LATE-QUATERNARY VEGETATION RESPONSE TO CLIMATIC-GLACIAL FORCING IN NORTH PACIFIC AMERICA

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Abstract
Late Quaternary pollen records of biogenic deposits of the American North Pacific coast show multiple responses of vegetation to forcing by climate and glaciers. Overall trends during the Holocene have been toward development of closed forest, but intervals are evident that were both progressive and retrogressive. Vegetation apparently responded in concert with fluctuating climatic and glacial episodes. Grass-sedge tundra, widespread initially in a relatively cold, late-glacial setting, was replaced by open arborial communities in the early Holocene during milder millennia of the thermal maximum. Climate did not support the development of structurally closed forest until the cool and humid late Holocene. With reactivation of glaciers during recent millennia, vegetation has been altered by a series of stadial and interstadial events. Current interglacial climate trends appear to involve a shifting pattern in the duration and intensity of seasonal atmospheric circulation centers over the North Pacific Ocean. Climatic-glacial forcing recorded in these studies is attributed to changes in solar radiation, among a number of other factors.