Root architecture of genetically-improved Sitka spruce clones

An examination was made into the effects of tree breeding on the properties of the root systems associated with anchorage. Comparisons between the strength properties of root and stem wood were also made. Five selected clones of 11-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) were used along with control trees grown from unimproved cuttings and transplants. The trees had been established on a shallow unploughed but relatively homogeneous soil to limit directional distribution of the roots. Results suggest that tree selection primarily based on improved stem growth, form and wood density did not have a negative effect on the Strength properties of the structural roots. Significant correlations between a number of stem and large root wood parameters suggest that selecting for stem strength should have a positive effect on the strength of the wood of the large roots. Despite clonal differences in cross-sectional root area, there was no difference in the proportion of large roots, which provide most of the anchorage, to small roots between treatments. There was also no difference in the cross-sectional area of root plate apportioned to north, east, south and west directions. The wide variation in strength characteristics observed suggests that both stem and root wood strength could be improved through clonal selection. (C) 2004 Elsevier B.V. All rights reserved.