Sand Dunes

Dunes are created when:
"1. a plentiful supply of sand combines with,
2. wind blowing mostly from one direction, and
3. a natural trap causes the wind to drop the sand" (United States).

Indiana sand dunes are part of the Lake Michigan border section located in the northwestern part of the state. Dune land is made up of sand and piles of rocky glacial till (a mixture of sand, clay, and gravel), which are called moraines. Moraines were formed by past glacier movement that deposited till along its path. The sand piles are evidence of the lake's annual recession. For example, due to the northwest winds, Mt. Baldy, which is one of the tallest sand dunes standing at 123 feet, advances inland at a rate of four to five feet a year.

The dunes are adjacent to Lake Michigan and occupy only a narrow strip of land, a few miles wide at most. A few remnants of "older" sand dunes that extended as far south as Valparaiso (older because, as the lake shrank back in stages, new shoreline formed farther north) still exist as well. However, most of these older dunes and their adjoining ecosystems (such as wetlands and forests) have been leveled and drained for industrial or agricultural purposes.

The first person to recognize the diversity of this rich collection of habitats was Henry Chandler Cowles, a professor at the University of Chicago. Because of Cowles' explorations, beginning in the late 1800s, ecology was developed as a scientific discipline on the Indiana shores of Lake Michigan.

Cowles noted and observed natural systems, such as plant succession, which is the "change from one type of habitat to another.... [It] explains the change from a simple to a complex plant community in a predictable, orderly process" (State of Indiana). The dunes ecosystem represents a thorough example of plant succession. The sand dunes are part of a 15,000-acre expanse of shoreline, forest, and wetlands. On the beach, only a few strong plants, such as sea rocket, bug-seed, and seaside spurge, survive. The next sandy layer back is called the foredune, which is characterized by deep-rooted grasses, such as the little bluestem, beach grass, sand-reed grass, as well as some shrubbery. Pannes, which are shallow depressions in the sand caused by the wind and that retain water much of the year, are scattered among the foredunes. The shoreline and foredunes could also be classified as prairie ecosystems since they are dry, and only deep-rooted, tough plants can survive there.

The foredunes are then followed by the high dunes, where two plant communities exist. The south-facing slopes are composed of a savanna of white and black oaks and wildflowers, while the north-facing slopes are covered with red oaks, basswood, and flowering dogwood. This high dune area gives way to upland and lowland forests, which together constitute the majority of the area. The upland forests are made up of three forest types: oak, coniferous, and mixed deciduous. The lowland forests are the second largest habitat in the area behind the upland forests.

Finally, within these habitats lie several types of wetlands, including marshes, aquatic shrublands, swamps, bogs, pannes, and open water.

Several animal species make up the population in the dune habitats, including the white-footed mouse (plus several other species of mice and rats), raccoons, white-tailed deer, short-tailed shrews, possums, woodchucks, rabbits, squirrels, bats, and, specific to the wetland area, muskrats.

It is hard to believe that an ecosystem that is home to so many plants and animals, and that supports several habitats, was once thought by the early settlers to be a wasteland. On the contrary, the sand dunes are a rich example of Indiana's diverse landscape.

Sources:

State of Indiana. Dept. of Natural Resources. "Natural Areas and Native and Exotic Species." A Synthesis of Major Topics in the Lake Michigan Coastal Area. 2000. 13 Nov. 2002 <www.state.in.us/nrc_dnr/lakemichigan/natural/
natural1.html>.

United States. National Park Service. "Geology Fieldnotes: Indiana Dunes National Lakeshore." Geology of Indiana Dunes National Lakeshore. 26 Jan. 1998. 27 June 2004 <www2.nature.nps.gov/grd/parks/indu/>.

Whitaker, John O., Jr., John Gibble, and Eric Kjellmark. Mammals of Indiana Dunes National Lakeshore. Washington: National Park Service, 1994.