Influence of precommercial thinning grade on branch diameter and crown ratio in Pinus sylvestris in southern Sweden

Precommercial thinning is regarded as one of the most important measures for influencing timber quality in stands of Scots pine ( Pinus sylvestris L.). The present study considers the influence of both thinning intensity and tree height at the time of thinning on diameter of the thickest branch and crown ratio. A total of 115 plots ( either naturally regenerated, planted or sown, and either thinned down to 528-8000 stems ha(-1) or untreated) included in 20 sites in southern Sweden were analysed. The average tree height after thinning varied from 1.2 to 8.3 m. An increasing number of remaining stems resulted in a reduction in branch diameter, although the reduction appeared to be only minor if the number of stems after thinning was more than 3000 stems ha(-1). It was found that late thinning reduced the diameter of the thickest branch. The crown ratio decreased with stand height, number of stems after thinning and average height at thinning. The results were consistent for all trees and for the 500 thickest trees per hectare.