Surface Fuel Load Of Main Forest Types And Its Influencing Factors In Shexian County

Forest fire is a major threat to the safety of forest resources.Forest fuel is the material basis for forest combustion.Finding out the load of forest fuel is of great significance to objectively analyze and evaluate the risk level of forest fire,to effectively launch forest fire prevention and control,and to secure forest resources.Based on the survey data of forest resources in Shexian County,67 rectangular standard plots with an area of 666.7 m²were set into each layer by using the stratified area ratio method.The standard plots were set up and trees were investigated.Minimum measured diameter was from 5.0 cm.At the same time,four fuel load plots of shrubs,herbs and litters were set in each standard plot to collect and analyze fuel samples.The fuel load per unit area of tree,shrub,herb and litter was calculated respectively.The relationship model between the fuel load of shrub,herb and litter layer and each influencing factor was established respectively.The related factors of affecting the fuel load for different level were analyzed.The main results were as follows:（1）The total surface fuel load of the main forest type ranged from 156.33 t/hm²to228.78 t/hm².The order of average total fuel load was as follows:Cunninghamia lanceolata forest>coniferous and broad-leaved mixed forest>Pinus massoniana forest>hard broadleaf forest.Cunninghamia lanceolata forest has the highest fuel load in tree layer.Pinus massoniana forest has the highest fuel load in shrub layer and litter 1 layer.Coniferous and broad-leaved mixed forest has the highest fuel load in herb layer.Common distribution characteristics of under-forest fuel load in Pinus massoniana forest,hard broadleaf forest,Cunninghamia lanceolata forest and coniferous-broadleaved mixed forest is litter 1（dead branches less than 0.6cm in diameter and leaves）>herb layer>litter 3（dead branches with diameter form 2.5cm-7.62cm）>litter 2（dead branches with diameter form 0.6cm-2.5）.With the increase of stand age in each forest type,the fuel load of tree and litter layer increased,while the fuel load of shrub and herb layer decreased.（2）Among the surface fuels of main forest types,fuel load of tree layer and total fuel load are mainly related to average tree height and average diameter at breast height（DBH）.Fuel load of litter layer was mainly positively correlated with crown density.Fuel load of tree layer did not correlate significantly with that of other layers.（3）The survey data of 47 surface forest fuel standard plots with different forest types was used to build the fuel load models,which was verified with the data of 20 plots.Multivariate linear model was used to estimate forest fuel quantity.Model parameters were fitted by stepwise regression,Lasso regression and PLS regression.The results show that the fitting effect of stepwise regression was the best.Model formula is=-462.860+0.082X₂-0.090X₃+16.689X₇+15.004X₈,the stand density（X₂）,gradient（X₃）,average tree height（X₇）and DBH（X₈）are model variables.Similarly,based on the survey data of surface forest fuel load of 31 sample plots of Pinus massoniana forest,the above three model parameters fitting methods were used.The results showed that the fitting effect of stepwise regression was also the best.The fuel load model formula of Pinus massoniana forest was=-490.97+0.098X₂-1.109X₃+13.254X₇+19.156X₈,the stand density（X₂）,slope（X₃）,average tree height（X₇）and DBH（X₈）were model variables.Due to the small number of sample plots,the fuel load model of other forest types needs to be further studied.