Historical patterns of western spruce budworm and douglas-fir tussock moth outbreaks in the northern Blue Mountains, Oregon, since a.d. 1700. Forest Service research paper
Tree-ring samples from 21 mixed-conifer stands in the Blue Mountains of northeastern Oregon were analyzed for evidence of past western spruce budworm and Douglas-fir tussock moth outbreaks. Comparison of host and nonhost tree-ring growth provided an objective basis for distinguishing climatic effects from insect defoliation effects. Our reconstruction shows that since ca. A.D. 1700 at least eight regional budworm outbreaks occurred at intervals of about 21 to 53 years. Reduced radial growth periods caused by defoliation lasted from 13 to 17 years. Two regional budworm out-breaks occurred in the 19th century (ca. 1806 to 1822 and ca. 1851 to 1867), three outbreaks occurred in the northern Blue Mountains in the 20th century (ca. 1898 to 1910, ca. 1946 to 1958, and ca. 1980 to present), and an additional outbreak occurred in the Eagle Cap Wilderness (ca. 1925 to 1939). These findings generally lend support to the hypothesis that budworm outbreaks have increased in frequency and severity in the 20th century in northeastern Oregon.
- Research Organization:
- Forest Service, Portland, OR (United States). Pacific Northwest Research Station
- OSTI ID:
- 236925
- Report Number(s):
- PB-96-158829/XAB; FSRP-PNW-484; TRN: 61211396
- Resource Relation:
- Other Information: DN: Errata sheet inserted; PBD: Oct 1995
- Country of Publication:
- United States
- Language:
- English
Similar Records
Forest defoliators and climatic change: Potential changes in spatial distribution of outbreaks of western spruce budworm (Lepidoptera: Tortricidae) and gypsy moth (Lepidoptera: Lymantriidae)
Case history of population change in a `bacillus thuringiensis`-treated versus an untreated outbreak of the western spruce budworm. Forest Service research note