Study On Combustible Characteristics And Fire Resistance In Dominant Forests In Karuo District,qamdo City,Tibet

Forest fire is a serious natural disaster,its destructive nature includes burning trees,reducing the ability of forest regeneration,causing poor soil,reducing the ability of forest water conservation,harming the animals in the forest,causing air pollution,and even affecting the ecological balance.Forest fire has the characteristics of strong harmfulness and high difficulty to extinguishing,"prevention in burning" is especially important.China adopts the forest fire prevention strategy of "prevention first and active elimination",divides the fire resistance intensity of the forest through scientific methods,rationally distributes the fire belts,and realizes the effective prevention and control of forest fires.In this paper,the fire resistance of seven dominant forests in Karuo District,Qamdo city,Tibet,determined the four fire resistance indexes of the dominant forest,compared the fire resistance difference between the dominant stands,ranked the tree species from strong to weak,divided the fire risk grade,and evaluated the fire resistance of the dominant forest.Strictly monitor the flammable forest concentrated areas,enhance the intensity of inspection,in order to timely find and extinguish fire sources,reduce the frequency of forest fires as far as possible,reduce the loss of life and property.The fire resistance study is to evaluate the fire resistance index of the superior forest on the basis of the comprehensive analysis of the forest combustible materials.The study of fire resistance is of great significance to the formulation of forest emergency plan for fire prevention,the prediction of forest fire occurrence,predicting the fighting situation,the protection of forest ecosystem,and dividing the key areas of forest fire risk patrol and patrol.According to the construction principle of "fire triangle",the forest fuel is the key factor that causes the potential fire behavior,and is the material basis for the spread of forest fire.The study of physical and chemical indexes of forest combustible materials plays an important role in studying the development law of forest fire.Using the seven dominant forests in Karuo District,Qamdo city,Tibet,the shrub layer I,herbaceous layerⅡ,humus layer Ⅲ and litter layerⅣ(d<0.6cm),V(0.6cm d <2.5cm)and litter layerⅥ(2.5 cm d <7.The fire resistance index of 62cm),that is,the dry-fresh ratio,balanced moisture content,ignition point and calorific value of the forest combustible,and the fire resistance index of the forest was preliminarily evaluated by entropy weight method,principal component analysis and cluster analysis.The results indicate that:(1)The dry-fresh ratio of combustible in underforest is located in 35.61% ～ 86.71%,and the dry-fresh ratio of coniferous mixed forest is the largest,and there are significant differences between different combustible types(P <0.01).(2)The changes of humusⅢ,litterⅣ,litter V and litter Ⅵ contents of the seven dominant forests were38.67%～43.23%,45.32%～55.32%,56.83%～63.85% and 63.81%～75.32%,respectively;the equilibrium water content of combustible was significantly different among the four combustible types(P <0.01).(3)The ignition points of the humus layer and litter layer-mixed sample(litter layer(d<0.6cm),V(0.6cm≤d<2.5cm)and 2.5cm≤d<7.62cm)are265.12-287.68℃ and 240.82℃-272.0.82℃,respectively,and the ignition points and calorific values are different forests(P <0.01).Classification of Pearson correlation analysis and fire resistance intensity:(1)positive correlation between six types of forest combustible I-dry ratio;positive correlation between four types of forest combustible-balanced water content;positive correlation between four types of forest combustible-balanced water content and two points of forest combustible(humus layer and litter layer-mixed sample).(3)Negative correlation: I-dry-fresh ratio of six sub-forest combustible and four sub-forest;combustible I-dry and fresh ratio of two sub-forest combustible ignition points(humus layer and dead litter layer-mixed sample).(2)The entropy weight method was used to rank the fire resistance of 7 dominant forests and the fire resistance from strong to weak was poplar forest>broad-leaved mixed forest>needle and broad-leaved mixed forest> spruce forest> coniferous mixed forest> birch forest> cypress forest.(3)The average chain method between groups(Between-groups link-age)was applied to systematically cluster the fire resistance indexes of 7 dominant forests,and obtained the fire resistance classification of 7 dominant forests in Karuo District,Qamdo city,Tibet.The intensity of fire resistance index is divided into three categories,category 1 is poplar forest,strong fire resistance forest,category 2 is broad-leaved mixed forest,needle-broad-leaved mixed forest and spruce forest,moderate fire resistance forest,category 3 includes needle-broad-leaved mixed forest,birch forest and cypress forest,relatively weak fire resistance forest.