| Great Xing’an Mountains is a fire-prone area comparing with other parts of our country. Forest fire has a direct or indirect influence on soil nutrients dynamics of forest, vegetation regeneration and rehabilitation. In this paper, burned area of Ass.Pinus pumila, Larix gmelinii forest in Huzhong Forestry Bureau of Great Xing’an Mountains were studied to explore the changing rules of soil nutrients, the situation of vegetation regeneration and rehabilitation after fire and soil seed bank spatial distribution of natural Pinus pimila under different burning time(in 1996, in 2010) and fire intensity conditions(mild fire, moderate fire and severe fire).Variance analysis method was used to explore the influences of different burning time and fire intensity conditions on pH value and soil nutrients. Using stratified sampling method and calculating weighted average to show regeneration and rehabilitation situation of vegetation after fire disturbance, and setting quadrat for field investigation of soil seed bank spatial distribution of natural Pinus pumila, the results are as follows:under the same burning time condition, pH value of soil increased with fire intensity increasing. With the time increasing after fire, pH value decreased under the same burning intensity, but pH value in burned area was more than that in unburned area. Under the same fire intensity condition, soil nutrients content of Ass.Pinus pumila, Larix gmelinii forest in burned area was different according to burning time (1996,2010, unburned), but without significant difference (P>0.05).Soil organic matter and total nitrogen level of Ass.Pinus pumila, Larix gmelinii forest was significantly different (P<0.05) under same burning age condition with various fire intensities. There were significant differences (P<0.05) among soil organic matter content in mild, moderate and severe fire conditions, and that of unburned forest also had significant difference (P<0.05) between moderate and severe fire conditions, respectively; for soil nitrogen content, significant differences (P<0.05) were found between condition of unburned and mild fire, condition of moderate and severe fire, separately. pH value, total phosphorus, total potassium and C/N value did not change dramatically (P>0.05) 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. Ass.Pinus pumila, Larix gmelinii forest located in high altitude and soil-depleted area, which was vulnerable to fire disturbance. The regeneration and rehabilitation of vegetation was difficult after fire disturbance; Vegetation regeneration and rehabilitation of Ass. Pinus pumila, Larix gmelinii forest was getting better with recovery time prolonging after fire disturbance; Under different burning time and fire intensity conditions, the recovery level of arbors:mild fire in 1996> mild fire in 2010> moderate fire in 1996> moderate fire in 2010> severe fire in 1996> severe fire in 2010, the regeneration of shrubs also generally accorded with the law; the recovery level of herbs:moderate fire in 2010> severe fire in 2010> mild fire in 2010> severe fire in 1996> moderate fire in 1996>mild fire in 1996. The coverage of shrubs and herbs increased obviously with time prolonging after fire disturbance, but the rehabilitation of arbors was much slowly; The coverage of mosses and lichens increased with fire intensity increasing and shortening time after fire disturbance. In terms of species richness, it increased under the condition of mild fire.Overall, the annual increasing quantity of total vegetation coverage reflected an upward trend, and the variation tendency of coverage increased with fire intensity increasing. After studying soil seed bank spatial distribution of natural Pinus pimila forest, we found that horizontal distribution and vertical distribution of natural Pinus pumila has regularity. As the distance increases from the mother tree, the seed number showed a decreasing trend. Seeds number of the four directions followed decreasing order as South>West>East>North, the difference of horizontal distribution was not significant (P>0.05).The seeds number was drop off gradually from litter layer to the depths of the soil direction, the difference was significant (P<0.05), seeds number in litter layer and 0-5cm soil layer was account for 82.9%. Seed quality survey results showed that 63.2%of the soil seed bank was empty seeds.25.1%of rotting seeds, intact seed only accounted for 11.7%of total. |
