Microfossils of Polynesian cultigens in lake sediment cores from Rano Kau, Easter Island |
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Authors: | M Horrocks W T Baisden M K Nieuwoudt J Flenley D Feek L González Nualart S Haoa-Cardinali T Edmunds Gorman |
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Institution: | (1) Microfossil Research Ltd, 31 Mont Le Grand Rd., Mt Eden, Auckland, 1024, New Zealand;(2) School of Environment, University of Auckland, Auckland, New Zealand;(3) National Isotope Centre, GNS Science, PO Box 31312, Lower Hutt, 5040, New Zealand;(4) Department of Chemistry, University of Auckland, Auckland, 1142, New Zealand;(5) Institute of Natural Resources, Massey University, Private Bag 11222, Palmerston North, 4442, New Zealand;(6) Hanga Roa, Easter Island, Chile |
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Abstract: | 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 in-washed 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 an 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. |
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