Background Forest fires can cause severe disturbances to forest ecosystems and are not easily recovered in the short term. To investigate the short-term effects of fires of different intensities on soil chemistry at different depths in different forest stands, and to provide a reference for the restoration of forest ecosystem functions after fires and the use of fire to promote stand regeneration, it is important to study the changes in soil chemistry in the burned area in the short term (within 1 week) of recovery.

Methods Three 20 m×20 m sample plots were set up in coniferous broad-leaved mixed and bamboo forests in Jinyun Mountain, which were lightly, moderately and severely burned areas and one unburned sample plot respectively. Soil sampling was carried out at different depths (0-10 and 10-20 cm) in the set plots, and chemical indicators such as soil pH, cation exchange capacity (CEC), organic matter content and soil available nutrient content were determined. Significant differences and trends in soil chemical properties between different stands and different intensities of fire were investigated by descriptive statistical analysis, one-way ANOVA and Fisher LSD test.

Results 1) Soil pH and available potassium content showed an increasing trend with increasing fire intensity in both stands, while soil organic matter and total phosphorus content showed a decreasing trend with increasing fire intensity, while total nitrogen, available nitrogen, available phosphorus content and cation exchange capacity (CEC) did not change significantly with increasing fire intensity. 2) At the same fire intensity, there were significant differences (P < 0.05) in soil organic matter, total N, available nitrogen, available phosphorus, available potassium and CEC between the two stands, while pH and total phosphorus were not significantly different. 3) Fire had a significant effect on the chemical properties of the surface soil, and the changes in soil pH, CEC and organic matter, total N, total phosphorus, available phosphorus, available potassium and available nitrogen contents reached significant levels under the interaction of different stand types and different fire intensities.

Conclusions Fire has a significant impact on the soil chemistry of different forest stands, especially high-intensity fire, which significantly reduces the soil nutrient content at different soil depths, thus post-disaster revegetation work should focus on soil nutrient restoration and fertility improvement, with site-specific restoration measures tailored to the specific changes of different forest stands.