Western Great Lakes forests

The Western Great Lakes Forests stretch from northern Michigan and the Upper Peninsula through northern Wisconsin, much of northern Minnesota, and into the southern portion of northwestern Ontario and extreme southeastern Manitoba. Characteristic forests in this region are more closely identified with the warmer, more humid southeastern mixed forests, than with the colder, drier boreal regions to the north.

This region is characterized by moist low boreal and subhumid transitional low boreal ecoclimates. The mean annual temperature ranges from 1°C to 2°C; mean summer temperature ranges from 14°C to 15.5°C; and mean winter temperature is -13°C. Mean annual precipitation ranges from 500 mm in the west to 700-800 mm in the east. Generally, this ecoregion experiences warm summers and cold winters.

The effects of the Great Lakes upon climate, commonly called the "lake effect," are of considerable importance to the biota. Lake effects occur along the shorelines of all the Great Lakes, increasing the length of the growing season and influencing average temperatures, extreme temperatures, and the amount and timing of precipitation. Lake effects play a lesser role in the western portions of this ecoregion than in northern Michigan because winds generally blow from the Great Plains to the southwest. As a result, the climate is considerably more "continental," with extreme minimum winter temperatures and short growing seasons. Because Lake Superior is the coldest of the Great Lakes, its ameliorating effect on temperature is less than that of the other Great Lakes.

Glaciers once covered this entire ecoregion, much of which is now mantled with thick deposits of glacial drift. As a result of the glaciation, nearly all of the soil has developed on glacial deposits and lake beds, or on rock surface scraped bare by the ice. Rock outcrops and glacial moraines provide a varied landscape, although the region is generally rolling with little change in elevation. Paleozoic marine and nearshore deposits underlie much of the region. In the Upper Peninsula of Michigan, extensive exposures of basaltic bedrock occur on Isle Royale, the Keweenaw Peninsula, and the Porcupine Mountains. The flora of Isle Royale and the Keweenaw Peninsula is rich in disjunct species from the Pacific Northwest (Cordilleran region), presumably because of the chemical characteristics of the basalt, a bedrock type that is also abundant in the West. The resistant limestones and dolomites of the Niagara Escarpment form cliffs along Lake Michigan’s northern shoreline and form the spine of the Bruce Peninsula on Georgian Bay’s western shore.

Within the Canadian portion, this ecoregion takes in a portion of the Severn Upland, and is underlain by massive, crystalline, acidic, Archean bedrock, forming hummocky, broadly sloping uplands and lowlands. Bedrock outcroppings are common throughout the region. Small to medium-sized lakes are numerous in the south-central area and many are linked by bedrock-controlled networks of streams. Wetlands are also widespread and are characterized by bowl bogs that are treed and often surrounded by peat margin swamps (ESWG 1995).

Characteristic vegetation is a mixed forest that includes a succession from quaking aspen (Populus tremuloides), paper birch (Betula papyrifera) and jack pine (Pinus banksiana) to white spruce (Picea glauca), black spruce (Picea mariana) and balsam fir (Abies balsamea). Forest species assemblages are highly influenced by drainage characteristics and topography. In low, wet areas, black spruce is likely to be the dominant species. Northward into Canada, black spruce takes on a more dominant role and often grows in extensive stands covering thousands of acres on the uplands (Tester 1995).

Characteristic mixed forests are distinct from the predominantly deciduous boreal forests of the west and cooler boreal forests to the north. The region includes northern coniferous forests, northern hardwood forest, boreal hardwood-conifer forest, swamp forest, and peatland. Minnesota’s peatlands are still relatively intact despite efforts in the early 1900s to ditch and drain large tracts in the north (Tester 1995).

Ecologists subdivide the pine forest of this ecoregion into Great Lakes pine forests of white pine and red pine (Pinus resinosa) with paper birch and aspen, and jack pine forests of jack pine, red pine, oak (Quercus spp.), and hazel (Corylus cornuta). Sandy, acid, nutrient-poor soils, and high frequency fires characterize all pine forest habitat in the northern Great Lakes. Jack pine historically occupied the most extreme, drought-prone sites, especially extensive outwash plains. Northern pin oak (Quercus ellipsoidalis) was a common associate. Red pine occupied slightly more mesic sites, either on outwash deposits, sandy end moraine, or sandy beach ridges and small transverse dunes. White pine was once common on sandy lake plains, occupying sites from poorly drained embayments to excessively drained sand dunes. Intensive logging of white pine and red pine between 1850 and 1900 and widespread fires resulted in the replacement of many pine forests by red maple and light-seeded, wind-dispersed aspens and paper birch (Albert 1994).

Wetlands are widespread in this ecoregion, with conifers dominating most of the wetlands, although hardwoods still grow along stream margins and well-aerated wetlands in stream headwater areas. The most extensive conifer swamps occur in the glacial-lake basins of eastern upper Michigan.

Common species of the northern hardwoods include sugar maple (Acer saccharum), red maple (Acer rubrum), American beech (Fagus grandifolia), hop hornbeam (Ostrya virginiana), basswood (Tilia americana), yellow birch (Betula alleghaniensis) and eastern hemlock (Tsuga canadensis). Some authorities separate this community into two types distinguished by the presence or absence of beech (Fagus grandifolia). The western half of Michigan’s Upper Peninsula does not contain beech, probably because of extremely low winter temperatures. Fire, while rare, occurs often enough to maintain the presence of white pine and red oak. Fire is a more important factor in stands of spruce and balsam fir.

  • Scientific Code
  • Ecoregion Category
  • Size
    105,800 square miles
  • Status
    Relatively Stable/Intact
  • Habitats

Biological Distinctiveness
Characteristic wildlife in the Western Great Lakes Forests include moose (Alces alces), black bear (Ursus americanus), wolf (Canis lupus), lynx (Lynx canadensis), snowshoe hare (Lepus americanus), white-tailed deer (Odocoileus virginianus), and woodchuck (Marmota monax). Bird species include ruffed grouse (Bonasa umbellus), hooded merganser (Lophodytes cucullatus), pileated woodpecker (Dryocopus pileatus), bald eagle (Haleaeetus leucocephalus), turkey vulture (Cathartes aura), herring gull (Larus argentatus), and waterfowl. American black duck (Anas rubripes) and wood duck (Aix sponsa) occur in the eastern part of the ecoregion (ESWG 1995).

Isle Royale National Park supports an intact predator/prey system, including a breeding wolf population and large numbers of white-tailed deer, moose, snowshoe hare, and beaver (Castor canadensis). The park also contains perhaps as much as 350 km2 (86,000 acres) of old-growth forest (Davis 1996). Wolves appear to be expanding their range to the southwest in Minnesota, and in 1994 the state population was estimated at 2,000 (Tester 1995). This ecoregion contains several areas suitable for supporting wolf packs, and there is the potential for a rebound in the wolf population. Other endangered mammals include marten (Martes americana), and lynx. Threatened and endangered birds include Kirtland’s warbler (Dendroica kitlandii), merlin (Falco columbarius), and yellow rail (Coturnicops noveboracensis).

The southern shorelines of Lake Superior and Lake Huron are crucial for migrating birds, serving as migratory stopover points and major breeding areas. Terns and plovers nest on islands. The lakeshores are also important areas of aquatic insect diversity, while estuaries serve as important fish hatcheries for Great Lakes fisheries.

The acidic, Archean bedrock outcrops in many areas attract lightening strikes. As a result, fire is an important disturbance regime in the region, particularly on conifer-dominated dry sites.

Conservation Status

Habitat loss
Only 20 percent of the western Great Lakes forests remains as intact habitat. Minnesota has some 2630 km2 (650,000 acres) of old-growth forest, more than any other state in the east (Davis 1996). Much of this habitat is concentrated in the Boundary Waters/Quetico area straddling the Minnesota-Ontario boundary. While in some areas, particularly in the northern reaches of the ecoregion, the coniferous forests still exist much as they did hundreds of years ago, much of the landscape is in transition from its presettlement status. Most of the original mature white and red pine forests have been logged and have been replaced by younger stands of birch and aspen with only scattered pine. This has resulted in major forest conversion across much of the ecoregion, causing far-reaching changes to the biota found within the ecoregion.

In addition, extensive areas throughout the ecoregion have been converted to agricultural production, or are increasingly being developed for new housing.

Remaining Blocks of Intact Habitat
Several relatively large blocks of more or less intact habitat remain and a number of smaller patches. Important blocks include:

•Boundary Waters Canoe Area Wilderness - northeastern Minnesota - 4300 km2 (American area contiguous to Quetico)
•Quetico Provincial Park - northwestern Ontario (Canadian area contiguous to Boundary Waters).
•Porcupine Mountains National Forest Shequamagon National Forest - northern Wisconsin
•Nicollet National Forest - northeastern Wisconsin
•Superior National Forest - northeastern Minnesota
•Chippewa National Forest - northern Minnesota
•Ottowa National Forest - northwestern Michigan
•Hiawatha National Forest - northwestern Michigan
•Voyageurs National Park - northern Minnesota
•Isle Royale National Park - northern Wisconsin
Degree of Fragmentation
A forest matrix still characterizes this ecoregion, although parts of the ecoregion are fragmented by both public and logging roads. Within the United States, more than half of all fragments have some interaction with other intact habitat blocks, resulting in relatively low fragmentation pressure.

Degree of Protection
The Western Great Lakes forests include several large protected areas. The most important areas include:

•Boundary Waters Canoe Area Wilderness, northern Minnesota
•Quetico Provincial Park, northwestern Ontario - 4,758.19 km2
•Voyageurs National Park, northern Minnesota
•Isle Royale National Park, northern Michigan
•Apostle Islands National Park, northern Michigan
•Porcupine Mountains State Park - northern Michigan
•Turtle River Waterway Provincial Park - northwestern Ontario- 400.52 km2
•La Verendrye Provincial Waterway Park - northwestern Ontario - 183.35 km2
•Whiteshell Provincial Park - Manitoba (Backcountry zones) - 913 km2
•Nopiming Provincial Park - Manitoba (Backcountry zones) - 316 km2
•Lake of the Woods Provincial Park, northwestern Ontario - 129 km2
•Lola Lake Provincial Nature Reserve, northwestern Ontario - 65.72 km2
•Sandbar Lake Provincial Park, northwestern Ontario - 50.83 km2
•Winnange Lake Provincial Park, northwestern Ontario - 47.45 km2
•Portions of the National Forests (Wilderness Areas, RNAs, etc.) also provide significant protection to the diversity of this ecoregion.
Types and Severity of Threats
The most significant conversion threat in this ecoregion is the conversion of pine to aspen forest. Logging is a significant cause of this conversion throughout the ecoregion. Paper mills and oriented strand board mills are now harvesting second growth forests. Much of the forest outside core protected areas has been converted to young, successional stands of birch and aspen. Although aspen-dominated forests provide habitat for wildlife, they have crowded out the native white pine forests. Agriculture, scattered throughout the ecoregion, and development, especially for second homes along the lakeshores, also pose conversion threats.

Large deer populations threaten to degrade some southern areas of the ecoregion, as excessive browsing harms hemlock and white spruce. While changing water levels in the lakes once played an important ecological role, inlet and outlet controls have now stabilized the water levels leading to significant changes in the lakeshore ecology. The cumulative effects of industrial toxins in the lakes, and along the shorelines, pose another threat to the health of the ecoregion. Overall, many populations of plants species are experiencing high mortality and low recruitment due to habitat degradation. Woodland caribou (Rangifer tarandus) have essentially been extirpated from this ecoregion, with only infrequent sightings in the extreme northern areas bordering ecoregions 93 and 94.

Suite of Priority Activities to Enhance Biodiversity Conservation
In all National and Regional Forests:

•Maintain existing large, intact habitat blocks and corridors.
•End logging practices that result in forest conversion from pine-mixed hardwoods to aspen.
•Restore conifer forests where conversion has already occured, including re-establishing the natural fire regime in the Boundary Waters-Quetico area.
•Protect the wetlands of Kakagen slews and the Door County Peninsula.
•Protect the undisturbed vegetation of the sea caves on Apostle Island.
•Conserve the rare species of the limestone grasslands (alvars) of northern Lake Huron.
•Protect the forests of Menomenee County, Wisconsin, which have never been cut and may be the most mature forests in the U.S. portion of the ecoregion.
•Upgrade the protection standards of provincial forests in Manitoba.
•Protect the wild and scenic Wolf River.
•Protect Aulneau Peninsula in Lake of the Woods - northwestern Ontario.
Conservation Partners

•Endangered Spaces Campaign - Manitoba
•Environment North
•Federation of Ontario Naturalists
•Friends of the Boundary Waters Wilderness
•Manitoba Naturalists Society
•Michigan Environmental Council
•Michigan Natural Areas Council
•Michigan Nature Association
•Quetico Foundation
•Resource Conservation Manitoba
•The Nature Conservancy, Manitoba
•The Wildlands League
•World Wildlife Fund Canada

Relationship to other classification schemes
The Western Great Lakes forests include both hardwoods and conifers, unlike the deciduous forests to the south and the boreal forests to the north. This ecoregion largely corresponds to Omernik’s Northern Lakes and Forests ecoregion, though Omernik creates a separate ecoregion for the Northern Minnesota wetlands. The Western Great Lakes Forests of southeastern Manitoba and northwestern Ontario fall within the Boreal Shield Ecozone, incorporating the Lake of the Woods, Rainy River and Thunder Bay-Quetico areas (TEC 91-93) (ESWG 1995). This ecoregion includes the Lower English River area in the Boreal forest zone (14), and the Quetico and Rainy River areas within the Great Lakes-St. Lawrence forest region (11, 12) (Rowe 1972).

Prepared by: S. Chaplin, A. Perera, S. Robinson, J. Adams, T. Gray, G. Whelan-Enns, K. Kavanagh, M. Sims, G. Mann.