INFLUENCE OF INITIAL SPACING AND ROW-TO-ROW DISTANCE ON THE GROWTH AND YIELD OF SILVER BIRCH (BETULA-PENDULA)

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 400-50 00 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 addres ses 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 o bserved to begin to slow down. At the age of 20 yrs the highest increm ent of stem wood was observed at two densities, i.e. 2500 and 5000 tre es ha(-1). The yield of pulpwood was 20 m(3) ha(-1) less with initial spacing of 1600 trees ha(-1) compared with the denser stands. The diam eter growth of the dominant trees was reduced when the stem number exc eeded 1000 trees ha(-1). At the lowest density of 400 trees ha(-1), bi rch height increment was redued. The skewness value of the diameter di stribution was mostly negative. At the first thinning age, the normali ty of this distribution was reduced by wider spacing. Increasing the r ow-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 distanc e was at least three times that of the plant-to-plant distance, the di ameter and volume increments were slightly reduced. Extending the row- to-row distance hastened the differentiation into distinct canopy laye rs 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.