Historical patterns of western spruce budworm and Douglas-fir tussock moth outbreaks in the northern Blue Mountains, Oregon, since A.D. 1700.

Abstract

Dendroecology methods were used to reconstruct a three-century history of western spruce budworm and Douglas-fir tussock moth outbreaks in the Blue Mountains of northeastern Oregon. Comparisons of 20th century Forest Service documentary records and host and nonhost tree-ring width chronologies provided an objective basis for distinguishing climatic effects from insect-caused defoliation effects. Budworm outbreaks were more confidently reconstructed than were tussock moth outbreaks. Since A.D. 1700, at least eight regional budworm outbreaks have occurred at intervals of about 21 to 53 years. Reduced radial growth caused by defoliation lasted from about 13 to 17 years. Two regional budworm outbreaks occurred during the 19th century, and at least three and possibly four regional outbreaks have occurred during the 20th century. These findings generally support the hypothesis that budworm outbreaks have increased in frequency and severity in the 20th century in northeastern Oregon.

Citation

Swetnam, Thomas, W.; Wickman, Boyd E.; Paul, H. Gene; Baisan, Christopher H. 1995. Historical patterns of western spruce budworm and Douglas-fir tussock moth outbreaks in the northern Blue Mountains, Oregon, since A.D. 1700. Res. Pap. PNW-RP-484. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 27 p