Correction: Social network analysis of obsidian artefacts and Maori interaction in northern Aotearoa New Zealand.

[This corrects the article DOI: 10.1371/journal.pone.0212941.].

Early tropical crop production in marginal subtropical and temperate Polynesia.

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.

Social network analysis of obsidian artefacts and Maori interaction in northern Aotearoa New Zealand.

Over the span of some 700 years the colonizing populations of Aotearoa New Zealand grew, with subsequent changes in levels of interaction and social affiliation. Historical accounts document that Maori society transformed from relatively autonomous village-based groups into larger territorial lineages, which later formed even larger geo-political tribal associations. These shifts have not been well-documented in the archaeological record, but social network analysis (SNA) of pXRF sourced obsidian recovered from 15 archaeological sites documents variable levels of similarity and affiliation. Three site communities and two source communities are defined based on the differential proportions of obsidian from 13 distinct sources. Distance and travel time between archaeological sites and obsidian sources were not the defining factors for obsidian source selection and community membership, rather social considerations are implicated. Some archaeological sites incorporated material from far off sources, and in some instances geographically close sites contained material from different sources and were assigned to different communities. The analytical site communities constitute relational identifications that partially correspond to categorical identities of current Maori iwi (tribal) territories and boundaries. Based on very limited temporal information, these site communities are thought to have coalesced sometime after AD 1500. By incorporating previously published and unpublished data, the SNA of obsidian artefacts defined robust network communities that reflect differential levels of Maori interaction and affiliation.

Stable carbon and nitrogen isotopes in kukui (Aleurites moluccanus) endocarp along rainfall and elevation gradients: Archaeological implications.

Stable carbon and nitrogen isotopes are often used to make inferences of past environments and social patterns. We analyze δ 13C and δ 15N values in contemporary kukui (Aleurites moluccanus) endocarp to examine the effects of site environment. Results from across environmental transects on Hawai'i Island show strong patterns for both stable isotopes. For δ 13C a robust linear relationship with elevation is exhibited, strengthened by the inclusion of rainfall. This relationship breaks down at a minimum threshold of annual rainfall, possible relating to physiological responses to drought. For δ 15N, the only significant relationship observed pertains to substrate age. The endocarp from kukui is one of the most readily identified plant remains in the Pacific archaeological records and is often targeted for radiocarbon dating. We discuss the potential implications of our results regarding ancient climate, inferred diets, and habitat composition.

Variation in Rapa Nui (Easter Island) land use indicates production and population peaks prior to European contact.

Many researchers believe that prehistoric Rapa Nui society collapsed because of centuries of unchecked population growth within a fragile environment. Recently, the notion of societal collapse has been questioned with the suggestion that extreme societal and demographic change occurred only after European contact in AD 1722. Establishing the veracity of demographic dynamics has been hindered by the lack of empirical evidence and the inability to establish a precise chronological framework. We use chronometric dates from hydrated obsidian artifacts recovered from habitation sites in regional study areas to evaluate regional land-use within Rapa Nui. The analysis suggests region-specific dynamics including precontact land use decline in some near-coastal and upland areas and postcontact increases and subsequent declines in other coastal locations. These temporal land-use patterns correlate with rainfall variation and soil quality, with poorer environmental locations declining earlier. This analysis confirms that the intensity of land use decreased substantially in some areas of the island before European contact.

Household expansion linked to agricultural intensification during emergence of Hawaiian archaic states.

The Leeward Kohala Field System (LKFS) covering ∼ 60 km(2) on Hawai'i Island is one of the world's best-studied archaeological examples of preindustrial agricultural intensification. Archaeological correlates for households over a 400-y period of intensification of the LKFS (A.D. 1400-1800) indicate that household age, number, and distribution closely match the expansion of agricultural features at both macro- and microscales. We excavated and dated residential complexes within portions of five traditional Hawaiian land units (ahupua'a), two in the central core of the field system and three in the southern margins. Forty-eight radiocarbon dates from 43 residential features indicate an overall pattern of exponential increase in the numbers of households over time. Spatial distribution of these dates suggests that the core of the LKFS may have reached a population saturation point earlier than in the southern margins. Bayesian statistical analysis of radiocarbon dates from residential features in the core region, combined with spatial analysis of agricultural and residential construction sequences, demonstrates that the progressive subdivision of territories into smaller socioeconomic units was matched by addition of new residences, probably through a process of household fissioning. These results provide insights into the economic processes underlying the sociopolitical transformation from chiefdom to archaic state in precontact Hawai'i.

Sources of nutrients to windward agricultural systems in pre-contact Hawai'i.

Prior to European contact in 1778, Hawaiians developed intensive irrigated pondfield agricultural systems in windward Kohala, Hawai'i. We evaluated three potential sources of nutrients to windward systems that could have sustained intensive agriculture: (1) in situ weathering of primary and secondary minerals in upland soils; (2) rejuvenation of the supply of rock-derived nutrients on eroded slopes and in alluvium; and (3) transport of rock-derived nutrients to crops via irrigation water. Our results show that most windward soils are infertile and suggest that weathering of minerals within upland soils was insufficient to sustain intensive agriculture without substantial cultural inputs. Erosion enhances weathering and so increases nutrient supply, with soils of the largest alluvial valleys (>200 m deep) retaining 37% of calcium from parent material (compared to 2% in upland sites). However, soils of smaller valleys that also supported pre-contact agricultural systems are substantially less enriched. Isotopic 87Sr/86Sr analyses of stream water demonstrate that at low to moderate stream flow over 90% of dissolved strontium derives from weathering of basalt rather than deposition of atmospheric sources; most other dissolved cations also derive from basalt weathering. We calculate that irrigation water could have supplied approximately 200 kg ha(-1) yr(-1) of calcium to pondfield systems, nearly 100 times more than was supplied by weathering in soils on stable geomorphic surfaces. In effect, irrigation waters brought nutrients from rocks to the windward crops.