| Forest fires are a kind of disturbance to forests.As global temperatures rise,forest fires in our country present a trend of shifting from temperate areas to subtropical areas,and an increase in frequency.Wuhan is rich in forest resources,evergreen vegetation is the main vegetation type,and there are many fuels on the surface.Forest fires behaviour in Wuhan has been less studied,but the high rate of garden greening and high density ofpopulation lay a hidden danger for forest fire.We chose Wuhan City as the research area,this study chose four forest types,Pinus massoniana forest,Cunninghamia lanceolata forest,Cinnamomum camphora forest and Pterocarya stenoptera.Based on the historical fire data and wind speed data of Wuhan,site factors,stand characteristic factors and surface fuel data of the sampled areas were obtained through field investigation.The fuel load,calorific value,and ignition point were measured in laboratory.Pearson correlation analysis and PCA were used to screen the impact factors of surface fuel.The regression equations of surface fuel load of four common forest types were established through regression analysis.Behave Plus 5software’s Rothermel forest fire spread model was used to simulate the surface fire behavior of four forest types by setting parameters to improve the accuracy of the model.The following conclusions are drawn:1.Cinnamomum camphora forest had the highest surface fuel load of 1544 g/m~2,which was significantly higher than the other three forest types.Cunninghamia lanceolata forest’s load was 845 g/m~2,Pinus massoniana forest’s load was 761 g/m~2,Pterocarya stenoptera forest’s load was 658 g/m~2.The fuel composition of the four forest types was different,but the 1-h fuel load accounted for the largest proportion,reaching 54%to 87%,and the 100-h fuel load accounted for the smallest proportion.The moisture content,calorific value and ignition point of the forest fuels were close,but the difference of surface fuel bed depth was large,the Pterocarya stenoptera forest was the smallest,the Cinnamomum camphora forest was the largest.2.The relationship between the fuel load and the site factor and stand factor of the four forest types was different.The factors that had the greatest influence on the fuel load were selected by Pearson correlation analysis and principal component analysis,and the regression equations of the fuel load were established.In Pinus massoniana forest,1-h fuel load was related to subbranch height and total load was related to slope position.In Cunninghamia lanceolata forest,1-h fuel load and total load involved tree height and DBH.In Cinnamomum camphora forest,1-h fuel load was related to canopy density,total fuel load was related to canopy density and subbranch height.In Pterocarya stenoptera forest,the 1-h fuel load was related to slope position,and the total fuel load was related to canopy density and slope position.3.According to Rothermel forest fire spread model,the maximum spread speed,heat per unit area,fire line intensity and other fire behavior indexes of the four forest types were different.Under the same conditions,the surface fire behavior of Cinnamomum camphora forest was the largest,and that of Pterocarya stenoptera forest was the smallest.An increase in wind speed and slope can lead to an intensification of fire behavior.The fire intensity of the four forest types was within the range of professional machine and human control.However,under the conditions of maximum wind speed and high slope,the Cunninghamia lanceolata forest and Cinnamomum camphora forest will be transformed into canopy fire.To sum up,forest fire fighting equipment should be prepared and ready for the possible forest fire situation in each forest type.In addition,forest fire preventionpublicity and education should be strengthened,for the Cinnamomum camphora forest and other forest areas with a large amount of surface fuel load,cleaning management should be strengthened,and forest fire monitoring should be done well in the high fire period. |
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