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Robert Thorson, a professor of Earth sciences at the University of Connecticut, has been thinking for many years about stone walls, those iconic structures that fill the woods of New England. This thinking has led him to what sounds like a ridiculous conclusion: They’re just like wetlands.

OK, that’s a slight exaggeration: They’re not just like wetlands. For one thing, they’re rarely wet. But he has realized that they are surprisingly wetlands-like.

Like wetlands, stone walls are small, discrete ecosystems that can have specific plant and animal populations that vary over short distances, such as the uphill side of the wall compared to the downhill side.

And like many wetlands, stone walls are the result of human activity but have become part of the surroundings, an unnatural creation incorporated into the natural world.

And most importantly from his point of view, they are rarely approached from a scientific standpoint, as was the case with wetlands (a.k.a. “swamps”) until not too long ago.

“Wetlands were just terrible, useless, people didn’t care about them … or got rid of them. Then there was this complete flip beginning the ‘90s, all of a sudden now we have a whole industry at identifying and protecting wetlands,” said Thorson.

He’d like to see the same happen for stone walls, starting with an agreed-upon taxonomy.

Thorson, a Wisconsin native. says he became interested in the topic during a sabbatical at Dartmouth years ago.

“I showed up in New England and I was just astonished by the stone walls. They’re everywhere!” he recalled. As an academic he, naturally, headed for the library to see what other researchers had done but says “I found hardly anything. There were copious allegorical, literary devices, tropes that involve stone walls, but it was mostly tradition … not science.”

“I was interested in why is it as high as it is, why is it packed like that, … why this stone is here and not others? There are a thousand questions when you look at it as if it was something that came from outer space.”

The interest has stuck. He has been publishing on the topic for 25 years in academic papers and popular books, which is how I found out about him.

Like all reporters in New England I have interviewed people about stone walls many times. Some are interested in aesthetic reasons (few things are prettier than fluffy snow atop a long jumble of granite stones, as the weekend storm reminded us); others for historic reasons (stone walls can help determine the past life of a property); and others for technical reasons (looking down with LIDAR, a radar-like technique that uses light, is a major way to find and map often-forgotten stone walls as a UNH citizen-science program shows).

However, from the point of view of Thorson, a geologist, and a few other researchers, these approaches lack something: Objective criteria that allow independent observers to agree on what they’re studying, which is the necessary first step in any science.

“We’re trying to germinate a science here, a taxonomy, with classification. Classification needs definitions, or you just get in a mess,” he said.

The lack of definitions already shows up in the legal realm. Stone walls can be important in property-line disputes and there are laws about who can and cannot move any given stone wall. (NH protects them pretty well – see RSA 539:4

But if there are no accepted criteria about which line of stones is a wall it’s hard to conclude.

Over decades of walking the woods, asking people what they think a stone wall is, doing measurements and otherwise gathering data, Thorson has developed a list of five criteria that separate a stone wall from, say, a field of glacial till or a concrete abutment.

It’s a stone wall if it’s made of any type of stone (mortar is allowed, much to the dismay of dry-stone-wall purists); if it’s granular (made up of discrete pieces of rock); if it has continuity (not just scattered stones); if it’s tall enough (Thorson uses knee-high as a minimum but admits “this is the hardest criteria”); and has enough “elongation,” a 4-1 ratio of length to width because “if they’re not long enough they’re not walls, they’re like cairns.”

Under this criteria, incidentally, the line I made at the edge of my yard using stones dug up when my septic system was installed isn’t a wall: It’s not tall enough. And that seems right because these stones haven’t developed a personality, so to speak; they haven’t changed the character of the ground around or under them, there are no little creatures living amid them. It’s just a long pile of rocks that I can easily step over, not a separate entity.

Getting enough people to agree on these criteria will not, of course, be easy. The history of science is full of long debates about how to describe things.

But with any luck, Thorson said, it can help us better incorporate the role of stone walls as we struggle to protect and use New England’s landscape.

“These are ecosystems that everybody knows but they haven’t paid attention to it … haven’t protected it. You don’t even need a permit to strip-mine a wall,” he said. “That should change.”

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