Sunday, June 30, 2024

Nature: A portal to Ohio's glacial past can be found at Cedar Bog


A fen meadow, full of rare plants, surrounded by white cedar, can be seen at Cedar Bog/Jim McCormac

The Columbus Dispatch
June 30, 2024

Jim McCormac

One of Ohio’s greatest biological hotspots lies less than an hour’s drive west of Columbus.

Cedar Bog is a fascinating place; a glacial relict populated with flora that one would normally have to venture far to the north of Ohio to see.

At the time of European settlement, the Mad River Valley west and south of Urbana harbored a massive 7,000-acre “swamp”. The word swamp is a catch-all term for a variety of wetlands, and the Mad River swamp deserves more discriminating nomenclature.

In 1974, geologist Jane Forsyth did just that, coining what by then had become known as Cedar Bog as a boreal fen.

Boreal refers to northerly regions and is an apropos descriptor for Cedar Bog. The Pleistocene epoch brought the last global ice age, commencing about 2.5 million years ago. As the sheets of ice slowly expanded south, they bulldozed the landscape, creating valleys and depressions suitable for northern plant species.

As the climate then was much colder, boreal plants, such as spruce, fir, tamarack and many others, flourished in what would much later become known as Ohio.

A warming climate eventually spurred the retreat of the glaciers and they had receded to the north of Ohio by about 12,000 years ago. Boreal flora was slowly replaced with more southerly plants, except around the margins of cold glacial lakes and specialized peatlands known as bogs and fens.

Cedar Bog was one of the largest and is exceptional in that it hosts plants of boreal regions and westerly wet prairies. It should be noted that Cedar “Bog” is really a fen. Fens are fed by groundwater while bogs receive water from rainfall.

Soon after settlers pushed into the Mad River Valley, they set about clearing timber and draining the great swamp. Ultimately, all but the 450-acres that comprise present-day Cedar Bog were destroyed, the once tremendous floristic diversity replaced by the ubiquitous fodder of America’s bread basket: corn, soybeans and wheat.

Well over 90% of Ohio’s peatlands that were documented post-settlement have been destroyed. Fortunately, conservationists were able to rally to protect what remained of Cedar Bog, and in 1942, the state provided funds for its purchase and the site was turned over to the Ohio Historical Society (now Ohio History Connection).

The National Park Service designated it a National Natural Landmark in 1967, and it was dedicated as a state nature preserve in 1979.

I’ve visited Cedar Bog scores of times, most recently on June 22. It was a special-event day, with Chelsea Gottfried, co-author of the book "Gardening for Moths," speaking about our nocturnal butterflies to about 55 people.

Shauna Weyrauch and I attended and arrived an hour early to explore the extensive boardwalk.

Immediately obvious upon entering Cedar Bog are the namesake white cedars. This is a northern tree, and Cedar Bog is the only wetland in Ohio dominated by white cedar. One must venture about 250 miles to the north before cedar “swamps” start to become common.

The bright orange flowers of Michigan lilies caught our eye. The spectacular plants are having a boom year and can’t be missed. Showy grass-pink orchids dotted the fen meadows, and there were large drifts of fen Indian plantain, a strange member of the sunflower family.

Brilliant magenta spikes of spotted phlox provided jots of color amongst the sedges, and we were pleased to see the wand lily in peak bloom. The latter sometimes goes by the name “death camas” due to its toxic alkaloids.

Cedar Bog hosts one of the highest densities of rare plants of any site in the state. Probably the most famous of these is the showy lady’s slipper, a huge orchid with massive pink and white flowers. There are only about five Ohio sites, and Cedar Bog is by far the largest. They’re through for the season, but plan on visiting late spring/early summer next year to see them at prime time.

Visitors are often surprised to see lizards racing along the boardwalk. They’re five-lined skinks and are common. So is America’s smallest dragonfly, the endangered elfin skimmer. It’s less than an inch in length and is a fen and bog specialist.

Elfin skimmers lurk in the sedges, along with a threatened damselfly, the seepage dancer. Sharp-eyed observers will find them right along the boardwalk.

Mark your calendar for July 6 when firefly expert Matthew Speights delivers a presentation followed by a nocturnal foray into the fen to see an amazing insectivorous lightshow.

Cedar Bog offers a portal into Ohio’s glacial past, without having to drive several hundred miles to the north.

A visit is always interesting and the dedicated volunteers and Maddie Brown, the site manager, are a wealth of information. For hours and other details, visit

Naturalist Jim McCormac writes a column for The Dispatch on the first and third Sundays of the month. He also writes about nature at jim

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