Effects of spacing and genetic entry on radial growth and ring density development in Scots pine (Pinus sylvestris L.)

The objective of this work was to study how spacing and genetic entry and/or origin group affect radial growth (ring width and cumulative diameter development) and ring density from pith to bark in Scots pine (Pinus sylvestris L.) and in what sense their annual variability could be explained by the climatic variables. The spacing trial was located in central Finland, with current stand density range of 2,000-4,000 trees per hectare. All the six genetic entries had Kanerva pine (plus tree S1101) as a father tree, whereas the mother tree represented Finnish plus trees from southern, central and northern Finland. In the early phase of the stand development, no significant differences (p < 0.05) were found for mean ring width (RW), cumulative diameter (Dt1) and mean ring density (RD) development between different spacing and/or origin groups (southern, central and northern ones). Both cambial age and spacing affected RW and RD development from pith to bark. In addition, RD development was affected by the origin group (OG), unlike RW. The annual radial growth also decreased slightly earlier and much faster in the narrowest spacing. The annual variation in RW could not be explained by the climatic factors considered (e.g. temperature sum during the growing season or June and/or July mean temperature). However, the mean temperature for current June and the temperature sum during the current growing season partly explained the annual variation in RD (p < 0.05).