• Terrestrial Overview
• Aquatic Overview
• Land-cover Change Trends
• Invasive Species
• Aquatic Contaminants
• Disease and Pathogens
• Altered Natural Processes

Terrestrial Overview
Michigan contains a broad diversity of terrestrial ecosystems that are differentiated by variations in regional climate, physiography (glacial landform and geologic parent material), soils and vegetation (Albert 1995). In an effort to better understand and communicate information on this diversity, researchers have developed a hierarchical classification of regional landscape ecosystems that divides the State into four major sections or ecoregions, each containing additional levels of differentiation (Albert et al. 1986, Albert 1995). This ecoregional classification provides a framework for understanding broad patterns of natural community and species occurrences, natural disturbance regimes, and land-use patterns across the State. Because the distribution of plants and animals in Michigan is influenced by the factors that shape ecoregions (climate, geology, soils, vegetation), these ecoregions are a useful tool for integrated resource management, planning, and biological conservation. The four major ecoregions in Michigan are the Southern Lower Peninsula, Northern Lower Peninsula, Eastern Upper Peninsula, and Western Upper Peninsula (Albert 1995).

The Southern Lower Peninsula (Southern Continental Michigan) Ecoregion (Section VI) is characterized by rolling moraines and flat lake plains. This ecoregion experiences the warmest climate and longest growing season in Michigan. Historically, much of Southern Lower Michigan supported open oak savannas and prairies, which were maintained in a non-forested condition by frequent fires (Albert 1995). Dry upland ridges supported oak-hickory complexes. Also common were forests of American beech and sugar maple and a diversity of wetland natural communities including prairie fen, lakeplain prairie, southern wet meadow, southern swamp and floodplain forest. Today, much of the region is dominated by agricultural and urban development.

The Northern Lower Peninsula (Northern Lacustrine-Influenced Lower Michigan) Ecoregion (Section VII) is characterized by extensive, sandy outwash plains and large moraines. Although the climate of the ecoregion is strongly moderated by the Great Lakes, the interior portions experience the greatest temperature extremes in Lower Michigan. Historically, the ecoregion supported extensive northern hardwood forests of sugar maple, American beech, eastern hemlock and white pine. In addition, the ecoregion supported large areas of fire-dependent ecosystems such as jack pine barrens, oak-pine barrens, and white pine-red pine forest. A diversity of wetland natural communities, including bog, northern fen, northern wet meadow, hardwood-conifer swamp and rich conifer swamp, continues to thrive. Today, much of the ecoregion remains forested by northern hardwood, aspen, oak, pine plantations, and lowland conifer.

The Eastern Upper Peninsula (Northern Lacustrine-Influenced Upper Michigan) Ecoregion (Section VIII) is characterized by relatively flat lake plain and areas of exposed bedrock. The climate is strongly influenced by the Great Lakes and experiences warmer temperatures than the western Upper Peninsula. Historically, most of the ecoregion was forested and remains so today. As in other ecoregions in northern Michigan, the original northern hardwood forests in the Eastern Upper Peninsula generally supported a greater diversity of conifers, which provided structural complexity and a diversity of wildlife habitats. Smaller areas of fire-dependent ecosystems such as white pine-red pine forest and jack pine barrens also occurred within this ecoregion. The region continues to support a diversity of wetland natural communities including bog, northern fen, northern wet meadow, hardwood-conifer swamp, rich conifer swamp, and extensive areas of muskeg and patterned fen.

The Western Upper Peninsula (Northern Continental Michigan) Ecoregion (Section IX) is characterized by a diverse landscape of moraines, lake plains, outwash channels, outwash plains, and glacially scoured bedrock ridges. This ecoregion experiences the most extreme winter temperatures and shortest growing season. Historically, a diversity of forest types occurred throughout the entire ecoregion. Northern hardwood forests dominated by sugar maple, eastern hemlock, basswood, yellow birch, and in some locations white pine were the most prevalent forest community. The ecoregion contains numerous bogs, tamarack-black spruce swamps, and hardwood-conifer swamps. Today, most of the region is managed as either private or public forest. Prevalent forest types today include northern hardwood, aspen, pine plantations, and conifer swamp.

Aquatic Overview
Aquatic ecological frameworks in Michigan were derived through analysis of climate, geology, soils and vegetation, using a similar approach to that of the terrestrial classification system (Albert et al. 1986). Although aquatic and terrestrial frameworks share the same environmental variables, distinct and different classification schemes are used because aquatic species, unlike terrestrial species, tend to be more limited in their dispersal pathways between waterbodies. This difference requires a different classification framework because the watersheds that compose the Great Lakes basins and that form these pathways cross multiple terrestrial ecoregions (Seelbach et al. 1997).

Michigan resides in the Arctic-Atlantic subzone within the Nearctic zone of North America, as defined by Maxwell et al. (1995). It occurs in three subregions of the Mississippi region: Superior, Michigan-Huron and Erie-Ontario. These subregions can be further divided into the Great Lakes basins of Superior, Michigan, Huron and Erie. Each basin consists of the Great Lake itself and all lakes, rivers, streams and other hydrologically significant resources that flow into it. These basins provide the broad framework for understanding aquatic communities, species and habitats in Michigan.

The distribution of aquatic animals and plants in Michigan has been most strongly influenced by the last glaciation period, the Wisconsinan. Approximately 4,000 years ago, the Great Lakes first began to assume their present shapes. Rebound of the earth's crust after the last glacial retreat determined the current drainage pattern: Lake Superior drains through the St. Mary's River; Lakes Huron and Michigan drain through the St. Clair River at Port Huron into Lake Erie (Farrand 1988).

Land-cover Change Trends
Estimates of pre-settlement conditions indicate that forests comprised approximately 90% of the Michigan land area. Unsustainable logging practices, extensive conversion to agriculture, and the occurrence of catastrophic fires nearly eliminated all of these forests by the early 20th century. With implementation of sustainable forestry practices and abandonment of farms, which allowed ecological succession to forested lands, Michigan's forests began to recover. Currently, forest covers approximately 50% of the acreage of the State (Smyth 1995). Although this percentage has remained relatively stable since the 1950s, the standing timber volume has more than doubled (Harrison 2003). The volumetric increase is due both to maturation of naturally regenerated and planted trees, and suppression of natural fire regimes. Changes have also been seen in the composition of Michigan's forests, with a gradual transition toward more shade-tolerant, late-successional tree species and a corresponding decline in some wildlife species dependent upon early successional landscapes. From 1982 to 1997, forest acreage on non-Federal lands in Michigan increased by approximately 538,000 acres (U.S. Department of Agriculture 1997), primarily due to further loss of farmed acreage. However, many Michigan forests are being replaced by residential and commercial development, and if current patterns of development continue, forest acreage in Michigan may decrease by 2 to 7% by 2040 (Public Sector Consultants 2001).

Historically, Michigan contained approximately 11 million acres of wetlands. The perception that these areas should be converted to a 'better' use predominated most of the nation's history. Accordingly, Federal and State governments enacted legislation to promote the conversion of these habitats. Prior to World War II, most wetland loss resulted from filling and draining for agricultural purposes. After World War II, commercial, industrial and residential development became the major cause of wetland loss. In 1978, 6.2 million acres of the original 11 million acres of wetlands remained in Michigan (Smyth 1995). Federal and State legislation enacted during the 1970s slowed the rate of loss, but small wetlands (<5 acres) on private lands continue to be lost at a rapid pace; projections indicate Michigan may lose an additional 10% of its remaining wetlands by 2040 (Public Sector Consultants 2001).

Coastal wetland losses have been particularly substantial, declining 70% from historic levels (Comer et al. 1995). The Great Lakes are the largest freshwater system in the world, supporting extensive coastal wetland complexes along the shoreline and in conjunction with drowned river mouths, connecting waters and other tributaries, and embayments. At least six types of Great Lakes wetlands have been identified: lagoon and barrier, ridge and swale, shoreline, embayed, riverine and delta (Michigan Sea Grant 2002). Coastal wetlands are important aquatic habitats and also provide recreational, cultural and economic benefits. Although the importance of coastal wetlands has been well documented, they continue to be lost under increasing development pressure. Wetland modifications due to development include artificial manipulation of water levels, shoreline alteration, pollution, vegetation removal, and other forms of habitat fragmentation. Another associated threat to coastal wetlands is modification through establishment of invasive species such as reed grass. See the discussion of wetland modifications in the Statewide Priority Threats for details on how loss of and modifications to wetlands threaten wildlife and wildlife diversity.

In specific areas of the Southern and Northern Lower Peninsula, oak savanna, tall grass prairie, and barrens dominated the landscape in the early 1800s. Although the exact number of prairies that existed prior to European settlement is unknown, researchers have identified 39 known prairie areas, mostly in the southern Lower Peninsula. These areas ranged in size from less than 100 acres to 25 square miles, and may have covered 2.3 million acres (Sargent and Carter 1999). European settlement converted most of the grassland sites to agriculture. Fire suppression allowed additional acreage to follow successional pathways and become forested. Residential development is now threatening what remains of this community type. More than 99% of Michigan's grasslands are gone, and the remnants that persist are primarily small, isolated patches.

Invasive Species
Since the first European settlers began arriving on the North American continent, hundreds of new species of plants, animals and pathogens have been either intentionally or accidentally introduced. Although many have been incorporated into the landscape with little or no effect, others are more aggressive and threaten both species and landscapes (MDEQ 2003a). Additionally, changes caused by European settlement have altered the landscape, allowing species such as alewives, sea lamprey and Cowbirds to expand their ranges. Without natural predators or parasites, invasive species often outcompete and displace indigenous populations. As the number of introductions continues to increase, so do the potential ecological and economic consequences. See the discussion of invasive species within the Statewide Priority Threats for details about these consequences.

The Great Lakes waterways have experienced an extremely high rate of non-indigenous species introduction and establishment (Mills et al. 1994, Ricciardi 2001). The earliest recorded aquatic invasive species in the Great Lakes was the sea lamprey, which gained access from the Atlantic Ocean through the Erie Canal in the 1820s. Since then, more than 160 additional aquatic invasive species have been introduced into the Great Lakes basin (Harrison 2003). More than one-third of these species were introduced in the second half of the 20th century following expansion of the St. Lawrence Seaway. Ballast water from ocean-going ships is believed to be one of the primary vectors of aquatic introductions, including that of the zebra mussel.

Hundreds of non-indigenous plant and insect species now occur in Michigan. As many as one-third of our plant species may now be non-native (Herman et al. 2001). In the Great Lakes basin, at least 37 terrestrial plant species and seven terrestrial insect species are invasive (Harrison 2003) and pose threats to natural communities in Michigan. Several of the plants, including buckthorn, purple loosestrife and garlic mustard, were introduced deliberately for use as ornamentals or herbs.

Aquatic Contaminants
With 95% of the surface fresh water in the U.S., 11,000 inland lakes and 36,000 miles of streams, Michigan's waters are one of the State's greatest resources. Water quality standards and pollution controls implemented in the 1970s continue to successfully reduce some contaminants. However, chemicals, such as polychlorinated biphenyls (PCBs), mercury, lead and other toxins, are persistent in the environment; they take a long time to break down and may still occur in high or increasing concentrations, posing serious threats to natural communities and human health. The Michigan Department of Community Health recently issued advisories for all inland Michigan lakes, recommending that people limit their ingestion of wild-caught fish due to health concerns related to contamination with mercury, dioxins and PCBs. See the discussion of urban, municipal, and industrial pollution in the Additional Statewide Priority Issues for details about how contaminants are threatening wildlife species and the landscapes they use.

When present in the environment, PCBs, mercury and other toxins can bioaccumulate (accumulate and concentrate) in the tissues of animals at the top of the food chain, such as Bald Eagles and predatory fish. PCBs were previously used more commonly in manufacturing processes, and although in many cases they have been replaced by other materials, their use has not been completely eliminated. Analyses of Bald Eagle, lake trout and chinook salmon tissues show significant decreases in PCB levels between the late 1980s and the late 1990s (Harrison 2003), indicating a decease in environmental levels. Since the mid 1990s, PCB levels in sampled fish have remained relatively stable; however, these toxins often remain captured in sediments, and re-suspension in water is a concern.

Mercury may occur naturally in the environment, but the primary sources for contamination are human-induced, and include mining and smelting of mercury ores, industrial processes using mercury, and combustion of fossil fuels. Unlike PCBs, mercury levels in Bald Eagles did not change significantly between 1985 and 2001. In 2002, mean mercury levels exceeded the Michigan water quality standards (1.3 parts per trillion) in 19 of 24 Michigan rivers sampled (Harrison 2003), and monitoring between 2000 and 2002 indicated increased mercury levels in eight Michigan rivers, four of which occur in the Upper Peninsula (MDEQ 2003b).

Historically, lead was used in fuel and manufacturing processes, and was introduced into the environment through leaking underground storage tanks, fuel spills, spent lead shot and fishing tackle left by anglers. Accumulation rates of lead into lake sediments increased from 1900 through the 1970s, but began to decline following the ban of leaded gasoline in the 1970s. Southern Michigan has shown and continues to show higher rates of lead accumulation than northern areas (Harrison 2003).

Agriculture is yet another source of contamination, introducing fertilizer, herbicides and pesticides into Michigan's water systems through run-off and soil percolation. Since first used in the mid 1940s, application of pesticides throughout the world has grown from 50 million kilograms per year to approximately 2.5 billion kilograms per year (Kiesecker et al. 2004).

Disease and Pathogens
The potential effects of infectious and zoonotic (transmitted between animals and humans) wildlife diseases on wildlife conservation, as well as domestic animal and human health, have long been recognized. However, interest in recent years has increased for several reasons: modification and loss of habitat can result in increased population densities, with associated increases in risk of disease transmission; increasing speed and intensity of international trade in wildlife has meant more rapid spread of diseases and pathogens worldwide; wildlife re-introduction efforts are being limited by disease concerns; human encroachment into wildlife habitats has increased the potential for zoonotic disease transmission; and recognition of the possible use of wildlife species as indicators and sentinels for potential human and domestic animal health threats is growing (National Biological Information Infrastructure 2005).

Overall, the past ten years has shown some changes in fish health in Michigan, including elimination of infectious pancreatic necrosis virus (IPN) in wild fish, and reduction of bacterial kidney disease (BKD) in chinook and coho salmon, as well as the emergence of new diseases such as heterosporis, piscirickettsia and largemouth bass virus (LMBV). New diseases are discovered regularly and are suspected of being transported into Michigan by freighter ballast water, introduced with released infected aquarium fish or baitfish, introduced with illegally stocked or imported fish, or introduced through recreational boat bilge water transported from outside Michigan. Little is known about diseases to aquatic organisms other than fish, but epizootic events, with similar sources, are probably occurring throughout the aquatic ecosystem.

New disease threats affecting terrestrial wildlife are also increasing. Some of the causes of amphibian declines have been linked to disease and pathogens (Kiesecker et al. 2004). Although not currently known to affect Michigan's wildlife, avian influenza and raccoon rabies are other examples of potential threats. The bovine tuberculosis epidemic that threatened Michigan's deer herd is now showing signs of decline. An increasing number of diseases affecting forested landscapes are being found in Michigan, including beech bark disease and oak wilt. Wildlife species that have obligate relationships with the affected tree species, or depend on the structure they provide within an ecosystem, will also be indirectly affected by these diseases. See the discussion of disease and pathogens within the Statewide Priority Threats for more information about specific disease threats and associated conservation needs.

Altered Natural Processes
Various natural processes are required to maintain certain landscape features that are used by wildlife in Michigan. Over time, many of these processes have seen changes, both in the spatial extent affected and the rate at which they occur or return. In many cases, these changes are due to human-influenced alterations or disruptions, but in others, may be the result of natural fluctuations and variation or the activities of wildlife species. Human activities have both increased undesirable disturbances and decreased desirable disturbances at different temporal and spatial scales. Examples of natural processes that may be intricately tied to the survival of certain wildlife include hydrologic regimes, fire regimes and climate change (e.g., glacial cycles and other changes). The following discussion focuses on the first two of these processes, because alterations to them are identified as statewide priority threats.

Altered Hydrologic Regimes
Following wetland drainage, extensive stream channelization, groundwater withdrawals, dam construction, and large-scale changes in land use, much of Michigan has experienced considerable changes in hydrologic processes. These alterations include changes in streamflow patterns, lake levels, and groundwater hydrology.

People use streams for drinking water, navigation, municipal and industrial uses, irrigation, hydroelectric power, sewage treatment (and dilution), recreation and aesthetic benefits. These values of flowing water attract people who subsequently build homes, factories and cities on riverbanks, but development often modifies stream channels and alters stream functions, negatively affecting natural processes and ultimately reducing stream values (Annear et al. 2004). Harnessing streams and rivers for human purposes has incurred significant ecological costs.

Many other practices have also altered or reduced connectivity within hydrologic regimes. In the late 1800s and early 1900s, logging deforested entire watersheds, causing tremendous volumes of sediment to erode into rivers and streams. This was compounded by early agricultural practices that caused extensive soil erosion and contributed additional quantities of sediment far above the load generated by natural processes. Construction of drains and addition of drainage tiles to prepare lands for agricultural efforts and modification of wetlands in preparation for development have changed surface and groundwater regimes. The use of impervious surfaces, such as asphalt roads, buildings and parking lots, has further altered surface and groundwater regimes.

Changes in populations of beaver can influence the distribution and intensity of their activities across the landscape and alter previously existing hydrologic regimes. Beaver affect hydrologic flows by damming and slowing water, which creates wetland habitat beneficial to some species, but creates impediments to movement for other species. These activities can also alter water temperatures in these systems.

All of these changes have created disruptions in the natural movements of water through Michigan's lands, lakes, rivers, streams and wetlands. More details about threats resulting from these changes and conservation actions, research and monitoring needed to address them are provided in various places throughout the Statewide Assessments.

Altered Fire Regime
Many of Michigan's landscape features, including certain grasslands, forests and wetlands, were historically maintained through natural (e.g., lightning) or human-induced (i.e., set purposely by Native Americans) fires. Fire is likely as important an element as climate in the establishment and maintenance of Michigan's grasslands; fire helps prairies to grow by stimulating grass and wildflowers to reproduce, reducing competition from weeds, and discouraging the encroachment of shrubs and trees. For thousands of years, tree growth in tall grass prairies and shrublands was discouraged by the occasional wildfires that cleared the landscape every two to 50 years (Sargent and Carter 1999). Native Americans discovered that fire killed woody plants, but encouraged fruit-bearing shrubs and forage-producing grasslands. Albert (1994) identified no less than 16 ecological units where evidence of fire was a significant notation of the original Michigan land surveyors.

However, fire was greatly feared by many European settlers and continues to be feared by many of the more recent residents. This fear has resulted in a pattern of fire suppression, both of naturally caused wildfires and human-induced fires that are used as management tools for improving and maintaining habitats. This suppression has influenced both the rate of occurrence and the spatial extent of fires that occur. As a result, many of Michigan's fire-dependent systems have undergone considerable structural changes, or have completely succeeded to something else.