New Zealand Journal of Botany abstracts

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Mid and late Holocene pollen diagrams and Polynesian deforestation, Wanganui district, New Zealand

M. ROYD BUS SELL

Department of Biogeography & Geomorphology
Research School of Pacific Studies
The Australian National University
G.P.O.Box4,A.C.T.2600
Australia

Abstract Two sites near Waverley, western North Island, provide a mid to late Holocene vegetational, climatic, and fire history for the area. A mid Holocene flora at Waverley Beach includes a local fossil Podocarpus totara forest preserved as in situ stumps exposed in Hauriri Terrace cover beds. Fossil pollen suggests the presence of surrounding podocarp-hardwood forest dominated by Beilschmiedia tawa(1) andDacrydium cupressinum but with common Ascarina lucida and Dodonaea viscosa in the understorey, suggesting a maritime, moist, warm-temperate climate was present. At Waverley Beach, the local, dense forest phase of Podocarpus totara appears to have been eliminated by water table elevation following the post-glacial rise in sea level up to 6500 BP. The decline in abundance of Ascarina and Dodonaea pollen from the mid to late Holocene is suggestive of a milder climate during that period. Around Lake Waiau swamp, pre-clearance podocarp-hardwood forest was probably dominated by B. tawa(l), D. cupressinum, Prwnnopitys taxifolia, Metrosideros, and Knightia excelsa. Deforestation by Polynesian burning is recorded at 1 m depth in Lake Waiau swamp by the abrupt decline in arboreal pollen values. This event is poorly constrained by radiocarbon dating, and at present an age range of c. 685 CAL BP-210 BP is suggested. The scatter in radiocarbon ages for the Lake Waiau swamp peat provides a warning against the simple interpretation of ages of similar material, where few dates have been obtained. Fire activity at both sites is indicated by measurement of microscopic charcoal particle area. Pre-Polynesian fires may have been significant in affecting the vegetation composition. The chronology for dune-sand deposition does not correspond with previously described periods of dune formation. At Waverley Beach, dune-sand was deposited soon after 6600 BP and stopped prior to c. 5750 BP. A second period of dune-sand deposition occurred after 5700 BP. At Lake Waiau, dune movement blocked off Waiau Stream before c. 3500 BP; aeolian transport of sand continued for a short time after the lake was first formed.

Keywords Wanganui; palynology; Holocene; pollen analysis; Aranuian; Polynesians; Maori; deforestation; marine terraces; swamps; bogs; peat; lignite; charcoal; fires; sea level; dune activity; fossil forest; radiocarbon dates

Received 3 August 1987; accepted 8 March 1988
New Zealand Journal of Botany, 1988, Vol. 26: 431-451
0028-825X/88/2603-0431$2.50/0 © Crown copyright 1988

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