Properties and Depth-Related Changes in Moderately Fire-Affected Pedunculate Oak Wood

Wildfires significantly affect wood properties and usability, yet their impact on hardwood species remains insufficiently understood. This study presents an exploratory characterization of moderately fire-affected pedunculate oak (Quercus robur L.) wood, combining physical, mechanical, chemical, and thermal analyses to evaluate depth-related changes within outer stem zones. Samples were collected from bark and from wood originating approximately 1 cm and 1–2 cm beneath the cambial region to evaluate radial variation associated with moderate surface fire exposure. The oven-dry density of fire-affected wood reached 720 kg·m−3, corresponding to values marginally below the literature reference ranges reported for unaffected oak wood. Bending strength decreased to 85.56 MPa, while compressive strength remained within or marginally above the literature reference (71.16 MPa), and Brinell hardness (42.75 MPa) stayed within the typical range for oak. Chemical and elemental analyses revealed degradation of polysaccharides and carbon enrichment in surface layers. FTIR and DSC analyses suggested partial hemicellulose degradation, structural modification of cellulose, and reduced thermal reactivity in outer stem regions. Despite these changes, the higher heating value (19.09–19.56 MJ·kg−1) remained within the literature reference ranges reported for oak wood. The results suggest that under moderate surface fire conditions, fire-induced changes were primarily concentrated in outer stem layers, while inner wood retained properties comparable to the literature reference values for unaffected oak wood. These findings indicate that moderately fire-affected oak wood may remain suitable for selected material or energy-related applications following appropriate quality assessment and removal of thermally altered surface zones.