Table 1. Definitions of thinning treatments in the experiments. In all treatments, the width of the strip road was between 4.0–4.5 m, and the strip roads were pre-marked in the centre of the plot. In selective thinning (Sel) treatments, the areas between strip roads were thinned from below, removing the smallest, poorer and possibly damaged trees. In systematic boom corridor (BCTp, BCTf) treatments, 2.5 m-wide corridors, with 7 m between the machine position, were harvested. In all BCT treatments, the areas between the corridors were left untreated.
Treatment Definition
Sel1 Selective thinning, no pre-clearing needed.
Sel2 Selective thinning, pre-cleared (i.e., undergrowth hindering harvester work was removed before test cutting).
BCTp Completely systematic perpendicular boom corridor thinning, no pre-clearing needed. Corridors 90° from each machine position were harvested. The trees to be removed from the corridors were marked.
BCTf Completely systematic fan-shaped boom corridor thinning, no pre-clearing needed. Corridors 30° from each machine position were harvested. The opposite corridors of the machine positions were staggered at 2 m. The trees to be removed from the corridors were marked.
BCTsemi1 Semi-selective boom corridor thinning, no pre-clearing needed. In the middle of the plot, the advisory corridor locations on opposite sides of the strip road were marked. The width and distance of the corridors were, on average, the same as in BCTp and BCTf. The operator chose the exact location of the corridors based on the standing trees. The trees to be removed from the corridors were not marked.
BCTsemi2 Semi-selective boom corridor thinning, pre-cleared. In the middle of the plot, the advisory corridor locations on opposite sides of the strip road were marked. The width and distance of the corridors were, on average, the same as in BCTp and BCTf. The operator chose the exact location of the corridors based on the standing trees. The trees to be removed from the corridors were not marked.
BCTsemi3 Semi-selective boom corridor thinning, no pre-clearing. In the middle of the plot, the advisory corridor locations on opposite sides of the strip road were marked. The width and distance of the corridors were, on average, the same as in BCTp and BCTf. The operator chose the exact location of the corridors based on the standing trees. The trees to be removed from the corridors were not marked.
BCTsel Selective boom corridor thinning, no pre-clearing needed. The width and distance of the corridors were, on average, the same as in BCTp and BCTf. The operator independently chose the location of the corridors based on the standing trees.
Table 2. Tests of thinning treatment effects and estimated marginal means (adjusted by covariate effects) and standard errors (SE) in ANOVA for stand characteristics 4–5 growing seasons after selective thinning (Sel) and boom corridor thinning (BCT) treatments (Eq. 1). Thinning treatments are described in Table 1. Significant treatment effects are shown in bold.
Experiment No. of plots Stand basal area (m2 ha−1) Volume (m3 ha−1) Mean diameter (cm) Mean height (m) Mean stem volume (dm3)
Mean SE Mean SE Mean SE Mean SE Mean SE
Seeded pine
Treatment F = 0.59 p = 0.630 F = 0.52 p = 0.676 F = 0.21 p = 0.891 F = 1.49 p = 0.257 F = 0.58 p = 0.637
   Sel1 5 15.0a 0.14 109.5a 1.10 16.4a 0.06 14.6a 0.02 138.4a 1.13
   BCTp 5 15.0a 0.11 109.1a 0.83 16.3a 0.06 14.6a 0.02 136.4a 1.10
   BCTf 5 15.1a 0.11 110.2a 0.83 16.4a 0.06 14.6a 0.02 137.9a 1.15
   BCTsemi1 5 15.2a 0.12 110.5a 1.00 16.4a 0.06 14.6a 0.02 137.5a 1.11
Planted pine
Treatment F = 0.65 p = 0.542 F = 0.66 p = 0.537 F = 0.72 p = 0.506 F = 0.81 p = 0.470 F = 0.80 p = 0.474
   Sel1 5 17.8a 0.30 126.3a 2.38 16.9a 0.22 14.4a 0.07 139.7a 2.71
   BCTsemi1 4 17.7a 0.33 125.3a 2.63 16.8a 0.24 14.3a 0.08 136.8a 2.90
   BCTsel 6 18.1a 0.26 128.8a 2.10 17.2a 0.19 14.4a 0.06 141.4a 2.33
Planted birch
Treatment F = 9.20 p = 0.021 F = 3.80 p = 0.099 F = 0.26 p = 0.778 F = 0.62 p = 0.575 F = 0.22 p = 0.808
   Sel2 3 10.7a 0.11 82.1a 0.74 14.7a 0.12 15.8a 0.16 115.7a 1.65
   BCTsemi2 3 11.1ab 0.11 84.7a 0.73 14.7a 0.09 15.9a 0.11 115.6a 1.14
   BCTsemi3 3 11.4b 0.11 84.6a 0.74 14.9a 0.11 15.7a 0.15 114.5a 1.40
Data for the same experiment marked with different letters are significantly different (p < 0.05) based on the estimated marginal means and post hoc LSD tests after Levene’s test for equal variances.
Table 3. Tests of thinning treatment and tree location effects and estimated marginal means (adjusted by covariate effects) and standard errors (SE) in mixed model ANOVA for annual increment of diameter (dbh), height and stem volume of trees during 4–5 growing seasons after selective thinning (Sel) and boom corridor thinning (BCT) treatments (Eq. 2). Thinning treatments are described in Table 1. Significant treatment and tree location effects are shown in bold.
Experiment No. of trees Dbh increment (mm year–1) Height increment (m year–1) Volume increment (dm3 year–1)
Mean SE Mean SE Mean SE
Seeded pine
Treatment F = 3.29 p = 0.035 F = 5.60 p = 0.003 F = 3.35 p = 0.032
   Sel1 340 3.0a 0.12 0.30a 0.003 7.1a 0.21
   BCTp 416 2.7a 0.13 0.28bc 0.004 6.7a 0.23
   BCTf 443 2.9a 0.12 0.29ac 0.004 7.0a 0.22
   BCTsemi1 436 2.7a 0.13 0.28b 0.004 6.6a 0.24
Tree location F = 45.54 p < 0.001 F = 26.19 p < 0.001 F = 41.10 p < 0.001
   0 450 2.3a 0.08 0.27a 0.003 5.9a 0.15
   1 173 3.0b 0.13 0.29bc 0.005 7.1b 0.25
   2 729 2.7b 0.07 0.28b 0.002 6.6b 0.13
   3 283 3.4c 0.09 0.30c 0.003 7.9c 0.17
Treatment × Location F = 1.40 p = 0.201 F = 1.68 p = 0.111 F = 0.99 p = 0.435
Planted pine
Treatment F = 1.40 p = 0.278 F = 3.36 p = 0.061 F = 1.02 p = 0.385
   Sel1 405 4.2a 0.23 0.57a 0.011 11.2a 0.60
   BCTsemi1 391 3.7a 0.26 0.54a 0.013 10.3a 0.68
   BCTsel 555 4.2a 0.21 0.57a 0.010 11.4a 0.55
Tree location F = 20.73 p < 0.001 F = 11.85 p < 0.001 F = 5.66 p < 0.001
   0 451 3.7a 0.15 0.54a 0.008 10.3a 0.43
   1 223 4.3b 0.17 0.56b 0.010 11.2ab 0.52
   2 518 3.6a 0.17 0.55ab 0.008 10.4a 0.45
   3 159 4.5b 0.19 0.59c 0.011 12.1b 0.57
Treatment × Location F = 3.76 p = 0.005 F = 0.95 p = 0.433 F = 1.02 p = 0.397
Planted birch
Treatment F = 1.02 p = 0.394 F = 0.76 p = 0.489 F = 0.25 p = 0.784
   Sel2 177 4.9a 0.23 0.56a 0.021 10.6a 0.33
   BCTsemi2 238 4.8a 0.25 0.60a 0.022 10.6a 0.37
   BCTsemi3 259 5.3a 0.24 0.56a 0.022 10.6a 0.35
Tree location F = 9.10 p < 0.001 F = 3.28 p = 0.020 F = 11.03 p < 0.001
   0 153 4.4a 0.20 0.54a 0.019 9.4a 0.33
   1 101 5.4bc 0.25 0.59bc 0.023 11.2bc 0.42
   2 308 5.0b 0.17 0.57ab 0.015 10.4b 0.23
   3 112 5.5c 0.21 0.61c 0.019 11.6c 0.32
Treatment × Location F = 1.88 p = 0.113 F = 0.57 p = 0.682 F = 0.82 p = 0.515
Data for the same experiment marked with different letters are significantly different (p < 0.05) based on the estimated marginal means and post hoc LSD tests after Levene’s test for equal variances. Tree location: 0 – not at the edge of the strip road or corridor, 1 – at the edge of the strip road, 2 – at the edge of the corridor, and 3 – at the edge of both the strip road and corridor.