On the islands of Kauai, O'ahu and Molokai, the principal crop was taro a starchy plant grown in irrigated wetlands where the supply of water was usually abundant.
But on Maui and the Big Island of Hawaii, the main staple was the sweet potato a more labor-intensive crop planted in relatively dry fields where success depended on adequate seasonal rainfall. Some anthropologists say that, by the late 1700s, sweet potato production had reached its maximum capacity. As a result, the chiefdoms on Maui and Hawaii began aggressively coveting the taro ponds that flourished on other islands. Pressure to find new sources of food may be one reason why Kamehameha, chief of the island of Hawaii, launched an invasion in 1795 that culminated in his eventual conquest of the entire island chain.
But one question has long troubled anthropologists, ecologists and historians alike: Why was large-scale sweet potato farming confined to just a few areas of Maui and Hawaii? After all, the Polynesians first arrived in the Hawaiian archipelago around 800 A.D., so they had hundreds of years to develop potato fields throughout the islands.
The answer, according to an international research team, may lie in the soil. Writing in the June 11 edition of the journal Science, the researchers conclude that relatively recent volcanic eruptions on Maui and the island of Hawai'i produced a handful of sites with soil nutritionally rich enough to raise large quantities of sweet potatoes. What's remarkable, say the authors, is that early Polynesian settlers found these fertile farmlands, which were originally covered by thick tropical forest, and successfully exploited them for hundreds of years.