Thinning strategies based on release of individual crop trees sacrifice some Dominant trees to provide prescribed growing space. This study uses increment cores to reconstruct early growth and post-thinning response of Dominant, Codominant, and Intermediate white spruce released on two, three, or four sides. Three stands planted in the 1990s were commercially thinned in the winter of 2017/18, during the 2017–2021 drought period. Analysis of covariance was used to assess drought resistance in 2018, growth release relative to prior basal area increment, and absolute 5-year basal area increment, controlling for 2017 diameter. Intermediate trees showed significantly lower drought resistance and growth release with a 3-sided vs. 2-sided release, though resistance scores were all greater than 1.0. Dominant trees maintained stable resistance and growth release across thinning intensities. Years to breast height and diameter in 2008 were significantly different between crown classes and had strong, positive relationships with post-thinning basal area increment. Results suggest low thinning to the same residual stocking will avoid shock to Intermediate trees while maintaining the high growth potential of Dominant and Codominant trees, warranting further study to assess duration of the effect across a range of residual stocking.
Neil P. Thompson (Wed,) studied this question.