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Microfossils of Polynesian cultigens in lake sediment cores from Rano Kau, Easter Island

by Mark Horrocks last modified 2012-08-15 07:48 AM

Horrocks M, Baisden WT, Nieuwoudt MK, Flenley J, Feek D, González Nualart L, Haoa-Cardinali S, Edmunds Gorman T. 2012. Journal of Paleolimnology 47: 185-204.


Previous wetland vegetation records from Easter Island showing deforestation and Polynesian agriculture are limited to cores that rely on pollen, with a single cultigen pollen type identified: Urticaceae/Moraceae, possibly Broussonetia payrifera (paper mulberry). Here we redress this by also using phytolith and starch analyses on four lake sediment cores on a ~350-m transect along the southwest edge of Rano Kau, focusing on inwashed basal clayey layers. We also use a new method, Fourier transform infrared spectroscopy, to positively identify degraded starch collected from sedimentary deposits. The cores are the first samples recovered from an area in the lake that a) lies below the relict village of Orongo, b) is near a section of the crater believed to be most accessible from the Pacific coast, and c) is far from the northern crater rim and receives high solar radiation, a likely benefit for crops of tropical origin.

Pollen and phytoliths are abundant in the clayey layers and sparse in overlying layers of organic lake detritus and living rhizomes. Mixing of core deposits as a result of human activity has disordered the radiocarbon sequence, precluding development of a reliable chronology. Containing microfossils of several introduced cultigens, the clayey layers represent gardened terraces that have slumped into the lake. The data indicate large-scale deforestation and a mixed crop production system including Broussonetia papyrifera, Colocasia esculenta (taro), Dioscorea alata (greater yam), Ipomoea batatas (sweet potato), Lagenaria siceraria (bottle gourd) and Musa (banana) sp. The data show (a) the potential for using the combined analyses to provide direct evidence of Polynesian horticulture on Easter Island and (b) that the island’s wetlands potentially hold extensive horticultural records. The study highlights the concept of ‘transported landscapes,’ whereby colonising people replace indigenous forests with artificial, imported agricultural landscapes.


Pollen, phytoliths, starch, Fourier transform infrared spectroscopy, agriculture, Easter Island.

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