By Gail Gallessich

Oliver Chadwick is a doctor of dirt. The soil scientist––or biogeochemist, as he is known in some circles––is helping to shed light on the historical interactions between people and the soils of Hawaii.

One of the world leaders in relating soils to ecology and earth system science, Chadwick’s research utilizes Hawaii as a model ecosystem to understand changes in the sources of rainforest nutrients.

The professor of geography and environmental science explains that Hawaii is a natural laboratory since it is enclosed and isolated, and because humans arrived there relatively recently, perhaps around 1,200 years ago. The results of his work have been published in scientific journals in the past year.

For these studies, Chadwick and his team––which includes ecologists from Stanford University and the University of Wisconsin––joined archaeologists from UC Berkeley and the University of Hawaii. Together they discovered that the emergence of warriors, priests, and rulers in Hawaii before the Europeans arrived in 1778 ultimately depended upon the quality of soil available for cultivation.

“Environment, Agriculture, and Settlement Patterns in a Marginal Polynesian Landscape,” co-authored with archaeologists and other soil scientists, was published in the Proceedings of the National Academies of Science. It recounts the study of more than 3,000 archaeological features on the southern flank of Haleakala Volcano in Maui, a wedge-shaped area called Kahikinui.

Beginning at approximately 1400 A.D., Polynesian farmers established permanent settlements in Kahikinui based on the sweet potato as the main crop. These settlements were ultimately devastated by disease after the arrival of Captain Cook in 1778.

“Geological and environmental factors are the most important influences on Polynesian farming and settlement practices in an agriculturally marginal landscape,” according to the authors. The differences in soil quality stemmed from variability in lava flows ranging in age from 3,000 to 226,000 years.

It is more difficult to grow crops on the younger, rockier lava flows. Soil quality is patchy due to the way lava flows. Additionally, the rainfall at higher elevations washes out essential soil nutrients while lower elevations do not get enough rain to grow crops.

“As subsistence increases, society can produce surplus and afford to have different classes, including warriors, priests, and rulers,” said Chadwick. “The basis of the hierarchy of groups, or classes, is the ability to produce a surplus of basic foodstuffs.”

However, it isn’t clear whether the warrior class drove peasants to produce in agriculturally marginal areas, or if the class system developed out of surplus agriculture, he explained.

Another article, “Soils, Agriculture, and Society in Precontact Hawaii,” published in Science, analyzes the dryland field system of Kohala, located on the island of Hawaii. It was farmed around 1200 to 1300 A.D.

“In Kohala we found evidence that the Hawaiians discovered a naturally augmented area of nutrients that had enough rain, a perfect matching of natural processes to human need,” said Chadwick.