Number and diameter of breast-height region branches in a Douglas-fir spacing trial and linkage to log quality

A Douglas-fir (Pseudotsuga menziesii, Mirb. Franco) spacing trial, planted at 480, 540, 750, 840, 1100, and 1680 trees/ha was studied to investigate the relationship between planting spacing, number and diameter of branches in the breast-height region, and first 5 m log quality. The 540 and 840 tree/ha plantings were in a rectangular design with the distance between rows double that between trees within a row while the others planted in a square design. At age 18, number and diameter of branches 8 mm in diameter were measured in a 0.61 m region centered at breast height (BH, 1.3 m). There was no significant effect of planting density on number of BH region branches. The rectangular designs had significantly more branches than the square designs, but this difference was small. The mean diameter of BH region branches was significantly related to both planting density and type of design while the largest diameter of BH region branches and branch index of the BH region were related only to planting density. A subsample of trees was climbed to measure the diameter of the largest branch and branch index corresponding to the 5-m butt log. Highly significant relationships were found between the largest branch diameter and branch index of the butt log and the BH region counterpart measures of trees. Measuring the diameter of the largest branch in the BH region provided superior equations predicting the butt log and is a simple, fast measure to acquire in the field.