Spiral Grain in Second Growth Douglas-Fir and Western Hemlock

The spiral habit of growth of Douglas-fir (Pseudotsuga menziesii (Mirb) Franco) and western hemlock (Tsuga heterophylla (Raf)Sarg) was studied. Specimens were taken from sample plots on the University of Columbia Research Forest at Haney, B.C. in the Lower Fraser Valley. The samples were taken from an even-aged stand, from three sites of poor to good forest growth. Trees were selected from two crown classes, the Dominant-Codominant and Intermediate. Three individuals from each crown class for each species were collected. Thus a total of 36 trees, 18 from each species, six from each site per species, were used. Cross sectional disks were taken at breast height, split through a diameter to expose the-spiral grain, and the grain angle measured with relation to the pith. The primary influences were tested in analysis of variance. Regression analyses were made with respect to effect of age and diameter in spirality. Conclusions were that there is a general pattern of spiral development in both species on the three sites studied. The pattern takes form of an initial left spiral which decreases, passes through zero, and becomes a right spiral with increasing age and radius. However, individual trees vary considerably in their individual spiral development. The highest average actual spirals were associated with the poorest sites, so the slowest growing trees exhibit the greatest amount of spiral development. On slow growing sites the change indicates the spiral is highly correlated with age. On sites of higher quality, radius exerts the strongest influence on spirality.

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