## 1 Introduction  
Wildfires and resultant forest disturbances have become common globally, and their scale and severity have increased since the beginning of the 2000s [1, 2, 3, 4]. This has mostly been attributed to climate change and sudden regional weather phenomena, such as droughts and heat loads during summer seasons, but partly due to human behavior and machine work activities in nature and the built environment [5, 6, 7, 8, 9, 10]. Most wildfires, with respect to the overwhelmingly largest areas, have been in the Russian Federation, Canada, the U.S. West, Australia, and Mediterranean countries [2]. In Finland, the forest fire incidence level is very low [3]. For example, 470 hectares of land damaged by forest fires was reported in 2017, and the benchmark of over 1000 hectares was destroyed only in 2006 [11]. There is a short span of seasons when forests are vulnerable to fire, ranging from May to September, with June and July remaining as the peak periods; relatively cool and rainy summers, high forest and second-home road densities, and efficient aerial fire control and prevention have contributed to the low incidence rate [12]. However,with climate change causing drought periods during summer, more trees suffering and drying from bark beetle damage, and the practice of leaving standing and wind-fallen trees for biodiversity management after final harvesting, vulnerability to fires is predicted to increase in the coming decades [13]. The forest stand structure and site, tree species, and fire intensity largely determine the consequences for trees and their probability of surviving a forest fire [7; 14; 15]. A dense stand, dry site, small diameter, thin bark, and large crown have been observed to lead to a high mortality of trees [5; 6; 7; 8; 9; 10]. Owing to fire, drying that results in checking may occur in sapwood if the bark deteriorates first; additionally, notable charring and grayish discoloration occur because of char and soot, but the heartwood should remain essentially unchanged [6; 8; 12; 15; 16]. In wood material, drying starts slowly due to direct heating at a temperature as low as 20-100 \({}^{\circ}\)C; thereafter, the rate increases, and the intensity multiplies [17]. Chemical transformation affecting the physico-mechanical properties starts at 50-100 \({}^{\circ}\)C with the decomposition of certain extractives, and the major changes begin at 160-180 \({}^{\circ}\)C with the decomposition of hemicelluloses and above 250 \({}^{\circ}\)C with lignin [18]. Physical changes start above 150 \({}^{\circ}\)C with a decrease in the equilibrium moisture content and a reduction in hygroscopicity, absorbability, and surface activity; these changes continue and later cause an increase in dimensional stability, color changes, and a decrease in some mechanical properties [17; 18; 19]. Few studies have considered the effects of forest fires on the physico-mechanical properties of wood or wood products. No effects on density or shrinkage properties have been found in the wood of loblolly pine in Brazil [20] or maritime pine in Portugal [21]. However, significant reductions in the bending properties (the modulus of rupture, MOR, and the modulus of elasticity, MOE), compression strength, and toughness values have been observed for loblolly pine when flames consume the total crown, and the compression strength has been shown to be reduced when the crown is partially consumed [20]. Maritime pine wood showed a similar response in a severe forest fire, but the reduction in the properties was traced more to biological degradation due to prolonged wood harvesting than the fire [21]. Fire effects on physico-mechanical properties and chemical composition do not cause sufficient chemical degradation or strength reduction, which would cause the rejection of these woods for commodity uses of mechanical wood processing; however, in structural uses, caution should be taken for wood from trees that have been fully or partially consumed by fire.