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Fig. 1. Eight controlled burning sites in southern Finland marked with black dots. The test sites ‘Kivimäensalo’, ‘Liesjärvi’, ‘Pyhä-Häkki’, ‘Nuuksio’, and ‘Seitseminen’ were burned in 2021, whereas ‘Evo’, ‘Ruunaa’, and ‘Salamajärvi’ in 2022. All the test sites are located within national parks or protected areas.

Table 1. Coordinates of the center of each test site, forest types, and dates of controlled burnings and pre- and post-fire terrestrial laser scanning (TLS) measurements. The test sites are located in southern Finland.
Site Coordinates (N, E) Forest type Pre-fire TLS Burning Post-fire TLS
Kivimäensalo 62°18.419’, 27°41.495’ mesic heath 10 Jun 2021 6 Jul 2021 9 Sep 2021
Liesjärvi 60°39.043’, 24°1.070’ sub-xeric heath 16 Jun 2021 17 Jun 2021 5 Sep 2021
Pyhä-Häkki 62°51.358’, 25°25.417’ sub-xeric heath 13 Jun 2021 30 Jun 2021 7 Sep 2021
Nuuksio 60°19.484’, 24°32.349’ sub-xeric heath 6 Jun 2021 7 Jun 2021 30 Jun 2021
Seitseminen 61°58.080’, 23°24.735’ sub-xeric heath 20 Jun 2021 1 Jul 2021 6 Sep 2021
Evo 61°13.342’, 25°11.761’ mesic heath 3 Jun 2022 15 Aug 2022 18 Aug 2022
Ruunaa 63°22.814’, 30°30.132’ sub-xeric heath 9 Jun 2022 30 Jun 2022 3 Jul 2022
Salamajärvi 63°17.267’, 24°37.976’ dry heath 13 Jul 2022 16 Aug 2022 13 Sep 2022
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Fig. 2. The test site ‘Evo’ two months before (left) and a few days after (right) the controlled burning.

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Fig. 3. Pre-fire point clouds (left) were aligned with post-fire point clouds (right) using a 3D transformation derived from common tie points, e.g., the large black dots in the figure. The tie points were manually extracted from the point clouds.

Table 2. Stand characteristics and mean elevation of controlled burning sites. N = number of stems, G = basal area, Dg = basal area weighted mean diameter at breast height, Hg = basal area weighted mean height, Vol = stem volume, CC = canopy cover. The test sites are located in southern Finland.
Site Area
(ha) 		N
(ha–1) 		G
(m2 ha–1) 		Dg
(cm) 		Hg
(m) 		Vol
(m3 ha–1) 		CC
(%) 		Stand age
(~y) 		Elevation
(m)
Kivimäensalo 1.2 732 17.1 18.7 16.9 140 54 60 164
Liesjärvi 1.0 527 12.7 19.2 16.1 93 42 60 140
Pyhä-Häkki 1.0 1 147 31.4 21.7 18.3 261 79 70 176
Nuuksio 1.1 369 21.2 31.0 20.6 205 55 150 100
Seitseminen 1.0 687 25.3 24.3 21.6 260 55 50 184
Evo 1.2 751 23.7 26.3 18.6 210 68 60 171
Ruunaa 0.9 948 28.5 21.5 19.6 274 76 120 152
Salamajärvi 1.0 919 30.7 23.0 19.6 272 65 70 190
Table 3. Recall, precision, and F1-score quantifying the performance of the classification method for identifying ‘burned’ and ‘unburned’ areas for each controlled burning site.
Site Recall Precision F1-score
Kivimäensalo 0.95 1.00 0.98
Liesjärvi 0.77 1.00 0.87
Pyhä-Häkki 0.95 0.95 0.95
Nuuksio 0.94 0.80 0.86
Seitseminen 0.80 1.00 0.89
Evo 0.87 0.65 0.74
Ruunaa 0.95 0.95 0.95
Salamajärvi 0.94 0.75 0.83
Mean 0.90 0.89 0.88
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Fig. 4. Three 1 × 1 m cells from the test site ‘Evo’, classified as ‘burned’ by the developed classification method but as ‘unburned’ through visual interpretation (a), and three 1 × 1 m cells from the test site ‘Kivimäensalo’ classified as burned both by the developed method and visual interpretation (b). Pre-fire (green) and post-fire (red) point clouds are overlaid. View larger in new window/tab.

Table 4. Proportions of 1 × 1 m cells classified as ‘burned’ and ‘unburned’ for each controlled burning site.
Site Proportion of 1 × 1 m cells
‘Burned’ ‘Unburned’
Kivimäensalo 95% 5%
Liesjärvi 95% 5%
Pyhä-Häkki 92% 8%
Nuuksio 83% 17%
Seitseminen 94% 6%
Evo 51% 49%
Ruunaa 96% 4%
Salamajärvi 71% 29%
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Fig. 5. Spatial distribution of 1 × 1 m cells classified as ‘burned’ and ‘unburned’ for each controlled burning site. Test sites are oriented in a north-south direction. 1 = Kivimäensalo, 2 = Liesjärvi, 3 = Pyhä-Häkki, 4 = Nuuksio, 5 = Seitseminen, 6 = Evo, 7 = Ruunaa, 8 = Salamajärvi.

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Fig. 6. Ground vegetation volumes (including tree stems below 2 m) before and after controlled burnings (a), and total changes (black) with burned (red) and growth (green) volumes (b) at a resolution of 0.1 m. Negative values indicate a decrease and positive values an increase in ground vegetation volume.

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Fig. 7. Variation in ground vegetation volume changes in 1 × 1 m cells classified as ‘burned’ and ‘unburned’ in the controlled burning sites. The line in the box center represents the median value; the box represents the middle 50% of the cell values; 25% of the values fall below the lower quartile (bottom of the box), and 75% fall below the upper quartile (top of the box); whiskers represent minimum and maximum cell values. Outliers (i.e., 0.35% of the observations both above and below the whiskers) are not shown in the figure to enhance the display of data distribution and variability. View larger in new window/tab.