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Fig. 1. Effective temperature sums (+4 °C threshold) in Kuusamo, Sodankylä and Kevo and annual precipitation sums (columns) in Sodankylä from 1977 to 2013. The climate datasets (thin lines, columns) are provided in a yearly resolution by European Climate Assessment & Dataset (Klein Tank et al. 2002) and smoothed by using a Fast Fourier Transformation (thick lines).

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Fig. 2. Monitoring locations of spruce and pine in Finnish Lapland as well as the forest lines of both species. The locations were divided on the basis of predominant species and geographical areas into a northern and southern region of pine and into a western and eastern region of spruce.

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Fig. 3. Examples of the forest stands in the a) forest zone (Yllästunturi), b) timber-line zone (Kevo) and c) tree-line zone (Urupää) (Photos by Seppo Neuvonen and Anna Franke).

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Fig. 4. Sampling design in each of the 13 locations. The sampling was done on three sample plots in forest and timber- and tree-line zones in 1983, 1994, 1999, 2004 and 2009.

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Fig. 5. Example of a sampling location (Sarmitunturi) showing the position of the timber-line and tree-line zones (Photo by Raimo Sutinen). The forest zone is located further downhill and therefore not shown in the photo.

Table 1. Coordinates, altitude, temperature sum, and horizontal distance between the zones in each location. Coordinates and temperature sums are focused on the timber-line zones. The average temperature sums (+5 °C threshold) were provided in a climatic grid (1961–90 standard period) by using the model of Ojansuu and Henttonen (1983).
  Altitude (m a.s.l.)   Horizontal distance (m) between
Location Latitude Longitude Dominant conifer1 Forest zone Timber line Tree line Temperature
sum (d.d. 5 °C) 		Forest and
timber line 		Timber line
and tree line
Kevo Tsieskuljoki 69°41’ N 26°59’ E P 110 180 190 773 310 180
Kevo, nat. res 69°45’ N 27°03’ E P 185 210 225 741 230 100
Karigasniemi 69°25’ N 25°53’ E P 225 275 420 770 840 810
Syysjärvi 69°17’ N 27°12’ E P 215 220 225 781 1280 11460
Lemmenjoki 68°43’ N 26°06’ E P 285 375 415* 782 460 130
Urupää 68°28’ N 27°26’ E P 315 340 370* 745 140 210
Alajoenpää 68°28’ N 27°22’ E P 340 380 400* 748 250 270
Ylläs 67°34’ N 24°11’ E P 380 410 465* 900 240 210
Lommoltunturi 68°00’ N 24°09’ E S 410 445 465* 874 250 120
Pallaskero 68°02’ N 24°06’ E S 465 480 500* 892 220 110
Sarmitunturi 68°39’ N 28°23’ E S 340 370 410* 842 150 160
Pyhätunturi 67°01’ N 27°07’ E S 380 400 420 914 300 260
Riisitunturi 66°13’ N 28°33’ E S 420 440 460* 943 120 190
1 Dominant conifer species: P = pine, S = spruce.
* Indicates that a larger sample plot area (500 m2) has been used.
Table 2. The estimates and Likelihood-ratio tests of the models for Norway spruce, t-values for the coefficients and χ2 – values for the Likelihood ratio tests are presented in t/Chisq. Tests show the significance of the variables in the model and the significance of the coefficients related to the reference categories (given in parentheses). A non-significant interaction term means that the coefficients do not differ from the coefficient of reference category.
Variable / term Coefficient Std. error Df t/Chisq p
Norway spruce, number of trees and seedlings ha–1
Intercept 7.000 0.376 56/1 18.62/346.54 0.000
Region (ref. Western)     1 4.28 0.039
-Eastern -0.854 0.412 3 -2.07 0.130
Zone (ref. Forest)     2 3.70 0.157
-Timber line 0.333 0.342 8 0.97 0.359
-Tree line -0.325 0.342 8 -0.95 0.370
Time 0.018 0.010 56/1 1.77/3.13 0.077
Region*Time     1 1.81 0.179
-Eastern*Time -0.013 0.010 56 -1.35 0.184
Zone*Time     2 3.49 0.175
-Timber line*Time 0.006 0.012 56 0.48 0.630
-Tree line*Time 0.021 0.012 56 1.80 0.077
Random effects Estimate Cl 95%  
Location 0.107 0.007 – 1.682
Zone nested Location 0.187 0.061 – 0.579
Error (compound symmetry) 0.141 0.098 – 0.205
Norway spruce, volume of tree stock, m3ha–1
Intercept 7.970 1.073 56/1 7.43/55.19 0.000
Region (ref. Western)     1 0.65 0.420
-Eastern -1.031 1.278 3 -0.81 0.479
Zone (ref. Forest)     2 67.50 0.000
-Timber line -2.056 0.717 8 -2.87 0.021
-Tree line -5.812 0.717 8 -8.10 0.000
Time 0.043 0.010 56/1 4.27/18.21 0.000
Region*Time     1 2.85 0.091
-Eastern*Time -0.017 0.010 56 -1.69 0.097
Zone*Time     2 8.10 0.017
-Timber line*Time 0.012 0.012 56 1.04 0.301
-Tree line*Time -0.021 0.012 56 -1.77 0.082
Random effects Estimate Cl 95%  
Location 1.530 0.197 – 11.853
Zone nested within Location 1.186 0.443 – 3.177
Error (ARH-1, phi = 0.55) 0.398 0.165 – 0.957
Table 3. The estimates and Likelihood-ratio tests of the models for Scots pine, t-values for the coefficients and χ2 – values for the Likelihood ratio tests are presented in t/Chisq. Tests show the significance of the variables in the model and the significance of the coefficients related to the reference categories (given in parentheses). A non-significant interaction term means that the coefficients do not differ from the coefficient of reference category.
Variable / term Coefficient Std. error Df t/Chisq p
Scots pine, number of trees and seedlings ha–1
Intercept 6.577 0.695 90/1 9.43/88.90 0.000
Region (ref. Northern)     1 0.84 0.359
-Southern 0.729 0.795 6 0.92 0.395
Zone (ref. Forest)     2 10.12 0.006
-Timber line -1.040 0.710 14 -1.47 0.165
-Tree line -2.256 0.710 14 -3.18 0.007
Time 0.012 0.009 90/1 1.36/1.85 0.174
Region*Time     1 12.95 0.000
-Southern*Time -0.032 0.009 90 -3.60 0.001
Zone*Time     2 0.91 0.635
-Timber line*Time -0.010 0.011 90 -0.89 0.377
-Tree line*Time -0.008 0.011 90 -0.74 0.464
Random effects Estimate Cl 95%      
Location 0.591 0.050 – 7.018      
Zone nested Location 1.876 0.882 – 3.990      
Error (compound symmetry) 0.185 0.138 – 0.248      
Scots pine, volume of tree stock, m3ha–1
Intercept 7.124 1.166 90/1 6.11/37.34 0.000
Region (ref. Northern)     1 0.00 0.997
-Southern -0.005 1.296 6 -0.00 0.997
Zone (ref. Forest)     2 24.57 0.000
-Timber line -3.665 1.247 14 -2.94 0.011
-Tree line -6.145 1.247 14 -4.93 0.000
Time 0.054 0.015 90/1 3.64/13.27 0.000
Region*Time     1 0.50 0.478
-Southern*Time -0.011 0.015 90 -0.71 0.479
Zone*Time     2 5.47 0.065
-Timber line*Time 0.026 0.018 90 1.43 0.155
-Tree line*Time -0.016 0.018 90 -0.89 0.377
Random effects Estimate Cl 95%      
Location 1.287 0.084 – 19.753      
Zone nested within Location 4.968 2.348 – 10.513      
Error (ARH-1, phi = 0.91) 1.325 0.533 – 3.294      
Table 4. Significances (p-values) of asymptotical tests for the coefficients of the interaction terms (Time*Region or Time*Zone) in the models. Hypothesis is that the coefficients = 0. The arrows denote either a significant increasing or decreasing change in time, or non-significant change (flat arrow).
Coefficient Scots pine,
number of
trees ha–1 		Scots pine,
volume of
tree stock, m3ha–1 		Norway spruce, number of
trees ha–1 		Norway spruce, volume of
tree stock, m3ha–1
Region: northern (pine), western (spruce) 0.327 → 0.000 ↗ 0.000 ↗ 0.000 ↗
Region: southern (pine), eastern (spruce) 0.000 ↘ 0.000 ↗ 0.026 ↗ 0.000 ↗
Zone: forest 0.590 → 0.000 ↗ 0.127 → 0.000 ↗
Zone: timber line 0.078 → 0.000 ↗ 0.041 ↗ 0.000 ↗
Zone: tree line 0.120 → 0.011 ↗ 0.000 ↗ 0.086 →
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Fig. 6. The stem number ha–1 (a) and volume of growing stock m3 ha–1 (b) of spruce during the study in each location (raw data) as well as the predicted values of the models for each zone (thick line).

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Fig. 7. The stem number ha–1 (a) and volume of growing stock m3 ha–1 (b) of pine during the study in each location (raw data) as well as the predicted values of the models for each zone (thick line).