Does wildfire severity reduce soil multifunctionality in the short-term? A matter of depth

Abstract

High-severity wildfires can alter soil properties through direct heat transfer and post-fire processes, yet soil has a high capacity to buffer these changes with depth. In this study, we assessed the short-term (three months post-fire) effects of a severe wildfire on soil functions in a Pinus sylvestris L. forest in Spain. Soil samples were collected at two depths (0–5 cm, 5–10 cm) from unburnt areas, areas burnt at low severity (intact canopies), and areas burnt at high severity (completely scorched canopies). High-severity plots were further categorized by slope (moderate/steep) to determine the potential synergistic effects of fire severity and slope. By measuring 24 soil indicators, we assessed key soil functions (e.g., carbon sequestration, soil fertility, nutrient cycling) and calculated the Effective Multifunctionality index (EMi) to capture the overall soil performance. Our results revealed that: (i) most soil functions drastically declined in the topsoil of burnt plots, but not so in the subsoil; (ii) fire reshaped the vertical stratification of soil indicators; (iii) no significant synergistic interactions were observed between high fire severity and steep slopes; (iv) the EMi, primarily driven by carbon sequestration, was significantly reduced by fire severity in the topsoil; (v) subsoil remained largely unaffected by fire. These findings underscore the short-term resilience of subsoil processes to high-severity wildfires, and highlight the importance of distinguishing aboveground fire severity from soil impacts. They also emphasize the need for targeted post-fire management strategies to support soil recovery and sustain ecosystem functionality.