Abstract: Taking the burnt area in the northern forest area in Inner Mongolia Greater Khingan Range as the study area,soil chemical properties of the different fire years (2003 and 2012)and fire severity (mild and severe)as the study objects.The results show that in 1 year after the fire,compared with the control sample plots and mild fire severity,organic carbon and available phosphorus content in soil increased significantly,pH value,total phosphorus,available nitrogen content increased,but the difference was not significant;soil total nitrogen content decreased significantly,the total potassium and available potassium content decreased too,but the difference is not significant.After severe burn,pH value,available nitrogen and available phosphorus content increased significantly,organic carbon,total nitrogen and available potassium content reduced significantly,the total phosphorus and total potassium content reduced,but the difference was not significant.In 10 years after the fire,compared to the control plots,only organic carbon and total nitrogen content in severe burned area decreased significantly,other indicators of soil chemical properties also decreased,but not significantly.

Key words: forest fire, fire intensity, soil chemical properties, Larix gmelini forest