Structure transformation and volume increment in Norway spruce-dominated forests following contrasting silvicultural treatments

The study deals with two field experiments totalling 52 sample plots in naturally uneven-sized Norway spruce ( Picea abies (L.) Karsten)-dominated mixed forests on fertile upland sites in Southern Finland. The stands were treated with alternative methods in the first-thinning and in the advanced thinning stage. Low thinning and dimension cutting were used for levelling the structure. These treatments changed the structure towards even-sizedness and decreased growing stock diversity. In contrast, single tree selection enhanced uneven-sizedness in structure (stem distribution resembling a reversed J). Volume increment after first-thinning during its 11-year monitoring period was significantly smaller in dimension cutting (CAI 5.8 m 3 ha −1) as compared to single tree selection system (11.8 m 3 ha −1) and low thinning (10.7 m 3 ha −1). In advanced stands, monitored 10–13 years, the respective values were 3.8, 4.6, and 3.9 m 3 ha −1 but without significant differences.