Volcanic Soils Yield New Clues About the Development of Dryland Agriculture and Powerful Chiefdoms in Hawaii
Findings by research team including UH anthropologist featured in June 11 issue of the journal ScienceUniversity of Hawaiʻi at Mānoa
Department of Anthropology
Peter Vitousek, (650) 725-1866
Department of Biological Sciences
New and innovative studies link soil nutrient abundance and availability to the prehistoric development of dryland agriculture in Kohala on the island of Hawaiʻi. The archaeological remnants of a large dryland agricultural system on the leeward slope of the Kohala mountains match the precise locations where volcanic soil nutrients, necessary for sustained farming, are most abundant. Traditional agriculture in this area focused on growing sweet potatoes and the surplus it produced supported population expansion and the development of competitive chiefdoms beginning in the 17th or 18th centuries. By the end of the 18th century, this agricultural zone had expanded geographically to its limits, in turn, underwriting the efforts by Kamehameha I to unify all of the Hawaiian Islands under his rule.
These conclusions are reported in an international and inter-disciplinary research team‘s findings published in the June 11 issue of the journal Science. UH Mānoa Department of Anthropology Chair and Archaeologist Michael Graves is a member of the research team and contributed to the report.
After conducting analyses of soil samples from Kohala on the Big Island, the research team concluded that relatively recent volcanic eruptions on the island of Hawaiʻi produced a handful of areas, some of them more than 25 square miles in size, with soil nutritionally rich enough to raise large quantities of sweet potatoes. Sweet potatoes were a major staple on the leeward portions of the Big Island, as well as on Maui, where this crop was planted in relatively labor intensive systems of fixed fields with the success of these systems dependent on adequate seasonal rainfall.
Until now, anthropologists, ecologists and historians were not sure why large scale sweet potato farming had been confined to these areas on Maui and the Big Island. Their analyses show that this rare combination of rainfall and fertile soil did not exist on Kauaʻi, Oʻahu and Molokaʻi, as the soils on these older islands had been depleted of their nutrients, even at lower elevations and rainfall levels. By the late 1700s, sweet potato production may have reached its maximum capacity as these fertile leeward areas were pushed to their limits, and the chiefs would have been attracted to the irrigated wetlands where taro was grown, especially on the islands of Kauaʻi, Oʻahu and Molokaʻi.
"Clearly, the Hawaiians were pushing agriculture to its limits," said Patrick V. Kirch, a professor of anthropology at the University of California-Berkeley and one of the co-authors of the Science study. As Graves and his colleague, Thegn Ladefoged of the University of Auckland have documented in a series of published studies, individual fields in Kohala were getting progressively smaller and smaller, and there were fewer and fewer places for the Hawaiian farmers to expand geographically.
According to Peter Vitousek, a professor of biological sciences at Stanford University and lead author of the Science study, the shortage of arable land probably played a role in the rise of expansive chiefdoms on Maui and Hawaiʻi in the 18th century.
"The Hawaiian Islands had a true class system led by chiefs who enjoyed elite privileges," Kirch noted. "To maintain the social order at the level they were accustomed to, the chiefs had to go into a mode of aggressive action. It‘s interesting that the really aggressive chiefdoms came from the highly intensified dryland systems on Maui and Hawaiʻi, where per capita yields were declining. They probably looked up the chain of islands toward Molokaʻi and Oʻahu and said, ʻI‘d love to get hold of those taro paddies.‘"
By the early 1800s, just a few decades after European contact, the remarkable agricultural system that once prospered on Maui and Hawaiʻi had collapsed. Most historians blame its demise on the introduction of human diseases, which caused a drastic reduction in the size of the Hawaiian population. As a result, there were no longer enough people to work the labor-intensive fields, and as the population fell, the demand for sweet potatoes also declined.
According to Vitousek, the successes and failures of the early Polynesians offer important lessons for tropical forest management today.
"Just as land influenced Polynesian societies, Polynesian societies influenced land," he wrote. "Those societies faced the challenge of making a transition from intensive, exploitative use of their island‘s obviously limited resources, to more sustainable use of those resources. We ourselves now face the challenge of global transition to sustainability; can we learn from societies that succeeded or failed on smaller worlds?"
The Science article is authored by P. Vitousek of Stanford University; T.N. Ladefoged of the University of Auckland; P.V. Kirch of the University of California-Berkeley; A.S. Hartshorn of the University of California-Santa Barbara; M.W. Graves of the University of Hawaiʻi at Mānoa; S.C. Hotchkiss of the University of Wisconsin; S. Tuljapurkar of Stanford University; and O. A. Chadwick of the University of California-Santa Barbara. The research was supported by a Biocomplexity in the Environment grant from the National Science Foundation.
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The study, "Soils, Agriculture and Society in Precontact Hawaiʻi," will be published in the June 11 edition of Science. For a copy, call the AAAS Office of Public Programs at (202) 326-6440 or email firstname.lastname@example.org.
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