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Natural Areas and Native and Exotic Species

The Extraordinary Natural Habitats of Northwest Indiana

The extraordinary diversity of the flora and fauna in the Lake Michigan coastal area is a result of several natural processes that have contributed to the formation of the shoreline. As the glacial ice retreated about 12,000 years ago, fluctuating lake levels in combination with wind and wave actions contributed to the formation of the physiography of the coastal area and influenced the distribution of the plant and animal species. Habitat formation resulted from the development of the Calumet Lacustrine Plain, the Valparaiso Morainal Area, and the stabilization of these areas by vegetation. The species diversity and complexity of the initial stabilizing plant communities changed with time, subsequently resulting in a series of habitat types ranging from bare sand to forest, and from open water to marsh.1

As the glacier retreated north, erosion continued to cut new channels and deepen existing channels, causing the elevation of the glacier formed lake to rise and fall - and rise and fall again. Three times the elevation of the lake stabilized at a particular level, marking these stages clearly in the Indiana Dunes in the form of beach ridges and wetland complexes. The sand hills, lined up in rows parallel to the lakeshore represent old shoreline dune complexes. The wetlands were lagoons or near shore channels between the beaches and offshore sand bars. The water level fluctuated many times before stabilizing approximately 2,000 years ago at approximately 575 to 585 feet above sea level; however, these stages are less distinct.2

The Indiana Dunes are known to biologists around the world. It was on the Indiana shores of Lake Michigan that ecology was developed as a scientific discipline. Here, at the turn of the century, Henry Chandler Cowles of the University of Chicago made his first observations on plant succession. The variety of species and habitats in general is also unusually large for such a small geographic area.3

This change from one type of habitat to another, such as bare sand to forest, is called plant succession. Plant succession explains the change from a simple to a complex plant community in a predictable, orderly process. During succession, the replacement community will continue to replace the less developed community until the ultimate community is developed, or the habitat is altered. Plant succession is influenced by surficial geology, soil type, nutrient availability, drainage, exposure, slope, and other factors. The general trend of plant succession in the coastal area, if undisturbed by man, is from (1) bare sand to forest, (2) old field to forest, and (3) open pond to swamp.4

A system of beaches and dunes is located on the immediate shore of Lake Michigan. The beach is formed by the erosion and deposition of sand by the lake. Sand dunes are formed by wind blown sand. The continual wind and wave action fuel the beach and dune system which is void of vegetation.

Beach grass is the first vegetation to become established in shifting sand beginning the gradual process of dune stabilization. Bearberry, a procumbent evergreen shrub, begins to occur just north of the beach grass. Species such as sumac, sand cherry, cottonwood, and prostrate juniper are present as elevation increases.

The dunes are characterized by a series of hills comprised of foredunes, interdunes, and backdunes. The interdunes are protected by the foredunes and as a result, moisture availability increases. The moisture allows the occurrence of basswood, oaks, tulip poplar, white pine, and ash. On drier ridges and slopes of the interdunes, black oak is the dominant species. The backdunes, the third row of sand hills from the lakeshore, are forested with black oak, white oak, and sassafras. Blueberry, greenbriar, false solomon's seal, and bracken fern occur in the understory. As moisture increases, Canada mayflower, Indiana cucumber, cinnamon fern, and royal fern begin to occur.

Interdunal Ponds at the Indiana Dunes National Lakeshore

Wetlands are numerous behind the backdunes and throughout the Calumet Lacustrine Plain. The majority of the wetlands were found during an inventory in 1976 to be present in the Indiana Dunes National Lakeshore and the Indiana Dunes State Park. There are site specific plants and animals that would perish without wetland habitats. Pitcher, sundew plants, and wild orchids are a few examples of plants dependent on wetlands. Animals dependent on wetland habitat include furbearers, marsh hawk, least common bittern, flycatchers, and herons.

Pitcher's Thistle and Black Tern

The Valparaiso Morainal Area, just south of the Calumet Lacustrine Plain, still contains forest areas although most of this area has been developed for urban or agricultural use. Forests include red oak, white oak, red maple, basswood, wild black cherry, white ash, and bluebeech. Forest types vary with exposure, soil type, nutrient, and soil availability.

Dune and Swale

Twenty-six percent of plants considered endangered or threatened in Indiana are found at the dunes; many of those plants are thriving here at the edges of their natural ranges. Other species are relics from glacial periods that are totally isolated from other populations of their kind.

Examples include two North Wood trees, the white cedar and the jack pine. Other northern plants surviving here include trailing arbutus and bearberry. Sea rocket and marram grass are usually found in the Atlantic coastal plain. Other species found near the shore are characteristic of the Appalachians such as the tulip tree and sassafras. Many of these species have adapted to their "new" habitats through changes. For example, leaves of the prickly pear cactus have all but vanished, a characteristic useful on sunny slopes of dunes. The bearberry's habit of growing in low, flat, clumps enables it to survive the harsh cold of northern winters as well as the winds blowing over the dunes. Species only found on the shores of Great Lakes also thrive here. These plants include silver-foliaged sand thistle and the glowing Kalm's St. Johnswort.5 The reptile and amphibian species not likely to occur outside the region include the western painted turtle, six-lined race runner, plains garter snake, western ribbon snake, and the western smooth green snake.

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