POSTGLACIAL VEGETATION AND CLIMATE OF THE CASCADE RANGE, CENTRAL OREGON

Pollen data from two sites provide information on the postglacial vege tation and climate history of the Cascade Range. Indian Prairie in the western Cascade Range was colonized by subalpine forests of Pinus, Pi cea, and Tsuga and open meadows prior to ca. 12,400 C-14 yr B.P. The t reeline lay 500 to 1000 m below its modern elevation and conditions we re cooler than at present. From ca. 12,400 to ca. 9950 C-14 yr B.P. Ab ies became important and the forest resembled that presently found at middle elevations in the western Cascade Range. The pollen record impl ies a rise in treeline and warmer conditions than before. From ca. 10, 000 to 4000-4500 C-14 Yr B.P., conditions that were warmer and effecti vely drier than today led to the establishment of a closed forest comp osed of Pseudotsuga, Abies, and, at lower elevations, Quercus and Cory lus. During this period, Gold Lake Bog in the High Cascades was surrou nded by closed forest of Pinus and Abies. The early-Holocene pollen as semblages at both Indian Prairie and Gold Lake Bog lack modern analogu es, and it is likely that greater-than-present summer radiation foster ed unique climatic conditions and vegetation associations at middle an d high elevations. In the late Holocene, beginning ca. 4000-4500 C-14 yr B.P., cooler and more humid conditions prevailed and the modern veg etation was established. A comparison of these sites with others in th e Pacific Northwest suggests that major patterns of vegetational chang e at individual sites were a response to large-scale changes in the cl imate system that affected the entire region. (C) 1995 University of W ashington.