Sinuous stem growth in a Douglas-fir (Pseudotsuga menziesii) plantation: growth patterns and wood-quality effects

Stem sinuosity is thought to negatively impact wood quality, but no studies have characterized its vertical and radial effects on wood properties. Here we study wood quality along the entire stem in 25-year-old plantation-grown Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) trees (32 trees total) that had been scored for sinuosity at age 12. We also study compression wood formation in the radial direction for one internode that had been scored for sinuosity at age 12 and subsequently produced 13 more annual rings. Trees with highly sinuous leaders at age 12 were more likely to be sinuous in other years, and developed more slope of grain defect (approximately 15% log volume) than less sinuous trees, but did not differ in the size of the pith-containing core. Leaders originally scored as highly sinuous developed more compression wood than control trees but only near the pith. Internode length did not differ among sinuosity classes. The size of the pith deviations (radial distance from centreline) remained constant up the stem despite a decline in internode length. However, the frequency of pith deviations was highest at 10-15 years, when internode length reached a peak. The relationship between temporal patterns of growth rate, sinuosity, and tree biomechanics deserves further attention.