Canadian Forest Service Publications
Growth differentiation in white spruce crop tree progenies. 1993. Magnussen, S. Silvae Genetica 42 (4-5): 258-266.
Issued by: Pacific Forestry Centre
Catalog ID: 4412
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Stem analysis of 288 36-year-old dominant and codominant 'crop' trees in 18 white spruce open-pollinated families revealed a strong genetic control of height growth (heritabilities of 0.3 to 0.6). Heritability estimates for volume growth peaked around age 20 when they reached a level of 0.3 only to decline rapidly thereafter. Rank stability and the coefficient of genetic prediction between age 36 family means and means obtained at earlier ages were not sufficiently strong to warrant early selection for either height or volume. Height-age and volume-age relationships were successfully modelled with a quadratic log-linear model with three interpretable parameters. Heritabilities of the growth curve parameters varied from 0.14 to 0.72. The opportunity to improve the growth curves by 20% for all ages was explored by using a restricted selection index of the growth curve parameters. An improvement of 6% to 12% in both height and volume per breeding cycle and unit selection intensity is realistic. Growth curve analysis is recommended for the analysis of longitudinal growth series.