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Date of Award
Master of Science (MS)
Bunn, Andrew Godard
Bach, Andrew J.
Medler, Michael J.
As the oldest known conifer species in the Pacific Northwest (PNW), yellow cedar (Callitropsis nootkatensis (D. Don) (Spach)) represent an underexploited paleoclimate resource of significant dendroclimatological value. This is the first dendroclimatological study of high elevation yellow cedar within the North Cascades of Washington. In addition, I explored the coherence of yellow-cedar chronologies at the regional scale. I established master tree-ring chronologies and radial-growth characteristics of 50 high-elevation yellow cedars from four sites along the west slope of the North Cascades. Significant (p≤0.05) mean inter-series (r̄=0.61) and inter-site (r̄=0.75) correlations in radial-growth pattern revealed a common limiting factor to yellow-cedar growth within the region. Correlation (r=0.23-0.54) between PRISM climate data and the master chronologies indicated that summer minimum temperatures were the dominant limiting factor of growth for North Cascades yellow cedar. By expanding the sample area to include yellow-cedar chronologies from Mount Rainier WA and Vancouver Island BC, I showed a significant shared pattern of radial growth between these regions. In order to determine the influence of multi-decadal climate forcings associated with the Pacific Decadal Oscillation (PDO), I constructed an averaged PNWtree-ring chronology. Correlation analysis detected the influence of the PDO throughout the chronology. Wavelet analysis revealed the low-resolution (150-250 year) influences of temperature across the regional chronology and significant suppressed growth at all sites in response to stratospheric volcanic eruptions during the 1810's. Further sampling and the inclusion of yellow cedar in multi-proxy reconstructions could improve scientific understanding of paleoclimate in the PNW.
Western Washington University
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Robertson, Christopher S., "Dendroclimatology of yellow cedar (Callitropsis nootkatensis) in the Pacific Northwest of North America" (2011). WWU Graduate School Collection. 185.