Fire disturbance drives depth-dependent soil organic carbon loss and recovery in a cold temperate forest: interactions with land-use transitions and stand structure

Background Wildfire is a primary disturbance controlling soil organic carbon density (SOCD) in cold temperate forests. However, depth-dependent fire effects are rarely evaluated together with land-use transitions and forest stand structure within a single process framework, limiting fire–carbon management in northern forests. Methods In Yakeshi City, western Greater Khingan Mountains, China, we integrated fire records (2000–2023), multi-temporal land use/cover data, 91 soil profiles (0–100 cm), remote-sensing stand classification, and plot surveys. Fire intensity × recovery-time effects were tested using two-way ANOVA. Carbon-loss rates were compared across fire intensities and frequencies. Land-use transition effects on 0–30 cm SOCD and stand-structure controls were quantified using ANOVA and generalized linear models (GLMs). Results Fire was the strongest near-surface carbon-loss process. Fire intensity, recovery time, and their interaction significantly affected stratified SOCD ( P < 0.05). Severe fires caused the largest losses, mainly in 0–40 cm soils. One year after fire, 0–100 cm SOCD declined by approximately 27.5%; after 5 and 10 years it recovered to approximately 87.2% and 94.9% of pre-fire levels, yet severe-burn sites remained approximately 8.7% below unburned references after a decade. Single-fire 0–100 cm loss rates ranged from 13.8% to 41.3% and increased with intensity; sites burned ≥ 3 times lost approximately 35.7%. Forest-to-cropland, forest-to-grassland, and forest-to-unused-land transitions reduced 0–30 cm SOCD by 34.8%, 22.7%, and 17.4%, whereas cropland-to-forest conversion increased SOCD by 12.8%. Larix gmelinii had the highest 0–100 cm SOCD (4.21 kg m⁻²), followed by Pinus sylvestris var. mongolica (3.83 kg m⁻²). GLMs showed that dominant species, stand density, and canopy closure significantly regulated SOCD; a 10% increase in canopy closure was associated with + 1.09 kg m⁻² in 0–100 cm SOCD. Conclusions In this cold temperate forest landscape, fire attributes shape the depth and persistence of SOCD loss and recovery, while land-use transitions and stand structure modify carbon baselines and within-forest retention. Reducing high-severity short-interval reburns, limiting forest conversion, and maintaining structurally stable coniferous stands are process-consistent priorities for soil carbon conservation, within the constraints of the chronosequence sample.