Long Environmental Records Derived From Tree-ring Sequence In Washington And Northern Oregon

Abstract

Tree-growth records provide an important source of proxy climatic data for evaluating the uniqueness of 20th-century climates in the Pacific Northwest. Reconstructions of mean annual temperature from upper treeline sites show a prolonged temperature increase during the 20th-century that exceeded the magnitude and duration of any warm period over the past four centuries. Growth of low to mid-elevation continuous forests of western Washington increase during the 20th-century, suggesting an amelioration of climatic limitations. In contrast, tree growth reached minimum values during the 20th-century at drought-sensitive, forest-grassland borders east of the Cascade Mountains. Precipitation reconstructions based on lower treeline sites show severe droughts during 20th-century, but no longterm change in mean precipitation compared to earlier centuries.