Effect of growth rate on wood properties of genetically improved Sitka spruce

This study examined the wood properties of 24-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) progenies with highly contrasting growth rates. The progenies were established as part of a breeding programme to improve growth rate and stem form. Trees from three progenies were selected with a high growth rate relative to an unimproved control of directly imported material from the Queen Charlotte Islands (QCI), British Columbia, Canada. Trees from a further three progenies were selected that displayed a similar growth rate to the QCI control. At the time of sampling, the fastgrowing progenies had a mean volume gain over the QCI and slow-growing progenies of ~70 per cent. Trees from the fast-growing progenies were found to have significantly larger branches, less latewood, and more compression wood in comparison with the QCI control and the slow-growing progenies. On the other hand, trees from the fast-growing progenies had a smaller grain angle than the QCI control. While fast-growing progenies had lower wood density than the control, this was not significantly different. These findings suggest that, in general, the criteria used to select Sitka spruce trees in the forest as potential candidates for the breeding population would indeed lead to significant improvements of the growth performance and grain angle from improved planting stock. Breeders need to be aware, however, of possible negative influences of such selection criteria on other stem and wood properties known to influence wood strength.