Study On Potential Fire Behavior And Forest Combustion Of Miaofeng Mountain In Beijing

This paper takes 12 major forest types and 104 small classes in Miaofengshan Forest Farm in Beijing as the research object.Using field investigation,internal industry measurement,control experiment,statistical analysis and model checking to quantitative evaluation and classification of forest combustion Analysis of the relationship between the main impact factors,and put forward effective measures to reduce forest combustion.The following conclusions were drawn:(1)The physical and chemical properties of different plants and fuels are quite different,especially the canopy load and density characteristics of Pinus tabulaeformis and Platycladus orientalis are significantly different.The herbaceous water content has a large change range,the largest surface area to volume ratio,the highest ash content and the lowest calorific value.For shrubs,the moisture content is generally less stable than herbs,surface area-volume are relatively small,ash content is low,and calorific value is small.Leaf,branch,big branch,100hr,10hr,1hr of water content decreased gradually,leaf ash was larger than branches,dead branches were larger than live branches.For canopy load and density,live fuels are larger than dead fuels,and Pinus tabulaeformis is larger than Platycladus orientalis.In the vertical direction,the different levels of the canopy are different,showing an "inverted U-shaped" trend of increasing first and then decreasing.(2)The potential fire behavior of the main dominant tree species in the small class is from coniferous forest>broad-leaved mixed forest>shrub forest>broad-leaved forest.The potential fire behavior of the small class surface and the potential fire behavior of the canopy have a mutual transformation and interdependence,and the surface fire plays a key role.The surface fire spread speed,fire intensity and flame height are between 0.072-0.620 m/min,5.445～178.227 kW/m and 0.169～0.689 m,respectively.The canopy fire spread speed,fire intensity and flame height range are 7.57～70.56 m/min,2 460.27～35647.99 kW/m,2.81～9.62 m.Forests with extremely high potential fire behavior are generally located in the north and northwest of the forest farm.At the same time,due to the influence of wind speed and surface combustible load,surface fire,passive crown fire and active crown fire have interdependence and mutual transformation(3)According to the two processes of forest fire occurrence and development the ignition probability and ignition time of fuels are determined to indicate the flammability.The flame height,spread speed and energy release after combustion of fuel bed are measured to indicate the burning intensity of fuels.Fuels flammability consists of five grades that are extremely high flammable,high flammable,flammable,low flammable,and extremely low difficult flammable.Fuels burning intensity includes 5 levels of extremely high strength,high strength,medium strength,low strength and very low strength.Combining the flammability and burnig intensity of fuels,the forest combustion is divided into 25 grades.(4)Through the quantitative evaluation of forest combustion,the forest combustion of the main forest types of forest small classes from large to small for coniferous forest>coniferous mixed forest>coniferous and broad-leaved mixed forest>shrub forest>broad-leaved forest,and the small class of high combustion is concentrated in the northwest of the forest farm.Fuels flammability has four grades in small class that are extremely flammable,more flammable,flammable and low flammable.The dominant tree species in the small class are coniferous forest,coniferous and broad-leaved mixed forest,shrub and broad-leaved forest.Small classes with high flammability are distributed in the northwest and middle of the forest farm.The fuels burning intensity has five grades of high strength,high strength,medium strength,low strength and very low strength,corresponding to coniferous forest,coniferous and shrub mixed forest,coniferous and broad-leaved mixed forest,shrub and broadleaf mixed forests,and small classes with large burning intensity are distributed in the west of the forest farm.(5)Based on the forest combustion model and its impact factor analysis,some effective control measures such as large branch embedding,cutting irrigation,fuels material cleaning,pruning and crowning method,and control of mixing ratio are proposed.The surface fine fuels use large branch embedding method to suppress the flammability,and the uncompressed fine fuels load is controlled below 0.03 kg/m2.In the shrub,irrigation control measures are stronger than the surface fuels cleaning measures.The effect of cutting and clearing fuels in broad-leaved forest is not obvious.The surface fuels cleaning of coniferous forest is better than the effect of cutting irrigation.Canopy fuels were treated with controlled mixing ratio and cut crown treatment,Platycladus orientalis forest pruning height was lower than Pinus tabulaeformis forest.The canopy density and coniferous forest mixed ratio of the Platycladus orientalis is greater than that of the Pinus tabulaeformis forest.The regulation of forest combustion should be based on the type of forest,the condition of fuels and the structure of the canopy,etc.,and various control methods can be combined scientifically and organically to achieve the best results.