SPIRAL GRAIN IN A CLONAL TRIAL WITH SITKA SPRUCE

Grain angles to the left in seven clones of Sitka spruce (Picea sitche nsis (Bong.) Carr.) decreased from the pith and outwards and with heig ht. Effects of compression wood and compass directions were nonsignifi cant. Clones differed significantly but interacted with height levels, ring numbers, compass direction, and compression wood. However, the i nteraction with compression wood was small. Furthermore, some interact ion with compass direction could possibly be attributed to eccentric s tems and stem axis choice. The repeatability was 72% for averages of r amets measured in five height levels and most rings from the pith. The mean spiral grain was 2.2 degrees, and the phenotypic standard deviat ion between averages of ramets was 1.07 degrees. Genetic gains of 1 de grees from phenotypic selections based on several measurements were su ggested using these values. Variations between ramets and residual var iances accounted for most of the variation. Thus, as many ramets as po ssible should be sampled to obtain the best estimates of mean clonal l evels. Clone interactions with height levels and ring numbers from the pith were less important. This was also explained by correlations of 0.83-0.98 among clone averages at 1.3 m for single rings and overall c lone means. Only significant effects ring widths were present within c lones.