| This paper takes the typical species of Platycladus orientalis in Beijing as the research object.Forest tending measures could reduce the spatial continuity and the load of fuel.By setting up control stands,fire behavior simulation software is used to compare potential fire behaviors,providing scientific basis for forest fire prevention and fuel management.The forest tending measures are pruning and cutting shrub.According to China’s forest tending regulations,1-2 rounds of live branches under the crown and dead branches are pruned.Investigating forest stand information and geographic information,and using the harvest method to investigate surface fuel loads.Correlation analysis is performed using statistical analysis software to explore the effects of stand factors and topographic factors on fuel materials.Multivariate regression analysis is used to establish different types of fuel load models,and BehavePlus fire behavior software is used to simulate surface fire behavior and output corresponding fire behavior indicators.The main findings are as follows:(1)The average fuel load of 1h time lag in the control stand is 936.7g/m2,56.0g/m2 for 10h time lag,and 1120.1 g/m2 for the total fuel load.After pruning and cutting and shrubs,the average fuel load of 1h time lag in the control stand is 470.6g/m2,the average fuel load of 10h time lag is 48.2g/m2,and the average total fuel load is 518.9g/m2.The average fuel load of shrubs in the control stand is 127.3g/m2,and after pruning and cutting shrub,the fuel load of shrubs in the control stand is Og/m2.The amount of fuel with lh time lag in the forest of Platvcladus orientalis is significantly higher than thatwith 10h time lag.By contrast,after pruning and cutting shrub,the total fuel load decreasedsignificantly.(2)Correlation analysis results of Platycladus orientalis surface fuel load with stand factor and terrain factor:altitude and height under the first branch have a significant negative correlation with 1h time lag fuel load at the level of 0.05,and a significant positive correlation with density at the level of 0.01.The fuel load of 1h time lag has a significant positive correlation with tree height and altitude,and has a significant negative correlation with density at 0.01 level.There is a significant negative correlation between shrub fuel load and forest density.The greater the density,the weaker the shrub.The total fuel load on the surface is mainly related to density.According to the correlation analysis results,the density,altitude,first branch height and tree height are all significant factors affecting the fuel load,especially the density factor,which has different effects on different types of fuels.The absolute value of the correlation coefficient is 0.358.-0.598 is higher than other factors,indicating that density has an important influence on fuel load.(3)Stepwise regression analysis results show that the 1h time lag surface fuel load model has four variables:DBH,stand density,slope and height under the first branch,with the highest R2 value and the best fitting effect.The optimal multiple linear regression model of 10h time lag surface fuel load constructed by two factors of altitude and density,R2 is 0.35.The multiple linear regression model R2 of total surface fuel load is 0.39.The model of shrub fuel load is poor,with only density factor,R2 is 0.13.P values of each model were significant,and all variables are detected by multicollinearity.(4)The average wind speed in Beijing reached 3 m/s,and the simulation results of fire behavior under the wind speed condition show that the surface fire spreading speed of pruning and cutting shrub stands is similar to that of the control group,which is 0.3 m/s and 0.2 m/s,respectively.The intensity of the fire line on the pruning and cutting shrub stands is 1555 kW/m,and the intensity of the fire line in the control group is as high as 4423 kW/m,which can burn all the animals and plants on the ground,causing great damage and difficult recovery after the disaster.Surface fire in pruning and cutting shrub stands and control stands may change into crown fire.The flame height in the control group is 3.7 m,the flame height of the experimental group is 2.3 m,and the flame height decreased by 1.4 m.In the control group,the canopy fire conversion rate is 31.3%,and the crown fire conversion rate of experimental group is only 1.5%,and the canopy fire conversion rate decreased by 29.8%.The simulation results of fire behavior show that the fire behavior indexes are significantly lower than those in the control group after the pruning and cutting shrub.(5)There is a significant positive correlation between the surface fire spreading speed and wind speed.The surface fire spreading speed of the experimental group and the control group is similar.When the wind speed is I 1 m/s,the surface fire spreading speed is 1.6m/s.The fire line intensity,flame height and crown fire conversion rate of the experimental group decreased significantly,and the reduction of crown fire conversion rate is the most obvious.The greater the wind speed,the greater the intensity of the fire line.When the wind speed reaches the maximum value of 11 m/s,the fire line intensity of the control group and the experimental group are 27644 kW/m and 9584 kW/m,respectively,both exceeding the medium intensity,which will burn the surface plants and destroy the soil.The potential fire behavior is not conducive to the sustainable development of the ecological environment.In the windless condition,the flame height of the control group is 1.5 m,and the flame height in the experimental group is 1 m.As the wind speed increases to 11 m/s,the flame height of the control group and the experimental group become 8.6m and 5.3 m,and the flame height difference is 0.5.m is increased to 3.3 m.In the absence of wind and low wind speed(wind speed is 0-1 m/s),the surface fire in the stand after pruning and cutting shrub will not spread to the canopy,so it will not cause the canopy fire.The control group may have a canopy fire at any wind speed condition. |
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