INFORMATION NOTE An Indication of the Likely Volume Gains from Improved Sitka Spruce Planting Stock

SUMMARY Volume gains from an old Sitka spruce tree breeding experiment were evaluated, allowing predictions to be made of the likely volume increases which could be expected from modern tested seed orchards and family mixtures. Estimation of stem volume was carried out in a 38-year-old open-pollinated Sitka spruce progeny trial growing in Clocaenog Forest, north Wales, which had previously been measured for 10-year height. The mean volume production of all the families grown from selected plus-trees was estimated to be 21% greater than the Queen Charlotte Island (QCI) control; the mean of the best three families in the experiment was 32% greater than the QCI control and the estimated volume of the very best family was 42% greater than the QCI control. If the results of this study were to be extrapolated to seed stock currently available from tested clonal seed orchards, final rotation volume gains could be expected to exceed unimproved QCI seed stock by between 21% and 29%.