Postfire management actions are used to mitigate damage caused by wildfires. Salvage logging, often employed to restore ecosystem functions in burnt stands, plays an essential role in reducing economic losses and the burn severity of future wildfires. However, its ecological implications for soil functionality still need to be understood, especially in the Mediterranean basin, which is prone to erosion and desertification. This study aimed to investigate the effects of fire on (i) soil organic matter (SOM) quality and composition using differential scanning calorimetry-thermogravimetry (DSC-TG) and solid-state nuclear magnetic resonance (C-13 CPMAS NMR) and (ii) phosphorus (P) forms using solid-state( 31) P NMR spectroscopy in a wildfire that affected 3200 ha in southeastern Spain in July 2017. One year after the fire, we monitored four Pinus halepensis Mill. stand categories based on soil burn severity (SBS): unburnt, low SBS, high SBS and high SBS areas with salvage logging (n=36, nine plots per SBS level). We collected soil samples and analysed soil pH, SOM content and SOM quality, along with biological activity indicators (carbon biomass, basal respiration, beta-glucosidase, phosphatase activities) and P forms. We ran ANOVA statistical tests to identify significant differences in soil properties among SBS levels. We also established general linear regressions of thermo-recalcitrance values and aromaticity with biological soil quality indices to compare both techniques for detecting changes in SOM quality and composition. The results indicated that fire increased soil pH (up to 0.3), particularly in the plots with higher SBS levels. SOM decreased significantly with increasing SBS level (down to < 5 % at the high SBS level), with a shift from labile compounds (carbohydrates) to more recalcitrant ones (aromatics). Organic P forms were depleted, while orthophosphate levels rose, increasing the risk of irreversible fixation. This study also highlights that DSC-TG is a cost-effective technique for assessing SOM quality changes. Understanding these effects is essential for developing policies to conserve and restore fire- affected areas and to promote practices that enhance soil functionality and resilience.

Burn severity maps are typically generated using spectral indices and used in classifying the spatial distribution of damage caused by fires. In densely vegetated forests, even when overstory crowns are severely affected by the high-intensity fire, the topsoil may not experience high temperatures which makes spectral indices inadequate for assessing soil burn severity. On the other hand, field observations of soil burn severity can be subjective. For this reason, horizon-based soil sampling and extensive soil testing (physical, hydrological, chemical, mineralogical, and mechanical properties) were conducted in this study. Statistical tests have been employed to identify the most representative soil parameters of soil burn severity in the area. The remote sensing data (differential spectral indices and land surface temperature), field observations, and site-specific burned soil data were combined through weighted overlay analysis in the Geographical Information System (GIS). Accordingly, an improved soil burn severity map for the area affected by a forest fire in Kavaklidere, Mugla, Turkiye was produced to show the post-fire soil erodibility potential. The findings of this study indicated that the effect of fire on soil properties was limited to the upper 0-4 cm of the soil profile with surface temperatures reaching a maximum of 300 degrees C for the high burn severity. The liquid limit, shear strength, organic matter, water repellency, and mean grain size were determined to be promising parameters to represent the soil burn severity. The map produced using the novel approach outperformed conventional burn severity maps. In addition, the high soil burn severity class can serve as a parameter to indicate erosion susceptibility after a wildfire.