Effect of stand density on the branch development of silver birch (Betula pendula Roth) in central Finland

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Branch development of silver birch (Betula pendula Roth) was studied in a planting-design experiment in central Finland. Data was collected from 18 trees growing in stand densities of 400, 1,600 and 5,000 stems ha–1. Annual radial increments were measured from branches systematically sampled between the stem apex and crown base. Sawn specimens that included the thickest branch or knot were taken from the stem below the living crown, and the years of suppression, death, and occlusion of the branches were determined. After initial years of irregular radial increment, branch increment declined gradually with increasing branch age. In the lowest part of the crown, the branches remained alive for 3–4 years without forming annual rings. Wider spacing of trees delayed the reduction in branch increment and increased branch longevity. Branches were occluded 7–10 years after their death. The number of years from branch initiation to occlusion was 20 on plot 400. This period decreased to 13 years on plot 5,000. When the width of annual rings in the stem formed during each development period of branches was examined, the differences between the stand densities were more apparent due to the rapid stem diameter increment on sparse plots. A model was developed for predicting branch increment at different heights in the crown. The best independent variables for predicting branch increment were branch age and stem radial increment.