ObjectiveBased on the analysis of nutrient content, correlation and main nutrient ratio under different fire intensities in Beijing Pinggu District, the effects of forest fire on soil chemical properties of Pinus tabuliformis forest in Pinggu District, Beijing were studied. The reconfiguration of soil nutrient resources and their spatial differences provided a theoretical reference for vegetation restoration and management in burned areas.

MethodAccording to the fire intensity, the forest areas with light intensity (L), moderate fire (M) and heavy fire (H) were divided into research sites, and adjacent unfired forest land (C) was selected as control. The soil nutrient content of 0-10 cm, 10-20 cm, 20-30 cm after 0.5 year fire was investigated and determined. The analysis method used single factor, two-way ANOVA, correlation analysis, and LSD post-test to research soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), total potassium (TK), available potassium (AK), total phosphorus (TP), available phosphorus (AP) content, carbon to nitrogen ratio (C/N), nitrogen to phosphorus ratio (N/P) under different fire effects.

Result(1) In the same soil layer under different fire intensities, the forest fire had no significant effect on TN (P>0.05), and had significant effect on TP (P < 0.05), and had extremely significant influence on all other indexes (P < 0.01). Under varied soil layers, the impact of forest fire on TK was not significant, and the impact on all other indexes was extremely significant (P < 0.01); all the soil nutrients were vertically distributed in the soil; (2) The burned fire made the soil SOC, TN, AN content showed a significant downward trend, and the TP, AP, TK, AK content showed an overall increase trend; (3) The slight over-fire caused the soil NH₄⁺-N and NO₃^--N content to decrease; the moderate over-fire caused the soil surface NH₄⁺-N content to increase, the NO₃^--N content to decrease, the lower layer NH₄⁺-N content to decrease, and NO₃^--N content increased; severe over-fire increased the content of NH₄⁺-N in the soil and the content of NO₃^--N in the soil surface, and the content of NO₃^--N in the lower layer decreased. (4) The correlations between the main elements C, N and P were extremely significant (P < 0.01), and the correlations between TK and other soil nutrients were not obvious (P>0.05). (5) The C/N ratio decreased slightly after a mild to moderate over-fire, and rised after a severe over-fire. N/P decreased after over-fire, and the depth of soil layer increased before the over-fire, and vice versa after the over-fire, with the depth of soil layer decreased.

ConclusionForest fire has significant effects on soil chemical properties, and same fire intensity has varied effects on the soil chemical properties in different soil layers. Different fire intensities can cause significant changes in each soil chemical properties, and have important effects on the reconfiguration of soil nutrient resource.