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Fig. 1. Uprooting device connected to a harvester boom. Photo: Erkki Oksanen, Luke.

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Fig. 2. Location of the uprooting sites in Finland. Regions: SK = South Karelia, SS = Southern Savonia, CF = Central Finland, KYM = Kymenlaakso, NK = North Karelia, NS = Northern Savonia.

Table 1. The number of uprooted sites and sample plots in different regions and uprooting years inventoried in autumn 2017.
Region*
SK SS CF KYM NK NS Total
Number of uprooted sites 12 11 8 12 11 12 66
Number of sample plots 194 182 154 202 199 196 1127
Uprooted in 2012 52 61 44 64 78 58 357
Uprooted in 2013 74 74 72 67 74 70 431
Uprooted in 2014 68 47 38 71 47 68 339
* SK = South Karelia, SS = Southern Savonia, CF = Central Finland, KYM = Kymenlaakso, NK = North Karelia, NS = Northern Savonia
Table 2. The main characteristics on the 20 m2 sample plots inventoried on 66 uprooted stands (N = 1127).
Continuous variable Mean Std. dev. Range
No. of crop-trees per 20 m2 3.9 1.2 1–6
No. of competing trees per 20 m2 12.9 11.1 0–80
No. of competing birches per 20 m2 7.6 9.7 0–80
No. of freely growing crop-tree spruces per 20 m2 2.2 1.3 0–6
Proportion of freely growing crop-tree spruces, % 65.0 33.1 0–100
Mean height of crop-tree spruces, cm 277 84 60–580
Mean height of competing trees, cm 183 52 100–450
Time from planting to uprooting in years 4.8 0.9 2–7
Time from uprooting to measurement in years 4.2 0.8 3–5
Mean height of crop-tree spruces at uprooting, cm 114 41 25–272
Topographic wetness index (TWI) 7.1 1.4 4.3–14.7
Thickness of humus layer, cm 3.4 1.1 1–13
Categorical variables N %
Stump harvesting No 634 56
Yes 493 44
Soil preparation method Spot mounding 1064 94
Mounding with ditches 49 4
Disc trenching 14 1
Site fertility Rich (Oxalis-Myrtillus type) 165 15
Medium (Myrtillus type) 739 65
Sub-dry (Vaccinium type) 223 20
Soil texture Coarse 133 11
Medium 954 85
Fine 20 2
Peat 20 2
Ground moisture a Sub-dry 611 54
Fresh 310 28
Moist 206 18
a Ground moisture: sub-dry, fresh and moist – the cover of sphagnum or haircap mosses ≤1%, 1–10% and >10%, respectively (Tamminen and Mälkönen 1999).
Table 3. Parameter estimates and goodness-of-fit statistics of the multi-level quasi-Poisson model (Eq. 1) estimated for the number of birches on the 20-m2 sample plot 3 to 5 years after uprooting. χ2 is the joined Wald χ2 test of the categorical fixed effects (type III test), the degrees of freedom in parentheses. Fitting statistics using only fixed effects and both random and fixed (in parentheses) are given. The modelling data consist of 1127 sample plots.
Fixed effects Estimate Std err. t-value p
Intercept 0.260 0.274 0.946 0.344
Mean height of crop-tree spruces at uprooting, cm –0.011 0.010 –1.090 0.276
Topographic wetness index (TWI) 0.153 0.020 7.566 <0.001
Thickness of humus layer, cm 0.072 0.025 2.84 0.005
Site fertility (ref. Sub-dry) χ2 (2) = 45.90 <0.001
   Medium 0.628 0.098 6.41 <0.001
   Rich 0.799 0.132 6.06 <0.001
Years since uprooting, a (ref. 5 years) χ2 (2) = 5.31 0.070
   3 years –0.348 0.183 –1.90 0.064
   4 years –0.291 0.152 –1.91 0.063
Random effects Variance
   Region (N = 6) 0.085
   Municipality (N = 22) 0.042
   Uprooted site (N = 66) 0.202
Snowdon’s bias correction ratio 1.161
Pearson correlation (predicted vs measured) 0.38 (0.63)
Proportion of explained variance R2 (%) 14.2 (40.1)
Root mean square error RMSE (birches per 20 m2 8.95 (7.48)
Relative RMSE (%) 117.1 (97.9)
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Fig. 3. Predicted number of competing birches ha–1 three (solid lines) and five years (broken lines) after uprooting as a function of (A) topographic wetness index (TWI) and (B) thickness of humus layer on rich, medium and sub-dry site fertility. Other predictors: mean height of crop-tree spruces is 75 cm; thickness of humus layer is 3 cm (A); TWI is 7 (B).

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Fig. 4. Number of freely growing crop-tree spruces in the uprooted stands 3–5 years after uprooting as a function of the mean height of crop trees at uprooting operation.

Table 4. Parameter estimates of the multi-level binomial model (Eq. 2) estimated for the probability of freely growing crop-tree spruce 3 to 5 years after uprooting. χ2 is the joined Wald χ2 test of the categorical fixed effects (type III test), the degrees of freedom in parentheses. The modelling data consist of 3694 crop-tree spruces.
Fixed effects Estimate Std err. t-value p
Intercept –0.154 0.352 –0.44 0.661
Height of spruce at uprooting, cm 0.018 0.001 15.41 <0.001
Topographic wetness index –0.143 0.036 –3.94 <0.001
Thickness of humus layer, cm –0.021 0.047 –0.44 0.660
Site fertility (ref. Sub-dry) χ2 (2) = 7.58 0.023
   Medium –0.253 0.123 –2.05 0.040
   Rich –0.494 0.184 –2.69 0.007
Years since uprooting, a (ref. 5 years) χ2 (2) = 2.04 0.360
   3 years 0.201 0.188 1.07 0.292
   4 years 0.203 0.157 1.29 0.203
Random effects Variance
Region (N = 6) 0.077
Municipality (22) <0.001
Uprooted site (N = 66) 0.175
Sample plot (N = 1130) 0.682
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Fig. 5. Predicted probability of freely growing crop-tree spruce 3 to 5 years after uprooting as a function of topographic wetness index (TWI) three (solid lines) and five years (broken lines) after uprooting on rich, medium and sub-dry site fertility when mean height of crop-tree spruces is 75 cm (A) or 125 cm (B). Other predictors: thickness of humus layer is 3 cm.

Table 5. Accuracy of the classification of the crop-tree spruces as freely growing trees, i.e., the height of competing broadleaves or conifers was not more than 2/3 of the height of the crop-tree spruce. The predicted categories have been calculated using the fixed part of the model (Eq. 2); the classification using both fixed and random effects are given in parentheses.
Predicted
Observed Freely growing Suppressed Total Accuracy
Freely growing 1507 (1795) 918 (630) 2425 62% (74%)
Suppressed 457 (250) 812 (1019) 1269 64% (80%)
Total 1964 (2045) 1730 (1649) 3694 63% (76%)
Table 6. The main characteristics of the uprooted stands at the first commercial thinning phase (N = 69). The stands were simulated from the inventory moment to the first commercial thinning phase using the Motti simulator.
Variable Mean Std. dev. Range
Stand age, a 32.6 2.0 29–38
Stem number of spruces, ha–1 1822 355 901–2758
Stem number of birches, ha–1 1125 489 263–2343
Proportion of birch in stem number, % 36.5 14.1 10.2–68.9
Dominant height of spruces, m 14.4 1.4 12.3–18.8
Dominant height of birches, m 15.1 1.5 12.4–20.9
Stand volume, m3 ha–1 182 36 144–306
Proportion of birch in volume, % 11.2 9.3 0.8–46.7
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Fig. 6. Ratio of dominant height of birch and spruce in the uprooted stands at the time of the inventory and first commercial thinning (N = 69). The stands were simulated from the inventory moment to the first commercial thinning phase using the Motti simulator.

Table 7. Parameter estimates and fitting statistics of the multi-level binomial model (Eq. 3) estimated for the proportion of birch of the stand volume in the uprooted stands at the first thinning phase. Fitting statistics using only fixed effects and both random and fixed (in parentheses) are given. The modelling data consist of 69 stands.
Fixed effects Estimate Std err. t-value p
Intercept –0.569 0.992 –0.57 0.570
Mean height of crop-tree spruces at uprooting, cm –0.016 0.364 –4.37 <0.001
Topographic wetness index 0.192 0.105 1.84 0.073
Thickness of humus layer, cm –0.330 0.147 –2.24 0.030
Rich site fertility (ref. Medium) –0.429 0.270 –1.59 0.119
Random effects Variance
   Region (N = 6) 0.096
   Municipality (N = 22) <0.001
Snowdon’s bias correction ratio 1.024
Pearson correlation (predicted vs measured) 0.66 (0.76)
Proportion of explained variation R2 (%) 43.7 (56.5)
Root mean square error RMSE (proportion of birch) 0.07 (0.06)
Relative RMSE (%) 62.3 (54.8)
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Fig. 7. Predicted proportion of birch of the stand volume in the uprooted stands at the first thinning phase as a function of topographic wetness index (TWI) on rich and medium site fertility when mean height of crop-tree spruces is 75 cm (solid lines) or 125 cm (broken lines). Other predictors: thickness of humus layer is 3 cm.