A number of basic wood quality characteristics were evaluated in 10 European larch (Larixdecidua Mill.) trees, 5 from each of two rapidly growing plantations in eastern Ontario (approximately 30 years old) and western Quebec (approximately 25 years old). Characteristics evaluated included growth rate, relative density, fibre dimensions, longitudinal shrinkage, alcohol–benzene and water-soluble extractives, and Klason lignin. Radial and longitudinal patterns of variation in wood characteristics were examined and particular attention was given to the distribution of juvenile wood within the stems. Extractive contents were more closely related to the extent of heartwood and sapwood in the stems than to differences between juvenile and mature wood. Relative density was generally lower at the centre of the stem than in the mature outer wood, but the change was usually gradual, with no distinct boundary between juvenile and mature wood zones. The most useful characteristic for delimiting the juvenile wood zone appeared to be longitudinal shrinkage. On this basis, the transition from juvenile to mature wood occurs at about 15 rings out from the pith at breast height. Ranking of individual trees for wood density was judged to be reliable at about 7 years of age at this height level.
Six selection strategies aimed at genetically improving volume production and wood quality factors such as density, heartwood content, and stem taper are compared in a 20-year-old jack pine progeny trial. Selection indices were computed under various assumptions about economic values of the traits under selection and with contraints on the magnitude and direction of expected genetic gain. Stem taper, wood density, and heartwood content were under strong genetic control; however, the low phenotypic variation of wood density limits its potential for genetic improvement. Heartwood content emerged as a trait amenable for rapid genetic improvement. Despite low heritabilities the prospect of improving size-related traits was promising due to substantial phenotypic variation. Economic weights were important for the selection outcome and good progress was reported in all traits when volume received the highest weight. It was feasible to limit genetic gain in individual traits to predetermined relative levels but the cost in terms of reduced gain in unrestricted traits was economically debilitating. Concerns about undesirable concomitant changes in wood density, heartwood, and stem taper when breeding is based solely on growth traits were not confirmed by our data.
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