A survey of thinning and pruning studies.

Abstract

This article begins with a brief overview of a number of thinning and pruning experiments in South Africa and the United States. Pruning is an essential operation following wide spacing or heavy thinning to avoid the production of coarse knotty timber. Thinning is carried out to improve the stand, either for hygienic purposes or the concentration of increment on the best stems in the stand. Thinning may be broken down into a number of types or methods e.g.: (i) stem or low thinning; (ii) crown thinning; (iii) selection thinning; (iv) mechanical thinning. Thinning grades may be described either qualitatively, e.g. the removal of dead and dying, suppressed, sub-dominants, whips and defective co-dominants and dominants, or numerically i.e. the reduction of the number of stems per acre to a certain number. The effect of stocking on growth is considered under four headings: (1) effect on height growth; (2) effect on diameter growth; (3) effect on form; (4) effect on basal area and volume. Two experiments designed to investigate the differences between methods are described...