## 2 Materials and Methods  
Wood samples of forest fire trees were collected from burned stands of Norway spruce and Scots pine in an area of 227 hectares in Kalajoki, Western Finland (64\({}^{\circ}\)00\({}^{\prime}\)15.0\({}^{\prime\prime}\) N 24\({}^{\circ}\)08\({}^{\prime}\)09.0\({}^{\prime\prime}\) E), in November 2021, four months after the fire in July 2021. In Kalajoki, flammability was high before the fire. The local temperature was 27 \({}^{\circ}\)C, and the air humidity was 44% on the first day of the fire, 26 July 2021. The wind speed was 3.5 m/s, and in gusts, it was 9-10 m/s. In the beginning, the fire spread 2-3 m/min, and at its highest, the rate of spread was 15-20 m/min. The fire reached the entire area in two and a half days (until 28 July 2021), and in its most intense phases, it spread into forests as a crown fire [33]. Figure 1: Effects of forest fire on the deterioration of softwood timber according to time from harvesting in the northern and western regions of the United States and Canada [16]. The studied stands are presented in Figures 2 and 3. The samples of the reference trees were collected simultaneously from stands located near the fire area in Kalajoki and supplemented with trees in February 2022 from Raahe (64\({}^{\circ}\)23\({}^{\prime}\)36.8\({}^{\prime\prime}\) N 25\({}^{\circ}\)03\({}^{\prime}\)01.8\({}^{\prime\prime}\) E) to obtain comparable reference data in terms of tree age and diameter. The stems of the burned trees and reference trees were cut in the forest into 4 m logs up to a top diameter of about 10 cm, which is close to the commercial minimum diameter of small-diameter logs. Four normal-sized log burned trees (diameter at breast height, DBH, about 25-30 cm) and four small-log burned trees (DBH, about 14-18 cm) of both Norway spruce and Scots pine were selected, and the total number of logs with references was 24 (Table 1). Before the cut, the length of the area damaged by the fire was measured on the burned trees based on the signs visible on the bark in two ways: (1) by considering the entire circumference of the stem, i.e., the shell surface burned, and (2) by considering all clear signs of the effects of the fire on the bark of the stem. From each 4 m log, a block of approximately 60 cm was further cut as the material to be used in physical and mechanical tests. The blocks (total number of 72) represented the butt, middle, and top logs. In the case of spruce, the diameters and lengths of the burned and reference trees were comparable, but the normal-sized log burned trees were younger than the reference trees (Table 2). For pine, the lengths and diameters of the burned and reference trees were comparable, but the burned trees were slightly older than the reference trees. Figure 3: The burned Scots pine stands studied in Kalajoki, Finland, at the time of sample collection in November 2021. Figure 2: The burned Norway spruce stands studied in Kalajoki, Finland, at the time of sample collection in November 2021. Sivty-centimeter blocks were through and through sawn with a band saw in Joensuu in February 2022. A 60 mm thick pitch-centered balk from each block was sawn towards the surface, totaling 72 balks for further tests. If there were visually noticeable differences in the intensity of the burning on different sides of the block, the direction of sawing was set in such a way that the most heavily burned area (the more damaged side) of the stem was placed on one edge of the pitch-centered balk. The slightly burned area (the less damaged side) was placed on the opposite edge of the balk. The sawing direction was set for the reference blocks and the blocks that were burned entirely around the circumference to minimize knots and other defects in the final balks. The balks were stored at room temperature (around 20 \({}^{\circ}\)C) for one week.