Effects of forest fire on soil nutrients of Ass. Pinus pumila-Larix gmelinii forest in Great Xing’an Mountains.

Great Xingan Mountains are a fire-prone area in China. Forest fire has a direct or indirect influence on chemical properties of forest soil. We explored the impacts of different burning time and fire intensity conditions on pH value and soil nutrients in the burned area of Ass. Pinus pumila-Larix gmelinii forest in Huzhong Forestry Bureau of Great Xing’an Mountains using two-factor variance analysis method. The results showed that under the same burning time condition, pH value of soil increased with fire intensity increasing. With the time increasing after fire, pH value decreased at the same burning intensity, but pH value in the burned area was higher than that in the unburned area. Under the same fire intensity condition, soil nutrient contents of Ass. Pinus pumila-Larix gmelinii forest in the burned area varied at different burning time (1996, 2010, unburned), but without significant difference(P0.05). Soil organic matters and total nitrogen level of Ass. Pinus pumila-Larix gmelinii forest were significantly different(P0.05)under the same burning time condition with varying fire intensities. There were significant differences(P0.05)among soil organic matter content in mild, moderate and severe fire conditions, and that of unburned forest also had significant differences(P0.05)between moderate and severe fire conditions, respectively; for soil nitrogen content, significant differences (P0.05)were found between conditions of unburned and mild fire, and between conditions of moderate and severe fire, separately; however, pH value, total phosphorus, total potassium and C/N value had no marked change(P0.05)under different burning time and fire intensity conditions. Ass. Pinus pumila-Larix gmelinii forest suffering fire in 2010 and 1996 did not recover to the previous growth condition without fire disturbance in five and even nineteen years. Our study provides a scientific reference for the quick and efficient rehabilitation of Ass. Pinus pumila-Larix gmelinii forest in Great Xingan Mountains after fire.