Graduate Thesis Or Dissertation
 

Early genetic selection for wood stiffness in juvenile Douglas-fir and western hemlock

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  • Wood modulus of elasticity (MOE), also known as wood stiffness, is one of the most important wood properties. Wood stiffness is a measure of the resistance to deflection, and is important because some products such as laminated veneer lumber, plywood, and dimension lumber require stiff and strong wood. Incorporating wood stiffness into breeding programs could help maintain acceptable wood quality and increase economic profits for wood producers. There is limited information on the genetics of wood stiffness in young Douglas-fir plantations, and the genetics of wood stiffness has not been studied in western hemlock. Therefore, my objectives were to use young (8- to 12-year-old) genetic test plantations of Douglas-fir and western hemlock to (1) determine the best approach for measuring acoustic velocity, and then use the best approach to (2) estimate additive and non-additive genetic variation, heritabilities, and potential genetic gains, (3) estimate genetic and phenotypic correlations between acoustic velocity and growth traits, and (4) discuss implications of these results for operational tree improvement. I studied acoustic velocity at two genetic test plantations of Douglas-fir (Fir Grove and Roaring River) and one test plantation of western hemlock (Toledo) using the TreeSonic and Microsecond Timer standing-tree tools, and two vertical placements of the sensors. These tools can be used to measure acoustic velocity in standing-trees, an indirect measure of wood stiffness. My results show that (1) the effects of standing-tree tool, vertical placement, and DBH-adjustment methods were non-significant, (2) acoustic velocity had significant genetic variation in Douglas-fir and western hemlock, (3) heritability of acoustic velocity was higher than the heritabilities of growth and form traits, and (4) substantial genetic gains in acoustic velocity are possible. My results also indicate that the mean acoustic velocity and modulus of elasticity were higher in Douglas-fir than in western hemlock. Although mean stiffness was higher for Douglas-fir, the distributions of acoustic velocity and modulus of elasticity overlapped between the species. These results indicate that comparable genetic gains are possible using both the TreeSonic and Microsecond Timer tools. Because of practical considerations, and higher measurement rates, I recommend that breeders use the TreeSonic and the same-face approach. I found positive genetic correlations between growth and acoustic velocity in western hemlock. This provides an opportunity to focus on improving wood stiffness in western hemlock so that it can better compete with Douglas-fir for products in which stiffness is important. Near optimal genetic gains are possible using 10 trees per family for wood stiffness. Because dominance variation was non-significant for Douglas-fir and western hemlock, near optimal gains in wood stiffness and growth traits can be obtained by collecting open pollinated seed from orchards (i.e., without control crossing) as long as pollen contamination is not a problem.
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