|Abstract or Summary
- 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.