Linking juvenile growth of white spruce with site index

Abstract

The goal of this study was to link the growth of juvenile white spruce stands with an estimate of their site index. We applied a previously developed technique for correcting the height bias created by dominance switching among juvenile trees before trees reached the site index base age (50 years at breast height), using stem analysis data of white spruce from five mixedwood stands in central Alberta. For white spruce of approximately 15 years total age, we found the height of the current top height trees was approximately 14% greater than the height of the top height trees that would be selected close to breast height age 50. This height correction is essential to avoid an overestimate of site index. Secondly, to avoid the difficulties of determining breast height age or growth increment required for juvenile site index determination, we developed a linkage to site index using data from 168 white spruce trees that were longitudinally sectioned along the pith, selected from juvenile (age 6–15) spruce stands. Using this new equation, coupled with the correction for bias, we found that site index for white spruce from 49 test stands in Alberta, ranged from 9.0 to 31.8 m at base age 50, with a mean of 17.8 m; these values are in the range for spruce in mixedwood stands in Alberta. Key words: juvenile stand, height age curve, height bias adjustment, site index