## 4 Discussion  
Due to the global increase in forest fires during the 2000s, the direct and indirect damage that deteriorates raw wood materials has become more frequent in tree stock, resulting in challenges in the allocation of salvaged wood to the roundwood market and profitable utilization in forest industries [3; 16; 24]. The risk increase is not only commonly traced to climate change, regional droughs, and heat loads but also to human behavior and working with machines in nature and the built environment [5; 6; 7; 8; 9; 10]. The data from this study represent a typical forest fire in Finland in terms of vastness, intensity, and season. According to our visual observations in the studied stands, the mortality of trees and fire patterns were consistent with previous findings in practical forestry. Based on the crown's status, most spruces were judged as dead or dying, whereas almost all pines remained living. The vertical length of the fire effect, starting from the base of the tree, was relatively short, with values of 9% for spruce and 12% for pine when the bark was required to have burned for the entire circumference, but the values were as high as 39% for spruce and 20% for pine when any signs of the fire effect were considered on bark. In a study on two forest stands in northern Europe, 20% of Scots pine trees survived in a heavy forest fire, with the proportion reaching 50% for trees with a DBH of 20 cm or more if the fire remained at a low height and below the living crown, whereas 99% of Norway spruce trees and 98% of broadleaved trees died [42]. Our results show that fire damage had only minor or no significant effects on the wood properties studied, evident only in sapwood. The changes in wood properties were more substantial in spruce than in pine, presumably because of the thinner bark, especially in the lower parts of the trees, that protects wood less from deterioration, and the longer crown that accelerates the spread of fire in the middle and top parts of trees [12; 15; 23; 42]. In the mechanical tests, the physical properties and position of a tree explained most of the variation in wood properties. As expected, wood density proved to be the strongest predictor by far, followed by height location and the radial position. The fire damage class of trees at respective heights was identified as a significant factor only for the MOR in Scots pine (decrease) and for HB in Norway spruce (increase). In general, the models obtained were more accurate in predicting the mechanical properties of Scots pine. In Norway spruce, the bias and variation by random effects were relatively high, and the R\({}^{2}\) values were relatively low. This indicates that only some of the essential factors in modeling the bending properties of spruce are recognized. In flexural strain at maximum force, no clear differences were detected between the burned and the reference trees. In spruce logs, flexural strain decreased towards the top, but in pine, the lowest values were observed in the middle logs. In studies on Brazilian loblolly pine and Portuguese maritime pine, where the forest fire intensities were heavier than in our study, more substantial effects on wood properties were observed. The consumption of the full crown of loblolly pine by fire led to a decrease in the MOE and MOR in static bending by 17% and 12%, respectively, in addition to decreases in ultimate stress and stress at the proportional limit in parallel compression by 19% and 34% and the resilience coefficient for toughness by 17% [20]. Similar reductions in these properties have been observed for maritime pine, albeit associated with reductions \begin{table}
\begin{tabular}{l l r r} \hline
**Fire Damage Class** & **Radial Position** & **Norway Spruce** & **Scots Pine** \\ \hline More damaged side & Sapwood & 4.61 & 5.29 \\ More damaged side & Heartwood & 1.98 & 3.66 \\ Less damaged side & Sapwood & 4.77 & 4.77 \\ Less damaged side & Heartwood & 1.53 & 1.74 \\ \hline \end{tabular}
\end{table}