Monday, February 18, 2008

Glacial relicts


Many great writers have tried to explain the Pleistocene Epoch in Missouri. It's a daunting task, because the Pleistocene covers 2-3 million years of history, four major ice advances, and four interglacials, extended periods of warming and thawing. To really understand the Ice Age in Missouri, we need to understand that during alternating periods of freezing and thawing, different plants and animals rose to the foreground, creating their own distinct communities. That being written, the ice sheets never made it to the Ozark Highlands, but the climatological effects are evident even today. Thousands of years after the last glacial retreat, tucked away in cool, moist places, thrive small, relictual plant and animal communities that represent our definitive link to the Pleistocene.

While the land north of the present-day Missouri River was locked under 2,500 feet of ice, the Ozarks were a thriving boreal forest, rich with spruce and jack pine. When we think of glaciers, we must think of a long time frame as ice sheets moved across the landscape. It never was a fast process as the neighborhood kids tell me the films show, sending mammoths and sloths running for cover. Whether advancing or retreating, ice sheets demanded thousands of years to reach their extent or withdraw completely. During those alternating cooling and warming periods, a dozen generations of trees lived and died before the land was ousted by a glacier.

The Ozarks, while untouched by the glaciers, were directly impacted by the cooling and thawing periods. Century after century, as the climate changed in response to the retreat and advance of the glaciers, seeds and sprouts of one kind of forest were replaced by others. As the glaciers retreated for the last time 11,000 years ago (the beginning of the Holocene), the boreal forest moved north, into Wisconsin and Canada. The oak-hickory forests that now define the Ozarks moved in after the last glacial retreat, during a warm spell that spruce and pine couldn't handle.

But in a few sinkholes, on a blufftop along the Jack's Fork River, at Taum Sauk Mountain, some of the plants and animals present during the Pleistocene never left, living now as they did then, though in very small, specialized communities. Moist, cool fens house Riddell's goldenrod, with the only known populations in Missouri in the Ozarks. Wood frogs were left behind, living in small, scattered populations (well, until a state agency decided to introduce them outside of St. Louis) in the Ozarks. On the Jack's Fork, if you park your canoe around a certain bend, you can hike up a north facing slope and witness a plant community that is well represented in Wisconsin and no where else but in this one spot in Missouri.

These areas where glacial relicts still live deserve protection. With increasing temperatures, they might disappear from the landscape altogether, but in the meantime, we should appreciate Goldie's fern by just knowing it's growing in a sinkhole in Camden Co. We shouldn't have to see it, because aesthetically it's really not anything special. Looks a lot like your average Thelypteris. But scampering down into the sinkhole, tromping through relictual populations just to see it and other relicts seriously damages these very rare, very threatened populations.

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