The study reported was conducted on 20 fast-grown and 20 slow-grown Norway spruces (Picea abies (L.) Karst.) from an even-aged, plantation-grown stand near Rendeux, Belgian Ardennes. The objective was to test whether increasing the growth rate of Norway spruce by heavy thinnings had an effect on the temporal trajectories (i.e., fluctuations from year to year) of ring width, wood density, and mean tracheid length, all measured yearly from pith to bark. Since the data were chronologies (i.e., time series of yearly measurements), time had to be considered as a factor (i.e., the calendar year of ring formation) in the statistical analysis of the within-tree variation (repeated measures analysis of variance).While the effects of the growth category and its interaction with the year were highly significant after first thinning for ring width, a significant decrease in the wood density of fast-grown trees was observed in many years during that growing period; the decrease was small in magnitude, once averaged over years (-0.033 g/cm3). Tracheids were longer for the slow-grown trees after first thinning; although constant in sign and magnitude over years, the difference in mean tracheid length between growth categories was not statistically significant. In summary, increasing the growth rate in circumference of Norway spruce from 1.7 to 2.7 cm/year by heavy thinnings induced a limited decrease in wood density and mean tracheid length. These results support the statement that stand productivity might be improved without sensible loss of wood quality
