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UBC Theses and Dissertations
Genetic effects on wood shrinkage, relative density, grain angle, tracheid length, and fibril angle in Douglas-fir (Pseudotsuga menziessi var. menziesii (mirb.) franco) Koshy, Mathew P.
Seven wood traits: shrinkage (longitudinal, tangential, and radial), relative density, grain angle, tracheid length, and fibril angle, and two growth traits, height and diameter at breast height were analyzed in 413 trees belonging to 48 full-sibfamilies (4 pollen and 12 seed parents) from an 18- year-old coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) progeny test . Clones from six of the parents also were sampled. Six samples per age level (age levels 0 to 4 along stem radii), with two rings in each age level, were examined in a bolt taken at breast height of the tree for shrinkage and relative density. Smaller sample sizes were used for the other traits. Trends with age from the pith were decreasing longitudinal shrinkage and fibril angle and increasing radial and tangential shrinkage, grain angle, and tracheid length. Relative density first decreased and then increased beyond age level 2. Genetic effects were minimal for wood quality traits except for relative density. Most of the variation for wood quality traits was within tree and between individual trees within families. Genetic correlations between wood quality traits were minimal except between relative density and radial shrinkage, which was positive. Genetic correlations between growth characters like height and diameter at breast height and wood quality traits were also minimal except for relative density and longitudinal shrinkage at early age levels. Selection for increased height can be expected to reduce longitudinal shrinkage and relative density at early age levels, and have virtually no effect on the other traits studied. The results support current efforts to increase wood production through genetic improvement in growth rate by showing that current programs of selection for rapid early height growth will not (with the exception of relative density) result in substantial reductions in several wood quality traits beyond the first few years of tree growth. The demonstrated lack of substantial genetic effects for several traits indicated that genetic improvement can progress more rapidly by concentrating on a much smaller number of traits.
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