Influence of selective breeding on the development of juvenile wood in Sitka spruce

The effect of selective breeding on juvenile wood formation in 24-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) was investigated. Properties associated with juvenile wood in fast-growing progenies were compared with those from slow-growing progenies and an unimproved control of similar growth rate (origin Queen Charlotte Islands, British Columbia, Canada). Large differences in properties associated with juvenile wood, namely high annual ring width, high microfibril angle, low density, and low latewood proportion, were observed in the first 12 or so rings from the pith between treatments. These properties were significantly inferior in the fast-growing progenies in comparison with the slow-growing treatments. From the 13th ring outwards, no significant differences were found between treatments in all attributes measured. Coefficients of determination (R-2) between ring width and wood properties measured from rings 1 to 12 revealed only weak associations. Conversely, R-2 values calculated for rings 13-19 revealed significant associations, indicating that density, latewood proportion, and tracheid length and diameter declined, while microfibril angle increased, with increasing ring width. The period of formation and the properties of juvenile wood appear to be largely independent of growth rate. High growth rate in the mature wood remains a concern in terms of wood quality.