Postglacial vegetation and climate of the Cascade Range, central Oregon

Pollen data from two sites provide information on the postgla-cial vegetation and climate history of the Cascade Range. IndianPrairie in the western Cascade Range was colonized by subalpineforests of Pinus, Picea, and Tsuga and open meadows prior to ca.12,400 4t.,—
yr B.P. The treeline lay 500 to 1000 m below its mod-ern elevation and conditions were cooler than at present. From ca.12,400 to ca. 9950 14C yr B.P. Abies became important and theforest resembled that presently found at middle elevations in thewestern Cascade Range. The pollen record implies a rise in tree-line and warmer conditions than before. From ca. 10,000 to 4000-4500 14C yr B.P., conditions that were warmer and effectivelydrier than today led to the establishment of a closed forest com-posed of Pseudotsuga, Abies, and, at lower elevations, Quercusand Corylus. During this period, Gold Lake Bog in the HighCascades was surrounded by closed forest of Pinus and Abies. Theearly-Holocene pollen assemblages at both Indian Prairie andGold Lake Bog lack modern analogues, and it is likely thatgreater-than-present summer radiation fostered unique climaticconditions and vegetation associations at middle and high eleva-tions. In the late Holocene, beginning ca. 4000-4500 "C yr B.P.,cooler and more humid conditions prevailed and the modern veg-etation was established. A comparison of these sites with others inthe Pacific Northwest suggests that major patterns of vegetationalchange at individual sites were a response to large-scale changes inthe climate system that affected the entire regio