Why Ancient Hawaiians Built Stone Walls in the Kaʻū Fields, and What Farmers Can Learn

Windswept pasture on the leeward slope of Mauna Loa hides the remains of a huge farm. Under the thick grass at the Kahuku Unit of Hawaiʻi Volcanoes National Park lie the remnants of the Kaʻū Field System, farmland cultivated by ancient Hawaiian mahiʻai (farmers) who built stone walls in the fields to make the best of the terrain and weather. National Park Service (NPS) staff and archeologists at the University of Hawaiʻi at Mānoa want to know more about those walls, in the hope that they might shed light on ancient farming techniques and inspire farmers to build a more sustainable future for the islands. The article is by NPS historian Anna Christie.

Ridges in the fields of the Kahuku Unit of Hawaiʻi Volcanoes National Park. NPS photo.

How the walls worked

Hawaiian farmers had to overcome weather, erosion and volcanic soils. The fields were not irrigated; they were fed by rainfall, which makes them dryland agricultural systems. The stone walls, called kuaiwi, were the backbone of the system and appear in several field systems on Hawaiʻi island.

• Water: the walls blocked wind, which makes plants lose water faster, and farmers grew tall plants like kō (sugar cane) on top of them; these caught rain and fog and funneled it down to the soil and to crops such as sweet potato.
• Erosion: like a shelf on a hillside, the walls held the soil, so rain did not wash away its nutrients.

Excavated stones of kuaiwi. NPS photo.

The kuaiwi appear as lines crossing the Kaʻū Field System in this aerial shot. NPS photo.

Change on the land

Around the 1400s the sweet potato reached the islands. It survives in difficult terrain, became the basis of dryland farming and fed larger populations. In the 1800s Hawaiian royalty and foreign merchants drew the islands into a market economy that broke up traditional land and labor systems. Sandalwood, one of the first exports, was cut unsustainably until the trees were depleted. Hawaiians now needed money to pay taxes to royalty, and many farmers moved to port towns for work. Diseases brought by European and American colonizers decimated the population, and the labor-intensive fields were abandoned. After the sandalwood trade collapsed, Hawaiians turned to cattle ranching, and the Kahuku Ranch in Kaʻū became one of the biggest cattle ranches in Hawaiʻi, producing beef and hides for more than 150 years.

Rediscovering Kaʻū

The NPS acquired the Kahuku Unit in 2003 and over the next twenty years ran many archeological surveys, inventories and excavations. Staff suspected that the striations in the fields resembled well-known fields in Kohala and Kona, and in the late 2000s they used aerial photographs and predictive models to rediscover what was there.

NPS staff excavating at Kahuku. NPS photo.

University of Hawaiʻi at Mānoa archeologist Seth Quintus, who first explored the fields as a park intern in 2010, researched in 2017 when and why the walls were built where they were. His team's soil depth survey found that the walls were built directly on bedrock, where soil is shallow. Shallow soil dries out quickest, so farmers aimed their improvements there. The team also took apart some walls, collected charcoal from the soil beneath and used radiocarbon dating to date them. The earliest walls date to the 1400–1500s, the same period as other fields across Hawaiʻi, which shows knowledge and culture spreading.

Looking to the past for food

In 2023 the park offered local K–12 schools field trips for hands-on experience with Quintus and his college students, who taught younger students the site's history and archeological techniques, and everyone helped excavate. The article asks whether the past can help with a food system in need: Hawaiʻi imports over 85% of its food. Many people in the state call for more small farms to serve local communities, to give Hawaiians more control over land and food, cut reliance on imports and guard against shortages. Some researchers have started experimental plots testing the ancient techniques. The project was done in partnership with the University of Hawaiʻi at Mānoa through the Hawaiʻi-Pacific Islands Cooperative Ecosystem Studies Unit (CESU).

Sources

• National Park Service, “A Fertile Landscape: Unearthing Agricultural Archeology at Hawaiʻi Volcanoes National Park,” by Anna Christie, Historian (https://www.nps.gov/articles/000/a-fertile-landscape-havo.htm); photographs of the archeology team and of students are left out; rewritten in hubnx's own words.