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A Geologic Glance at Ohio’s Prairie Past

By the Ohio Department of Natural Resources Fringed Orchid

The prairies that once covered what we now know as “Middle America” began forming 25 to 50 million years ago, following the creation of the Rocky Mountains. The immense mountain range became a barrier to the moist winds blowing eastward off the Pacific Ocean, robbing plants and animals of a vital resource.

Over immense stretches of time, plants that were adapted to drier climates replaced the rain-dependent forests that formerly covered the interior of our country. This was the beginning of today’s vast prairies that extended from Texas northward into Canada, and from the Rocky Mountains eastward into Illinois.

But in nature, nothing remains the same. Between 25 and 2 million years ago, colder climatic conditions descended over the earth, ushering in the Ice Age. As the mercury dropped, isolated “islands” of prairie are thought to have intermittently extended into the hardwood forest of what would become Ohio, only to retreat westward with the onset of wetter conditions.

Continental glaciers repeatedly advanced into the future state of Ohio some 2 million years ago and continued this pattern until just 14,000 years ago. As glaciers pushed southward, a northern coniferous forest of pine, spruce and fir moved ahead of the ice, replacing the beech, oak, maple, elm and ash trees of a deciduous forest – and quite likely some prairie.

A “rapid” retreat of glacial ice began around 18,000 years ago, and as the earth warmed, trees of the northern coniferous forest began to disappear. By 6,000 years ago, our modern deciduous forest had begun to establish itself, consisting of familiar hardwoods of today such as oak, hickory, beech, elm, ash and ironwood.

As the climate continued to warm, and drier conditions followed, there was an eastward expansion of the western prairie into central Ohio. Still, the geologic time clock kept on ticking. By the time of European settlement, only a few small areas of prairie remained, as a moister climate helped the eastern forest expand its range westward into Indiana and Illinois.

Today, scattered pockets of prairie habitat can be found in places such as the Oak Openings region of northwest Ohio and elsewhere that environmental conditions favor the establishment of grasslands more than forests.

Kitty Todd and Irwin Prairie state nature preserves are two excellent examples of Ohio’s prairie past. You can explore these distinctive habitats in person or online. For more information, visit ohiodnr.com/dnap

Ohio Governor’s Residence and Heritage Garden
358 North Parkview Ave., Columbus, Ohio 43209
Phone: 614-644-7644 Fax: 614-252-7076