The Effect Of Forest Fire On Soil Environment

The effects of fire on ecosystems are complex, ranging from the reduction or elimination of aboveground biomass to impacts on belowground physical, chemical and microbial mediated processes and fine root. The effect of fire on soil is either beneficial or deleterious, which mainly depends on fire intensity. Severe fires can often cause changes in successional rates and soil hydrologic functions, degradation of soil physical properties, alter C:N ratios, and result in subsequent nutrient loss through accelerated erosion, leaching or denitrification, and alterations in microbial populations and associated process can occur.The paper is mainly focused on the effects of fires on physical, chemical properties, microbial and fine root of soil.The effects of forest fires on soil moisture content, separate coefficient, porosity, water-retaining capacity, organic matter, available N, available Ca, fungi and fine root significantly varied between the years after burning. The effects of forest fires on soil separate coefficients, porosity, saturated water-retaining capacity, available Mg, fine root significantly varied between the fire intensity.The effects of different fire intensities on soil moisture content had similar laws. Low and moderate intensity fire had no or little effects on soil unit weight and porosity, which was different from that on separate coefficient. The effects of high intensity fires on soil unit weight, porosity and separate coefficient were significant. The soil water-retaining capacity at low and moderate intensity burnt site returned to the level before burning faster than at high intensity burnt site. After yearly burning, soil moisture content, porosity, separate coefficient, capillary and field moisture capacity increased, however, soil saturated water retaining capacity and unit weight decreased. High intensity fire can significantly destroyed the soil structure. After low and moderate intensity fire had little effect on degree of soil solidity and porosity, which was different from that on soil capability of preservation of water and fertilizer. The changes of soil physical properties at burnt site were very great following rainfall.Fire raised soil pH, but the soil pH after low and moderate intensity fires returned to the lever before burning faster than after high intensity fires.The changes of soil organic matter and pH were similar after fires. Soil N decreased within 6 years following burning and increase after 6 years after fires. Generally, soil total P increases after burning, but the soil total P after moderate and high intensity fires returned to level before burning slower than after low intensity fires, which is consistent with soil available N. The changes of soil K, Mg are great after burning. Soil Ca leaches easily after fire. Then soil Ca can returned to level before burning gradually.Soil pH, available N and Mg increase on burnt sites following the first rainfall, however, soil organic matter, total N, total P, K and Ca decrease.The yearly burning raised soil pll, available N and K and reduced soil organic mater, total N, total P, available P and Ca.High intensity fires can significantly kill soil microorganism. After moderate intensity fires, the amounts of bacteria, fungi and actinomycetes increased significantly. After low intensity fires , those changed insignificantly . At the yearly burnt si tes, the amounts of bacteria declined, the amounts of fungi and actinomycetes increased significantly.The fine root biomass increased after fires, which was the most significant after high intensity fires, and the least significant after moderate intensity fires. The fine root biomass increased following a rainfall after any fire.