THE NORTH AMERICAN GREAT BASIN

LATE QUATERNARY

PALEOECOLOGY AND PALEOCLIMATOLOGY

By studying plant remains from ancient packrat middens; pollen and charcoal accumulations from lake, marsh and playa sediment cores, and from cave deposits and archaeological sites, and the isotopic content of these plant macrofossils, Peter Wigand and his colleagues and students have been shedding vital, new light on the problem of biotic response to climate change during the late Quaternary (~ the last 250,000 years of earth history). Paleoenvironmental studies of the forests of the central Sierra Nevada during the last ten years have been directed toward: 1) reconstruction of forest history to derive understandings of the relationships between climate and vegetation response - in particular, frequencies, rates and magnitudes of climate change and resulting forest response have been investigated; and 2) the relationship of climate, vegetation change and fire regime dynamics has been investigated.

To clarify these relationships a series of sites on the east slope of the Cascade/Sierra mountain chains have been cored for pollen ranging from the Summer Lake area in south-central Oregon through Little Valley just east of the Lake Tahoe Basin. Records spanning about 230,000 years (Summer Lake), 45,000 years (Eagle Lake), 9,000 years (Bicycle Pond) and 6,300 years (Little Valley) have been collected, analyzed, and are now in the process of being reported. Additional records within the area include a 2,300-year pollen record from the Stillwater Marshes that can be compared with the Little Valley record. In addition, almost 200 dated woodrat midden strata from east of the Sierra Nevada crest east, north and south of the Lake Tahoe area are being used as additional proxies to confirm regional climate changes against which forest response and changing fire regimes can be measured. These can be compared and contrasted with a detailed pollen record from Diamond Pond in the Steens Mountain area of south-central Oregon and from Lower Pahranagat Lake at the northern edge of the Mojave Desert in southeastern Nevada.

These understandings of how ecosystems work will help planners, managers and modelers administer today's resources and plan for the future especially as global change becomes more of an issue.

Below are brief descriptions of the research, and of the preliminary conclusions that have been generated.

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