Research On The Influence Of Thinning On Typical Forest Of Beijing Xishan Forest Farm

The typical Pinus tabuliformis and Robinia pseudoacacia forests were selected in Beijing Xishan Forest Farm.Thinning treatment were conducted with different intensities,unthinning(0%,CK),low intensity(15%,L),moderate intensity(35%,M),and high intensity(50%,H).Based on the field investigation,the fuel loading and vertical distribution characteristics of different thinning stands were studied.By using Rothermel fire model,the potential fire behaviors of different thinning stands were analyzed.The effects of different thinning intensity on understory vegetation Biological diversity and carbon stocks.The results indicated that:(1)The load of surface fuel in Pinus tabuliformis forest increased with the increase of thinning intensity,that was,H>M>L>CK.Shrub layer combustible load the most,9,1101kg/m2.The compressible load of the herbaceous layer increases with the enhancement of the thinning intensity.1,10 and 100 h delayed combustible load reduction.The variance analysis showed that the effects of different thinning intensities on the loading of different surface fuels were different(P<0.05).The total amount of surface fuel load of Robinia pseudoacacia forest increased with the decrease of leaf cutting intensity,and the variation law of soil cutting intensity was M>H>CK>L.100h delay combustible load in the surface of the proportion of combustible load the largest.The proportion of combustible load in herbaceous layer and shrub layer increased with the enhancement of thinning intensity.The results of variance analysis showed that the different cutting intensity had a significant effect on the loading of different surface fuels(P<0.05).(2)The vertical distribution of combustible in Pinus tabuliformis was the highest in 0-2m layer,which was 14.3957 kg/m2.Canopy combustible load is mainly distributed in the 4-5m layer.With the increase in canopy height,the load on combustibles is reduced.Robinia pseudoacacia is vertically distributed in the 0-2m layer of the largest load,6.2290 kg/m2.The canopy distribution of Robinia pseudoacacia forest was higher than that of Pinus tabuliformis forest,and the load of canopy combustible was up to 6-8m layer.After a different intensity of reduction in the amount of fuel load gradually reduced.(3)The change rule of potential fire behavior of forests surface with the thinning intensity was:L>CK>M>H.Pinus tabuliformis forest after low-intensity thinning(L),the surface of the potential fire behavior indicators but a slight increase.In the medium-intensity thinning(M),the potential fire behavior indicators have decreased significantly.After high-intensity thinning(H),the potential fire behavior of the non-fertile stands(CK)decreased by more than 90%.After high-intensity thinning(H),the fire spread rate and fire spread height of Robinia pseudoacacia forest are close to zero.(4)The changes of the biodiversity of understory vegetation were M>H>L>CK according to the species richness and evenness index after the different intensities of Pinus tabuliformis and Robinia pseudoacacia forests.The species richness increased slightly,Simpson dominance index,Shannon-Wiener diversity index and Pielou evenness index index increased significantly(P<0.05)(5)The results showed that the herbaceous plants had significant changes after low-intensity thinning(L),and the significant effect was more obvious after high-intensity thinning(P<0.05).The carbon storage of shrubs showed a significant change only after high-intensity thinning(H)(P<0.05).The results showed that shrubs and herbs had significant changes(P<0.05)after low-intensity thinning(L),and were significantly more significant after high-intensity thinning(P<0.05).Thinning significantly improved the lighting conditions,shrub growth was sufficient light,nutrients and water,so the carbon storage changes significantly(P<0.05)According to the results of the study and the ecological benefits and economic benefits of the study area,the effects of Pinus tabuliformis forest and Robinia pseudoacacia forest on the surface flammable characteristics,surface potential fire behavior,undergrowth vegetation biodiversity and carbon storage were significant after medium thinning(M,thinning intensity 35%).The results can provide the basis for the scientific management of combustible materials in the study area.