The Evolution Of Soil Habitat Quality After Severe Fire Disturbance In The Greater Xing’an Mountains

Severe forest fires lead to the destruction of large areas of forest resources, cased economic losses at the same time, also have serious influence on the quality of forest soil. In this paper, based on the Greater Xing’an Mountains catastrophic fire in 2010 as the research background, through the investigation and analysis of the forest soil habitat factors in three years, deeply studied the evolutions of soil habitat factors, soil habitat quality and habitat obstacle factors of base soil by severe forest fires, and their relationship with vegetation restoration to provide theoretical basis for the recovery of severe burns forest ecological system. Specific research results are as follows:First, the evolution of soil habitat factors of forest soil by severe burns:The litter layer almost disappeared under severe fire, and is not restored during the study period. The values of soil mean temperature at noon, soil density, exchangeable ammonium salt ions, soil ammonium nitrogen, nitrate nitrogen, available phosphate and soil pH were elevated significantly (p<0.01), which were 203%,22.5%,52.2%,482%,470%,232% and 14.2% respectively higher than those in the control area. The values of soil moisture content, waterstable aggregate, soil organic matter, soil microbial biomass carbon were decreased remarkably (p<0.01), that is 33.60%、10.0%、23.6%、69.24% lower than the control area respectively. During three years of recovery, the values of soil mean temperature at noon, waterstable aggregate, soil organic matter, exchangeable ammonium salt ions, soil ammonium nitrogen and soil pH were decreased year by year, and the values were declined by 39.3%,41.6%,18.4%,22.1%, 73.0% and 7.59% respectively. However, the values are still significant higher or lower than the control (p<0.01).The values of soil moisture content, soil density, soil nitrate nitrogen, soil microbial biomass carbon were increased by years, increased by 32.90%、23.4%、74.4% and 111% respectively. However, the values are still significant higher or lower than the control (p<0.01).The values of soil available phosphate were raised first and fell later, and still significant higher than the control (p<0.01).Second, the evolution of soil habitat quality of forest soil by severe burns:1) Severe forest fires significantly impacted on several soil habitat factors (membership value of vegetation support), the influences due to severe fires on some of factors such as the soil temperature at noon, soil moisture, soil ammonium nitrogen, waterstable aggregate, organic matter and microbial biomass carbon have negative impact on vegetation growth; the changes of other habitat factors such as litter layer, exchangeable base ions, nitrate nitrogen, available phosphate, soil pH and soil density by severe fires have positive impact on vegetation growth. After three years of recovery, the vegetation growth support from habitat factors such as soil temperature, soil moisture, soil ammonium nitrogen and microbial biomass gradually restored, but the support from other habitat indexes such as waterstable aggregate and organic matter continued to decline.2) This study applied three kinds of method to calculate soil habitat quality index (SQI). The results showed that, no matter what kind of analysis object, three kinds of evaluation results showed same evolution trend, the soil habitat quality index increased gradually over time, and also the vegetation growth support. Compared the method of SQI1 and SQI2, SQI3 calculation results was smaller, because the improved weight synthesis method (SQI3) highlighted the extreme actions of the limiting factors in evaluation.3) In severe burns, noon temperature, soil moisture content, ammonium nitrogen, exchangeable salt and soil microbial biomass carbon were significantly correlated (p<0.05), or extremely significant correlated (p<0.01) with vegetation restoration of that year and later. Soil density, waterstable aggregate, organic matter and other factors were not have significant correlation to the type of vegetation recovery during all years, but on the whole, they still have great influence on the vegetation restoration.4) In severe burns, soil habitat quality indexes have significant correlation with vegetation restoration situation, and have the biggest correlation coefficient with the vegetation restoration of trees, this shows that soil habitat quality plays a very positive role in promoting in vegetation restoration, especially for trees.Third, the evolution of soil habitat obstacle factor of forest soil by severe burns:1) In the natural state, litter thickness and moderate acidity constitutes the important obstacle factors, which affected vegetation updates, growth and sustain. In the burned area, soil temperature after fire, soil moisture content became the most important obstacle factors, seriously affected the renewal, growth and maintain of vegetation within the burned area. Although the toxicity of ammonium nitrogen affected by forest fires was appeared, but have less influence on the vegetation.2) This study applied two kinds of method to calculate soil habitat obstacle index (SOI). The results showed that, no matter what kind of method, the evaluation results calculated by the method of SOI1 and SOI2 showed same evolution trend that is, the soil habitat obstacle index increased gradually over time, and the soil habitat obstacle index of the burned area was significant higher than the control by 2013, the obstructive influence by fire was reduced. Compared the method of SOI1, SQI2 calculation results was smaller, because the superposition index method based on maximum limit factor (SOI2) highlighted the extreme actions of the maximum limit factors in evaluation.3) In severe burns, vegetation update obstacle and acid obstacle were not significant correlated with vegetation restoration (p>0.05), showed less effect on the recovery of vegetation. Vegetation recovery was significantly correlated (p<0.05), or extremely significant correlated (p<0.01) with high temperature obstacle, drought obstacle and ammonium nitrogen poisoning obstacle factors, showed more influence on the recovery of vegetation 4) In severe burns, the evaluation results calculated by the SOI1 and SOI2 were significant positively correlated (p<0.05), or extremely significant correlated (p<0.01) with vegetation restoration of that year. That means the low value of SOI (more obstacle), the worse of vegetation restoration; the high value of SOI (less obstacle), the better of vegetation restoration. The recovery of vegetation was also significant positively correlated (p<0.05), or extremely significant correlated (p<0.01) with SOI of former years, showed that soil comprehensive obstacle index which integrated by various obstacle factors, had long influence on vegetation restoration.