How is it measured
- Diameter is measured in centimetres at breast height (1.3m).
- Every tree in a field trial is measured including the unimproved control imported from Queen Charlotte Islands (QCI), BC, Canada. A mean value of each family of trees in test is estimated for the site and compared to the QCI control. In this way we can estimate the genetic worth of the parent tree and express that value relative to the QCI control as a +/- % deviation. The best parent trees selected for diameter may be +15% to 20% better than the QCI control.
What does it mean
- The values the SSBC quotes are weighted for genetic repeatability and also the average performance across all sites in which the treatment has been tested.
- Diameter is poorly correlated with wood density so fast growing trees with high wood density are hard to find.
- The correlation between diameter and straightness and branching quality is near to neutral meaning fast growing, straight and finely branched trees can be found.