Graduate Thesis Or Dissertation
 

Wood quality and strength relationships in Douglas-fir (Pseudotsuga mezieseii (Mirb.) Franco) wood of different maturity

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  • The objectives of this study were to determine: 1) differences in average wood quality and strength properties of clear-wood specimens sampled from juvenile, transition, and mature wood zones in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees from known forest sites; 2) relationships among wood quality properties [specific gravity (SG), rings per inch (RPI)] and strength properties [Modulus of Elasticity (MOE), Modulus of Rupture (MOR)] of small, clear-wood specimens from juvenile, transition, and mature wood; and, 3) relationships between strength properties in bending of small, clear-wood specimens and strength properties in bending and tension of the structural lumber from which the small specimens were cut. The lumber was provided by the Stand Management Cooperative from trees on 15 sites in Washington and Oregon. Statistical analyses showed that average SG increased from juvenile to mature wood zones and was significantly different in each of the sampling zones (juvenile, transition, and mature wood). Growth rate decreased in all stands from juvenile through mature wood as trees aged. Averages for MOR and MOE increased with maturity of wood. Regression of SG on NOR and MOE showed low R² values for the juvenile wood zone which may be the result of interacting juvenile wood characteristics. Regression of RPI on SG, MOR, and MOE showed that by itself, rate of growth had very little or no effect. Slopes for SG versus NOR and MOE for the three wood zones were similar. Intercepts were different between the juvenile-mature wood zones for NOR and between the juvenile-transition and juvenile-mature wood zones for MOE. Slopes for RPI versus SG and MOE for the three wood zones were also found to be similar. Intercepts were different between the juvenile-mature wood zones, but not different between the juvenile-transition and transition-mature wood zones. MOE regressed on MOR for the three wood zones showed no differences between any of the slopes and intercepts, although the R² was highest for mature wood samples. Correlations between similar properties of small, clear wood specimens and structural lumber were highest.
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