Holocene environments and vegetational change on four Polynesian islands

Abstract

The specific research objectives of this study are: to look at environmental changes that have occurred on several Pacific island systems from the pre- to post-settlement periods; to see whether the observed changes are natural or anthropogenic; to test the latest Polynesian settlement theory; and to contribute to the understanding of the vegetation history on these islands.This study reports the results of stratigraphic investigations from four Polynesian sediment sequences. The sediments of Lakes Lanoto'o (Upolu), Roto (Atiu), Temae (Mo'orea) and Vaihiria (Tahiti) have revealed a history of environmental and vegetational change during the Holocene, which include long-term climatic variations affecting broad scale vegetation changes on Upolu and Atiu; long term sea-level change influencing the local environment and vegetation on Atiu; localised disruption of vegetation in the Vaihiria basin of Tahiti resulting from natural landslides; and finally, major changes in local environment due to human activity, evident on all of the islands.Records from Lake Lanoto'o and Lake Roto extend into the early Holocene and span both pre- and post-settlement periods, with the latter providing a continuous vegetation record from around 9000 yr BP. Sequences from Lakes Temae and Vaihiria originated in the late Holocene; the Temae record also spans the estimated period of Polynesian expansion into the Society Islands and, consequently provides some insight into the nature of indigenous floras.Modifications attributed to human activity were recognised in the Lanoto'o catchment from 2425±70 yr BP (512 BC). Initial settlement of the Lake Roto basin has been dated from 1420±45 yr BP (AD 640), while a 1210±90 yr BP (AD 790) record of human influence has been determined from the Mo'orea sequence. Fossil pollen records indicate that Polynesian settlers modified the natural vegetation and encouraged the growth of open scrub and fernlands. However, declines in several primary forest plants, previously associated with anthropogenic deforestation, appear to have resulted from natural causes during pre-settlement times. The presence of coconut pollen in two of the lake sequences, dated at -8600 yr BP in Atiu and prior to 1400 yr BP in Mo'orea, strongly suggests that the dispersal of this palm was by natural, as opposed to human agents, in contrast to previous theories. The Polynesian settlement date for Atiu, which is earlier than any previous archaeological records, is in conflict with the views behind the "Orthodox Scenario" of prehistoric settlement, and necessitates a re-think of this theory.

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