## 2 Materials and Methods
Flexural stress (\(\sigma_{\text{f}}\), MPa) and strain (\(\varepsilon_{\text{f}}\), %) were calculated according to standard ISO 178 [37]:  
\[E_{12}=\frac{Pl^{3}}{4 bh^{3}f} \tag{1}\]  
\[\sigma_{\text{b},12}=\frac{3P_{max}l}{2 bh^{2}} \tag{2}\]  
\[\sigma_{\text{f}}=\frac{3P_{appl}l}{2 bh^{2}} \tag{3}\] \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & \multicolumn{3}{c}{**Norway Spruce**} & \multicolumn{3}{c}{**Scots Pine**} \\ \hline
**Wood Material** & **Butt Log** & **Middle Log** & **Top Log** & **Butt Log** & **Middle Log** & **Top Log** \\ \hline Sapwood, heavily burned side & 8 & 12 & 6 & 15 & 6 & 5 \\ Sapwood, slightly burned side & 8 & 12 & 4 & 15 & 6 & 5 \\ Heartwood, burned trees & 20 & 12 & – & 20 & 7 & – \\ Sapwood, reference trees & 12 & 8 & 8 & 16 & 8 & 6 \\ Heartwood, reference trees & 12 & 6 & – & 11 & 4 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The number of samples used for testing air-dry density, modulus of elasticity (MOE), flexural strain, and modulus or rupture (MOR) by species, damage class, radial position, and log type. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Norway Spruce**} & \multicolumn{3}{c}{**Scots Pine**} \\ \hline
**Burned Trees** & **Butt Log** & **Middle Log** & **Top Log** & **Butt Log** & **Middle Log** & **Top Log** \\ \hline Bark thickness, more damaged side & 3.30 & 3.02 & 3.02 & 4.56 & 1.71 & 1.71 \\ Bark thickness, less damaged side & 2.89 & 3.42 & 3.42 & 4.46 & 1.76 & 1.76 \\ Ring width, more damaged side & 2.71 & 2.69 & 2.55 & 2.06 & 1.73 & 1.24 \\ Ring width, less damaged side & 2.80 & 2.75 & 2.53 & 2.06 & 1.75 & 1.26 \\ \hline
**Reference Trees** & **Butt log** & **Middle log** & **Top log** & **Butt log** & **Middle log** & **Top log** \\ \hline Bark thickness, side of maximum & 4.33 & 3.87 & 3.87 & 5.58 & 1.89 & 1.89 \\ Bark thickness, opposite side & 4.19 & 3.93 & 3.93 & 5.42 & 1.73 & 1.73 \\ Ring width, side of maximum bark & 1.88 & 2.12 & 2.50 & 1.68 & 1.84 & 1.80 \\ Ring width, opposite side & 1.73 & 1.90 & 2.40 & 1.70 & 1.81 & 2.13 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mean bark thickness (mm) and annual ring width (mm) on the more damaged and less damaged sides of forest fire trees and on the two opposite sides of reference trees by species and vertical log location in the balks after being sawn. Middle logs and top logs have common means of bark thickness. \[\epsilon_{\rm f}=\frac{600 fh}{l^{2}} \tag{4}\]  
where \(P\) is the difference between the higher load and the lower load (N); \(l\) is the span (mm); \(b\) is the specimen width (mm); \(h\) is the specimen height (mm); \(f\) is the deflection (mm); \(P_{max}\) is the maximum load (N); and \(P_{appl}\) is the applied load (N). Stored energy (\(U\), MJ/m\({}^{3}\)) at maximum stress was calculated using the following formula:  
\[U=\int_{0}^{\epsilon_{max}}\sigma_{f}d\epsilon \tag{5}\]  
where \(\epsilon_{max}\) is the strain at maximum stress. The moisture content of the samples was determined after each mechanical test and oven drying, and it was calculated on a dry weight basis, according to ISO standard 13061-1 [38]. The samples were weighed, dried at 103 \({}^{\circ}\)C for 24 h, and weighed dry. On average, the moisture content was 9.9% in pine samples and 10.7% in spruce samples. An approximate adjustment of the MOE and MOR to 12% moisture content was performed according to the given ISO standard. HB was determined under air-dry conditions following standard EN 1534 [39]. A force of 1 kN was applied to a steel ball with a contact radius of 10 mm. In the test, defect-free spots from the outer edge of the sample were chosen. \[HB=\frac{2F}{\pi D\left(D-\sqrt{D^{2}-d^{2}}\right)} \tag{6}\]  
\[d=2\sqrt{\left(10h-h^{2}\right)} \tag{7}\]  
where _HB_ is the Brinell hardness (N/mm\({}^{2}\)); \(F\) is the maximum load force (N); \(D\) is the diameter of the ball (mm); \(d\) is the diameter of the residual indentation (mm); and \(h\) is the depth of the residual indentation (mm).