Pueblo La Plata didn't look like much -- a low rise of rubble where dwellings once stood, housing perhaps up to 50 people. Archaeologists figured the first inhabitants arrived about AD 1200. Block the rubble pile from view, however, and the modest mesa top in Agua Fria National Monument, just north of Phoenix looked, well, natural.
Until Arizona State University archaeologist Katherine Spielmann pointed to the stones around the base of the handful of agave plants that dotted the mesa top. The plants were scattered among grasses and other low-lying shrubs.
She explained that the agaves, which looked "natural" to me, were planted by the inhabitants, who placed the volcanic stones around the plants' bases to ward off frost damage.
The stones absorbed heat during the day, then returned it to the air during the chill of a desert night. Her point: What looks like natural grasslands to a 20th-century eye often hides the evidence of human manipulation.
If one has conservation in mind, which iteration of the site's ecosystem is the goal? It's the classic "baseline" problem in which the "pristine" landscape today could instead be landscape Version 50.0, "upgraded" by successive episodes of human intervention over hundreds or thousands of years.
I was reminded of this little field trip I took four years ago as I read about scientists who have discovered a network of pre-Columbian settlements in a part of the Amazon basin long thought too densely forested to have allowed for any degree of urbanization. The team published a report of its work in today's edition of the journal Science. The team of US and Brazilian researchers, led by University of Florida archaeologist Michael Heckenberger, first discovered evidence of these settlements five years ago. Since then, they have found more and have uncovered what they interpret as a pattern in the way the settlements are clustered and linked, suggesting that each had its own political organization, tied together with what looks to be a regional organization.
The area had long been viewed as dense forest devoid of any form of social or political organization more intricate that nomadic hunter-gatherers might have. Instead, they write that their finds in the state of Mato Grosso exhibit evidence of "land-use planning and modification of local and regional ecology ... no less remarkable than in other areas of early urban societies worldwide." These settlements – which include 150-acre towns, plus village- and hamlet-scale sites – roughly match the scale of average-sized medieval towns in Europe, Dr. Heckenberger explains. But the Brazilian settlements show evidence of land-use planning far more complex than medieval towns and included dams and artificial ponds.
Heckenberger maintains that the settlements might suggest approaches planners can take today for developing the region in a sustainable way. He points to Sir Ebenezer Howard, a British urban planner who, in 1902, offered a up a scheme he dubbed a "garden city." It consisted of networks of well-though-out towns, with plenty of woods and green space as the city "thinned" from urban to rural. The inhabitants of these Amazonia settlements appear to have beat him to the concept by about as much as 650 years as they manipulated their surroundings.
As in many things archaeological, it's likely to take many more years of studying the towns and villages – their pot shards, waste dumps, as well as the surrounding landscape – to see how effectively the inhabitants tailored themselves to local ecological conditions.
Authors like Charles Redman at Arizona State University ("Human Impact on Ancient Environments") or Jared Diamond at UCLA ("Collapse: How Societies Choose to Fail or Succeed") have tried to draw lessons for a sustainable future from histories of previous civilizations written in everything from grand palaces to humble mounds, pottery, bones, and fire pits. It will be interesting to see if these discoveries in the Amazon, a region so important today for its biodiversity and for its environmental "services" on a planetary scale, have something to tell us about prospects for meeting human needs in the region without undermining the vital services it provides.
Note: Eoin O'Carroll is on vacation. He will return Sept. 2