By Dan Vergano, USA TODAY
Easter Island's mystery — brooding statues atop a treeless Polynesian island — fascinates tourists and scholars alike. And inspires debate.
"Who or what destroyed the ancient palm woodland on Rapa Nui (Easter Island)?" ask German ecologists Andreas Mieth and Hans-Rudolf Bork, in an upcoming paper in the Journal of Archaeological Science. "The circumstances, causes and triggers of these environmental changes are the subject of persistent scientific discussion."
And how. In 2005, Pulitzer-prize winner Jared Diamond revived public awareness of the island with Collapse: How Societies Choose to Fail or Succeed. "What were they thinking when they cut down the last palm tree?" he asked in the book. The question had puzzled many scholars looking at the depopulated, deforested island, finally concluding the inhabitants had denuded it of food-providing palms to build sledges for statues and roofs for homes, an ecological parable of self-destruction.
But only a year later, another explanation surfaced in a series of papers by Terry Hunt and Carl Lipo of the University of Hawaii. First, they set the date for colonization of the island to 1200 A.D. in a radiocarbon dating paper in the journal Science, more recent by at least a century than past estimates. Next, they proposed, based on DNA evidence and chewed palm remains in the Journal of Archaeological Science, that Polynesian rats brought with those immigrants had been the culprits behind deforestation, eating palm tree nuts.
Without predators to keep rat numbers in check, the rodents ate most of the seeds and the older trees had mainly died out without reproducing by 1772 when Europeans arrived in ships. Those Europeans wiped out the islanders, they suggested, through disease and later enslavement. "It was genocide, not ecocide, that caused the demise of the Rapanui. An ecological catastrophe did occur on Rapa Nui, but it was the result of a number of factors, not just human short-sightedness," Hunt wrote in The American Scientist magazine.
In their new study, however, Mieth and Bork, both of Germany's Christian Albrechts University of Kiel, "disagree with the hypothesis of a major rat impact" to explain Easter Island's demise. In their study, they look at the charcoal remains from fires, evidence of the spread of slash and burn agriculture from the island's shore to its peak. "Over large areas, a single layer of charcoal and ashes several millimeters in thickness can be found deep below the recent surface and on top of the prehistoric garden soils that belong to the period of woodland gardening," they write. "The extensive distribution of charcoal layers can only have one explanation: widespread fires in the woodland of Rapa Nui."
Looking at the march of tree burning over time, cut palm stumps and a lack of rat bite marks on palm nuts found in the charcoal layers, they conclude "deforestation was an act of humans."
"But we were never talking about rats killing mature trees," Hunt says in an interview. "It's very tempting to see one explanation for everything, all people or all rats, but what we were saying was that rats surely played a role on Easter Island." He rejects the notion that a lack of rat-eaten palm nuts in charcoal layers proves anything, saying, "rats are unlikely to eat charcoal."
Besides, he says, "how can you explain the idea of rats not having an effect?" Unhindered by predators and provided ample food, the rat population must have exploded on Easter Island, he argues, eating nuts even as colonists raised farms.
About the only thing the competing viewpoints can agree upon is that drought, a third suspected cause, didn't have a big effect on Easter Island's palm forests, which in 1100 A.D. covered about 70% of the island. "The question is how much of a role did each player have and how did they interact?"
Of course, Hunt acknowledges, the early colonists likely brought rats with them. "But it's unlikely they could have seen ahead to the results of either farming or bringing rats," he says. "Blaming humans for everything is too simple."
Source:
http://www.usatoday.com/tech/science/columnist/vergano/2009-11-13-easter-island_N.htm
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