Influence of initial spacing and row‐to‐row distance on the growth and yield of silver birch(betula pendula)

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Abstract
The growth and yield of silver birch (Betula pendula Roth.), up to the first thinning stage and partly beyond, were studied in four planting design experiments. Stands were established using densities of 400–5000 trees ha−1 with even planting and row‐to‐row distances of 3.5 and 5.0 m. The tree quality was not studied but a subsequent study addresses this topic. In the densest birch stands, having 4000 live trees ha−1 at a dominant height of 15 m, height and volume increments were observed to begin to slow down. At the age of 20 yrs the highest increment of stem wood was observed at two densities, i.e. 2500 and 5000 trees ha−1. The yield of pulpwood was 20 m3 ha−1 less with initial spacing of 1600 trees ha‐1 compared with the denser stands. The diameter growth of the dominant trees was reduced when the stem number exceeded 1000 trees ha−1. At the lowest density of 400 trees ha‐1, birch height increment was redued. The skewness value of the diameter distribution was mostly negative. At the first thinning age, the normality of this distribution was reduced by wider spacing. Increasing the row‐to‐row distance did not influence the height growth of silver birch. Using a row‐to‐row distance of 5.0 m, mortality was about twice that found for even spacing at the same density. If the row‐to‐row distance was at least three times that of the plant‐to‐plant distance, the diameter and volume increments were slightly reduced. Extending the row‐to‐row distance hastened the differentiation into distinct canopy layers and the diameter growth of dominant trees suffered less from dense spacing than in even planting. Consequently, the first thinning may be postponed and thereby made economically feasible.