Table 1. Classification and site characteristics of the sample stands (PCT = Pre-Commercial Thinning, OMT = Oxalis-Myrtillus type, MT = Myrtillus type, VT = Vaccinium type).
Attribute No previous PCT done PCT has been previously done
Pine Spruce Hardwood Pine Spruce Hardwood
Regeneration method
Planting 30 176 31 19 46 13
Sowing or natural regeneration 34 16 14 15 15 14
Undefined 6 6 6 1 4 2
Site type
OMT 0 67 11 0 11 7
MT 38 118 40 17 48 22
VT 32 13 0 18 6 0
Soil texture
Mineral soil 66 189 46 28 63 25
Peatland 4 9 5 7 2 4
Soil preparation method
Continuous trace 27 104 26 15 27 18
Ploughing 7 25 3 0 5 1
Disc-trenching 20 79 23 15 22 17
Spots 27 85 19 15 27 4
Mounding with ditching 11 41 6 10 14 3
Spot- or invert mounding 2 17 5 2 6 0
Patching 14 27 8 3 7 1
Not prepared 16 9 6 5 11 7
Total 70 198 51 35 65 29
Table 2. Characteristics of the sample stands treated as continuous variables (PCT = Pre-Commercial Thinning).
Dataset General stand characteristics Young stand management
Area, ha Stand age, years Density, trees ha–1 Height, m Removal, stumps ha–1 Stump
diameter, cm 		Labour consumption,
days ha–1
No previous PCT done
Scots pine (N 70)
Mean 2.1 12.1 2231 4.2 12 308 2.5 1.6
SD 1.8 3.9 538 1.9 8204 1.1 1.3
Min 0.3 6.0 960 1.4 1400 0.7 0.4
Max 9 20.0 3840 9.0 39 800 7.3 8.9
Norway spruce (N 198)
Mean 2.4 10.7 2019 3.2 13 877 2.8 2.0
SD 2.0 3.2 495 1.2 7959 1.1 1.4
Min 0.2 4.0 1000 1.1 2000 0.7 0.4
Max 11.9 20.0 5520 7.1 58 400 6.5 9.6
Hardwood (N 51)
Mean 1.6 11.1 1973 5.2 12 682 2.4 1.5
SD 1.2 3.6 491 1.5 8386 0.8 0.8
Min 0.2 6.0 1200 3.1 1000 0.6 0.4
Max 5.4 20.0 3240 9.8 46 200 4.2 4.2
PCT has been previously done
Scots pine (N 35)
Mean 2.0 13.6 2402 4.7 11 091 2.1 1.2
SD 1.5 3.2 551 1.4 5032 0.6 0.4
Min 0.3 8.0 960 2.4 5200 1.0 0.6
Max 6.1 20.0 3440 7.1 32 200 3.5 2.4
Norway spruce (N 65)
Mean 1.7 11.9 2250 4.3 11 465 2.3 1.3
SD 1.2 3.3 636 1.6 6646 0.8 0.6
Min 0.2 7.0 1080 1.7 1800 1.2 0.4
Max 5.2 20.0 4280 9.0 45 200 6.2 3.9
Hardwood (N 29)
Mean 1.7 13.3 2167 6.8 10 766 2.3 1.2
SD 1.7 3.0 591 2.0 4490 0.6 0.4
Min 0.1 8.0 1200 2.2 3200 1.3 0.5
Max 6.7 20.0 3320 10.2 23 600 3.3 2.0
Table 3. Fixed effects of the mixed linear regression model for Labour Consumption of Pre-Commercial Thinning (PCT) on stands without previous PCT. The dependent variable is Ln(LCNPCT) and all denominators had 308 df.
Source Numerator df F Sig.
Intercept 1 26.116 0.000
Dominant tree species 2 2.053 0.130
Stand age 1 41.735 0.000
Stand age * Main tree species 2 3.066 0.048
Site type 2 25.845 0.000
Soil preparation method 2 9.955 0.000
Ln(Area) 1 15.349 0.000
Table 4. Mixed linear regression model for Labour Consumption of Pre-Commercial Thinning (PCT) on stands without previous PCT. The dependent variable is Ln(LCNPCT) in days ha–1, the random stand and plot level effects are uj (Var = 0.379^2) and eij (Var = 0.542^2), all variables had 308 df, and the model fit is 47.6%. OMT = Oxalis-Myrtillus type, MT = Myrtillus type, VT = Vaccinium type.
Parameter Estimate Std. error t Sig. 95% confidence interval
Lower bound Upper bound
Intercept –0.9762 0.2300 –4.245 0.0000 –1.4288 –0.5237
Dominant tree species (Ref. Hardwood)
Scots pine 0.0140 0.2794 0.050 0.9600 –0.5357 0.5638
Norway spruce –0.3550 0.2389 –1.486 0.1384 –0.8251 0.1152
Stand age 0.0321 0.0179 1.797 0.0733 –0.0031 0.0673
Stand age * Scots pine 0.0184 0.0227 0.809 0.4189 –0.0263 0.0630
Stand age * Norway spruce 0.0471 0.0208 2.267 0.0241 0.0062 0.0880
Stand age * Hardwoods 0.0000 0.0000        
Site type (Ref. VT)
OMT 0.7613 0.1059 7.189 0.0000 0.5529 0.9696
MT 0.5059 0.0885 5.719 0.0000 0.3318 0.6799
Soil preparation method (Ref. not prepared)        
Continuous trace 0.1067 0.0965 1.106 0.2697 –0.0831 0.2965
Spots 0.3163 0.0967 3.271 0.0012 0.1260 0.5066
Ln(Area), ha 0.1359 0.0347 3.918 0.0001 0.0677 0.2042
Variance components [Stand (uj), Plot (eij)]
Var(uj) 0.1436 0.0165   0.000 0.2715 0.3171
Var(eij) 0.2934 0.0116   0.000 0.1147 0.1797
Table 5. Mixed linear regression model for Labour Consumption of Pre-Commercial Thinning (PCT) on stands with previous PCT. The dependent variable is Ln(LCPCT) in days ha–1, and the random stand and plot level effects are uj (Var = 0.265^2) and eij (Var = 0.504^2), and the model fit is 6.7%.
Parameter Estimate Std. error df t Sig. 95% confidence interval
Lower bound Upper bound
Intercept –0.2905 0.0942 207 –3.085 0.002 –0.476 –0.105
Stand age, years 0.0249 0.0071 207 3.495 0.001 0.011 0.039
Variance components [Stand (uj), Plot (eij)]
Var(uj) 0.0706 0.0122     0.000 0.050 0.099
Var(eij) 0.2539 0.0124     0.000 0.237 0.287
1

Fig. 1. The back-transformed and bias-corrected a priori estimates (LC cor.), and the calculated values (LC) of labour consumption of Pre-Cmmercial Thinning (PCT) according to site type (OMT = Oxalis-Myrtillus type, MT = Myrtillus type, VT = Vaccinium type), stand age, and removal in Scots pine, Norway spruce, and hardwood stands which have no previous PCT done. In the estimates, variables “area” and “soil preparation” were set to “2.2 ha” and “Continuous trace”, respectively.

Table 6. Mixed linear regression model for stump diameter of the removed trees on stands which have not been previously pre-commercially thinned. The dependent variable is stump diameter in cm, the random stand and plot level effects are uj (Var = 0.674^2) and eij (Var = 1.110^2), all variables had 308 df, and the model fit is 45.6%. OMT = Oxalis-Myrtillus type, MT = Myrtillus type, VT = Vaccinium type.
Parameter Estimate Std. error t Sig. 95% confidence interval
Lower bound Upper bound
Intercept 0.3356 0.4279 0.784 0.433 –0.5063 1.1776
Dominant tree species (Ref. Hardwood)
Scots pine 0.5988 0.5198 1.1520 0.250 –0.4240 1.6215
Norway spruce –0.1462 0.4446 –0.329 0.742 –1.0210 0.7285
Stand age 0.1148 0.0333 3.451 0.001 0.0494 0.1803
Stand age * Scots pine –0.0219 0.0422 –0.519 0.604 –0.1050 0.0612
Stand age * Norway spruce 0.0459 0.0387 1.186 0.236 –0.0302 0.1220
Stand age * Hardwoods 0.0000 0.0000        
Site type (Ref. VT)
OMT 1.0663 0.1970 5.412 0.000 0.6787 1.4540
MT 0.5469 0.1646 3.323 0.001 0.2231 0.8707
Soil preparation method (Ref. not prepared)
Continuous trace –0.0662 0.1795 –0.3687 0.713 –0.4193 0.2870
Spots 0.2550 0.1799 1.417 0.157 –0.0991 0.6090
Ln(Area), ha 0.1487 0.0646 2.303 0.022 0.0217 0.2757
Variance components [Stand (uj), Plot (eij)]
Var(uj) 0.4536 0.0572   0.000 0.3542 0.5809
Var(eij) 1.2323 0.0488   0.000 1.1403 1.3317
Table 7. Mixed linear regression model for density of the removed trees on stands which have not been previously pre-commercially thinned. The dependent variable is density of the trees removed ha–1, the random stand and plot level effects are uj (Var = 6569.5^2) and eij (Var = 8333.9^2) all variables had 308 df, and the model fit is 16.2%.
Parameter Estimate Std. error t Sig. 95% confidence interval
Lower bound Upper bound
Intercept 2764.3 3862.7 0.716 0.475 –4836.3 10364.9
Dominant tree species (Ref. Hardwood)
Scots pine –1717.5 4692.0 –0.366 0.715 –10949.9 7514.9
Norway spruce –2554.6 4013.0 –0.637 0.525 –10451.0 5341.8
Stand age 90.0 300.3 0.300 0.765 –501.0 681.0
Stand age * Scots pine 313.3 381.3 0.822 0.412 –437.0 1063.6
Stand age * Norway spruce 271.8 349.0 0.779 0.437 –415.0 958.6
Stand age * Hardwoods 0.0 0.0        
Site type (Ref. VT)
OMT 7109.7 1778.5 3.998 0.000 3610.1 10609.2
MT 5928.1 1485.6 3.990 0.000 3004.9 8851.4
Soil preparation method (Ref. not prepared)
Continuous trace 1784.0 1620.0 1.101 0.272 –1403.6 4971.6
Spots 3784.2 1624.3 2.330 0.020 588.1 6980.3
Ln(Area), ha 2064.4 582.7 3.543 0.000 917.8 3210.9
Variance components [Stand (uj), Plot (eij)]
Var(uj) 43157746 4629589   0.000 34974317 53255967
Var(eij) 69436790 2749029   0.000 64252532 75039344
2

Fig. 2. The back-transformed and bias-corrected a priori estimates (LC cor.), and calculated values (LC) of labour consumption of Pre-Commercial Thinning (PCT) according to stand age and removal in stands which have previously had PCT.