LATE-GLACIAL VEGETATION END CLIMATE-CHANGE IN WESTERN OREGON

Pollen records from two sites in western Oregon provide information on late-glacial variations in vegetation and climate and on the extent a nd character of Younger Dryas cooling in the Pacific Northwest. A suba lpine forest was present at Little Lake, central Coast Range, between 15,700 and 14,850 cal yr B.P. A warm period between 14,850 and 14,500 cal yr B.P. is suggested by an increase in Pseudotsuga pollen and char coal. The recurrence of subalpine forest at 14,500 cal yr B.P. implies a return to cool conditions. Another warming trend is evidenced by th e reestablishment of Pseudotsuga forest at 14,250 cal yr B.P. Increase d haploxylon Pinus pollen between 12,400 and 11,000 cal yr B.P. indica tes cooler winters than before. After 11,000 cal yr B.P. warm dry cond itions are implied by the expansion of Pseudotsuga. A subalpine parkla nd occupied Gordon Lake, western Cascade Range, until 14,500 cal yr B. P., when it was replaced during a warming trend by a montane forest. A rise in Pinus pollen from 12,800 to 11,000 cal yr B.P. suggests incre ased summer aridity. Pseudotsuga dominated the vegetation after 11,000 cal yr B.P. Other records from the Pacific Northwest show an expansio n of Pinus from ca. 13,000 to 11,000 cal yr B.P. This expansion may be a response either to submillennial climate changes of Younger Dryas a ge or to millennial-scale climatic variations. (C) 1998 University of Washington.