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 in 3 ha(-1) but without significant differences. (C) 2001 Elsevier Science B.V. All rights reserved.