Fig. 1

Fig. 1. Location of the regeneration stands and schematic illustration of data hierarchy. Parameters were measured either at forest stand level, plot level (25 plots of 10 m2 on each stand) or seedling level (5 cm radius around a seedling).

Table 1. The characteristics of the forest stands (the averages at stand level). Expression “est. since cut” denotes the seedlings that have been emerged since seed-tree cutting.
  Mean 95% cl.
lower 		95% cl.
upper 		Sd Min Max Median
Temperature sum, d.d. 690 678 701 23 659 757 694
Elevation, m asl 257 242 272 30 207 310 260
Time since seed-tree cut, years 12 10 13 4 6 17 11
Number of seed trees ha–1 33 19 48 28 13 120 24
Thickness of humus layer, cm 2.0 1.4 2.6 1.2 0.5 5.8 1.7
Cover of crowberry, % 15.4 11.3 19.6 8.2 0.7 33.0 13.5
Cover of heather, % 11.1 5.9 16.2 10.2 0.0 34.2 11.8
Cover of lingonberry, % 2.0 1.1 2.8 1.7 0.4 6.5 1.7
Cover of bilberry, % 6.3 3.9 8.8 4.8 0.4 16.2 5.9
Cover of Polytrichum spp., % 8.8 5.1 12.5 7.3 1.1 23.3 7.9
Cover of other mosses, % 21.6 15.5 27.7 12.1 2.7 44.7 24.0
Cover of reindeer lichens, % 16.1 9.8 22.4 12.4 0.4 44.8 15.0
Cover of other lichens, % 3.2 1.5 4.8 3.2 0.0 10.5 1.6
Cover of exposed mineral soil, % 5.2 2.0 8.5 6.1 0.0 16.4 1.5
Number of pine seedlings
(est. since cut) ha–1 		1387 658 2116 1441 160 5200 1120
Total number of pine seedlings /
saplings ha–1 		1874 943 2806 1840 240 7033 1280
Total number of spruce seedlings /saplings ha–1 273 92 455 359 0 1120 120
Total number of birch seedlings /
saplings ha–1 		1167 662 1672 998 40 3680 920
Age of pine seedlings (est. since cut), years 6 5 7 2 3 10 6
Height of seedlings (est. since cut), cm 17.8 12.5 23.1 10.5 5.0 43.2 16.3
Table 2. The results of permutation tests for the CCA analysis. The test is for the marginal effects of the constraining terms. N.Perm denotes the number of permutations.
  Df Chi-square F N.Perm p
Thickness of humus layer, cm (HUM) 1 0.009 2.690 299 0.017
Stoniness, (S1, categories: 1 = stony, 0 = not stony, measured on a sample plot) 1 0.014 4.352 199 0.005
Total number of pine seedlings on a sample plot (PINE) 1 0.014 4.389 199 0.005
Total number of spruce seedlings on a sample plot (SPRUCE) 1 0.008 2.347 399 0.023
Residual 356 1.166      
Fig. 2

Fig. 2. Canonical correspondence analysis (CCA) plot describing the relations involved in the ground- and bottom-layer vegetation and the statistically significant (at 5% risk level) gradient variables indicated by gradient vectors.

Fig. 3

Fig. 3. The predicted seedling establishment probabilities by independent variables in Model 1. The covers were measured at plot level.

Table 3. The ordered multinomial regression model with a random factor for predicting the numbers of seedlings on a sample plot emerged after the seed-tree cutting (Model 1). The joined Wald tests were calculated as a general test for the categorical variables. Approximate confidence intervals for random and scale parameters are presented. Pl denotes measurement at plot and st at stand level (in the parenthesis).
Variable Estimate Std.error Wald df p
Fixed effects
Intercept (≥ 4 seedling on a plot, pl) –2.918 1.119 6.797 1 0.009
Intercept (≥ 3 seedling on a plot, pl) –2.423 1.116 4.714 1 0.030
Intercept (≥ 2 seedling on a plot, pl) –1.787 1.113 2.575 1 0.109
Intercept (≥ 1 seedling on a plot, pl) –0.603 1.110 0.295 1 0.587
Time since seed-tree cutting, years (st) 0.164 0.088 3.476 1 0.062
Thickness of humus layer, cm (pl) –0.332 0.076 19.089 1 0.000
Cover of moss species, % (pl) –0.039 0.007 30.527 1 0.000
Cover of heather, %, (pl) 0.014 0.006 5.037 1 0.025
Cover of exposed mineral soil, % (pl) 0.034 0.015 4.919 1 0.027
Abundance of slash and other cutting waste (joined test, pl)     12.619 2 0.002
Much –1.948 0.578 11.341 1 0.001
A little 0.080 0.223 0.129 1 0.719
Not any (ref. category) 0.000 0.000 - - -
Random effects Estimate 95 % confidence intervals
Variance of random intercept of forest stand σj2 1.162 0.244–2.080
Scale parameter (compare to 1) 0.814 0.754–0.874
Fig. 4

Fig. 4. The predictions for the effect of heather cover on the average height of the pine seedlings calculated at 5, 10 and 15 year seedling age (Model 2).

Table 4. The estimates and significance tests for the model of pine seedling height (median height on a plot) (Model 2). The response variable is the logarithm of the height of the seedlings on a sample plot that were emerged since seed-tree cutting. The model was done for the forest stands where the average of temperature sum during 1960–1991 was < 750 (one stand omitted), and the maximum age was 15 years (one sample plot omitted). The R2 basing on the fixed predictions was 71.5%. Pl denotes measurement at plot and st at stand level (in the parenthesis).
Variable Estimate Std. error df t p
Fixed part
Intercept (pl) –5.668 1.524 126 –3.719 0.000
Age of seedling of median height, years (pl) –0.195 0.071 126 –2.755 0.007
Square root of age of median height seedling, years (pl) 2.366 0.351 126 6.733 0.000
Cover of heather, % (pl) –0.002 0.001 126 –1.733 0.086
Cover of lingonberry, % (pl) 0.019 0.006 126 2.878 0.005
Temperature sum, d.d. (st) 0.005 0.002 12 2.602 0.021
Random part Estimate 95% confidence intervals
Variance of random intercept of forest stand σj2 0.002 0.000–0.742
Residual σij2 0.088 0.069–0.112
Fig. 5

Fig. 5. Predicted probability (p) of the occurrence of dead or dying seedlings by the independent variables (Model 3). The number of spruce and birch seedlings was measured at plot level and the cover of crowberry at the base of a seedling (at seedling level).

Table 5. The estimates of the model for predicting the probability of a seedling’s poor health (seedling classified as dead or dying) (Model 3). The maximum of the total number of seedlings was restricted as <20 seedlings on a plot for computational reasons. Thus the total number of seedlings in the model was 491 out of 510. Pl denotes measurement at plot and se at seedling level (in the parenthesis).
Variable Estimate Std.error t-value df p
Fixed effects
Intercept (se) –4.208 0.484 333 –8.690 0.000
Age of a seedling, years (se) 0.202 0.040 333 5.007 0.000
Total number of seedlings (pl) 0.081 0.040 139 2.084 0.039
Cover of crowberry at seedling’s base (se) 0.026 0.008 333 3.198 0.002
Cover of lichens at seedling’s base (se) 0.015 0.008 333 1.994 0.047
Random effects Estimate 95% confidence intervals
Variance of random intercept of forest stand σj2 0.024 0.000–1.230e+03
Variance of random intercept of sample plot σij2 1.429 0.800–2.553
Scale parameter (compare to 1) 0.624 0.542–0.719