IMPACT OF SPACING ON TRACHEID LENGTH, RELATIVE DENSITY, AND GROWTH-RATE OF JUVENILE WOOD AND MATURE WOOD IN PICEA-MARIANA

Ten 38-year-old trees of Picea mariana (Mill.) B.S.P., grown at each of three spacings (1.8 x 1.8, 2.7 x 2.7, and 3.6 x 3.6 m), at Stanley, 30 km west of Thunder Bay, Ont., were used to study the impact of spacing on growth rate, relative density, and tracheid length of juvenile and mature wood. Increment cores of 12 mm diameter were extracted from the south aspect of each tree at breast height. The boundary of juvenile and mature wood was demarcated by the variation in tracheid length, which varied among trees from ring 11 to 21. Average growth rate, relative density, and tracheid length were obtained between the pith and boundary point (juvenile wood) and beyond the boundary point (mature wood). Differences between the levels of spacing for the three response variables in both juvenile and mature wood were tested using contrasts. Properties of juvenile and mature wood were found to be affected differently by the plantation spacing. Juvenile wood has a faster growth rate and shorter fibres than mature wood. Relative density was similar in both wood zones. The growth rate in juvenile wood was found to be significantly different among the spacing levels. For mature wood, only the growth rate at the 3.6 x 3.6 m spacing was significantly different from the other two spacing levels. The highest relative density, 0.39, in both juvenile and mature wood was found at the 1.8 x 1.8 m spacing. No significant difference in the relative density between the two wider spacings was observed. At the widest spacing, the relative density was 8% lower than that at the 1.8 x 1.8 m spacing. The longest fibre lengths were found at the intermediate 2.7 x 2.7 m spacing, 2.05 mm in juvenile wood and 2.94 mm in mature wood. Tracheid lengths of the 3.6 x 3.6 m spacing were significantly shorter than those of the other two spacings. The relative density and tracheid length of plantation grown wood were lower than those of natural grown wood by at least 5% for relative density and 33% for tracheid length.