the rarest of the potential successional stages, because fire suppression has allowed woody vegetation to take over in most barrens communities. Similarly, oak savanna now shares equal billing with tallgrass prairie as the most threatened plant community in the Midwest and among the most threatened in the world. Intact examples of oak savanna vegetation are now so rare that less than 500 acres are thought to exist in a state similar to Euro-American settlement. This is less than 0.01% of the estimated 5.5 million acres of savanna historically found in Wisconsin.

Barrens occur on sandy soils and are dominated by grasses, low shrubs, small trees, and scattered large trees. Major types include pine barrens in northern and central Wisconsin and oak barrens in southern and west-central Wisconsin. Minor communities include sand barrens, bracken grassland, and Great Lakes barrens, an uncommon community associated with dunes or sandy ridges along Lake Superior and Lake Michigan.

Barrens are rare and imperiled globally. In North America, pine barrens exist primarily in the Midwest and along the east coast. Wisconsin has one of the best opportunities in North America for preserving and restoring this community. Significant opportunities for oak barrens protection and restoration also exist in Wisconsin, but most of these are at a relatively small scale of several hundred acres or less. Likewise, intact Great Lakes barrens are found only along undeveloped Great Lakes shorelines, primarily in Wisconsin and Michigan.

In pine barrens, the most common tree is jack pine, but red pine may also be present. Hill's oak and bur oak may be present as scrubs or as a scattering of larger trees. In oak barrens, black oak or Hill's oak are common, while jack pine is absent or in low abundance. The understory is composed of grasses, sedges, and forbs, many of them associated with dry prairies.

Historically, Wisconsin's most extensive barrens were in large areas of sandy glacial deposits, including outwash plains, lakebeds, and outwash terraces along rivers. Geographically, areas of extensive barrens were concentrated in the Northeast Sands, Northern Highlands, Northwest Sands and Central Sands Ecological Landscapes. They were also found on outwash terraces along the Lower Wisconsin, Lower Chippewa and Mississippi Rivers.

In the Midwest, savanna is generally used to describe an ecosystem that was historically part of a larger complex bordered by the prairies of the west and the deciduous forests of the east. This complex was a mosaic of plant community types that represented a continuum from prairie to forest. Savannas, which includes the community types oak opening and oak woodland, were the communities in the middle of this continuum. The mosaic was maintained by frequent fires and possibly by large ungulates such as elk. Oaks were the dominant trees, hence the term oak savanna.

Savannas grade into both prairie and forest. Curtis (1959) defined savanna as having no less than one tree per acre and no more than a 50% tree canopy. The more wooded part of the prairie-forest complex (i.e., woodlands with 50%-80% tree canopy) is termed an oak woodland. Although much work needs to be done in describing and understanding oak woodland, it should be viewed as separate from oak forest.

In the early to mid-19th century, the oak savanna as an ecosystem was thoroughly fragmented and nearly totally destroyed throughout its range. Most of its acreage suffered one of the following fates: (1) clearing and plowing, (2) overgrazing, or (3) invasion by dense shrub and tree growth due to lack of fire, lack of grazing, or both. As noted above, it is now one of the rarest and most threatened plant communities in the world.

Last revised: Tuesday, August 30, 2022