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The Geology and Ecosystems of the Great Lakes

The Great Lakes and surrounding waterways were formed by the Laurentide ice sheet, which covered most of Canada and the northern United States. around 20,000 years ago, the Laurentide ice sheet began to melt, as temperatures generally began to increase in the region, and the last Ice Age came to a close. As the mile-thick ice sheet retreated, the Great Lakes were carved, and they and many other lakes and rivers were filled and formed from the run-off meltwater from the receding glacier. The glacier also deposited and shifted sediments as it receded, creating the rolling hills that form some of the iconic landscapes of the St. Joseph County, such as the hills west of Three Rivers, and the hills north of Sturgis. These rolling hills formed from glacial sediments are called “moraines.”

By 2,000 to 4,000 years ago, the ecosystems of the Great Lakes were mostly defined. A mixture of pine forests, deciduous forests, swamps, prairies, and bogs comprise the majority of Michigans ecosystems, but many more could be found, with wondrous variation and interplay. Native American communities played a large role in the environment’s development as well. Many communities hunted, fished, and collected wild rice. The most important aspect of their influence, though, is their practice of setting controlled fires to clear land for domesticated crops, herd wild game to be hunted, maintain forest openings and trails, and fertilize land. These practices are credited for the establishment of one of the dominant ecosystems in the St. Joseph County region: the mixed oak savanna. The mixed oak savanna was a common ecosystem that accounted for nearly 6% of Michigan’s surface, common on sandy plains and rolling hills in southwest Michigan. James Fenimore Cooper, an American writer during the 19th century, described the oak savannas of Kalamazoo as such:

“The country was what was termed ‘rolling,’ … with some fancied resemblance to the surface of the ocean… the trees, with very few exceptions, were… ‘burr-oak’… and the spaces between them, always irregular, and often of singular beauty, have obtained the name of ‘openings’…’Oak Openings’ … the trees were of very uniform size, being little taller than pear trees… and having trunks that rarely attain two feet in diameter… in places they stand with regularity resembling that of an orchard, then, again, they are more scattered and more formal, … while breadths of the land are seen… that bear no small affinity to artificial lawns…”

These oak savannas are one of the ecosystems that prompted the first few American settlers and explorers to describe St. Joseph county as a Garden of Eden. Today, the oak savannas of Michigan are essentially non-existent, having been overrun since the forced removal of Native American communities from the area, and the conversion much of them into farmlands.

The Atlas of Early Michigan’s Forests, Grasslands, and Wetlands: An Interpretation of the 1816-1856 General Land Office Surveys, is considered an accurate representation of the ecosystems that have comprised Michigan for at least the last 2,000 years, and is digitalized in a tool that can be explored and utilized here:

Works Cited:

Albert, Dennis A., and Patrick J. Comer. Atlas of Early Michigan’s Forests, Grasslands, and Wetlands: An Interpretation of the 1816-1856 General Land Office Surveys. Michigan State University Press. 2008

Cooper, James F. Oak Openings; or, the Bee Hunter. Burgess, Stringer and Co. 1848

National Snow & Ice Data Center. “Glacier Landforms: Moraines.” All About Glaciers. 16 March 2020.

“Great Lakes ecoregion.” National Oceanic and Atmospheric Administration. 1 February 2019.

1827-1877 History of St. Joseph County, Michigan. L. H. Everts & Co. 1877.