Post‐Fire Soil Organic Carbon Dynamics: Decline and Recovery Over Two Decades

Wildfire can significantly alter soil organic carbon (SOC) dynamics in forest ecosystems, with complex temporal patterns following fire events. However, research on post‐fire SOC recovery remains limited, particularly in dry‐warm valley regions that are prone to frequent forest fires. This study, based on field investigations and experimental analyses, focused on severely burned sites in the dry‐warm valley of Anning River Basin, Hengduan Mountainous Region, China, from 1996 to 2021. The space‐for‐time substitution method was employed to reveal the patterns of SOC changes in burned sites at different recovery stages and explore influencing factors on SOC. The results showed that SOC and its components were significantly negatively correlated with soil depth and slope aspect ( p < 0.05) but significantly positively correlated with time since fire ( p < 0.01). Specifically, SOC, readily oxidizable carbon (ROC), non‐labile organic carbon (NLOC), particulate organic carbon (POC), and mineral‐associated organic carbon (MOC) decreased with the increase in soil depth, with higher content on shady slopes compared with sunny slopes for burned sites and unburned sites. Over a 26‐year recovery timeline, SOC and its components in severely burned sites exhibited an initial decline followed by a gradual increase, with the decline commencing approximately five years after the fire. During the first 10 years of natural recovery, SOC, ROC, NLOC, POC, and MOC contents decreased but thereafter started to increase, while POC content began to increase after 20 years of recovery. Soil physicochemical properties, including soil pH and bulk density, were significantly negatively correlated with SOC and its components ( p < 0.01). Soil porosity, clay, fine root biomass, total nitrogen, total phosphorus, and cation exchange capacity exhibited significant positive correlations with SOC and its components ( p < 0.05). ROC, NLOC, POC, and MOC contents were highly positively correlated with SOC content ( p < 0.01). Overall, the findings indicate that SOC loss after severe wildfire can persist for up to a decade, and that full recovery of some SOC components, such as POC, may require over 20 years.