VARIATION OF RING WIDTH AND SPECIFIC-GRAVITY WITHIN TREES FROM UNTHINNED SITKA SPRUCE SPACING TRIAL IN CLOCAENOG, NORTH-WALES

The aim of this work was to quantify patterns of change in ring width and specific gravity within trees of Picea sitchensis with ring number across juvenile and mature wood, in relation to height in tree, origi nal spacing, and crown dimensions. Five trees were sampled from each o f three plots on a 52-year-old unthinned spacing trial at Clocaenog, N orth Wales. The ring width of wood produced in early decades of the pl antation was most strongly correlated with original spacing, while tha t produced in later decades was more strongly correlated with branch d iameters of the upper crown. In later decades, trees originally at the widest spacing had higher specific gravity than those originally at c loser spacing, presumably associated with self-thinning of the narrowe r-spaced unthinned plots. Differences in amount of juvenile wood betwe en spacing plots were less marked than those reported from the same pl ots when harvested 7 years earlier; it is suggested that as trees surv iving after self-thinning are likely to be those with a competitive ad vantage from an early stage, differences between plots in amounts of j uvenile wood may become less apparent in trees harvested later in the rotation than in those sampled earlier. Underlying patterns of variati on in ring width and specific gravity across the tree were found to be modified by a progressive drift with height in the tree. Linear regre ssions between specific gravity and ring width also varied in a system atic way; the intercept and slope of these regressions tended to incre ase with ring number from the pith, and with height in tree at a speci fied ring number. Equations are given as a basis for quantifying these trends, but more data are needed from other sites to determine the ex tent to which these equations represent trends inherent to cambial and apical ageing, as distinct from influence of changing environment aro und the trees.