Preservation and origin of late-Holocene Polynesian sweet potato cultivation features in northern New Zealand
New Zealand was the last substantial landmass to be settled by humans. Both archaeological and palynological evidence, constrained in part by tephrochronology, show that the earliest environmental impacts associated with initial Polynesian settlement occurred c. 1250-1300 AD. A notable aspect of such settlement was the successful cultivation of several tropical plants in temperate conditions, chiefly the sweet potato or kumara (Ipomoea batatas), which became extremely important in the diet of early Polynesian (Maori) in New Zealand-Aotearoa. Because few physical remains of cultigens occur, studies of early Maori gardening rely mainly on inferences from archaeological features such as storage pits, stone rows and the properties of modified soils, and ethnographic/historical sources. Most prehistoric gardening sites are coastal, but extensive areas of gardens occur in the mid-Waikato region of northern North Island where Maori-modified soils cover 3000 ha. We studied an area of prehistoric Maori gardens, characterised by modified soils and adjacent ‘borrow pit’ excavations in coarse volcanogenic alluvium, at two archaeological sites in this region. Two groups of multiple, near-circular hollows, each ~0.3 m in diameter and infilled with gravelly sand, were exposed during roading excavations in Hamilton. The hollows, extending through modified soil A-horizon materials into upper B horizons, represent the lower part of small truncated mounds (puke) constructed by early Maori for growing kumara. With a density of around 100-150 hollows per 10 square metres, and originally ~0.6 m across, the puke formed a distinctive quincunx pattern. These features match historical descriptions (e.g. Joseph Banks, William Colenso) and are the first to be discovered in New Zealand. The soils were built into mounds by the addition of gravel, sand, and burnt scrub to ensure free drainage (critical), reduce risk of frost damage, raise soil temperatures, create sharp interfaces to encourage larger tubers, and improve nutrient levels especially K. These practises match traditional island Polynesian techniques for growing yams. Radiocarbon dates suggest the sites were occupied in the late 15th century or late 16th-early 17th centuries. Identification of charcoal fragments from the modified soil suggested that one site may have been cleared of large podocarp trees not long before gardening began. The word puke is a proto-Polynesian term originally for ‘yam planting mound’. The word kumara can be traced to a similar word in Ecuador-Peru from whence the sweet potato was initially transferred by eastern Polynesians. It was then brought to New Zealand perhaps via the southern Cook Islands.