Effects Of Fire Disturbance On The Vegetation And Soil In Typical Steppe Ofyunwu Mountains

The Yunwu Mountains locate in typical steppe of loess plateau, due to less rainfall, soil andwater loss and drought, the restoration of vegetation is difficult. Artificial grasslandconstruction and pasture enclosure were conducted as restoration measures of this region byprevious researchers, and had achieved many positive effects. However, in recent years,because of long-term enclosure and lack of appropriate interference, grassland appeared somedegeneration phenomenon, and causing the coverage of vegetation decreasing, many littersaccumulating."Moderate interference hypothesis" points out that only when the interferenceof medium frequency, the species had the most the chance of survival, species diversity wasthe highest. In this paper, we mainly focus on the effect of fire on the vegetation and soilnutrient characteristics.In present studies, three Stipa bungeana communities were selected as experimentalsamples that burned in2011(one year),2009(three years) and2000(eleven years),respectively, and the nearby sample without burned as control. In September2011, thevegetation characteristics and soil nutrient were determined. The aim of this study was toreveal the characteristics of vegetation and soil physical and chemical properties in differentburning periods. The resuts were as follow:Vegetation character of Stipa bungeana communities:(1) The number of species were37(burned one year),35(burned three years),38(burnedeleven years) and33(without burned), respectively. The number of species increased inburning sample. After fire, the advantage degree of S. bungeana were less than the advantagedegree of Stipa grandis in burned one year and three years, which explained that the dominantspecies S. bungeana was sensitive for fire experiment. The advantage degree of S. bungeanahad been restored in burned eleven years, which explained that fire had a positive effect onthe S. bungeana community in long-term development.(2) Changes of community density, height, coverage, above-ground biomass and theamount of litter. For burned three years, the height of the community reduced, density andabove-ground biomass increased, coverage had no significant change; For burned eleven years, the density and coverage of the community reduced, the above-ground biomassincreased, the height of the community had no significant change. The main reasons were thatthe S. bungeana was perennial grasses, tufted and inhibited the growth of other forbs. Forburned one year, fire had no significant effect on above-ground biomass, and reduced amountof litter significantly.(3) Changes of community diversity. Compare with without burned sample, the diversityindex had no significant change for burned samples.The evenness index decreasedsignificantly in burned one year, and compare with without burned sample, evenness indexhas no significant difference for burned three and eleven years. The abundance index wasincreased in burned one and three years, and the fire had no significant difference for burnedeleven years.Soil physical and chemical properties of S. bungeana community:(1) Affect of fire on soil moisture: The content of soil moisture changed significantly inburned one year, in the surface soil layer0-10cm water content were greater than withoutburned sample,10cm below the soil water content decreased gradually. Three years andeleven years after the fire, the soil moisture had no significant difference with unburningstand.(2) Affect of fire on soil bulk density was as follows: The soil bulk density changedsignificantly in burned three years, compare with witnout burned sample,0-20cm of soilbulk density was less,20-40cm was greater,40-50cm was same. For burned eleven years,soil layers of bulk density were basically same with without burned.(3) Change of soil chemical properties after fire was as follows: SOC, total N, total P andavailable K concentrations were significantly higher at all depths for burned samples thanwithout burned sample. SOC, total N, total P and available K concentrations had nosignificant differences at all depths in burned three years. Total N concentrations weresignificantly high at all depths in burned eleven years. SOC,total P and available Kconcentrations were significantly high at all depths(except0-10cm).For four samples, SOC,total N, total P and available K concentrations were decreasing in soil profile from up to down.Soil pH had no significant differences in burned three years.