Initial effect of thinning on stand gross stem-volume production in a 33-year-old Norway spruce (Picea abies (L.) Karst.) stand in Southern Sweden

A better understanding of the reaction to thinning is important in order to design new thinning regimes in a changing environment. The objective of this research was to increase the knowledge of the initial response to thinning in Norway spruce plantations. We investigated the effects of different thinning grades (0%, 30% and 61% basal area removal) on initial gross stem-volume production in a 33-year-old Norway spruce plantation on a fertile site in Southwest Sweden. All logging residues were concentrated on 4-m-wide strip roads. Data were analysed, respectively, for the strip-road zone (strip road and two tree rows on each side of the strip road) and the main stand (three tree rows on each side of the strip-road zone). Volume production was significantly lower in the main part of the thinned stands compared to the unthinned control plots during the first growing season; the differences were less during the second year and insignificant during the third. Furthermore, volume production was significantly higher in the strip-road zone than in the main part for both the heavily and normal thinning treatments. Because the basal area in the strip-road zone of the heavily thinned plots was equal compared to their corresponding main part, increased volume production per hectare in the former may have been an effect of the logging residues. Availability of soil water and nutrients supports this hypothesis. Needle biomass in the canopy recovered more slowly than stem-volume growth.