Friday, January 18, 2008

Was eastern North America a big marsh?

Whoa -- here's something different.

A couple of scientists at Franklin and Marshall College in Pennsylvania say that our image of the eastern North American landscape before the arrival of European settlers is all wrong.

You need to read the story at New Scientist and then the original paper to learn all about it. But, briefly, Robert Walter and Dorothy Merritts are saying that "the the 'original' North American landscape of forested hills and meandering streams that carved their way down the valleys and out to sea" is not what actually existed.

Instead of a land of rivers that were confined to single, winding channels, what the first European settlers found were "collections of many small channels spreading across broad wetlands." One botanist in 1750 reported a landscape of "swampy meadows," which these researchers say was more the rule than the exception. Here in the Appalachians, the terrain may have been more favorable to species like the one in the photograph above, the smaller purple-fringed orchid, Platanthera psycodes.

This state of affairs changed, and it changed fast, say Walter and Merritts. The settlers almost immediately constructed "tens of thousands" of dams to mill grain. The resulting series of "staircases" drained the water out of valleys. The remains of old mills and dams are, needless to say, a familiar sight in streambeds here in the southern Appalachians.

The two researchers started out trying to trace the source of sediment in storm runoff. "After every rainstorm, our creeks and streams run like chocolate milk," says Walters. Their original assumption was that it came from modern working farms.

They discovered that this sediment did not come from today's farms, but instead from ancient farmsteads high atop mountains in the Appalachian chain.

By 1840, the settlers had built more 65,000 dams between South Carolina and Maine, a number and a date that I find astounding.

I'm not competent to criticize the authors' research, but it reminds me of another bit of geographical revisionism here, in which geologist Robert Thorson presents good evidence that the stereotype of New England's soil as thin and rocky is an artifact of logging done by early settlers. I highly recommend Thorson's book.

In either case, it gives one pause to think that the landscape we consider "natural" may be an artifact of human modification.

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