Sitka spruce Population Study. A study in the natural variation of economic traits within an unselected population of Sitka spruce

The operational Sitka spruce selection and breeding programme commenced in 1963 with the selection in British forests of superior individuals for height, diameter, stem straightness and branching quality. Over 1800 plus-trees were selected over the next 20 years or so. Whilst these trees were thought to be of Queen Charlotte Islands origin (QCI; British Columbia, Canada) origin, forest records were often incomplete in this regard. Also there is known to be considerable variation in the performance of seed lots collected across the range of QCI. A regular programme of open-pollinated half-sib progeny testing of selected plus trees commenced in 1967. Only if variance components are derived from an unselected population will they be free of any artificially induced bias for the selected traits and other correlated traits. A soundly based breeding strategy is dependent on reliable information regarding the underlying variation and pattern of inheritance. When accurate estimates of unbiased genetic variances are available, it is possible to make realistic predictions of times and costs likely to be incurred under different breeding schemes and selection intensities which could be simulated with mathematical models. Ideally, a study into the variance components operating within an unselected population should be carried out prior to commencing a selection and breeding programme. This is rarely possible due to the time delay involved in obtaining data from genetic tests up to half a rotation length prior to starting a programme. At best, genetic field trials may be planned to run concurrently with the operational testing and selection programmes such that an existing programme may have its efficiency increased, or direction altered. In 1969 there was the opportunity to collect seed from a stand of known QCI origin in which cones were being produced on all size classes of trees. 150 coning trees were randomly selected from the across the dominance classes within the stand in approximate proportion to their respective contribution to the make-up (%) of the stand. Seed extracted from the cones collected from each tree were raised as parent-specific open-pollinated families in a research nursery prior to planting out onto randomised and replicated site in spring 1972. For more information see: Lee, S.J., Woolliams, J., Samuel, C.J.A. and Malcolm, D.C. (2002a). A study of population variation and inheritance in Sitka spruce II. Age trends in genetic parameters for vigour traits and optimum selection ages. Silvae Genetica, 51 (2-3), 55-65 Lee, S.J., Woolliams, J., Samuel, C.J.A. and Malcolm, D.C. (2002b). A study of population variation and inheritance in Sitka spruce III. Age trends in genetic parameters and optimum selection ages for wood density, and genetic correlations with vigour traits. Silvae Genetica 51, (4), 143-151. Lee, S.J., Woolliams, J., Samuel, C.J.A. and Malcolm, D.C. (2007). A study of population variation and inheritance in Sitka spruce IV. Correlated response in the progeny population based on selection in the parental population. Silvae Genetica 56, (1), 36-44 Samuel, C.J.A. and Johnstone, R.C.B (1979). A study of population variation and inheritance in Sitka spruce. I. Results of glasshouse, nursery and early forest progeny tests. Silvae Genetica 28(1), 26‑32.