Longitudinal Variation of Specific Gravity in Stems of Black Spruce, Balsam Fir, and Lodgepole Pine

Abstract

The relationship between disc specific gravity (dependent variable) and relative disc height was investigated for 50 black spruce (Piceamariana (Mill.) B.S.P.), 50 balsam fir (Abiesbalsamea (L.) Mill.), and 36 lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.). The sample trees represented various geographic areas and sizes. The simplest polynomial adequately describing the relationship was a parabola whose minimum was at mid-stem in spruce and fir and at 70% of the total height in pine. The linear term was significant only in pine and could be detected with 95% confidence if at least 14 trees were sampled. The quadratic term could be detected with 95% confidence if at least 48 spruce, or 8 fir, or 38 pine were sampled. It was concluded that the conflicting evidence in the studies concerned with the longitudinal variation of specific gravity in species of the genus Picea may be due to insufficient sample size of trees. Deviations of the sample averages from the fitted values exhibited a pattern that was similar for each species. This similarity suggested that the action of factors governing wood structure in stems of conifers depends more on the relative height in the stem than it does on species, geographic area, and absolute size.