Effects of Thinning Intensity on Annual Ring Properties in 60-year-old Picea Abies

The effects of thinning treatments on annual ring properties in an artificial plantation of European spruce (Picea abies) were determined by measuring the annual ring width and annual ring density using X-ray densitometry. Sixty-year-old sample trees from 5 examination plots with different thinning rates (ranging from 0 to 78%) were used. As the thinning intensity increased, a trend of wider annual rings was observed. The annual ring density was high near the pith, temporarily decreased until around the age of 20 years, and then showed a tendency to increase towards the bark. Additionally, when comparing the annual ring width between the plot with a thinning rate of 30% and the plot with a thinning rate of 15%, the plot with a thinning rate of 30% had narrower ring widths. This indicates that the influence of local environmental factors was recognized. It was confirmed that higher thinning intensity tends to suppress the increase in ring density with forest age. Therefore, high thinning intensity seemed to cause a decrease in wood density.