Comparing the characteristics, removals and incomes of zone- and low-thinned stands of Norway spruce

Zone thinning is designed to improve harvesting productivity in the first commercial thinning and facilitate the transition to continuous cover forestry by encouraging natural regeneration. In zone thinning, the density of the remaining stand varies between strip roads 30 m apart, from heavily thinned roadside zones to untreated zones >10 m from the road. In the subsequent thinning, strip roads are opened in the untreated zones. This study first compared the characteristics and removals of Norway spruce (Picea abies (L.) H. Karst.) dominated stands after zone and low thinning. Thinning treatments were applied in two planted stands on mineral soil at the first commercial thinning stage, and in two advanced thinning stands on drained peatlands. The harvested removals were obtained from the harvester records. Secondly, the post-treatment development and removal of the experimental plots were predicted using a distance-dependent, individual-tree simulator that had been developed for spruce-pine (Pinus sylvestris L.) mixtures. On zone-thinned plots of young thinning stands, the number of stems per ha was significantly higher, and the amount harvested was significantly lower, compared to low-thinned plots. In advanced thinning stands, the stand basal area and volume were higher on zone-thinned plots than on low-thinned plots. Total removals (harvested and simulated) and cutting incomes during the rotation period did not differ between zone and low thinning treatments. This suggests that zone thinning could be used for the first thinning without reducing timber production or revenues.