Effects of cambial age, clone and climatic factors on ring width and ring density in Norway spruce (Picea abies) in southeastern Finland

The aim of this study was to analyse the effects of cambial age, clone and climatic factors (i.e. monthly mean temperature and monthly total precipitation) on ring width (RW) and ring density (RD) development from pith to bark in 30-years-old Norway spruce (Picea abies) grown on a fertile agricultural soil in southeastern Finland. The material consisted of 20 Finnish clones, which represented south, southwest, southeast and central Finnish origins. We analysed the variability of RW and RD among years, individual trees and clones, by fitting mixed models into tree ring series, with a spline function (used to remove the effect of ring age). The results showed that cambial age, clone and mean temperature of July affected both RW and RD. Furthermore, total precipitation of August affected RW and total precipitation of May affected RD. However, these climate variables explained only 1.9% and 3.4% of the total RW and RD variability, respectively. This may be due to the good site fertility with no lack of soil water availability, but also due to relatively short tree ring series available for data analyses. The effect of mean temperature of July on RW varied among clones, but in general, RW increased with increase in temperature. The increase of total precipitation of August increased, in general, RD regardless of the clone, whereas the effect of mean July temperature on RD was much more variable. However, longer time series are needed in the future to provide a better understanding of the interactive effects of the climate variables and genetic origins, in addition to cambial age, on RW and RD development on different sites.

► We studied the effects of cambial age, clone and climatic factors on ring width (RW) and ring density (RD) in Norway spruce.
► Mixed models, with a spline function to remove the ring age effect, were fitted to RW and RD.
► The results showed that cambial age, clone, temperature in July, and precipitation in May and/or August affected RW and RD.
► Differences among Finnish Norway spruce clones were found regarding RW and RD and on their response to climatic factors.