Evaluation of soil degradation caused by wildfire through integration of remote sensing soil quality indices and micromorphological analyses

Soil, as a vital component of terrestrial ecosystems, plays a key role in environmental sustainability, biomass production, and food security. This study investigates the effects of wildfire on soil quality (SQ) and soil degradation (SD) in a part of Yunnan Province, China. The study area comprised agricultural lands, grasslands, and wildfire-affected forests. Burned areas were identified using multi-spectral Sentinel-2 imagery, and soil samples were collected from the 0–30 cm surface layer. After measuring the physical and chemical properties of the soils, SQ was assessed using the Total Data Set (TDS) and Minimum Data Set (MDS) approaches, as well as linear (IQI) and non-linear (NQI) indices. SD was quantified by comparing the soil quality indices (SQIs) of disturbed sites with those of grasslands, which served as reference conditions. Results indicated that grassland soils maintained the highest quality and structural stability, whereas agricultural soils exhibited moderate reductions in quality due to compaction, decreased silt and clay content, and losses in soil organic carbon (SOC). Wildfire-affected forest soils showed severe reductions in quality and markedly elevated SD, reflecting extensive structural and biological damage. Micromorphological observations revealed that soil aggregates in burned areas were dense and poorly cohesive, and fine roots were carbonized, leading to impaired water retention, nutrient cycling, and microbial habitat availability. In contrast, soils and roots from agricultural lands retained relatively intact structures and continued soil functionality. These findings demonstrate that the integration of remote sensing, quantitative SQ assessment, and micromorphological evidence provides a comprehensive framework for evaluating the effects of wildfire on SD and offers valuable insights for sustainable ecosystem management and soil restoration planning.