Variation of Density and Growth Ring Width in Stems of Sitka and Norway Spruce J. A. PETTY, D. C. MACMILLAN* and C. M. STEWARDt Department of Forestry, University of Aberdeen, St. Machar Drive, Aberdeen. AB9 2UD, Scotland SUMMARY The variation with height and radial distance from the pith of basic density and ring width has been determined in stems of 48-year-old Sitka and Norway spruce planted at two spacings at Durris, Kincardineshire. The pattern of radial variation of density was broadly similar at all heights: high near the pith, falling to a minimum and then a gradual increase. The mean whole-stem densities were significantly different at the two spacings in Sitka but not in Norway spruce. Density at breast height was inversely correlated with ring width, strongly in Sitka but weakly in Norway spruce. The density/ ring width regression equation for outer wood in Sitka spruce at age 48 differed from that at age 31. In Norway spruce a high correlation was found between whole-stem density and the density of rings 16-25 at breast height. INTRODUCTION The density of the wood of Sitka spruce (Picea sitchensis (Bong.) Carr.) is known to decrease in response to increased growth rate (Brazier, 1970a, 1970b; Gardiner and O'Sullivan, 1978; Savill and Sandels, 1983). The initial diameter growth rate of individual trees may be increased by increasing the initial spacing of the crop, but since most strength properties of wood are proportional to density this may contribute to an unacceptable loss of strength in the timber produced (Brazierera/., 1985). Brazier (1977) has reviewed the influence of silvicultural practice on wood properties, including density, and Elliott (1970) has reviewed the subject of wood density in general. Brazier (1970b) used samples from the Forestry Commission's Durris spruce spacing experiment, planted in 1935. This experiment, already depleted by wind damage, was recently clearfelled. The opportunity was taken to sample the Sitka spruce to see whether the relation between growth rate and density up to age 31 years found by Brazier (1970b) still obtained up to age 48. He used only breast height samples, and a further aim of the present work was to examine the variation of these quantities at other heights in the stem. Subsequently, as a result of a separate investigation of growth rate and branch size in Norway spruce (Picea abies (L.) Karst.), wood 'Present address: Macaulay Land Use Research Institute. Craigiebuckler, Aberdeen. tPresent address: Tilhill Forestry, Wraysbury House, Jarvis Brook, Crowborough, E. Sussex, TN62JE. Forestry, Vol. 63, No. 1,1990 at University of Kent on June 13, 2013 http://forestry.oxfordjournals.org/ Downloaded from