When Michigan became a state in 1837, nearly all of its land was forested. Northern Michigan was a mixture of conifer and hardwood forests dominated by hardwoods such as sugar maple, beech, yellow birch and oak, and softwoods such as pine, hemlock, spruce and fir. In contrast, most of the southern third of Michigan was covered by hardwood forests dominated by oak and hickory. Only a few small grasslands, called oak openings, with widely scattered white and black oak, were found in southern lower Michigan. It was said that a squirrel could have crossed the state without having to come down from the treetops.

Today only about half of Michigan's 36.4 million acres are forested. Although the lands that remain forested have changed a great deal in the past 150 years, they are still very special.

• Why Trees Grow Where They Do
• Forest Development
• Human Influence
• Present Day Forests
• Old Growth Forests
• Forests and Wildlife
• Michigan Timberland Highlights
• Forest/Tree Health
• References

 
Why Trees Grow Where They Do

To appreciate the wide variety of trees and forests that grow in Michigan, it is important to understand the basic needs of trees as well as the natural and human forces that have shaped and influenced forest development. There are many factors that determine which trees and which forests grow in any given area. Three of the most important are the soil, moisture and climate.

Soil serves as both an anchor and the source of essential nutrients for trees. The type of soil determines which nutrients are present and the quantities available. Clay and loamy soils are generally rich in nutrients. Sandy soils usually contain few nutrients. Hardwood (broad leafed) trees tend to dominate areas containing the richer loamy soils while coniferous (needle leafed) trees are more common on sandy soils.

Moisture is vital to all plants. Its availability throughout the growing season helps determine which species occupy which sites. Clay and loamy soils hold moisture from summer rains much better than porous sandy soils. Pines, particularly jack and red pine, tolerate the low moisture of droughty sandy soils. Hardwood trees, like the beech and sugar maple shown on this poster, require greater amounts of moisture and prefer loamy soils. Swamps (wet forested areas) are occupied by species such as black ash, red maple, black spruce and white cedar that can tolerate saturated conditions over much of the growing season.

Climate is a key determinant of where certain trees and forests occur. Temperature is the most important climatic factor affecting where different trees live within a particular climate or region. The decrease in average temperature from southern to northern Michigan brings about major changes in the distribution of trees and forest types. In southern Michigan deciduous hardwood trees are the dominant forest species. Although several of those species, including sugar maple, beech, and basswood, can be found in both southern and northern Michigan, most of the oaks and hickories are restricted to the Lower Peninsula, many to its southern half. Young oak and hickory trees are easily killed by low temperatures or late frosts during the growing season.

North of a line from Bay City to Muskegon, conifer trees, including balsam fir, white and black spruce, tamarack, hemlock, and white, red, and jack pine are more common. These species are adapted to heavy snowfall and long periods of freezing weather. Several hardwoods such as yellow birch, white birch, balsam poplar and trembling aspen are better suited to these harsher conditions and also become more common in the north.

Influence of the Great Lakes
The tremendous volumes of water in the Great Lakes modify the Michigan climate. As air temperatures change with the seasons, Great Lakes water temperatures are slow to respond. This moderates the state's climate, making winters somewhat warmer and summers cooler. Differences of as much as 10 degrees Fahrenheit are common between shoreline and inland counties. These differences affect the distribution of forest species along the coastline, allowing some southern species such as sassafras, hackberry, black gum and flowering dogwood to occur farther north along the coastline than inland. Conversely, northern species such as hemlock, Canada yew and white pine can be found in cool, sheltered areas to the south.

The Great Lakes also influence the amount of precipitation throughout Michigan. No parts of the state suffer from a lack of precipitation, although moisture often is in short supply in areas with sandy soil. Prevailing winds blowing across Lake Superior and Lake Michigan pick up moisture and deposit it inland as snow and rain. The west coast of Michigan's Lower Peninsula and the Keweenaw Peninsula in the Upper Peninsula are the areas most affected and receive much more precipitation, especially snow. Forests in these areas are highly productive.

 
Forest Development

Early Post Glacial Vegetation
After the last glaciers receded some 12,000 years ago, much of Michigan was barren sand and gravel with shallow ponds, deep lakes and rivers. Primitive plants, such as lichens and mosses, gradually appeared on the bare soil and rocks exposed by the retreating ice. These plants changed the local conditions, improving the soil nutrients and moisture, and making the area increasingly habitable for larger and more complex plants such as grasses, forbs, shrubs and trees. This progression from bare soil to lichens and mosses to complex plants is called primary succession.

Gradually, trees and other plants moved into Michigan from the east and south following the retreat of the glaciers. The climate was colder than today, and coniferous trees were the first to appear. The forests of southern Michigan were then similar to those of the boreal spruce fir forests of Canada. As the glaciers receded northward, the climate became warmer and drier. Southern species, including maples and oaks, slowly moved into Michigan and replaced the boreal upland spruce fir species.

Clues of these and other long term changes in climate and forest types can still be found by studying layers of pollen found in the bottom sediments of lakes and swamps. Relict pockets of black spruce, tamarack, and other northern species can also be found in cold, wet bogs and swamps in southern Michigan, where local conditions changed little over time.

Presettlement Forests
While there were large continuous blocks of the same community type prior to European settlement, there were also many smaller tracts of different forest communities within these blocks. Those smaller tracts occurred because of local differences in type of soil, amount of soil moisture, elevation, and steepness and direction of slope. That patchwork of forest communities was also caused by natural disturbances such as windstorms, insect damage and fires.

In presettlement times, trees varied in age from patches of saplings regenerating after a blowdown, to even aged communities originating from fires, to old growth stands that could range from 250 to 400 years old. It would be a misconception to view presettlement forests as all old growth. They were, rather, a rich mosaic of various ages.

Forest Succession
After a disturbance, such as wind throws, fire, or logging, a process of forest regeneration, called forest succession, occurs. For example, in rich northern hardwood forests, herbaceous vegetation such as sedges, grasses, and bracken fern may initially dominate after a severe fire destroys the large trees. These species are outcompeted by low woody vegetation or shrubs such as sumac, raspberry, and nannyberry. Large shrubs and scrubby trees usually follow. This stage may include chokecherry, mountain ash, witch hazel, and dogwood.

The first trees to appear, including aspen and white birch, are those that require abundant sunlight. These pioneer species grow rapidly in dense stands and are good competitors for sunlight, nutrients, and moisture. As they grow taller, their branches and leaf cover expands, shading the forest floor. The seedlings of these pioneer species cannot survive well in shade. Trees more tolerant of shade, such as sugar maple, beech and hemlock, can survive under the canopy of the pioneer species and appear in succeeding stages. If left undisturbed, the process terminates with a self perpetuating forest community. This final community is called the climax. When a climax community is severely disturbed, it begins anew its successional process.

The forest communities shown on the map are the major climax forest communities that occurred in Michigan before settlement. Each is dominated by trees best suited for the climate, soil and moisture occurring in those areas. Climax pine forests, for example, occur where the climate is generally cooler, and where soils are sandy, droughty, often acidic and low in nutrients. By contrast, the sugar maple beech community is found in areas with a longer, warmer growing season, and soils with good nutrient and moisture levels.

Natural Disturbances
These climax forest communities and some earlier successional forest types are dependent upon natural disturbances such as fires, windstorms and flooding. Some form of disturbance characterized all of Michigan's major forest communities. The driest sites, those typically dominated by pines and oaks, were fire prone. Lightning fires, common in late spring or early summer, swept rapidly through the dry grasses, sedges, and fallen needles, often igniting the forests over large areas. Fires in the red and jack pine forests burned forests over many square miles. Following the fires, pine seedlings established rapidly on the bare mineral soil.

Forests on moister sites dominated by beech, sugar maple, and other hardwoods were maintained primarily by extensive windfalls. Windstorms blew down the old hardwoods, removing the heavy forest canopy and allowing sunlight to reach the forest floor. Young hardwoods would take advantage of this opening and rapidly replace the older windfelled trees.

Trees in swamp forests generally have shallow roots. As a result, shallow rooted hemlock, white pine and cedar commonly blew down in swamps.

 
Human Influence

Before the arrival of European settlers, Native Americans had relatively minor impact on the forests. They cleared a few areas of several hundred acres for villages, crops, and mound building. They also set fires along the forest grassland borders, helping to maintain the fire dependent oak openings. Their accidental fires may have regularly burned through those openings, pine forests and along rivers.

With European settlement, human impact on the forests increased dramatically. The large pine forests of northern Michigan were the first to be cleared. They were very attractive to investors, many of whom had already cut the pine forests in Pennsylvania and New England.

Michigan led the nation in lumber production in the 1880s and 1890s. By the early 1900s, millions of Michigan pine trees worth more than all the gold mined in California had been felled in the Lower Peninsula. As the pine forests were becoming depleted in the Lower Peninsula, logging companies moved to the Upper Peninsula. At that time, hardwood forests were being cut to make charcoal for iron smelting, and timbers for building construction, posts for fences and firewood for fuel. Michigan forests were seen as inexhaustible.

Very few settlers paid any attention to what was happening to the forests that had taken thousands of years to develop. They were busy homesteading, starting farms where the magnificent forests had been. Remaining trees and brush had to be cut, stumps pulled, everything piled and burned. Fires often got away and burned huge areas before going out. Entire towns were lost, sometimes with great loss of life. Most of northern Michigan burned during this period, many areas more than once. The charred pine stumps still found throughout the northland attest to these widespread fires.

All this cutting and burning changed the landscape so drastically that it looked more like barrens than forest land. Animals requiring large areas of mixed conifer hardwood forests such as the fisher, the american marten and woodland caribou disappeared. The passenger pigeon, one of the most abundant birds in the Lower Peninsula, became extinct because of the destruction of the oak and beech maple forests upon which it depended, and also indiscriminate market hunting. Wildlife more common to prairies such as the coyote, cowbird, badger, prairie chicken, and meadowlark appeared, taking advantage of the changed habitat.

In 1903, the state government formed "forest reserves" from lands that had been cut over and returned to state ownership due to nonpayment of taxes. In 1920, the Conservation Department now the Department of Natural Resources was created. Its major duties were to control forest fires and to manage the forest reserves, later known as state forests, for timber, wildlife and recreation.

Many farms in the north were on poor, sandy soils, incapable of producing crops for more than five or ten years. Most of those farms were abandoned and, during the economic hard times of the Great Depression, reverted to state ownership. Most of that acreage was added to the state forests, bringing total state forest system lands to more than 3 million acres. (Today, Michigan's state forest system totals 3.9 million acres and is the largest in the United States.)

During the Depression, nearly a half billion pine trees were planted on state forest lands by young men working for the Civilian Conservation Corps. Lands no longer used for farming began returning to forest lands, as natural forest succession progressed throughout much of northern Michigan. Aspen and young hardwoods appeared on much of the forested area, leading to high populations of deer, ruffed grouse, and snowshoe hare, all species that do well with young, dense forest cover. Some sandier soils have been slow to recover because of the loss of soil nutrients and topsoil from the catastrophic fires.

 
Present Day Forests

Michigan's original forests were noted for their diversity and richness. Today's forests remain diverse and are continually changing through forest succession. Extensive pine forests found originally on sandier soils have been greatly reduced, despite large scale planting. Sandy soils where the original pine forests occurred and mixed loamy soils originally occupied by hardwood forests are now dominated by large, even aged stands of aspen and second growth hardwoods, especially red maple.

Fire control has eliminated the influence of fire, which was an important factor in maintaining the diversity in the age of forest stands before the state was settled. Northern hardwood forests now occurring throughout much of the northern Lower Peninsula are 60 to 90 years old. Fire control efforts have also reduced the amount of area covered by fire dependent jack pine. On many sandier sites, young white pine are appearing in the understory of the second growth hardwoods. If allowed to mature, they will be the dominant tree in the next stage of forest succession.

The oak hickory forests, oak openings and lowland hardwood forests of southern Michigan have, for the most part, been replaced by farmland and urban development. Mostly small, isolated woodlots remain and many of them are "second growth" stands that have regenerated after being logged in the early 1900s. The changes that have occurred are dramatic, especially on the more productive southern Michigan soils.

Present day forests are managed for timber, wildlife, recreation, aesthetic and ecological values. They play an important role in Michigan's economy. Abundant renewable timber resources provide thousands of jobs in logging and manufacturing. Abundant wildlife is enjoyed by hunters and wildlife viewers. Many people find comfort, beauty and solitude in wilderness and old growth timber areas.

 
Old Growth Forests

The term "old growth" describes an ecological condition where forest vegetation is dominated by trees in the mature stages of their life cycle. Although this may evoke an image of huge redwood trees with ferns dominating a shady forest floor, Michigan's forests do not always fit that picture. This state's forest landscape is dramatically different in species, topography, and human use when compared to that of the Western U.S., where the most publicized old growth issues have taken place.

The key difference between "eastern" and "western" old growth is that old growth efforts in the west gravitate toward preservation of forest ecosystems, while eastern old growth efforts typically revolve around restoration of forested ecosystems. These ecosystems include ecologically important openings that are not forested, early successional stands and extensive areas of catastrophic or frequent disturbance (e.g., windthrow). Given the importance of these ecological land form variations, the term "old growth" is not entirely accurate. Old growth/biodiversity stewardship is the term that is being used by the Michigan Department of Natural Resources (MDNR) to reflect the broad values of these forested ecosystems.

Michigan is one of the first states to formally develop a plan that specifically addresses native old growth forest condition and biodiversity restoration on state-owned forest lands and other state owned lands (such as state park and recreation areas). More information is available about the MDNR's Old Growth and Biodiversity Stewardship initiative.

Many convincing arguments have been presented about the value of features associated with old growth forests:

• Dead standing snags and fallen logs of old growth forests support teeming numbers and varieties of wildlife species from salamanders and snakes, to the saw whet owl and flying squirrel, and to the tiniest insects, invertebrates, fungi and bacteria.
   
• Downed logs decay and release valuable nutrients to future trees and other plants, and serve as nurseries for tree seedlings that cannot grow in the thick leaf litter on the forest floor.
   
• Old growth stands recycle many nutrients back into the soil, providing food and shelter to a wide variety of wildlife.
   
• Large snags, common in old growth stands, provide homes for cavity nesting wildlife such as woodpeckers, nuthatches, barred owls, gray squirrels, martens, and bats.

A few areas in the state escaped the axes and cross cut saws of the logging era. They can be visited today to experience the primeval character of the original presettlement forests. Most are now in public ownership, managed by the U. S. Forest Service, the National Park Service, the Michigan Department of Natural Resources (DNR) or state universities and colleges. Ongoing inventories conducted by the DNR Wildlife Division's Natural Heritage Program continue to locate additional stands. The linked chart highlights a few of those remnants of the past.

 
Forests and Wildlife

Like trees, animals have basic requirements that determine where they can and will live. All wildlife species need food, water, cover and safe areas to reproduce and raise their young. However, each species has a unique combination of life requirements and habitats differing from all others.

Two species of woodpeckers, the downy and the hairy, require dying and dead standing trees, called snags, for their habitat. These trees provide their food (insects living in the bark) and cover (cavities or holes in the snags). The hairy requires larger snags than the downy, so their habitat requirements are slightly different. In addition, the hairy woodpecker tends to eat larger insects than the smaller downy woodpecker, and searches for these on different parts of trees. Each fills a different niche or functional role in the forest ecosystem.

Many factors determine which wildlife will live in any forested area. Some of the more important are the type of forest community, the age or successional stage of the forest, the amount of habitat at different levels within the forest canopy, and the season of the year.

Forest type. Some of the greatest differences in wildlife species occur between coniferous and deciduous forests or stands. Red squirrels abound in coniferous forests where they feed heavily on the seeds of pine cones. Gray squirrels occur in deciduous forests and feed on acorns and beechnuts. Red eyed vireos and wood thrushes occur in deciduous forests, while blackburnian warblers and pine warblers prefer coniferous forests.

Other species occur in different forest types in response to the presence or influence of water. Amphibians, such as redbacked and spotted salamanders, prefer moist, mature deciduous forests and live in close association with downed, decaying logs on the forest floor. They have difficulty surviving on dry, sandy pine sites. Red shouldered hawks use extensive lowland deciduous forest types for nesting, while Kirtland's warblers nest only in young jack pine forests.

Forest age. Each successional stage, or age class, of a given forest type supports different wildlife. In northern hardwoods, early successional stages with dense cover near the forest floor support meadow voles, catbirds, chestnutsided warblers, and golden winged warblers. Intermediate successional stages, comprised of small diameter trees', will support deer mice and rose breasted grosbeaks. In mature and old growth stages of hardwood stands, wildlife dependent upon snags and downed woody material including pileated woodpeckers, brown creepers, chipmunks, and redbacked salamanders can be found.

Forest strata. Another way that wildlife have diversified their habitat requirements is by using different levels or vegetational strata within forest stands. Some species, such as ovenbirds, woodland jumping mice and wood thrushes occur at ground level. In mature forest stands, birds such as the American redstart are specialized for use of intermediate or middle strata vegetation at a height of 10 to 25 feet. This strata usually contains either sub canopy trees such as dogwoods or ironwood, or younger individuals of the dominant overstory trees such as sugar maple and beech. Other wildlife, such as red eyed vireos and scarlet tanagers, may spend much of their time in the upper canopy of the forest.

Seasonal change. The habitat requirements of wildlife frequently change with the seasons. Migratory songbirds avoid cold winter conditions and lack of food (such as flying insects) by migrating to southern climates. Non migratory species must survive winter conditions and may have specialized habitat requirements and survival skills to accomplish this. During winter months, woodpeckers dig out dormant insects and grubs from under the bark of trees. Cavity dependent species will seek out roosting cavities above a small opening in the tree, thus helping trap air warmed by the animal. Den trees with large hollow centers provide protection from cold weather to porcupines, raccoons, opossums and many smaller mammals.

Food becomes less available in the winter. Some species solve this problem by sleeping through the coldest part of winter, hibernating in a protected area such as a hollow tree, a brush pile or a hole underground. Some animals depend on special fat reserves stored in their bodies, while others must actively search out what little food remains.

With the arrival of spring, food becomes more available, and nesting and denning sites are selected to provide a safe location to raise young. Barred owls may seek out broken-topped trees for nesting. Tree frogs, toads, and salamanders move to temporary ponds for mating and egg laying. Black-capped chickadees search out loose bark on trees or softwood snags to excavate small cavities for a nest. Habitats providing different seasonal requirements must be located close enough together in an area for the non migratory species to be able to move to them as needed.

Thus, a great diversity of wildlife lives in each forest ecosystem, sorted according to forest age, type of trees available, location or height of different vegetation strata and the season. Each species has unique strategies and life requirements to help it survive. By maintaining healthy and diverse forest ecosystems through careful planning and conservation, we can be good stewards of this valuable and very important part of our rich natural heritage.

A selection of wildlife and plant species found in Michigan forests:

 
References

Michigan Trees A Guide to the Trees of Michigan and the Great Lakes Region, Burton V. Barnes and Warren H. Wagner, Jr., University of Michigan Press, Ann Arbor, Michigan, 1981.

The Lake States Forests, A Resource Renaissance, The Conservation Foundation, Bookcrafters, Chelsea, Michigan, 1988.

The Secret Life of the Forest, Richard M. Ketchum, American Heritage Press, New York, 1970.

The Forest, Peter Farb and the Editors of Life, Time, Inc., New York, 1963.