1

Fig. 1. Locations of the study stands in Finland.

Table 1. Main characteristics of the study stands at the beginning of the experiment in 1980.
Stand Location Coordinates (WGS84) Effective temperature sum (DD) Forest site type Origin Number of sample plots Stand age, yr. Dominant height, m
1 Lapinjärvi 60°31´N, 26°03´E 1386 VT Planted 4 12 3.4
2 Hausjärvi 60°41´N, 24°53´E 1309 VT Seeded 2 12 3.3
3 Vesijako 61°20´N, 25°07´E 1256 VT Naturally regenerated 10 15 2.6
4 Punkaharju 61°45´N, 29°23´E 1259 MT Naturally regenerated 4 10 3.4
5 Vilppula 61°60´N, 24°30´E 1195 VT Planted 7 8 3.0
6 Muhos 64°53´N, 26°06´E 1106 VMT Planted 6 14 2.8
7 Kivalo 66°20´N, 26°43´E 901 HMT Seeded 6 15 2.7
2

Fig. 2. Presentation of clipping treatments at the beginning of the experiments in 1980: 1) top shoot clipped along with all lateral twigs of the uppermost branch whorl, added with light clipping of branches; 2) main stem cut below the uppermost branch whorl, added with light clipping of branches; 3) main stem cut below the second branch whorl, added with light clipping of branches.

Table 2. Numbers of the sample trees according to clipping treatments, mean values of diameter at breast height (DBH) and height (standard deviations in the parentheses), and minimum and maximum values in 1980 (beginning of the experiment) and 2014 (felling) in the study stands.
First measurement in 1980 Last measurement in 2014
Number of sample trees in different treatments DBH, cm Height, m DBH, cm Height, m
Stand Control Clipping 1 Clipping 2 Clipping 3 All trees Mean (Std) Min–Max Mean (Std) Min–Max Mean (Std) Min–Max Mean (Std) Min–Max
1 15 15 9 7 46 2.4 (1.3) 2.2 (0.6) 14.0 (2.3) 12.5 (1.3)
0.0–4.9 1.1–3.3 9.0–18.8 9.9–15.6
2 6 4 4 2 16 2.5 (1.0) 2.5 (0.5) 14.4 (3.6) 13.5 (2.0)
0.7–4.7 1.5–3.5 5.9–22.3 7.8–15.8
3 18 13 12 7 50 1.3 (1.2) 1.6 (0.5) 16.8 (4.5) 16.6 (2.1)
0.0–4.8­ 0.8–3.2 8.1–28.0 11.5–20.2
4 12 8 8 5 33 3.2 (1.2) 2.6 (0.7) 18.7 (5.5) 18.3 (1.9)
1.4–5.4 0.3–4.0 9.1–28.9 13.6–21.5
5 18 16 15 12 61 2.7 (1.0) 2.3 (0.4) 15.8 (3.9) 18.4 (2.0)
1.1–5.3 1.6–3.5 7.6–23.2 12.7–22.2
6 17 12 8 6 43 2.1 (1.4) 2.0 (0.6) 16.3 (3.3) 15.2 (1.6)
0.0–5.7 0.9–3.7 8.2–24.3 11.1–19.1
7 18 8 6 6 38 1.5 (1.1) 1.8 (0.5) 17.4 (3.1) 12.3 (1.4)
0.0–3.6 0.9–2.8 10.0–23.1 8.7–14.5
All 104 76 62 45 287 2.2 (1.3) 0.0–5.7 2.1 (0.6) 0.3–4.0 16.2 (4.0) 5.9–28.9 15.6 (3.0) 7.8–22.2
3

Fig. 3. Location of damage point in a sample tree at the beginning of the experiment, and in a butt log cut from the respective sample tree after 34 years. The damage area is defined one metre downwards and upwards from the damage point.

Table 3. Quality requirements applied for butt logs of Scots pine in this study. These requirements were applied and generalized from bucking rules used by forest industries in Finland (Metsäkeskus 1999).
Characteristic Quality requirements for sawlog grades 1–3
Grade 1 Grade 2 Grade 3
Maximum branch diameter (mm)
- green branches 15 30 60
- dead branches 10 25 40
- vertical branches 0 25 40
Defects allowed
- only one vertical branch no yes yes
- scars (length < 90 cm) *) no yes yes
- sweep (over 1 cm m–1) no no no
- single crook no no no
- multiple crook, s-crook no no no
- fork no no no
- dead tree no no no
*) outside of top cylinder.
Table 4. Number of butt logs in different log grades and top diameter classes (over bark) in this study.
Sawlog grade Top diameter less than 15 cm Top diameter
15 cm or more 		All logs
Grade 1 1 0 1
Grade 2 43 5 48
Grade 3 10 26 36
Pulpwood 145 57 202
Total 199 88 287
Table 5. Number and main characteristics of sample trees and their butt logs according to clipping treatment. Numbers of sample trees and butt logs as well as mean values, standard deviations (in parentheses), and ranges (between minimum and maximum values) of the variables are presented for the different treatments and all data.
Variable Clipping treatment All data
No damage Damage 1 Damage 2 Damage 3
SAMPLE TREES
Number N 104 76 62 45 287
Diameter at breast height, cm Mean (Std) 17.6 (4.0) 15.8 (3.7) 15.1 (3.7) 15.3 (4.4) 16.2 (4.0)
Min-Max 9.9–28.9 8.4–28.0 5.9–24.3 7.6–23.6 5.9–28.9
Tree height, m Mean (Std) 15.9 (3.0) 15.5 (2.9) 15.5 (2.9) 15.3 (3.2) 15.6 (3.0)
Min-Max 8.7–22.2 9.6–21.5 7.8–19.9 9.1–21.2 7.8–22.2
Height increment 1981–85, dm a–1 Mean (Std) 4.4 (1.3) 4.4 (1.2) 4.4 (1.3) 4.2 (1.4) 4.4 (1.3)
Min-Max 1.1–6.9 0.8–7.8 1.3–6.2 1.6–6.5 0.8–7.8
Height increment 1981–90, dm a–1 Mean (Std) 4.5 (1.2) 4.6 (1.2) 4.6 (1.2) 4.6 (1.3) 4.6 (1.2)
Min-Max 1.3–6.8 1.3–7.4 1.8–6.3 2.1–7.0 1.3–7.4
Height increment 2009–2013, dm a–1 Mean (Std) 3.8 (0.7) 3.6 (0.9) 3.5 (1.0) 3.3 (1.4) 3.6 (1.0)
Min-Max 0.9–5.3 0.7–5.2 0.0–5.2 0.0–5.1 0.0–5.3
Height of the lowest dead branch, m Mean (Std) 1.7 (1.1) 1.5 (1.1) 1.2 (0.9) 1.4 (1.1) 1.5 (1.1)
Min-Max 0.2–6.8 0.5–5.9 0.2–5.2 0.2–5.8 0.2–6.8
Height of the crown base, m Mean (Std) 8.8 (3.3) 8.9 (3.3) 9.3 (3.1) 9.3 (3.3) 9.0 (3.2)
Min-Max 3.1–15.7 3.1–15.8 3.3–15.3 3.9–15.5 3.1–15.8
Tree volume, dm3 Mean (Std) 209 (119) 165 (93) 151 (83) 156 (102) 176 (105)
Min-Max 36–638 35–566 13–417 31–389 13–638
BUTT LOGS
Number of all butt logs N 104 76 62 45 287
Number of logs with top diameter
over 15 cm 		N 45 20 12 11 88
Number of logs with top diameter
less than 15 cm 		N 59 56 50 34 199
Top diameter of log, cm Mean (Std) 14.4 (3.6) 12.8 (3.3) 12.1 (3.3) 12.1 (3.8) 13.1 (3.6)
Min-Max 6.9–25.2 6.5–23.8 3.0–18.9 5.4–19.6 3.0–25.2
Height of the biggest dead branch
in a log, m 		Mean (Std) 3.2 (1.2) 2.8 (1.3) 2.7 (1.4) 2.4 (1.5) 2.8 (1.3)
Min-Max 0.7–5.0 0.5–4.8 0.6–5.0 0.4–4.9 0.4–5.0
Diameter of the biggest dead branch, mm Mean (Std) 24.0 (6.9) 22.1 (5.9) 21.5 (4.7) 22.7 (7.2) 22.7 (6.3)
Min-Max 11.0–46.0 9.0–35.0 14.0–34.0 11.0–49.0 9.0–49.0
Log volume, dm3 Mean (Std) 116 (54) 94 (44) 86 (41) 89 (49) 99 (50)
Min-Max 31–308 25–279 11–212 21–196 11–308
Average sawlog volume, dm3
(based on quality of sawlog grade 3) 		Mean (Std) 45 (66) 30 (51) 24 (42) 10 (32) 31 (54)
Min-Max 0–308 0–179 0–165 0–155 0–308
Table 6. Number of sample trees with different defects in butt logs, and proportions of butt logs with different defects according to clipping treatment and in all data. All defects were recorded within the damaged area of butt logs, but only the critical defects in terms of sawlog quality grading were taken into account. Respective proportions of defect-free butt logs are presented as well.
N Proportion of butt logs (%)
Control Clipping 1 Clipping 2 Clipping 3 All logs
Defects within damaged area in the butt log
  thickest green branch 11 2.9 2.6 4.8 6.7 3.8
  thickest dead branch 124 40.4 47.4 41.9 44.4 43.2
  vertical branch 80 8.7 25.0 48.4 48.9 27.9
  scar 13 5.8 5.3 3.2 2.2 4.5
  fork 5 1.0 0.0 1.6 6.7 1.7
Defects in butt logs according to the bucking rules
  green branch (>60 mm) 1 0.0 0.0 0.0 2.2 0.3
  dead branch (>40 mm) 2 1.0 0.0 0.0 2.2 0.7
  vertical branch (>40 mm) *) 35 5.8 10.5 16.1 24.4 12.2
  scar 23 7.7 7.9 6.5 11.1 8.0
  fork 7 1.9 0.0 1.6 8.9 2.4
  form defect 184 53.8 63.2 72.6 77.8 64.1
  dead tree 3 0.0 0.0 1.6 4.4 1.0
Defect-free logs according to the bucking rules **) 85 39.4 28.9 27.4 11.1 29.6
*) Only one vertical branch smaller than 40 mm in diameter allowed.
**) Log diameter not taken into account in grading.
4

Fig. 4. a) Proportions of straight, sweeped, crooked, s-crooked, and multiple crooked butt logs among sample trees 34 years after artificial moose browsing damage. b) Proportions of different timber assortments (sawlog grades 1–3 and pulpwood) in the grading of butt logs grouped according to a top diameter of under 15 and over 15 cm in the undamaged control and clipping treatments. The log diameter was not accounted for in grading.

Table 7. Parameter estimates, standard errors (SE) and p-values for ANCOVA models 1–3 (Eq. 1) predicting the diameter at breast height (DBH), height, and tree volume of trees 34 years after artificial moose browsing damage.
Variable Model 1: DBH, cm
(r2 = 0.259) 		Model 2: Height, m
(r2 = 0.713) 		Model 3: Volume, dm3
(r2 = 0.341)
Estimate SE p Estimate SE p Estimate SE p
Intercept 27.377 4.583 <0.0001 54.695 2.109 <0.0001 742.986 112.311 <0.0001
Tree height in 1980, cm 0.023 0.004 <0.0001 0.012 0.002 <0.0001 0.603 0.087 <0.0001
Treatment (ref. no clipping)
- Clipping 1 –1.589 0.534 0.0032 –0.498 0.246 0.0438 –40.840 13.086 0.0020
- Clipping 2 –2.422 0.569 <0.0001 –0.867 0.262 0.0010 –60.689 13.937 <0.0001
- Clipping 3 –2.830 0.635 <0.0001 –1.202 0.292 <0.0001 –68.654 15.564 <0.0001
Site MT 1) –12.081 5.238 0.0218 –57.079 2.410 <0.0001 –861.684 128.375 <0.0001
Temperature sum in Site MT 2) –0.001 0.002 0.5534 0.014 0.001 <0.0001 0.199 0.060 0.0010
Temperature sum in Site VT 3) –0.012 0.004 0.0008 –0.032 0.002 <0.0001 –0.524 0.087 <0.0001
1) Values: 1 for a tree in Myrtillus site (or corresponding); otherwise 0.
2) Values: temperature sum (DD) for a tree in Myrtillus site (or corresponding); otherwise 0.
3) Values: temperature sum (DD) for a tree in Vaccinium site; otherwise 0.
Table 8. Parameter estimates, standard errors (SE), and p-values for ANCOVA models 4–6 (Eq. 1) predicting the annual tree height increment of trees in years 1981–1985, 1981–1990, and 2009–2013.
Variable Model 4: Increment in
1981–1985, cm a–1
(r2 = 0.691) 		Model 5: Increment in
1981–1990, cm a–1
(r2 = 0.771) 		Model 6: Increment in
2009–2013, cm a–1
(r2 = 0.134)
Estimate SE p Estimate SE p Estimate SE p
Intercept 173.413 9.411 <0.0001 193.340 7.704 <0.0001 67.757 11.915 <0.0001
Tree height in 1980, cm 0.027 0.007 0.0003 0.023 0.006 0.0001 0.021 0.009 0.0248
Treatment (ref. no clipping)
- Clipping 1 –1.125 1.097 0.3059 –0.354 0.898 0.6937 –1.739 1.388 0.2115
- Clipping 2 –2.858 1.168 0.0150 –1.388 0.956 0.1478 –2.958 1.479 0.0464
- Clipping 3 –4.622 1.304 0.0005 –1.748 1.068 0.1027 –5.821 1.651 0.0005
Site MT 1) –226.552 10.757 <0.0001 –239.856 8.806 <0.0001 –53.590 13.619 0.0001
Temperature sum in site MT 2) 0.081 0.005 <0.0001 0.077 0.004 <0.0001 0.019 0.006 0.0032
Temperature sum in site VT 3) –0.103 0.007 <0.0001 –0.117 0.006 <0.0001 –0.028 0.009 0.0030
1) Values: 1 for a tree in Myrtillus site (or corresponding); otherwise 0.
2) Values: temperature sum (DD) for a tree in Myrtillus site (or corresponding); otherwise 0.
3) Values: temperature sum (DD) for a tree in Vaccinium site; otherwise 0.
Table 9. Parameter estimates, standard errors (SE), and p-values for ANCOVA model 7 (Eq. 1) predicting the diameter of the thickest dead branch in a butt log 34 years after artificial moose browsing damage.
Variable Model 7: Branch diameter, mm
(r2 = 0.303)
Estimate SE p
Intercept 61.297 6.940 <0.0001
Tree height in 1980, cm 0.025 0.006 <0.0001
Treatment (ref. no clipping)
- Clipping 1 –1.842 0.812 0.0240
- Clipping 2 –2.816 0.861 0.0012
- Clipping 3 –2.102 0.972 0.0315
Site MT 1) –62.165 7.934 <0.0001
Temperature sum in site MT 2) 0.019 0.004 <0.0001
Temperature sum in site VT 3) –0.034 0.005 <0.0001
1) Values: 1 for a tree in Myrtillus site (or corresponding); otherwise 0.
2) Values: temperature sum (DD) for a tree in Myrtillus site (or corresponding);    otherwise 0.
3) Values: temperature sum (DD) for a tree in Vaccinium site; otherwise 0.
Table 10. Parameter estimates for the logistic regression models 8–10 (Eq. 2) predicting the probability of vertical branches and stem form defects in a butt log 34 years after artificial moose browsing damage. Model 8: all vertical branches within the damaged area in a butt log. Model 9: vertical branches with diameters of 40 mm or more in a whole butt log. Model 10: all stem form defects (which are not allowed in the sawlogs; see Table 3 for bucking rules) in the butt log.
Variable Estimate SE Wald df p Exp(B)
Model 8: Vertical branches within damage area
(all branches)
(Nagelkerke R Square = 0.205)
Intercept –4.372 0.687 40.476 1 <0.0001 0.013
Tree height in 1980, cm 0.009 0.002 13.179 1 0.0003 1.009
Treatment (ref. no clipping) 34.899 3 <0.0001
- Clipping 1 1.337 0.448 8.889 1 0.0029 3.808
- Clipping 2 2.425 0.445 29.657 1 <0.0001 11.306
- Clipping 3 2.231 0.471 22.408 1 <0.0001 9.312
Model 9: Vertical branches in whole butt log
(branches of 40 mm or more)
(Nagelkerke R Square = 0.109)
Intercept –4.390 0.829 28.064 1 <0.0001 0.012
Tree height in 1980, cm 0.007 0.003 5.597 1 0.0180 1.007
Treatment (ref. no clipping) 8.676 3 0.0339
- Clipping 1 0.682 0.568 1.442 1 0.2298 1.977
- Clipping 2 1.189 0.550 4.676 1 0.0306 3.283
- Clipping 3 1.532 0.553 7.662 1 0.0056 4.627
Model 10: Stem form defects in whole butt log
(any crooks, sweep of 1 cm or more per one meter)
(Nagelkerke R Square = 0.267)
Intercept –7.943 1.335 35.411 1 <0.0001 0.000
Temperature sum, DD 0.005 0.001 26.029 1 <0.0001 1.005
Tree height in 1980, cm 0.009 0.002 14.132 1 0.0002 1.009
Treatment (ref. no clipping) 8.305 3 0.0401
- Clipping 1 0.323 0.341 0.897 1 0.3435 1.382
- Clipping 2 0.820 0.378 4.700 1 0.0302 2.269
- Clipping 3 1.100 0.458 5.777 1 0.0162 3.003
Table 11. Parameter estimates for the logistic regression model 11 (Eq. 2) predicting the probability of achieving a sawlog quality butt log 34 years after artificial moose browsing damage. The butt log was graded as a sawlog only if the quality requirements for log grade 3 were met. Log diameter was not taken into account in grading.
Variable Estimate SE Wald df p Exp(B)
Model 11: Probability of getting a sawlog according to the bucking rules
(only quality notified)
(Nagelkerke R Square = 0.283)
Intercept 4.249 1.7144 6.144 1 0.0132 70.064
Temperature sum, DD –0.003 0.0014 5.327 1 0.0210 0.997
Tree height in 1980, cm –0.007 0.0026 7.877 1 0.0050 0.993
Site MT 1) 0.842 0.3949 4.548 1 0.0330 2.321
Treatment (ref. no clipping) 8.397 3 0.0385
- Clipping 1 –0.301 0.3560 0.715 1 0.3978 0.740
- Clipping 2 –0.347 0.3795 0.834 1 0.3612 0.707
- Clipping 3 –1.611 0.5583 8.326 1 0.0039 0.200
1) Values: 1 for a tree in Myrtillus site (or corresponding); otherwise 0.