Unexpected discovery of early sweet potato cultivation in Polynesia

New University of Otago—Ōtākou Whakaihu Waka research has uncovered the unlikely location of one of the earliest securely dated sites of sweet potato (kūmara) cultivation in Polynesia.

The study, published in Antiquity, found evidence of microscopic kūmara starch granules alongside Asia-Pacific taro and Pacific yam (uwhi) at Triangle Flat in Golden Bay (Mohua) that were cultivated as early as AD 1290–1385.

These early dates correspond with the period during which settlement of Aotearoa New Zealand began and provide the first pre-1400 evidence for kūmara cultivation in Te Waipounamu—as early as anywhere else in Polynesia—and for the southernmost world attempt to grow uwhi.

The site is on a conservation estate under the customary jurisdiction of Manawhenua ki Mohua.

Lead author Professor Ian Barber, from Otago’s Archaeology Program, says the site incorporates evidence of the longest duration of māra (garden) conservation from a single place anywhere in Polynesia.

“The earliest māra pits incorporating kūmara-like starch at Triangle Flat date to the beginning of the fourteenth century when Polynesians first settled the motu.”

Despite its importance to Polynesian life both in the past and today, little is known about the timing and circumstances of the sweet potato‘s initial spread across Oceania.

Some botanists propose it drifted naturally into Polynesia thousands of years ago, but many anthropologists infer undated human mediation instead, especially since the Māori name kūmara is a variation on pre-Columbian American sweet potato names.

Given these uncertainties and intriguing possibilities, scholars have debated exactly when, and even if, sweet potato became important in early Polynesian colonization, Professor Barber says.

Existing views have assumed the first settlers turned instead to forage for the flightless moa, other birds and marine animals, with kūmara only becoming important later, especially in warmer areas central to northern Aotearoa New Zealand where pā earthworks proliferated.

“The Otago research now challenges standard archaeological assumptions that the first Polynesian settlers of Aotearoa, and Te Waipounamu especially, abandoned tropical horticulture largely if not entirely.

“The new Triangle Flat evidence points to the early adaptation of tropical crops, especially kūmara, from the outset of Polynesian settlement, even in unlikely places.

“In short, kūmara was not a colonization after-thought in Aotearoa.”

The early chronology supports those Māori traditions that speak of kūmara as a crop established in the central Polynesian homeland, Hawaiki, when the first voyagers ventured south for Aotearoa.

Co-author Rebecca Waikuini Benham (Ngāti Kahungunu ki Wairarapa, Ngāti Porou, Ngāti Awa), from Heritage New Zealand Pouhere Taonga, was responsible for preparing the microscopic starch granule samples.

This important microbotanical science has been used to identify ancient crops throughout Polynesia, including Aotearoa, that may leave no other traces.

She says Aotearoa offers a unique case study when compared to the other Polynesian Islands.

“There are significantly fewer starch producing crops that were cultivated here than compared to the more tropical islands.

“I am hopeful that the identification of granules, along with the possible raphides, may be able to be applied to other early sites across the motu to investigate the cultivation of taro and uwhi alongside kūmara from an archaeological perspective, of course in collaboration with local kōrero.”

The study also demonstrates that the first Aotearoa gardeners developed sophisticated planting pit and shell mulch technologies in local environments and soils, which helped secure kūmara horticulture in a marginal climate.

Currently, sweet potato is the world’s fifth most important edible crop but is under threat from climate and other environmental changes in many parts of the world, Professor Barber says.

“New knowledge from the past as well as the present may yet support food security science targeting sweet potato production.

“Archaeological knowledge of these ancient technologies might yet inform modern efforts to improve natural hardiness and nutrition in sweet potato.”