 Glaciers, Rocks, and Relics
The natural environment has its own story to tell at Fort Sheridan. Among the prairie, oak savanna, bluffs, ravines, and Lake Michigan shoreline lies a living tapestry of history, wildlife, and a landscape that once thrived across the Midwest heartland.
Glacial shaping
Fort Sheridan is situated on the Highland Park or Valparaiso glacial moraine. The origins of Lake Michigan and all of the Great Lakes started in the Pleistocene Epoch — the most recent Ice Age — which ended 10,000 years ago. As glaciers began to melt and move northward, the broad basins of the lakes formed. Further, runoff water from the glaciers combined with rainwater to carve out large gullies — called "ravines" — near the shorelines. The rocks, boulders, clay, and sand deposited by the advancing glaciers helped to create habitats that support Illinois' diverse biological ecosystems.
Six ravines, named for men who played a role in the fort's history, are located within Fort Sheridan's boundaries and support some rare examples of mesic and dry-mesic upland forests. These are hardwood-dominated forests found on sand or loamy sand soils left over from glacial outwash.
mesic: A moderately moist environment; one without moisture extremes
dry-mesic: An environment with well-drained soil; drier than a mesic environment
loamy: A soil comprised of a mixture of sand, clay, silt, and organic matter |
Ravines are sheltered from the wind, protected from prairie fires, and relatively shaded from sunlight, which makes them cool and moist habitats. Typically, the temperature in a ravine is noticeably lower and slower to change than the areas surrounding it. This fragile ecosystem provides a habitat for several endangered and threatened species. Certain plants thrive in the ravines' moist environment as well, including witch hazel, pagoda dogwood, sugar maple, and Canada mayflower. Because of their sensitive nature, Fort Sheridan's ravines are off-limits to the public.
Rarities of nature
The bluffs that border the fort along the shore of Lake Michigan provide a rare example of natural, open prairie-like vegetation that used to thrive along the lakeshore. Similarly, the open oak forest at Fort Sheridan is a rare find in the area. Located in an area between prairie and forest, it is characterized by small groves of oaks that tower above grassy areas and wildflowers.
Historically, natural fires eliminated competing trees and woody vegetation in savannas and prairies. Because oaks have a large root system and thick bark, they were more resistant to these fires. Open oak forests are rare ecosystems today because we generally suppress wildfires. Without these fires, woody plants and trees invade, turning these environments into brushy woodland areas with taller woody plants that shade out prairie grasses and wildflowers.
Along the shore
In addition to the nearly 60 species of birds that live in the area year-round, many other birds stop for only part of the year on their way to nesting grounds in other parts of the continent. Fort Sheridan is located along one of the busiest migratory bird flyways – the Mississippi Flyway. Warblers, waterfowl, shorebirds, sparrows, and birds of prey, such as hawks and falcons, are a sampling of the approximate 140 birds that migrate through Fort Sheridan each year.
Birds fly along the lakeshore for several reasons. The lake's vegetation, fish, and crustaceans serve as a valuable food source. The shoreline provides nutrient-rich aquatic plants, filled with insects and other invertebrates. If birds are tired from their flight, they rest along the beachfront or in surrounding trees.
An ongoing challenge to the Lake County Forest Preserves is the elimination of non-native plant species at Fort Sheridan. These invasive plants grow rapidly and spread freely, displacing existing vegetation and forming dense one-species areas. One such aggressive species, lyme grass, is found along the beaches and bluffs of the lakefront. The Forest Preserves has begun to replace lyme grass with native grasses such as little bluestem, sand reed, and Canadian rye. Because lyme grass helps protect the bluffs from erosion, native grasses must be substituted gradually to limit exposure to this damaging erosion.
Looking ahead
Fort Sheridan's natural landscape provided the ideal setting for the rigors of military training in the past, and its legacy will continue. The Lake County Forest Preserves has made a commitment to restore native plants to the natural prairie areas along the bluffs of Lake Michigan and to preserve the lakeshore ravine forests, including Janes Ravine in the northern part of the preserve. Restoration includes planting trees and vegetation and creating natural buffers along the tops of the ravines. Storm water will also be re-routed to prevent ravine erosion and access to fragile areas will be restricted, ensuring that the history of the land carries on into the future.
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