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Coastal Geomorphology & Habitats

The following information was developed by the Michigan Chapter of The Nature Conservancy.

Cobble & Bedrock Beach
Conifer Swamp
Great Lakes Marsh
Sand Beach & Open Dunes
Wooded Dune & Swale

Cobble & Bedrock Beach

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Click here to view full size picture Cobble beach and bedrock beach are two rocky beach types that occur where limestone bedrock forms the shore of Lake Huron or Lake Michigan. From the air, this narrow beach zone is dramatically white due to the limestone cobblestones, boulders or fractured bedrock there. Occasionally cobble-bedrock beach areas include sandy beach or dunes in small sheltered bays where sand collects on top of cobbles. In other places sand is rare and huge boulders deposited by glaciers now lie exposed, hewn by wind and waves.

The Great Lakes limestone that forms cobble-bedrock beaches is part of a large geologic formation called the Niagara escarpment. This formation is responsible for Niagara Falls to the east, the cliffs in Wisconsin's Door Peninsula to the west, and parts of the Upper Peninsula's southern shoreline. Limestone is chalky and calcium-rich and erodes to make soils that are highly alkaline. Such soils help provide habitat for a number of rare plants, some found only along northern Lake Huron and Lake Michigan.

Only certain plants can survive in the chalky, calcium-rich soil on these rocky beaches, which are constantly exposed to wind, ice, changing lake levels and lapping waves. Perhaps one of the most beautiful plants of this shoreline is the dwarf lake iris, a rare species that typically grows immediately out of reach of high waters under conifer trees and shrubs on the edge of the beach. Another rare plant is Houghton's goldenrod, whose seeds germinate in shoreline cleared of competing plants. It typically likes bedrock cracks or the wet, sandy margins of cobble beaches. Orange lichen survives in this beach zone by hugging tightly to the tops of rocks, keeping a low profile against summer waves and winter ice. Animals utilize cobble-bedrock beach for many reasons. Birds perch in nearby trees from which they can fly to feed on insects, frogs or fish in neighboring marshes, swamps or forests. Mammals use the shoreline as a travel and feeding corridor.

Conifer Swamp

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Click here to view full size picture Conifer swamp is a wooded wetland dominated by coniferous trees such as Northern white cedar, tamarack, balsam fir, and black spruce. Many people refer to conifer swamps as cedar swamps because Northern white cedar is often the dominant tree species.

Conifer swamps contain a waterlogged soil that is rich in nutrients and organic matter. Since conifer swamps are typically found in the floodplains of rivers and lakes, their soils frequently receive nutrients from early spring floodings. Conifer swamps are common on shorelines adjacent to Great Lakes marsh as well as inland around ponds, streams, and lakes.

The soils of a conifer swamp are rich in nutrients and moist most of the year, encouraging water and nutrient-loving plants to grow, such as Northern white cedar, black spruce, balsam fir, tamarack, and calyso orchid. This plant life supports a variety of animals. For example, white-tailed deer seek tasty cedar needles, while the bobcat and wolf seek the seclusion of evergreen trees to stalk prey such as mice, rabbits or deer. Birds enjoy the density and variety of trees to feed, rest, and nest. The hermit thrush builds its nest among dense jumbles of sticks, mosses and needles on the forest floor. The pileated woodpecker creates big holes in large white cedar and other trees, seeking insects which burrow into them. The black-backed woodpecker, rare in this region, flakes bark off of dead or dying trees to find beetle larvae. And black-throated green warblers prefer to hide their nests in conifer trees. The shallow waters in this natural community are also good feeding, breeding and egg-laying areas for amphibians such as the spring peeper, Michigan's tiniest frog.

Great Lakes Marsh

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Click here to view full size picture Great lakes marsh is an increasingly rare freshwater natural community of the Great Lakes watershed. This natural community can extend over several square miles and usually occurs in protected or semi-protected bays or at river mouths. Today 80% of the Great Lakes marshes have been destroyed for agriculture or development. Many of the best remaining marshes exist on the northern Lake Huron shoreline in Michigan and Ontario.

Freshwater marshes are the third most productive ecosystem on earth -- in terms of vegetation biomass -- after tropical rainforests and saltwater estuaries. Great Lakes marshes include underwater plants, partially submerged plants and onshore plants, all of which are dependent on natural water level fluctuations. A line of trees is usually found at a marsh's high water mark. The high productivity and variety of bulrushes, sedges, and other plant life in a marsh make it an important habitat for numerous insects and thus the base of the food chain for larger animals like fish, songbirds, waterfowl, and mammals.

Marshlands have a high production rate of plant and animal life. Emergent and submerged plants provide essential cover, spawning grounds and feeding areas for many native fish such as yellow perch, smallmouth bass and northern pike. Many familiar flying insects such as mayflies, mosquitoes and midges spend their juvenile stages underwater in a Great Lakes marsh. In their different life stages they provide food for many types of predatory animals, such as dragonflies, tree swallows, and fish. The reeds, rushes and sedges in a Great Lakes marsh provide cover for the nesting of several kinds of birds such as black tern and American bittern. For protection from predators, bitterns rely on camouflage in the marsh more than flight. The marsh waterline is an important area where wave action erodes marsh plants, leaving bare mud or rock where exposed plant seeds can germinate. As Great Lakes water levels naturally rise and fall, all plants -- from submerged to emergent to onshore --move landward or lakeward seeking the growing conditions they prefer.

Sand Beach & Open Dunes

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Click here to view full size picture The collection of freshwater sand beaches and open dunes in the Great Lakes watershed is the largest in the world. Sand beaches and open dunes are closely linked ecologically and in the way they are formed. Sand beaches form when small pebbles and sand are deposited on sheltered shores and bays by wind, waves, and nearshore currents. Dunes form above the sandy beach as winds blow eroded and dried sands inland.

These sandy areas are subject to constant erosional change. Although erosion is a natural process, overuse of these areas, particularly dune areas, accelerate erosion and destroy plant life. Building and road construction and off-road vehicles are particularly damaging.

This is a highly dynamic natural community based on sand. The movement of sand ranges from free-blowing sand to sands that have become stabilized by plants. Despite strong wind, blowing sand, waves and severe extremes of drought and flooding, many plant species have specialized adaptation to these conditions. Sea rocket and clumps of marram grass tend to be the first plants to colonize sand beach areas. They are often followed by beach pea, bearberry, Lake Huron tansy, hoary puccoon, Pitcher's thistle, among other plants. As these early colonizing grasses develop and begin to hold more sand on dune ridges, woody plants such as white pine trees can grow. Despite inhospitably hot, cold, dry, wet and windy conditions, insects such as tiger beetles, ants and butterflies inhabit this area. Several kinds of shorebirds nest along the beach or in the dunes. One such shorebird is the spotted sandpiper, which lays its eggs in a small nest directly on thesand. Sandpipers, plovers, and other shorebirds feed on tiny insects and plants at the water's edge and in interdunal wetlands.

Wooded Dune & Swale

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Click here to view full size picture Wooded dune and swale is a natural community that began developing in certain sheltered, shallow, sand-receiving bays when Great Lakes water levels were higher than they are today. As lake levels dropped, new dunes formed in front of older ones, creating long, parallel ridges a mile or more deep. Slowly, over thousands of years, dune and swale habitat formed through the combined processes of water level changes, sand deposition, and wind. Today the higher, gently-rolling dunes are covered by a mixture of conifer and deciduous trees, while the low-lying swales contain conifer swamps, wet meadow and marshes.

One of the finest and largest examples of dune and swale habitat in the world is adjacent to Pointe Aux Chenes on Lake Michigan, east of St. Ignace in the Hiawatha National Forest. This area contains hundreds of successive dunes interwoven with wetlands.

Dry lands and wetlands sit side by side in a wooded dune and swale community, which provides a unique concentration of homes for plants and animals -- from osprey, to waterfowl, to beaver, to Houghton's goldenrod. The wetlands of this habitat are often close to Great Lakes shorelines and consequently support many insects and small amphibians, such as frogs, which provide food for area birds, mammals, reptiles and fish within the shoreline ecosystem.

Swales are low troughs between two successive dunes, forming a marsh that often resembles a Great Lakes marsh but is less dependent on lake-level fluctuations to maintain itself. These wetter areas are perfect for birds such as the common yellowthroat, which nest in shrubs close to water. Animals such as red fox, American redstart and white-tailed deer, most often occupy the drier areas, while others such as moose enjoy both wet and dry places.
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