Reconstruction of historic insect outbreaks in Lake Clark and Katmai National Parks and Preserves: Final Report
Sherriff R and Berg E. 2011. Reconstruction of historic insect outbreaks in Lake Clark and Katmai National Parks and Preserves: Final Report. Natural Resource Technical Report. NPS/SWAN/NRTR—2011/482. National Park Service, Natural Resource Stewardship and Science. Fort Collins, Colorado
Recent spruce bark beetle (Dendroctonus rufipennis) activity in south-central and southwest Alaska has resulted in widespread mortality of mature white spruce. We used tree-ring data to examine the occurrence of and climatic influences on historic spruce beetle outbreaks at 15 sites on the Alaska Peninsula and compared our findings with known beetle activity on the Kenai Peninsula over the last 300 years. At each site, we collected stand structure data (i.e., species composition, density, and size structure) and tree cores for the determination of age structure, growth trends, and tree death dates. In addition, we compared our regional dataset of spruce beetle outbreaks across the Alaska Peninsula with three climate reconstructions that tracked (1) regional temperature and precipitation; (2) El Niño-Southern Oscillation (ENSO); and (3) and the Pacific Decadal Oscillation (PDO) conditions. Our results indicate significant growth releases attributed to spruce beetle outbreaks in the 1810s, 1830s, 1870s, 1900-1910s, and late 1970s-early 1980s. These periods coincided with a previously published record of beetle activity on the Kenai Peninsula. Our study suggests that moderate to high severity spruce beetle outbreaks occurred episodically (mean return interval of 55 years) over the past 250 years across areas of south-central and southwest Alaska, and were associated with multi-year periods of warm and dry conditions related to El Niño and warm-phase PDO conditions. This apparent relationship between beetle activity and climate indicates that high-frequency (multi-year) climate variability has been the primary driver of widespread, epidemic-proportion outbreaks. The spatial extent of recent bark beetle activity appears to be within its historical geographic range, but outbreaks since the late 20th century show greater synchrony across sites than in the past, suggesting that the severity of the recent outbreak may be unprecedented.
- Type
- Published Report
- Authors
- Sherriff, Rosemary; Berg, Ed
- Date of Issue
- 2011-08
- Publisher
- National Park Service, Natural Resource Stewardship and Science
- Units
- KATM , LACL , NRSS
- Keywords
- Climate, Dendroctonus rufipennis, dendroecology, forest disturbance, Picea Glauca, Southwest Alaska, Spruce Beetle, tree-ring data, White Spruce