Contrasting burn legacies in Eucalypt forest soils of different textures in Southwest Australia

Abstract Purpose We sought to understand potential legacy impacts of wildfire on loamy soils from karri ( Eucalyptus diversicolor ) forest compared to sandy soils from jarrah ( Eucalyptus marginata ) forests in southwest Australia. Methods We sampled soils (0–5 and 5–10 cm) from forest burned five years previously at high and low severity as well as unburnt forest. Replicate plots for each forest type and burn severity were analysed for particle size analysis (PSA), total carbon (%C), total nitrogen (%N), organic and inorganic phosphorus, nitrate, ammonium, pH, and stable isotope composition (δ 13 C, δ 15 N). Results Loamy soils showed clear evidence of effects of fire on soil properties regardless of fire severity after five years, but these effects were less pronounced in sandy soils. In loamy soils, clay content, % C and %N were significantly lower in burnt sites compared to unburnt sites. Conversely, sandy soils only recorded an increase in inorganic nitrogen and a higher pH in burnt sites. Both loamy and sandy soils burned at high severity had more enriched δ 13 C signatures compared to other sites. Additionally, loamy soils burned at high severity also had more enriched δ 15 N signatures. Conclusion Different legacy effects of fire on the two soil types are likely associated with dissimilarities in soil texture. A higher percentage of clay in unburnt loamy soils contributes to greater retention of soil C and N in burnt soils. This study emphasises the importance of soil texture in carbon and nutrient retention, suggesting that soils in karri forests, while fire-prone, may be more “carbon-sensitive to fire” than previously believed.