THE INFLUENCE OF PLANTING DISTANCE ON STRUCTURAL WOOD YIELDS OF UNTHINNED SITKA SPRUCE

The effects of planting distance at establishment on the structural performance of timber from unthinned crops of Sitka spruce are examined. Initial plant spacing is an important factor affecting the structural performance of timber with loss in performance particularly marked as planting distances increase from 1.5 to 3.0 m. Factors associated with planting distance that affect structural performance include log grade, determined mainly by stem straightness, knot number and knot size, and the proportion of juvenile wood; all are adversely affected and contribute to a lowering in the structural performance of sawn wood as planting distances widen. It is recommended that in order to obtain acceptable yields of structural timber meeting Strength Class 3 from unthinned crops, planting distance should not exceed 2 m and it is considered prudent to adopt the same spacing for crops where line or other systematic methods of thinning are anticipated. However, Strength Class 3 is a minimum requirement for structural timber and every effort is needed to improve on it by the use of superior stock and by management that favours the production of quality logs and timber.