Wild Cranberry Bogs–A Relic Ice Age Landscape of the Upper South

The Nature Conservancy is successfully protecting habitat in Shady Grove, Tennessee for the federally threatened bog turtle (Clemmys muhlenbergii), a species small enough to fit in the palm of the hand.  In fact, it’s America’s smallest turtle species.  The bog turtle, as the name would suggest, is dependent on bog habitats, particularly the kind where wild cranberries grow.  Bogs are wetlands that differ from swamps in that they’re poorly drained, whereas swamps may appear stagnant but actually consist of slowly moving water.  Bogs are also more associated with cooler climates.

Range map for the bog turtle.  Part of its present range was under glacial ice during the ice age.  This map isn’t entirely accurate because one of the areas the Nature Conservancy has protected for this species is in Tennessee, which according to this map is outside its range.  During the Ice Age, this species probably had a more continous range and wild cranberry bogs were more common due to differences in climate.

There exists two distinct populations of bog turtles–one in northeastern states, and the other in high elevations of the southern Appalachians.  During the last Ice Age these ranges were likely continuous.  The southern population is threatened by agricultural practices, including the drainage of bogs to increase land for cultivation.  To protect the present day habitat of the bog turtle, The Nature Conservancy, over the past few decades, has purchased small parcels of remaining habitat–the last of the southeast’s wild cranberry bogs, a landscape that was probably more widespread in the upper south during the Ice Age when cool, rainy climate prevailed.  Now, the Conservancy is restoring cranberry bogs by building berms to stop drainage.

The Conservancy leases the land around these bogs to farmers because livestock grazing improves habitat for bog turtles which need more open ground for foraging on insects, berries, and succulent plants.  Modern day livestock play the beneficial ecological role that extinct or extirpated megafauna–mastodons, bison, horses, etc.–used to provide for the turtles.  The turtles need large ungulates to keep excess plant growth in check.

Wood Turtles

The wood turtle (Clemmys insculpta) is a closely related but larger species that also used to range farther south during the Ice Age.

Range map of the wood turtle.  Fossils of wood turtles, a species that prefers cooler climate, have been recovered from Ladds Mountain, in Georgia.

Paradoxically, fossils of the red-bellied turtle, a species that today is limited to Florida, have also been found at Ladds.  Based on carbon dates, at least one scientist believes they occupied the same range during the same period of time, suggesting a more moderate phase of climate occurred during one particular point of time compared with today.  During this climate phase summer must have been cooler but winters must have been warmer.

Source:

Kingsbury, Paul

Turtle Power: A rare reptile helps restore a Tennessee wetland”

Nature Conservancy  Autumn 2010

 

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