Temporal variation of the ring width-wood density relationship in Norway spruce grown under two levels of anthropogenic disturbance

The ring width-wood density relationship (RW-WDR) is somewhat controversial. Most of the. literature reports negative, but weak relationships, while others found no significant relationships at all. This study analyses the RW-WDR using a dataset of twenty even-aged Norway spruce trees grown at two different levels of air pollution in the Eastern Ore Mountains, Germany. Ring width, latewood proportion and wood density were measured in each tree ring. The year-to-year (temporal) variability of the RW-WDR was calculated by sequentially taking the rings grown in the same calendar year in trees within a site. In addition, RW-WDR was also calculated across tree rings (pith to bark) of given trees. During the observed period, the temporal RW-WDR fluctuated between negative and positive correlations with certain climatic patterns, as well as forest operations, playing a prominent role. It was shown that increased late-season rainfall favoured a more positive relationship. The temporal RW-WDR illustrated, for given trees of a site, that smaller rings formed in certain years might be related to higher wood density while other years may result to lower wood density. This finding is useful for an improved understanding regarding the effect of ring width on wood, density.