We humans have a spotty record when it comes to how our decisions play out over the long term. Jennifer Kahn says we’re particularly bad when it comes to long-term sustainability.
Kahn is a member of a group that believes archaeology provides a singularly excellent lens to evaluate the lasting effects of a society’s life choices. Kahn, an associate professor in William & Mary’s Department of Anthropology, is a co-author of the study “Why are sustainable practices often elusive? The role of information flow in the management of networked human-environment interactions,” recently published in Global Environmental Change.
“I think we published this in this specific journal, because this is a journal that is read by people involved in policy decisions for environmental management,” Kahn said. “We wanted to show how archaeology is really a field that can speak to long-term management or mismanagement of resources. And we wanted to bring that theme to a broader audience.”
“New Zealanders, on the South Island, are one of the only examples of agriculturalists going back to being hunter-gatherers. The South Island just wouldn’t support the agriculture of the suite of crops that they had brought from tropical Polynesia.”
Jennifer Kahn
Kahn and her collaborators compared and contrasted archaeological case studies of societies across the globe that had to deal with sustainability challenges of one sort or another. The studies included Medieval Norse settling Iceland, the Ancestral Pueblo in the American Southwest and, Kahn’s research focus — the Eastern Polynesians who settled islands across the easternmost part of remote Oceania.
“These case studies don’t have a lot of similarities,” she said. “Some of them are contrastive.” Kahn went on to explain that the “archaeo-ecology” initiative brought together ecologists, ecological modelers and archaeologists to examine how different peoples in varied parts of the world adapted to social and environmental changes.
Kahn has been researching the archaeology of Polynesian communities beginning around A.D. 1000. She said these seafaring colonists encountered conditions on each new island that were often vastly different than the one they just left.
“Polynesians had experience settling new islands,” Kahn said. “And they knew that many of the islands they were going to settle did not have all of the things they needed to make a life.”
So, plants went into the canoes, particularly food plants such as breadfruit, bananas, taro and coconut. “People think that these food plants were on all these islands to begin with,” Kahn said. “But in many cases, they were brought there by the Polynesians.”
The voyagers also brought along food animals: dogs, pigs and chickens. But Kahn said that those three animals were not necessarily found together on every island. Rapa Nui — also known as Easter Island — was one example.
“Rapa Nui only had chickens,” she said. “Pig and dog never made it to Rapa Nui. We don’t know if they died on the voyage out there, but there is no evidence of pigs on Rapa Nui.”
Kahn added that there is evidence of resource competition among the Rapanuians. With no dog or pig to eat, the people were careful of their flocks, even building fortified chicken houses.
“They’re called hara moi,” she explained. “They appear to be built to keep people from being able to steal your chickens. So they’re paying very close attention to their main source of protein.”
Kahn said the Polynesians brought a culturally established set of environmental practices to Rapa Nui, the exercise of which made for both good and bad environmental results. The island presented a set of particular challenges in that it is far enough south to have a subtropical climate, rather than the warmer conditions found in the islands the voyagers had left.
An example of a benign practice is what anthropologists call lithic mulching, she said. In addition to being cooler than the islands the colonists were used to, Rapa Nui is windy and arid, making it even more challenging to grow food crops.
“Lithic mulching is basically putting stones in your garden to retain water,” Kahn explained. “From a Eurocentric point of view, you’re always going to remove stones from where you grow food, but in a place like Rapa Nui, where soil nutrients are poor and you have issues with wind, putting stones in your soil is a way to keep in moisture and to reduce erosion.”
One cultural practice that turned out badly on Rapa Nui, and oftentimes on other Polynesian islands as well, is the cutting down of endemic tree species. Kahn said that Polynesians arriving on a new island began conducting what amounts to tree triage, selecting for the most immediately helpful varieties.
“Hardwood trees,” she said. ”You’re going to keep those because they are super useful for making weapons and making canoes and building houses. But there are other trees that aren’t as useful.”
Those less-useful trees were thinned out, replaced by coconut palms, taro patches and other food producing plants. The Polynesian’s cultural practice of replacing endemic trees with familiar cultivated plants worked better on some islands than others, Kahn noted. And sometimes it failed miserably.
“New Zealanders, on the South Island, are one of the only examples of agriculturalists going back to being hunter-gatherers,” she said. “The South Island just wouldn’t support the agriculture of the suite of crops that they had brought from tropical Polynesia.”
Pigs and dogs may not have made it to each new Polynesian island, but Kahn said there was one universally successful animal passenger — the rat. She said it isn’t clear whether rats were stowaways or brought along in the canoes intentionally.
“Rats basically make it everywhere that people make it,” she said, adding that rats virtually always create their own suite of environmental problems, as they did on Rapa Nui.
“Rats probably had an impact on the Jubaea palms which covered all of Rapa Nui,” Kahn said. The island was essentially treeless at the time of European contact.
There is evidence that Polynesians were capable of seeing that their cultural practices weren’t working and taking steps to change course. Kahn gave the example of Mangareva, where the people decided to quit raising pigs.
“That is a really big decision,” she said. “It’s sort of like Americans deciding to give up beef. It’s a small island, and they could see that pigs and humans were competing for the same foodstuffs. So it made sense to get rid of pigs.”
Kahn stresses that the ancient Polynesians were experienced, even expert, colonizers of new and challenging places — but they still got it wrong sometimes by following set of practices that had worked quite well on other islands.
“The Rapanuians were making decisions to try to deal with the environment at hand. But the chopping down of trees, which was a cultural template they brought with them, probably was not the best template to use. I’m trying to argue that they didn’t know; the Rapanuians didn’t have the information to act otherwise until it was too late,” she said.
“But today,” she added, “we have a better information flow.”
Joseph McClain, Research Writer