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Fig 1. Location of study area in northwestern Estonia. Yellow dots represent pine stands (n = 6) with different age (time since fire) in the post-fire chronosequence. View larger in new window/tab.

Table 1. Main characteristics of studied stands (n = 6) in the post-fire chronosequence in northwestern Estonia.
Years since fire Coordinates* Area burned* Forest site type* Tree species
composition (%)
Pi – Scots pine;
Bi – Silver birch* 		Tree diameter
(mean, cm)* 		Tree height
(mean, m)* 		Living trees ha–1 Soil type
(World Reference Base classification)* 		Canopy openness
(mean ± SE, %) 		Basal area
(m2 ha–1)
12 59°11´N, 23°46´E about 800 ha Vaccinium uliginosum 56 Pi, 44 Bi 1.9 1.1 1442 gleyic podzol 80.6 ± 2.4 0.4
23 59°12´N, 23°49´E about 700 ha Calluna 91 Pi, 9 Bi 3.9 2.9 2684 gleyic podzol 35.3 ± 2.8 3.2
38 59°11´N, 23°46´E about 200 ha Calluna 100 Pi 7.2 5.5 3167 gleyic podzol 19.2 ± 1.1 12
69 59°14´N, 23°49´E about 2000 ha Calluna/Cladina 93 Pi, 7 Bi 12.5 11.1 1583 gleyic podzol 27.6 ± 0.8 19.4
80 59°10´N, 23°42´E about 200 ha Vaccinium uliginosum 100 Pi 10.4 9.4 3117 gleyic podzol 22.1 ± 1.2 24.2
183 59°13´N, 23°36´E about 200 ha
(exactly unknown) 		Calluna 100 Pi 21.8 13.4 558 gleyic podzol 31.5 ± 0.3 21
* data originates from Köster et al. 2016
Table 2. Floristic variables in vegetation plots (n = 18) and the effects of environmental factors (standardized coefficients) on them, based on final linear mixed models after backward variable selection. PC1 and PC2 – principal components representing soil variables (detailed description of PCs is provided in the Data analysis section).
Response variable Mean Min Max Factor effect, standardized coefficient
Time since fire Transmitted total radiation PC1 PC2
Cover of understorey vascular plant layer 43.6 7 70 0.94 ± 0.24 0.75 ± 0.24 - -
Cover of bryophyte layer 52.9 15 90 0.78 ± 0.16 - - -
Richness of vascular plants 7.8 5 13 - - - -
Shannon’s diversity index of vascular plants 1.2 0.6 2.0 - - - -
Richness of shrubs and young trees 1.8 0 4 - - - –0.61 ± 0.20
Richness of dwarf-shrubs 3.6 1 6 0.60 ± 0.20 - - -
Richness of graminoids 1.4 0 4 - –0.45 ± 0.17 - –0.65 ± 0.17
Richness of forbs 1.0 0 2 - - - -
Richness of bryophytes 10.9 5 21 - 0.44 ± 0.16 –0.61 ± 0.16 –0.49 ± 0.15
Shannon’s diversity index of bryophytes 1.3 0.7 1.7 - - - –0.49 ± 0.22
Richness of liverworts 1.7 0 5 –0.74 ± 0.16 - –0.61 ± 0.16 -
Richness of mosses 9.2 4 18 - - –0.45 ± 0.18 –0.57 ± 0.18
Richness of ground-dwelling bryophytes 8.3 3 18 - 0.42 ± 0.19 - –0.52 ± 0.19
Richness of bryophytes on pine trees 2.1 0 5 - –0.69 ± 0.18 - -
Richness of bryophytes on birch trees 1.3 0 11 - - - -
Richness of bryophytes on dead-wood 3.6 0 12 - - –0.55 ± 0.15 –0.59 ± 0.15
Table 3. Relationships between vascular plant and bryophyte species composition (non-metric multidimensional scaling, Fig. 2) and environmental variables in a post-fire chronosequence in northwestern Estonia. R2 – correlation between environmental variable and ordination. P-values are based on random permutations of the data, significant relationships (p < 0.05) are shown in bold.
Environmental variable Vascular plants Bryophytes
r2 p-value r2 p-value
Time since fire 0.62 0.001 0.60 0.001
Canopy transmitted direct radiance 0.56 0.006 0.65 0.001
Canopy transmitted diffuse radiance 0.57 0.003 0.65 0.002
Canopy transmitted total radiance 0.57 0.004 0.65 0.001
Canopy openness 0.58 0.003 0.63 0.002
soil pH 0.36 0.033 0.30 0.064
soil N 0.13 0.383 0.38 0.023
soil P 0.25 0.121 0.47 0.007
soil K 0.33 0.045 0.53 0.004
soil C 0.25 0.112 0.49 0.006
soil Ca 0.34 0.046 0.19 0.219
soil Mg 0.28 0.081 0.36 0.033
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Fig. 2. Non-metric multidimensional scaling of a) vascular plants (2-dimensional solution, stress 0.12) and b) bryophytes (stress 0.14) from vegetation plots (n = 18) in a post-fire chronosequence in northwestern Estonia. Environmental factors that were significantly (p < 0.05) related to ordination axes (Table 3) are presented (Time – time since fire, Trans.dir. – canopy transmitted direct radiance, Trans.dif. – canopy transmitted diffuse radiance, Trans.tot. – canopy transmitted total radiance; Canopy open. – percentage of canopy openness, Soil pH – soil pH, Soil N – content of soil N, Soil P – content of soil P, Soil K – content of soil K, Soil C – content of soil C, Soil Ca – content of soil Ca, Soil Mg – content of soil Mg). Circles – vegetation plots in stands with 12 to 38 years since fire, triangles – vegetation plots in stands with 69 to 183 years since fire. Characteristic species of Indicator Species Analysis are underlined. Species abbreviations are provided in Supplementary file S1.