Further Wet-Taro Evidence from Polynesia's Southernmost Neolithic
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LETTER Further wet-taro evidence from Polynesia’s southernmost Neolithic production margins LETTER Ian G. Barbera,1 For Prebble et al. (1), the cultivation of introduced fields (ref. 2, pp. 106–107), comparable to Polynesian semiaquatic tropical taro (Colocasia esculenta)on production systems of record for wet taro (1, 6). This cooler southern Pacific islands during the Polynesian engineering feat is mirrored in ditch networks that “initial colonization period” (ICP) (1200 to 1500 CE) extended wet cultivation over lacustrine and flood- “ ” represents a striking Neolithic example of nonopti- plain lands at the Aupouri Peninsula base (Fig.1), mal, marginal crop production. In that respect, ICP where soils from site O4/237 also incorporate taro-like taro pollen from Ahuahu, a warm-temperate, northern starch granule aggregations (3). In Maori oral history, New Zealand (NZ) offshore island, is especially nota- these extensive systems predate the 19th century (ref. ble (1). However, the suggestion that NZ wet-taro cul- 2, p. 106). tivation “may have been confined” to such offshore Radiocarbon dates by SHCal13 (7) on plant detritus islands (ref. 1, p. 8828) overlooks important mainland from peaty samples of an uncomplicated Motutangi archaeological evidence (Fig. 1). system (western N3/639) include terminus ante quem Prebble et al. (1) cite the report of microscopic C. age NZ5626 on basal ditch fill at cal AD 1460 to 1670 esculenta starch granules from a Maori ditch system of (95% probability). Age NZ6358 from the native an- northern North Island’s Aupouri Peninsula (a tombolo) with records of “tentatively identified” ICP crops (ref. thropic section of a soil profile 50 m away is identical 1, p. 8824). Yet this taro evidence from former inter- at 94% probability, while lower NZ6388 around the dune swamp site N3/638, Motutangi, is far more sub- palynological marker of wetland management be- stantive in context. Although reserve C. esculenta ginnings is cal AD 1320 to 1480 (95% probability) starch granules that are generally <8μm can be difficult (Fig. 1). to characterize alone, taro corm granules are “most Collectively these data identify the Aupouri region easily” identified in the size range <1to3μm when as Neolithic NZ’s wet-field production hub. The iden- aggregated in masses (refs. 2, p. 113, and 3–5). From tification of perennial wet taro from pre-1500 Ahuahu N3/638, multiple ditch-base and interdrain peaty sam- (1) is important nevertheless and may elucidate aban- ples present just such discrete, dense taro-like aggre- donment of ancient Polynesia’s southernmost wet gations of hundreds of small reserve starch granules, fields. Marginal wet agronomy disappeared from the mostly <4 μm, along with native NZ pollens and Aupouri region and Ahuahu by or during the Little Ice spores only as one would expect in pre-19th century Age (LIA) NZ duration, ∼1450 to 1850 CE (8). Cooler “ ” Neolithic contexts (2, 3). Reserve starch granules LIA temperatures might have influenced the later of other Polynesian and native NZ plants, including northern Maori production shift to more resilient dry- widespread semiaquatic Typha orientalis,arealways land taro varieties and sweet potato/kumara Ipomoea > μ – predominantly 3 m in any concentration (2 5). batatas (1). Ditch networks provide further archaeological ev- idence. Contiguous Motutangi ditch systems integrated Acknowledgments irrigation, reticulation, and drainage functions to create I acknowledge Royal Society of New Zealand Marsden Award >50 ha of bordered, raised, and possibly flooded UOO1415. Les O’Neill completed Fig. 1. aArchaeology Programme, School of Social Sciences, University of Otago, Dunedin, Otago 9054, New Zealand Author contributions: I.G.B. designed research, analyzed data, and wrote the paper. The author declares no competing interest. Published under the PNAS license. 1Email: [email protected]. www.pnas.org/cgi/doi/10.1073/pnas.1918374117 PNAS Latest Articles | 1of2 Downloaded by guest on September 28, 2021 173°E North Island (Te Ika-a-Māui), New Zealand Ahuahu 40°S N 0 200 km Aupouri Peninsula N3/638 N3/639 Motutangi Rangaunu Harbour 35°S O4/237 0 10 20 km Oruru R. Awanui River KEY Lake Tangonge Kaitaia N3/639 Site record number Pukepoto Indicative area of extensive, former wetland ditch systems OxCal v4.3.2 Bronk Ramsey (2017); r:5 SHCal13 atmospheric curve (Hogg et al. 2013) Lab No./14C age BP NZ5625/266±55 Lower ditch fill NZ5626/343±55 NZ6358/338±56 Anthropic NZ6388/545±52 soil profile 1200 1400 1600 1800 2000 Calibrated date (calAD) Fig. 1. (Upper) Map of Aupouri Peninsula and lands at the tombolo base (“Aupouri region” in text), northern North Island, New Zealand, showing archaeological ditch systems that once extended wet production for tens of hectares. The relative location of Ahuahu (1) is shown in Inset map. (Lower)Radiocarbon(14C) calibration ranges (95% probability) by laboratory number for atmospheric plant detritus from the western area of ditch system site N3/639, Motutangi. Calibrations are by SHCal13 in OxCal v.4.3.2 (7) on conventional 14Cages(incitationsinref.2, p. 107). Base data are sourced from ref. 2 which is licensed under CC BY 4.0. 1 M. Prebble et al., Early tropical crop production in marginal subtropical and temperate Polynesia. Proc. Natl. Acad. Sci. U.S.A. 116, 8824–8833 (2019). 2 M. Horrocks, I. Barber, Microfossils of introduced starch cultigens from an early wetland ditch in New Zealand. Arch. Oceania 40,106–114 (2005). 3 M. Horrocks, S. L. Nichol, P. C. Augustinus, I. G. Barber, Late Quaternary environments, vegetation and agriculture in northern New Zealand. J. Quat. Sci. 22, 267–279 (2007). 4 R. Fullagar, J. Field, T. Denham, C. Lentfer, Early and mid Holocene tool-use and processing of taro (Colocasia esculenta), yam (Dioscorea sp.) and other plants at Kuk swamp in the highlands of Papua New Guinea. J. Archaeol. Sci. 33, 595–614 (2006). 5 J. J. Maxwell, M. Tromp, Corynocarpus laevigatus: Where art thou? Finding evidence of this elusive tree crop. Rev. Palaeobot. Palynol. 234, 198–210 (2016). 6 P. V. Kirch, The Wet and the Dry: Irrigation and Agricultural Intensification in Polynesia (University of Chicago Press, Chicago, IL, 1994). 7 A. G. Hogg et al., SHCal13 Southern Hemisphere calibration, 0–50,000 years cal BP. Radiocarbon 55, 1889–1903 (2013). 8 A. Lorrey et al., The Little Ice Age climate of New Zealand reconstructed from Southern Alps cirque glaciers: A synoptic type approach. Clim. Dyn. 42, 2039–2060 (2014). 2of2 | www.pnas.org/cgi/doi/10.1073/pnas.1918374117 Barber Downloaded by guest on September 28, 2021.