Early tropical crop production in marginal subtropical and temperate Polynesia

Abstract

Polynesians introduced the tropical crop taro (Colocasia esculenta) to temperate New Zealand after 1280 CE, but evidence for its cultivation is limited. This contrasts with the abundant evidence for big game hunting, raising longstanding questions of the initial economic and ecological importance of crop production. Here we compare fossil data from wetland sedimentary deposits indicative of taro and leaf vegetable (including Sonchus and Rorippa spp.) cultivation from Ahuahu, a northern New Zealand offshore island, with Raivavae and Rapa, both subtropical islands in French Polynesia. Preservation of taro pollen on all islands between 1300 CE and 1550 CE indicates perennial cultivation over multiple growing seasons, as plants rarely flower when frequently harvested. The pollen cooccurs with previously undetected fossil remains of extinct trees, as well as many weeds and commensal invertebrates common to tropical Polynesian gardens. Sedimentary charcoal and charred plant remains show that fire use rapidly reduced forest cover, particularly on Ahuahu. Fires were less frequent by 1500 CE on all islands as forest cover diminished, and short-lived plants increased, indicating higher-intensity production. The northern offshore islands of New Zealand were likely preferred sites for early gardens where taro production was briefly attempted, before being supplanted by sweet potato (Ipomoea batatas), a more temperate climate-adapted crop, which was later established in large-scale cultivation systems on the mainland after 1500 CE.

Reply to Barber: Marginal evidence for taro production in northern New Zealand between 1200 and 1500 CE

“…We welcome Barber's (1) comments and are grateful for the opportunity to respond. Our study of wetland taro (Colocasia esculenta) gardens during the initial colonization period (ICP) (1200 to 1500 CE) in New Zealand did not overlook the evidence from the Aupouri Peninsula (2)(3)(4). We agree that gardens were probably established on mainland New Zealand, within the climate envelope shown in figure 1 of our paper (4), but in areas that lacked large-statured forests at Polynesian arrival.…”

Perception gaps that may explain the status of taro (Colocasia esculenta) as an “orphan crop”

“…Most pollen is likely to rot together with the fallen spadix and spathe of the inflorescence. Recently, a pollen record for taro has been established in early cultivation sites in subtropical and temperate Polynesia (Prebble et al., 2019), a region first reached by humans around 1,000 years ago. The pollen records indicate that, outside the likely natural range of taro, the plant was carried and replanted as part of the initial colonization of Remote Oceania.…”

Archaeological science meets Māori knowledge to model pre-Columbian sweet potato (Ipomoea batatas) dispersal to Polynesia’s southernmost habitable margins

“…In the warmest island localities of (and off) North Island/Te Ika-a-Māui, Indigenous Aotearoa Māori cultivated at least four, originally tropical Asia-Pacific cultigens, including geophytes C . esculenta and Dioscorea alata and two tree crops, before Europeans introduced new crops from 1769 CE [ 6 , 12 – 15 ]. Earlier 19th-century Māori grew C .…”