A dendroclimatic analysis of mountain hemlock (Tsuga mertensiana) ring-width and maximum density parameters, southern British Columbia Coast Mountains, Canada

Abstract

The growth of mountain hemlock trees in Pacific North America demonstrates a complex relationship to two or more seasonal environmental variables. In order to examine the radial growth response of mountain hemlock to subseasonal climate variables, ring-width and X-ray densitometric analyses were used to construct intra-annual dendroclimatic records. The intent was to highlight the difference between the dendroclimatic outcomes of standard ring-width analyses to those derived from density chronologies collected at high elevation locations in the British Columbia Coast Mountains. This study highlights the importance of using multiple tree-ring parameters to better define the complex growth behaviour in mountain hemlock trees for the construction of more robust proxy climate records. Tree-ring chronologies from three sites were used to describe the inherent climate-growth trends. Maximum tree-ring density values provided a robust data series for constructing site-specific proxy records of late-summer temperature. Annual ring-width measurements provided independent proxies of spring snowpack trends. Significant decreases in temperature and an increase in snowpack depth during the early 1700s and early 1800s coincides with documented PDO phases and Little Ice Age glacier advances. Identification of early and late growing season climate signals within mountain hemlock trees demonstrates the value of documenting the characteristics of multiple tree ring parameters in future dendroclimatic studies.