THE ECONOMICS OF PRUNING

Abstract

The need for pruning of Douglas fir is urgent. Research has shown that acceptable tools and techniques are available and has evaluated the effects of pruning. This report considers the costs and possible profit in pruning and concludes that for site III Douglas fir, pruning is profitable in all d.b.h. classes from 4" to 22".Volume and growth relationships between clear-shell thickness and diameter at the time of pruning are determined using both the International rule with ¼-inch kerf for board feet and the Smalian formula for cubic feet. A correction is made for slab allowance to give the net clear-wood scale of sawn material.Factors affecting lumber value of pruned trees are illustrated by examples of Douglas fir with and without natural pruning. Pruning profit per tree and per M.f.b.m. are calculated from value comparisons of clear and knotty lumber in pruned and unpruned trees. A formula is presented to aid in the choice of trees and stands to prune in the Douglas fir and other regions. Largest returns may be expected when rapidly growing trees are pruned at an early age. Additional profits may be secured by growing clear shells larger than four inches in diameter. Pruning is shown to be a safe and profitable investment at 2½ per cent without considering increased returns which may come from salvage of pruned-tree mortality and acceleration of growth by thinnings.