|Abstract or Summary
- Intensive management of young-growth Douglas-fir plantations has emphasized volume growth over wood quality. A better understanding of the variables that affect wood quality is needed so that wood quality and stand yield can be systematically combined into a silviculture program. This experiment utilized two separate experiments to establish the relationship bebtwen wood quality, stand density, and artificial pruning. The influence of initial stand density on branch diameter, wood density, and tracheid length was explored utilizing 56 trees, 19 and 21 years old, at two sites in central western Oregon. Trees were sampled from Nelder plots ranging in density from 309 trees/ha to 18,730 trees/ha. The effects of fixed-height pruning on wood
density and tracheid length were investigated using trees 23, 26, and 28 years
old, after ten years of growth following pruning. Mean branch diameter, maximum branch diameter, number of branches/m, longevity of radial branch growth, and longevity of terminal branch growth all increased with decreasing initial tree density. After accounting for initial tree density, 1:2 rectangularity of spacing did not affect indicators of wood quality relative to 1:1 rectangularity of spacing.
When age was held constant, there was no evidence that either wood density or tracheid length at breast height varied with initial tree density or crown characteristics. In contrast, there was evidence that ring density, earlywood density, and percent latewood increased linearly with initial tree density at the
5.27 m sampling height. There was no significant change in growth rate or wood density at breast height (1.37 m) or 5.27 m as a result of pruning 15% or less of the live crown length. In contrast, pruning to 5.5 m at age 13 resulted in a one-year decrease in earlywood width and an increase in percent latewood at 1.37 m. At the 5.27 m
sampling height, there was a temporary increase in earlywood density, percent
latewood, and mean ring density. Pruning at age 13 to 3.4 m and 5.5 m resulted in an increase in mean, earlywood, and latewood tracheid length of approximately 6% for three years. Wide initial spacing, combined with pruning appears to be the best choice
for improving wood quality of Douglas-fir. Even though juvenile wood volume will be greater due to wide spacing, the increase in log diameter and clear wood volume will enhance log grade, especially if pruning occurs early in the rotation and is combined with commercial thinning to promote diameter growth.