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Coastal Dunes

The windswept dunes gracing Michigan's Great Lakes shoreline represent the largest collection of freshwater dunes in the world. The diversity of environmental elements wildlife, topographic relief, vegetation, habitats, and climatic conditions occurring within these landforms represent a phenomenon unique to the State of Michigan.

 
History

Michigan's glacial history provides an explanation for the formation of dunes. The Great Lakes dune complex is relatively young, in terms of geological time. As recently as 16,000 years ago, Michigan was covered with glacial ice thousands of feet thick. This glacial ice contained a mix of boulders, cobbles, sand, and clay. During glacial melting, this deposit was left and is known as glacial drift.

This glacial drift is the source of sand in most of Michigan's dunes. The sands were either eroded from glacial drift along the coast by wave activity or eroded from inland deposits and carried by rivers and streams. Only the hardest, smallest, and least soluble sand grains were moved. Waves and currents eventually moved these tiny rocks inland, creating beaches along the Great Lakes shoreline.

Winds, blowing shoreward at speeds of 8 to 25 miles per hour, begin to move the sand grains. The size of grains which are moving is directly related to wind velocity larger grains require higher wind speeds. These bouncing sand grains resemble tiny, skipping ping pong balls as they are moved by the wind through a process called saltation. Colliding with each other, barely a foot or two off the ground, they may meet a slight obstruction, such as a clump of grass, which deflects the wind and allows sand grains to drop. Thus a slight mound or hummock is created.

The wind continues to push sand grains up the windward side of the dune crest, causing the dune to grow in the downwind direction. Many sand grains continue moving and eventually roll down the steep backslope. A dune is slowly being formed, and its continued growth depends upon perennial vegetation, wind, and sand. Because dune plants act as barriers to sand movement and hold migrating sand, they play a critical role in the formation and stabilization of dunes.

 
Major Dune Types

Parallel dunes are series of low, linear dunes formed parallel to the shores of large shallow bays. The parallel dunes along the eastern shore of Lake Michigan were formed about 4,000 years ago during the Lake Nipissing stage of Lake Michigan, when water levels were 25 to 30 feet higher than present day Lake Michigan water levels. Rivers entering the bays carried abundant sand, which was then moved along the shore by lake currents.

On shore winds formed these sands into low lying dunes. As the water level of ancient Lake Nipissing dropped, a series of parallel dunes were created. They occurred in areas that were formerly wide bays in Lake Nipissing.

Today, some examples of parallel dune complexes can be seen at the mouth of rivers, including the Muskegon, Kalamazoo, and Grand. Remnants of several ancient bays now are coastal lakes, such as Hamlin Lake in Mason County, Silver Lake in Oceana County, and White Lake in Muskegon County.

Blowouts are saddle shaped or U shaped (parabolic) depressions in a stabilized sand dune, caused by the local destabilization of the dune sands. Blowouts, which originate on the summit or windward face of a dune, are often rapidly formed by the wind, creating narrow channels and exposing plant roots. Blowouts can create interruptions in the shape of parallel dunes that may result in deeply carved indentions called parabolic dunes. It is the combination of interwoven parallel dune ridges and U shaped depressions, including parabolic dunes, that characterizes the classic dunes from Indiana, northward to Ludington, in Michigan.

The moving sand from the blowouts often buries forests on the steep lee slopes. Blowouts may also uncover the bleached trunks of trees still standing after being buried in the dry sand for hundreds of years. These "ghost forests" are silent testimonials to ancient forests buried by blowouts in the past.

Blowouts have historically been caused by natural disturbances, such as fires, wind storms, or plant diseases. However, in recent decades, human activities and disturbance or destruction of sand holding vegetation has initiated blowouts. Off road vehicle traffic and human foot traffic are major causes, but clearing of protective dune vegetation to build homes, cottages, and commercial buildings has also resulted in large scale wind erosion man made blowouts. Continuous human disturbance has the potential for much more widespread destabilization because it does not allow blowouts to stabilize.

Perched dunes are some of the more famous and most spectacular land features in Michigan. They are actually wind blown sand dunes perched atop glacial moraines. Glacial moraines, common landforms in Michigan, are ridges of sand, gravel, stone or clay left by retreating glacial ice. The moraines lying along the present shoreline of the Great Lakes were subjected to wind and wave erosion. Sand, moved by waves and long shore currents, was blown up the steep faces of the moraines by on shore winds, accumulating along the summits and leeward sides, forming perched dunes. The famous dunes at Sleeping Bear Dunes National Lakeshore are a well known example. Others include those on the Manitou and Fox Islands in northern Lake Michigan and Grand Sable Banks near Grand Marais in Lake Superior.

 
Dune Life Zones

The dune ecosystem is made of several zones with very different physical characteristics. They are as follows:

Beaches are zones where water meets land. The constant movement of sand by the wind, pounding storm waves, and winter ice and snow make this a formidable habitat for any living thing. For this reason, few plants or animals live on the beach. Most wildlife seen there are just visitors. Among these visitors are scavengers ranging in size from small flies and beetles to shore birds, herring gulls, and even bald eagles. The remains of fish, birds, and insects washed ashore provide food.

Mammals that venture down to the beach include the raccoon, skunk and fox, which wait until dark to search the shoreline for food. A recent study conducted on North Manitou Island revealed an unexpected scavenger: white tailed deer that feed on dead alewives.

The sea rocket is one of the few plants specially adapted to withstand the pounding of waves and other adverse conditions. It sinks its roots to the water table and stores water in its succulent leaves.

The foredune is the first ridge behind the beach. Although foredunes are above wave action most of the time, they are regularly subject to storm waves.

Like the beach, life in the foredune is a daily struggle against shifting sand, scarcity of nutrients, rapid water drainage, high evaporation rates, and storms. Out of the reach of waves, a few hardy plants, such as marram grass and sand reed grass, are able to survive. These grasses are known as pioneer species, because they are one of the first plants to become established, and they create habitat for other plants by stabilizing the soil with their extensive root systems, thus increasing the soil's capacity to retain water and nutrients. Marram grass spreads quickly by sending stems to the surface to form new plants. As drifting sand accumulates in the marrarn grass, the central stem continues to grow, keeping the plant's leaves exposed to the sun and air. This keeps the grass from being buried and increases the height of the foredune.

A foredune stabilized by these grasses can host a wide variety of wildflowers and shrubs. They include beautiful clusters of the yellow hairy puccoon, the common milkweed, beach pea, sand cress, smooth rose, bearberry, poison ivy, wild grape and sand cherry. Foredunes will remain stable as long as the vegetation is undisturbed.

Unlike plants, animals can escape the extreme temperatures and harsh conditions. Most birds migrate seasonally or retreat daily to the cover of heavy vegetation. Many animals are nocturnal and are most active during the cooler nighttime hours. Like the plants, animals that live on the grass covered foredune have special adaptations that help them survive the extreme temperatures of summer and winter. Surface temperatures on the open dunes can reach 120 degrees Fahrenheit. The sand wolf spider is adapted to extreme temperatures by living in a burrow deep under the sand. Its sandy brown color also helps it blend into its surroundings when leaving its burrow home.

Interdunal wetlands are shallow ponds or pools located between dunes. They typically are found between low dunes or sand spits created when water levels drop or as shoreline currents change. Ponds may vanish during dry periods. These fluctuations in water table are important for plants such as the threatened Houghton's goldenrod.

The animals and plants found in and around interdunal wetlands are similar to those inhabiting most ponds. Insects like water striders may skate across the surface. Whirligig beetles make erratic patterns on the surface. Shorebirds, like the greater yellow legs, feed on the rich insect life. Spikerushes and sedges grow in the shallows.

Dune forests can be found on stabilized dunes protected from intense wind erosion. The dominant forest type varies as one travels north along the coastline. In southern Michigan dunes, oak hickory forests are common. Northern dune forests are dominated by beech, maple and hemlock.

The uniqueness of dune forests stems from the fact that they develop on steep, barren sand slopes that are a short distance from open dunes. The contrast between the cool, shaded dune forest and the extreme temperatures and intense sunlight of the open dune can be striking. Though thin and slow to accumulate, the topsoil of dune forests supports a variety of spring wildflowers and woodland plants.

Studies of dune slopes reveal varying patterns of vegetation, depending on the direction of sunlight and the amount of shade, moisture, and protection from the wind. For example, Eastern hemlocks prefer shady, north facing slopes. Spring wildflowers such as the white trillium bloom in abundance on south facing slopes where they can absorb more sunlight.

 
Vegetation and Ecology

Lichens, fungi, mosses, grasses, wildflowers, shrubs and trees all are part of a dunescape. All dune plants must adjust their survival to the harsh environment. Drying winds, low soil moisture and fertility, and intense sunlight along with blowing sand are conditions that affect the growth of dune vegetation. In the most active parts of the dune, only a few species of grass and shrubs can survive; on more protected areas, forests become established.

Dune plants have evolved special adaptations to the harsh environment. Some are gray green and covered with tiny hairs that act like a reflective blanket, reflecting light to prevent heat loss and aiding in transpiration. The sea rocket, a member of the mustard family, has fleshy stems that hold moisture. Its root system is able to withstand continual wave action at the shoreline.

As sturdy as they seem, dune plants are especially sensitive to human disturbance. Walking or driving all-terrain vehicles on them may cause destruction of surface vegetation and root die off. This exposes a dune to wind erosion, allowing the sand to move or open up channels in its form. Without sand dune plants, the integrity and preservation of a stable dune complex cannot exist.

Many of the fundamental concepts of plant succession and ecology were first identified as a result of studies made on Lake Michigan's sand dunes. The struggle of plant communities to pioneer and evolve on barren sand is a complex process known as succession, in which natural communities replace each other. Each stage of plant succession creates different microenvironments. These microenvironments are created by changes in temperature, moisture, and light intensity caused by plants and animals occupying the site.

Dune systems are well suited for the study of succession and ecological change because of the rapid changes which occur. For example, when drops in lake levels expose sand spits or create new foredunes, these features are rapidly colonized by beach grass. Within one or two human generations the vegetation can change from beach grass to shrubs to trees. Storms and high lake levels can cause an even more rapid change in plant communities.

 
Sand Dune Legislation

Coastal dunes are in danger of being destroyed by overuse, misuse, and unwise development. They are popular sites for home building, off road vehicle use and other intensive recreational uses, as well as sand mining and other commercial activities. Such activities, when allowed to continue in an uncontrolled and improper way, may result in dune destruction. Recognizing this threat, the people of Michigan enacted legislation in 1989 to more adequately ensure protection of the dunes. The Sand Dunes Protection and Management Program, being part of 353 of the Natural Resources and Environmental Protection Act, 1994 PA 451, forms the basis for protecting sand dunes from indiscriminate development. Part 353 establishes protective standards on dunes considered to be the most sensitive. Such areas are now legally defined as critical dunes and include approximately 70,000 acres along the shorelines of Lakes Michigan and Superior. Critical dunes are designated by the acts and are identified in the Atlas of Critical Dunes, dated February 1989, developed by the Land and Water Management Division, Department of Environmental Quality (DEQ).

Passage of Part 353 came after years of effort by Governor James J. Blanchard, a number of legislators, representatives of local governments, environmental groups, the Natural Resources Commission, and the DEQ. Part 353 originally amended the Sand Dunes Protection and Management Act, 1976 PA 222, by expanding regulated uses to include commercial, residential, and industrial developments, in addition to the mining industry already regulated by the existing act. The standards in the acts are intended to ensure that the dunes are protected when new uses and developments are proposed that significantly alter the physical characteristics of a critical dune area. The standards, among other things, require new uses to be set back behind the crest of a critical dune, limit the amount of grading and vegetation removal allowed, and prohibit construction on steep slopes.

 
Conservation

Michigan's shoreline is a showcase for 275,000 acres of sand dune formations. An interaction between blustery winds and waves has moved and carved fine sands into the largest display of freshwater dunes in the world. These beautiful sand formations contain a diversity of life, climatic conditions, and geological relief unique to Michigan.

The dunes are not only one of the State's most spectacular natural features, they also are one of its most fragile. Development and recreational pressures are increasing as more and more people seek the unparalleled scenery the dunes provide. This makes it imperative that people understand and appreciate the environmental sensitivity of sand dunes.

Approximately 40 percent of the coastal dunes are in public ownership and managed by federal, state, or local units of government. State owned lands are managed by the DEQ and DNR/Natural Resources Commission policy guidelines designed to fit the appropriate use with the sensitivity level of each dune area. The DEQ and DNR will continue to coordinate and cooperate with federal and local units of government to develop consistent management plans for all public sand dune areas.

A visit to a sand dune provides an opportunity to experience a landscape of natural sounds, smells, and sights. Feeling the clean sand beneath your feet as the fresh lake breezes bathe your face is one of the values of Michigan's magnificent sand dunes. We have a responsibility to protect and preserve this natural legacy for the enjoyment and wise use by our present and future generations.

 
Plants and Animals of Coastal Dunes

American Goldfinch
Bank Swallow
Beach Pea
Beech
Black-bellied Plover
Broad-winged Hawk
Caspian Tern
Clustered Broom-rape
Common Loon
Cormorant
Cottonwood
Creeping Juniper
Dune Willow
Eastern Box Turtle
Eastern Hog-nosed Snake
Greater Yellow-legs
Hairy Puccoon
Harebell
Herring Gull
Houghton's Goldenrod
Jack Pine
Lake Huron Locust
Maple (various species)
Marram Grass
Milkweed
Monarch Butterfly
Piping Plover
Pitcher's Thistle
Poison Ivy
Red Fox
Red-tailed Hawk
Ring-billed Gull
Riverbank Grape
Sand Cherry
Sand Reed Grass
Sanderling
Sea-rocket
Semipalmated Sandpiper
Turkey Vulture
White Cedar
White Pine
White-tailed Deer
Wormwood

 
Sand Dune Viewing Areas

Listed in the linked table are locations where sand dunes can be found and enjoyed in Michigan. Remember that dune habitats are fragile and easily damaged by human activity. Visit these areas in small groups and use boardwalks or special viewing platforms when available.


References

Dune Country A Guide For Hikers and Naturalists, Glenda Daniel, The Shallow Press, Inc. , Chicago, 1977.

The Geology of Michigan, John A. Dorr and Donald F Eschman, University of Michigan Press, Ann Arbor, Michigan, 1970.

Sand Dunes, A Geologic Sketch, Robert W. Kelley, Michigan Department of Natural Resources, Lansing, Michigan, 1962.

Pattern of Revegetation of a Shoreline Dune Area, Allegan County, Michigan, R. L. Reinking and D. G. Gephart, The Michigan Academician, Volume 11, Number 2, Fall 1978.

Vegetation and Common Plants of Sleeping Bear, P W. Thompson, Cranbrook Institute of Science, Bulletin 52, Bloomfield Hills, Michigan, 1967.

A Guide To Sand Dune and Coastal Ecosystem Functional Relationships, Joan M. Peterson and Dr. Eckhart Dersch, Michigan Cooperative Extension Service. Extension Bulletin E 1529 MICHU SG 81 501.

Coasts, Chapter 6 "Coastal Dunes", E. C. F. Bird Cambridge, Mass; M. 1. T Press 1969.