Vegetation History of Laysan Island, Northwestern Hawaiian Islands.

Abstract

Paleoenvironmental investigations were undertaken on Laysan Island in the remote Northwestern Hawaiian Islands to investigate its flora before historical observations. Substantial impacts occurred to the island as a result of late nineteenth- and early twentieth-century guano mining, commercial feather collecting, and denudation of vegetation by feral rabbits. An account of Laysan’s historically known vegetation is presented, followed by discussion of results from the investigation of a 16.41-m sediment core from Laysan’s central hypersaline lake. The 7,000-year pollen and seed record, besides indicating the former importance of Pritchardia palms on Laysan, showed the former presence of seven previously unknown taxa, only four of which could be identified. Diatom analysis indicated fresh to brackish lake water during the early Holocene, a finding supported by the mollusk assemblage. Diatom diversity gradually decreased over time until there is a near monoculture, with types indicating a gradual increase of salinity. Hypersaline conditions were first recognizable near the top of the sequence with the appearance of Artemia zooplankton. Generally wetter conditions seem to have characterized the island before about 5,150 yr B.P., with drier conditions thereafter. The pollen record also suggests two possibly very brief periods of much drier conditions, conceivably related to El Nin˜o– Southern Oscillation episodes.