Growth rate effects on correlations among ring width, wood density, and mean tracheid length in Norway spruce (<i>Picea abies</i>)

Abstract

The main hypothesis tested in this paper is whether heavy thinnings affect the correlations among ring width, wood density, and mean tracheid length. Within-tree correlations were calculated between time series of yearly measurements. Among-tree correlations were computed (1) between averages over a growing period and (2) year by year. Correlations were analyzed 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. In the within-tree approach, fast-grown spruces showed a stronger negative correlation between ring width and fiber length. In among-tree approach 1, the widely held negative correlation between ring width and wood density vanished when the spruce growth rate was above 2.2 cm/year in circumference. Among-tree approach 2 demonstrated that the magnitude and sign of the correlations also depended on the year; a few years showed a significant correlation between ring width and wood density for the fast-grown Norway spruces, whereas the correlation was systematically negative and significant on many years for the slow-grown spruces. This study may explain part of the contradictory results reported in the literature concerning hypotheses similar to ours.