Influence of initial spacing and row‐to‐row distance on the crown and branch properties and taper of silver birch(betula pendula)

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Abstract
The external quality of Silver birch (Betula pendula Roth.) was studied in four planting design experiments in stands aged 11–22 yrs. The stands were established using densities of 400–5000 trees ha−1 with even spacing and row‐to‐row distances of 3.5 and 5.0 m. The faster the growth of silver birch, the thicker were its branches. From the point of view of technical quality, high initial spacing had some advantages. Dense stands were characterized by thin branches, early branch death and early self‐pruning. Using 5000 trees instead of 2500 trees ha−1 did not, however, significantly improve the quality of the birch. Also, in stands with an initial spacing of 1600 trees ha−1, the butt log branches died before first thinning. This density was adequate except on the most fertile sites, such as abandoned agricultural land. Following the death of branches, high stand density slowed down the self‐pruning of dry branches. The diameter of the thickest branch on the butt log was 23 mm on average at the 5000 trees ha−1 spacing and 30 mm at the 800 trees ha−1 spacing. Stem taper was the foremost factor in explaining the variation in branchiness and therefore a useful variable to measure together with the diameter of the thickest branch. The rectangular shape of the growing space did not influence the overall branchiness of birch. However, sectors orientated towards the space between rows were clearly more heavily branched.