Historically, the regional landscape of the upper mid-west, largely Minnesota, Michigan, and Wisconsin, has been dominated by forest cover. Since retreat of the last continental ice sheet, approximately 11,000 years ago, various types of forests have developed according to climate, site capabilities, and natural and man made disturbance regimes.

Prior to Euro-American settlement, which began in earnest in the early 1800's, the predominant forest types in the region included upland boreal conifer forests, lowland conifer swamps, jack pine and red pine barrens and forests, mixed red and eastern white pine forests, oak-pine forests and oak savannas, mesic northern hardwoods, oak-hickory forests, deciduous wetlands, and aspen-birch forests. Most of these types persist today, although in vastly changed acreages. In particular, the aspen-birch type has greatly expanded at the expense of pine and oak-pine types.

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Figure 1. Presettlement vegetation map of the western Great Lakes region.¹

Map from www.usgs.gov

Disturbance Dynamics and Human History

The increase in aspen at the expense of pine reflects a changing landscape disturbance dynamic. Importantly, regional natural disturbances prior to Euro-American settlement, included fire, wind, insects and to a lesser extent, pathogens, ice storms, and floods. Fire in particular was key to shaping the type and distribution of forest ecosystems across the regional landscape. Jack pine forests were maintained by frequent stand replacing fires, mixed-pine forests experienced frequent (stand-maintaining) surface fires and infrequent stand-replacement fires. Boreal conifer forests burned regularly, as did oak and pine savannas. In contrast, deciduous wetland and northern hardwood forest were largely resistant to burning, except during extreme, prolonged drought conditions. Native Americans also used fire as a tool for vegetation management over local to large areas.

Early logging in Wisconsin.

This landscape fire regime was altered drastically by logging of the primary forest and Euro-American settlement that followed. After logging and land clearing for agriculture, slash-fueled wildfires burned through much of the region, particularly on dryer sites. In many cases this eliminated advance regeneration and local seed sources of pines. Fire suppression followed, allowing expansion of aspens, and to a lesser extent paper birch, on sites formerly dominated by pine types. The decline of agriculture, primarily in the north, also lead to aspen and hardwoods invading and reclaiming many old fields.

Contemporary Landscape Conditions

	Second growth Sugar Maples. Argonne Experimental Forest, Forest County, WI. (Terry Strong)

Forest management, including harvesting, site conversion, and planting, has replaced fire as the primary driver of forest dynamics in the region. Aspens are widely utilized commercially, are easily regenerated vegetatively after logging and, as such, forests dominated by aspens are still a prominent feature in the contemporary landscape. Northern hardwoods are still abundant in the region and important commercially in various locations, however, the composition of these systems has shifted from fairly species rich tree communities to largely sugar maple dominated.

Upland conifers including white spruce are important economically, and in some areas productive northern hardwood sites have been converted to white spruce. Lowland conifers are utilized commercially and the economic importance of these forest types will remain well into the future. Acreages of pine types, especially eastern white and red pines, have been drastically reduced, but there is growing interest in increasing the presence of these species and their respective forest types in the region.

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Figure 2. Contemporary forest of the western Great Lakes region.¹

Map from www.usgs.gov

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¹ Stearns, Forest W. 1997. History of the Lake States Forests: Natural and human impacts. In: Vasievich, J. Michael; Webster, Henry H., eds. Lake States Regional Forest Resources Assessment: Technical Papers. Gen. Tech. Rep. NC-189. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station: 8-29.