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Fig. 1. The location of study area (A) and sampling design of the sample plots per each study site (B).

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Fig. 2. Vegetation recovery after wildfire in Northern Latvia study sites dominated by Scots pine (Pinus sylvestris) (photo: Līga Liepa).

Table 1. Main characteristics of studied burned stands (n = 7).
No. Coordinates Forest site type* Stand age (2019)
1 57.329 N; 22.272 E Oxalidosa 67
2 57.329 N; 22.271 E Vaccinioso-sphagnosa 67
3 57.327 N; 22.270 E Vacciniosa 157
4 57.327 N; 22.268 E Vacciniosa 157
5 57.326 N; 22.268 E Vacciniosa 64
6 57.326 N; 22.270 E Vaccinioso-sphagnosa 157
7 57.325 N; 22.267 E Vacciniosa 167
* Forest types according to Bušs (1997).
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Fig. 3. Boxplots showing the median and the spread of the data with outliers of vegetation projective cover (%) for ground layer during four years after fire in sample plots (n = 112). MA – middle-aged stands, OM – over-mature stands.

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Fig. 4. Changes in ground layer vegetation projective cover (%) during four years after fire in sample plots (n = 112). Standard errors are shown.

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Fig. 5. Boxplots showing the median and the spread of the data with outliers of vegetation projective cover (%) for herb layer during four years after fire in sample plots (n = 112). MA – middle-aged stands, OM – over-mature stands.

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Fig. 6. Changes in herb layer vegetation projective cover (%) during four years after fire in sample plots (n = 112). Standard errors are shown.

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Fig. 7. Projective cover (%) by regenerating tree species in the middle-aged and over-mature stands (n = 112). Standard errors are shown.

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Fig. 8. Boxplots showing the median and the spread of the data with outliers of vegetation projective cover (%) for regenerating trees during four years after fire in sample plots (n = 112). MA – middle-aged stands, OM – over-mature stands.

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Fig. 9. Changes in average Ellenberg indicator values during four years after fire in sample plots (n = 112). Standard errors are shown.

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Fig. 10. Changes in vegetation projective cover (%) by C-S-R strategies during four years after fire in sample plots (n = 112). Standard errors are shown.

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Fig. 11. Changes in vegetation projective cover (%) by Raunkiær life forms during four years after fire in sample plots (n = 112). Standard errors are shown.

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Fig. 12. Changes in vegetation projective cover (%) by plant ecological groups during four years after fire in sample plots (n = 112). Standard errors are shown.

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Fig. 13. Changes in vegetation projective cover (%) by seed dispersal agents during four years after fire in sample plots (n = 112). Standard errors are shown.

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Fig. 14. Changes in vegetation projective cover (%) of four fire-adapted species during four years after fire in sample plots (n = 112). Standard errors are shown.

Table 2. Species diversity (Shannon-Wiener index H) and standard errors in sample plots (n = 112).
Year since fire
1 2 3 4
Ground layer
  Middle-aged stands 1.20 ± 0.09 1.31 ± 0.08 1.22 ± 0.08 0.83 ± 0.08
  Over-mature stands 1.50 ± 0.07 1.45 ± 0.06 1.23 ± 0.05 1.03 ± 0.05
Herb layer
  Middle-aged stands 2.00 ± 0.06 2.25 ± 0.08 2.57 ± 0.10 2.56 ± 0.08
  Over-mature stands 2.41 ± 0.08 2.50 ± 0.09 2.47 ± 0.08 2.58 ± 0.07
Tree species regeneration
  Middle-aged stands 1.42 ± 0.17 1.42 ± 0.11 1.44 ± 0.14 1.45 ± 0.14
  Over-mature stands 0.99 ± 0.09 1.41 ± 0.14 1.39 ± 10.14 1.53 ± 0.15
Table 3. Vegetation projective cover (%) p-values and significance levels for by layer between successive years since fire event (n = 434).
Vegetation layer 1st vs. 2nd year 2nd vs. 3rd year 3rd vs. 4th year
Ground 0.003** 0.542ns 0.969ns
Herb 0.088* 0.099* 0.292ns
Tree species regeneration 0.064* 0.143ns 0.083*
*** p < 0.001; ** p < 0.05; * p < 0.1; ns – not significant.
Table 4. p-values and significance levels for vegetation projective cover (%) by age groups (middle-aged and over-mature stands) during the four years since fire event (n = 434).
Vegetation layer 1st year 2nd year 3rd year 4th year
Ground 0.465ns 0.267ns 0.683ns 0.301ns
Herb 0.607ns 0.393ns 0.282ns 0.493ns
Tree species regeneration 0.000*** 0.011** 0.035** 0.049**
*** p < 0.001; ** p < 0.05; * p < 0.1; ns – not significant.