1

Fig. 1. Machines used in the study: Usewood Tehojätkä small-scale forest machine equipped with UW40-cleaning head (left) and Mense RP6L equipped on the boom of the harvester (right) Photos: Veli-Matti Saarinen and UW40-cleaning head: www.usewood.fi.

Table 1. Number of stumps, their diameter and height, and stand density before and after the early pre-commercial thinning.
Mense Tehojätkä* Control Pooled*
Number of stumps 111 150 (38) 100 361 (249)
   Birch 38 63 (11) 22 123 (71)
   Aspen 21 24 (3) 50 95 (74)
   Rowan 22 42 (15) 13 77 (50)
   Willow 30 21 (9) 15 66 (54)
Stump diameter (mm) 13.3 ± 4.7 11.4 ± 4.5 13.7 ± 6.9 12.6 ± 5.4
   Birch 13.2 ± 5.3 11.4 ± 5.1 13.7 ± 9.5 12.4 ± 6.2
   Aspen 15.9 ± 5.7 12.8 ± 4.5 14.5 ± 6.1 14.4 ± 5.7
   Rowan 12.6 ± 3.6 11.6 ± 4.0 12.6 ± 4.5 12 0 ± 3.9
   Willow 12.3 ± 3.2 9.7 ± 3.2 12.1 ± 6.7 11.3 ± 4.3
Stump height (cm) 34.9 ± 15.4 28.7 ± 10.7 32.2 ± 11.7 31.6 ± 12.8
   Birch 34.8 ± 14.5 29.8 ± 9.8 33.2 ± 14.5 32.0 ± 12.4
   Aspen 32.6 ± 12.8 28.7 ± 12.8 33.8 ± 10.7 32.3 ± 11.8
   Rowan 32.9 ± 19.9 28.8 ± 11.4 29.8 ± 9.4 30.0 ± 14.1
   Willow 37.9 ± 14.8 25.4 ± 8.8 27.8 ± 11.8 31.7 ± 12.8
Density (ha–1)
   Saplings (before) 12 591 ± 6543 15 420 ± 10 729 16 824 ± 7251 13 896 ± 8403
   Stumps 7851 ± 6635 10 610 ± 9693 7234 ± 4089 8575 ± 7641
   Saplings (after) 4739 ± 3693 4810 ± 3755 6438 ± 5717 5321 ± 3899
* Year 2018 value in parentheses (2/3 of blocks were destroyed due to land use changes in    the area).
Table 2. The effects of (1) the treatment (the control vs. the fungal treatments done by Tehojätkä or Mense), (2) tree species (birch vs. aspen, rowan or willow), (3) the number of saplings and stumps on a plot, and (4) the diameter of an investigated stump (mm) on the mortality of stumps (0 = alive, 1 = dead) one (2016, n = 361), two (2017, n = 361), and three years (2018, n = 249) after the early pre-commercial thinning, as well as on the number of sprouts in a stump one (2016, n = 282), two (2017, n = 282), and three years (2018, n = 194) after the early pre-commercial thinning (generalized linear mixed models). Statistically significant p-values (p < 0.05) are in bold and indicative results have been underlined (0.05 ≤ p ≤ 0.10). See also Fig. 2.
Explanatory variables Year 2016 Year 2017 Year 2018
Coeff. ± SE p Coeff. ± SE p Coeff. ± SE p
Mortality
Intercept –3.469 ± 0.765 <0.001 –3.628 ± 0.833 <0.001 –3.112 ± 0.985 0.002
Treatment (compared to the control)
   Tehojätkä 1.298 ± 0.446 0.004 1.551 ± 0.472 0.001 1.200 ± 0.646 0.006
   Mense 1.455 ± 0.445 0.001 1.601 ± 0.462 <0.001 1.521 ± 0.469 0.001
Tree species (compared to birch)
   Aspen 0.047 ± 0.356 0.894 –0.216 ± 0.362 0.550 0.206 ± 0.450 0.647
   Rowan –1.954 ± 0.574 <0.001 –2.504 ± 0.654 <0.001 –3.153 ± 1.08 0.003
   Willow –0.585 ± 0.407 0.150 –0.806 ± 0.412 0.050 –0.895 ± 0.492 0.069
Density (saplings per plot) 0.139 ± 0.056 0.013 0.068 ± 0.057 0.233 0.123 ± 0.102 0.226
Stump diameter (mm) 0.040 ± 0.028 0.146 0.087 ± 0.030 0.003 0.036 ± 0.032 0.252
Number of stump sprouts
Intercept 0.783 ± 0.199 <0.001 0.797 ± 0.182 <0.001 0.703 ± 0.230 0.002
Treatment (compared to the control)
   Tehojätkä –0.107 ± 0.132 0.416 –0.071 ± 0.106 0.500 0.046 ± 0.153 0.763
   Mense 0.107 ± 0.131 0.416 0.138 ± 0.104 0.185 0.126 ± 0.109 0.249
Tree species (compared to birch)
   Aspen –0.189 ± 0.114 0.097 –0.088 ± 0.110 0.425 0.084 ± 0.141 0.552
   Rowan 0.887 ± 0.100 <0.001 0.795 ± 0.100 <0.001 0.871 ± 0.131 <0.001
   Willow 0.434 ± 0.101 <0.001 0.434 ± 0.103 <0.001 0.418 ± 0.133 0.002
Density (saplings per plot) –0.031 ± 0.019 0.103 –0.037 ± 0.017 0.028 –0.051 ± 0.025 0.041
Stump diameter (mm) 0.038 ± 0.007 <0.001 0.034 ± 0.007 <0.001 0.026 ± 0.008 0.001
2

Fig. 2. The effects of the control (cutting only) and the fungal treatments done by Tehojätkä and Mense on a) the mortality of birch stumps (%), and b) the number of stump sprouts per stump one, two and three years after the early pre-commercial thinning. Figures have been drawn based on the predicted values of the generalized linear mixed models for birch, see Table 2.