Author : Starheim, C.C.A. Date : 2011. Title : Regional scale tree-ring reconstructions of hydroclimate dynamics and Pacific salmon abundance in west central British Columbia. Publication : Unpublished MSc thesis. University of Victoria, Victoria, British Columbia. Issue : Page(s) : 92 p.
Long duration records are necessary to understand and assess the long-termdynamics of natural systems. The purpose of the research presented in this thesis was to use dendrochronologic modelling to construct proxy histories ofhydroclimatic conditions and Pacific salmon abundance in central coastal regions of British Columbia. A multi-species regional network of tree ring-width and ring-density measurements was established from new and archived tree-ring chronologies collected in west central British Columbia. Using this regional treering network, multivariate linear regression models were constructed for records of nival river discharge, summer mean temperature, end-of-winter snow-water equivalent (SWE), the winter Pacific North America pressure pattern (PNA) and Pacific salmon abundance. All proxy hydroclimate records provide information back to 1660 AD. Reconstructions of July-August mean runoff for the Skeena and Atnarko rivers describe intervals of below-average runoff during the early to mid-1700s and parts of the early, mid and late 1900s. Models describe periods of above-average river discharge during the late 1600s, the early 1700s and 1800s, and parts of the early and mid-1900s. Fluctuations in the proxy reconstructions of July-August mean temperature for Wistaria and Tatlayoko Lake, May 1 SWE at Mount Cronin and Tatlayoko Lake and October-February PNA occurred in near synchrony withthe shifts described in runoff records. Episodes of higher than average runoffwere typically associated with periods of enhanced end-of-winter SWE, belowaverage summer temperature and positive anomalies in winter PNA. A history of Pacific salmon abundance was reconstructed for four species of salmon (Chinook, sockeye, chum and pink) that migrate to coastal watersheds ofcentral British Columbia. The proxy records vary in length and extend from 1400AD, 1536 AD and 1638 AD to present. Similar to the long-term records ofhydroclimate, salmon abundance was described to vary throughout the past sixcenturies. Significant collapses in the proxy records of Pacific salmon stocks were noted during the early 1400s, the late 1500s, the mid-late 1600s, the early 1700s, the early-mid-1800s and parts of the 1900s. Correlation and wavelet analyses of reconstructed hydroclimate and salmon population records revealed low and high-frequency cycles in the data. Findings related the reconstructions to atmospheric teleconnection indices describing the influence of both the Aleutian Low pressure centre and sea surface temperatures in the North Pacific Ocean. To a lesser degree relationships were also found between reconstructions and the El Niņo-Southern Oscillation. Results thusconfirm the long-term influence of large-scale ocean and atmospheric circulation patterns on hydroclimate trends and Pacific salmon abundance in central British Columbia. The reconstructions introduced in this thesis provide insights about the long-term dynamics of the central British Columbia environment. Several reconstructions presented in this thesis provide novel contributions to dendrohydroclimatic and paleoecologic research in Pacific North America. The melt-season runoff records for the Skeena and Atnarko are the first to be constructed for nival-regime basins in British Columbia. Similarly, the models of Skeena River runoff and Mount Cronin SWE are the first reconstructions of runoff and snowpack in Pacific North America based on a ring-density chronology, demonstrating the significant contribution that wood density measurements make to dendrohydroclimate research. The models of Pacific salmon stocks are also the first to utilize climate-sensitive tree-ring records to construct a history of regional salmon abundance and thus represent a significant advancement to paleoecological modelling.