Variation in radial growth patterns of Pseudotsuga menziesii on the central coast of British Columbia, Canada

Radial growth of trees in mountainous areas is subject to conditions associated with changes in elevation. We present ring-width chronologies for Douglas-fir trees (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) at nine sites spanning low to high elevations in the Bella Coola area of the central coast of British Columbia, near the northern limits of the species distribution, and investigate the variation in tree-ring growth patterns in relation to different elevations, using principal component (PC) analysis. We find that the first PC, which represents 55.6% of the total variance, reflects a common growth response at sites of different elevation. Response function analysis indicates that growing season precipitation is the major factor in controlling tree-ring growth. This factor explains more of the variance in low-elevation sites than it does in high-elevation ones. Temperature in August of the preceding year shows a negative relationship to ring-width growth. The second PC represents 16.7% of the total variance and reveals a distinct difference in growth response between low- and high-elevation sites. The length and temperature of the growing season seem to play an important role in tree-ring growth at sites of high elevation. Comparison of the Bella Coola records with those from southern Vancouver Island suggests that growing season precipitation influences growth of Douglas-fir on a macroregional scale, but other factors such as temperature modify the growth response at the limits of the distribution of the species.