WAIMEA, Hawaii » A study of a network of ancient earthen berms or windbreaks in North Kohala has led scientists to conclude that the population of the area quadrupled as farming intensified between 1400 and 1700.
The walls were built to protect crops, mostly sweet potatoes, from the strong prevailing trades, says Julie Field, an assistant professor of anthropology at Ohio State University in Columbus.
Field and colleagues from California and New Zealand studied ancient farmlands and abodes in five ahupuaa (land divisions) in what they call the Leeward Kohala Field System.
Their findings suggest that practical decisions made by individual households were eventually adopted by the alii (chiefs) as a means to improve agricultural productivity.
"Archaeologically this kind of research is really hard to do in most places since there is rarely a ‘signature’ for the agricultural activity or a strong connection between the remains of a house and a plot of farmland," says Field. "Our study is unique in that we can trace the activities of very, very small groups of people and, from that, try to glean the larger processes of society."
IN North Kohala the signature consists of stone or earthen berms or walls that run parallel to each other along the slope contours. Their archaeological importance was first noted in 1970.
Most likely the system was put in place by individual households that produced crops for their own consumption, Field said.
"It was then appropriated by the chiefs and turned into more of a surplus production system, where they demanded that the land be put into production and more people would produce more surplus food," she said.
The windward valleys of the Kohala peninsula were settled about A.D. 1100 to 1200, and the leeward coast about 1200 to 1400, the researchers estimate.
Forty-eight radiocarbon dates from 43 residential features indicate an "exponential increase" in the number of households over the next few centuries, says the research paper, published in the current issue of the Proceedings of the National Academy of Sciences. As the field system grew, more berms were built to subdivide the acreage, the scientists found.
"Within a 300-year period, 1400 A.D. to 1700 A.D., the data suggests that the population at least quadrupled, as did the number of houses," Field said. She had no estimate for the pre-1778 population.
From 2007 to 2009 the scientists mapped and excavated a range of residential features within two zones of the field system. Larger abodes were identified by terraces with sturdy stone walls on the upslope sides of the berms, which served as windbreaks and anchored more fragile thatched roofs, they report.
The researchers said that the next question is whether the field system was modified seasonally.
"That’s what it looks like happened, but we need more dating of different features at the sites to be able to figure that out," Field said.