Dendroclimatîc response of high-elevation conifers, Vancouver Island, British Columbia




Laroque, Colin Peter

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The aim of this research program was to examine the growth response of high-elevation conifers on Vancouver Island to past, present and future climates. Forty locations were sampled and 88 chronologies were used to describe radial-growth changes over time and space. Radial-growth trends have been similar across Vancouver Island for most of the past 500 years. Large-scale oceanic influences on climate were shown to be strong forcing mechanism to radial growth. Master chronologies were constructed for each of the five tree species examined: mountain hemlock, Tsuga mertensiana (Bong.) Carr., yellow-cedar, Chamaecyparis nootkatensis (D. Don) Spach, western hemlock, Tsuga heterophylla (Raf.) Sarg., Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, and western red-cedar, Thuja plicata Donn. The response of these species to climate were combined to develop multiple aggregate chronologies (MACs). The MACs are able to record a stronger relationship to climate than all but the best single-species chronologies, with relationships to seasonalized parameters improved to a greater degree than those of single-month variables. Using these MAC relationships, proxy information was derived for four climate parameters (April 1 snowpack depth, June–July temperature, July temperature, July precipitation). The explained variance of the models was higher in the two seasonal reconstructions (April 1 snowpack depth r 2 = 41%, June–July temperature r2 = 34%) than for individual monthly reconstructions (July precipitation r2 = 15%, July temperature r2 = 24%). A wavelet analysis showed that each of the four models contains dominant modes of variability throughout time at approximately 16, 32, 65 and 130–150 year periods. Each mode of variability seems to be linked to ocean forcing mechanisms. Climate/radial-growth relationships were used to predict radial growth under various future climate scenarios. TREE (Tree-ring Radial Expansion Estimator) was developed to present an interactive, internet-based radial-growth model, which calculates the short-term radial-growth response for each tree species to user-defined climate change scenarios. Long-term radial-growth responses were produced using data from general circulation models to develop relationships that predict future radial growth of each tree species. These predictions highlight which species are susceptible to future shifts in climate and indicate which climate parameters may drive changes in radial growth.



Conifers, Climatic factors, British Columbia, Vancouver Island, Growth