| Of the three basic conditions which are fuel,oxygen and fire that affect occurrence of forest fire,fuel is only factor that human beings can control.It is the material basis for occurrence and spread of forest fire and basic components of forest ecosystems.Four major forest types(broad-leaved forest,mixed forest,Phyllostachys heterocycla var.Pubescens forest,and Pinus massoniana forest)in Wuyishan Scenery District,a world natural and cultural heritage site,were analyzed to understand combustibility of different forest types surface fuel.We measured moisture contents(absolute moisture content and extinction moisture content),loading and physical-chemical properties of live fuel(shrub,herb)and dead fuel(1 hr,10 hr)on different slopes under different forest types.Based on determined data,we inverstigated the changes rules and influence of environmental factors on moisture contents and loading,and constructed multiple regression dynamics prediction models of different species of fuel aim to provide a basic data for management of forest surface fuel and scientific basis for forest fire managers forecasting potential forest fire.The results showed that:(1)The differences between moisture contents and loading of dead fuel in different forest types of the same species were greater than live fuel.Among various species fuel of four forest types,absolute moisture content showed that live fuel were larger than dead fuel,but the orders of extinction moisture content and loading were different.There were also differences in order of moisture contents and loading of the same species fuel on different slopes.Among various species of different forest types,absolute moisture content of Phyllostachys heterocycla var.Pubescens forest was highest and near-mature P.massoniana forest was lower;Extinction moisture content was represented by near-mature P.massoniana forest,mature and overmature P.massoniana forest were higher than other forest types whereas Phyllostachys heterocycla var.Pubescens forest was lower;Total loadings showed lower in Phyllostachys heterocycla var.Pubescens forest(220.58 g/m2),young P.massoniana forest(228.18 g/m2),middle aged P.massoniana forest(198.21 g/m2),and higher in broad-leaved forest(416.88 g/m2)and mixed forest(341.16 g/m2).(2)Redundancy analysis(RDA)showed that moisture contents and loading of live fuel and dead fuel were significant influenced by different environmental factors.Cumulation contribution ratio of environmental factors on moisture contents of dead fuel were higher than live fuel.Cumulation contribution ratio of dead fuel loading was lower than live fuel.Absolute moisture content of live fuel was main influenced by slope,elevation,illumination and average under branche height,two ordination axes together explained 40.40%;Absolute moisture content of dead fuel significant affected by soil humidity,average height,slope,illumination and average DBH,two ordination axes together explained 64.54%.Canopy cover and elevation were primary factors that affected extinction moisture content of live fuel,two ordination axes together explained 22.23%;Extinction moisture content of dead fuel was mainly affected by canopy cover,slope,elevation,soil humidity and slope position,first and second ordination axes respectively explained 66.44%and 1.51%of extinction moisture content of dead fuel.Average height,elevation,and aspect have higher impacts on live fuel loading,two ordination axes together explained 53.38%;Impact factors of dead fuel loading were slope position and soil humidity,first and second ordination axes together explained 43.34%.(3)Among absolute moisture content,correlation between mixed forest and average under branch height was highest in shrub,regression equation was:y1=268.64-16.633 x2;Correlation between young P.massoniana forest and slope,illumination and elevation was highest in herb,regression equation was:y2=782.86-3.393 x6-0.812 x1+0.029 x3;Correlation between Phyllostachys heterocycla var.pubescens forest and illumination,average DBH,soil humidity was highest in 1 hr,regression equation was:y3=-128.994+16.73 x4+7.55 x5+1.189 x3;Correlation between young P.massoniana forest and average DBH,average height was highest in 10 hr,regression equation was:y4=-58.576+30.768 x4-15.973 x7.For extinction moisture content,mixed forest and canopy cover showed significant negative correlation in shrub,regression equation was:y5=66.264-32.463 x8;Mature and overmature P.massoniana forest with elevation,canopy cover reached significant level in herb,regression equation was:y6=87.661-0.099 x6+24.779 x8;Phyllostachys heterocycla var.pubescens forest with soil humidity have significant negative correlation in 10 hr,regression equation was:y8=7.484-0.041 x5.In loading,relationship between mixed forest and average height reached significant level in shrub,regression equation was:y9=130.56-9.27 x7;Phyllostachys heterocycla var.pubescens forest significant negative correlated with average height in herb,regression equation was:y10=104.12-4.907 x7,1 hr have significant positive correlation with soil humidity,regression equation was:y11=91.634+9.665 x5.Different regression models have a good fitting effect which can used environmental factors to measure moistures contents and loading of surface fuel.It provided a scientific basis for management of forest surface fuel.(4)Physical-chemical properties of surface fuel reflected that ignition of Phyllostachys heterocycla var.pubescens forest was higher than other forest types in 1 hr of different forest types,but lower in near-mature P.massoniana forest which indicated that coniferous forests were more easier to be ignited;Ignition of broad-leaved forest in 1 hr and 10 hr were different,and 10 hr>1 hr,which indicated that 1 hr was easier to burn than 10 hr;There weren’t significant differences in ignition of dead fuel on different slopes of the same forest type.Surface forest fuel in different forest types of the same species,mature and overmatured P.massoniana forest had lower caloric value and ash content was higher while middle aged P.massoniana had higher caloric value and lower ash content in shrub.Young P.massoniana forest had higher caloric value and lower ash content while matured and overmature P.massoniana forest was opposite in herb.Phyllostachys heterocycla var.pubescens forest had lower caloric value and higher ash content whereas middle aged P.massoniana forest had higher caloric value and lower ash content in 1 hr and 10 hr.Average value of caloric value and ash content in different aspects of the same type,different types of the same aspect were various in different forest types.Extract content in different forest types of the same species were different.Among shrub,broad-leaved forest(1.29%±0.17%)and middle aged P.massoniana forest(1.39%±0.21%)were higher,followed by mixed forest(1.04%±0.18%),mature and overmature P.massoniana forest were lowest(0.72%±0.20%);Different ages of P.massoniana forest were significant higher than broad-leaved forest and Phyllostachys heterocycla var.pubescens forest in 1 hr and 10 hr.For forest surface fuel in different species of the same forest type,except for young P.massoniana forest and near-mature P.massoniana forest,there were significant differences among different species fuel and changes on different forest types and trends were inconsistent.Comparison extract content of live fuel and dead fuel on different slopes under four forest types,in live fuel,mixed forest reflected sunny slope>shady slope while mature and overmature P.massoniana forest demonstrated sunny slope<shady slope in shrub.The shady slope of mixed forest and near-mature P.massoniana forest were significant higher than sunny slope while middle aged P.massoniana forest was opposite in herb.From the point of view of dead fuel,only middle aged P.massoniana forest on shady slope was higher than sunny slope in 1 hr.Mixed forest,matured and overmatured P.massoniana forest on sunny slope>shady slope,near-mature P.massoniana forest,sunny slope<shady slope in 10 hr.(5)Thermogravimetric analysis showed that average constant rate of each component in different forest types was basically positively correlated with content of each component.Cellulose content in 1 hr of dry branches and 10 hr of dry branches were higher than in leaves which resulted in faster average rates and more dramatic reactions.Ash content of leaves part were higher than 1 hr of dry branches and 10 hr of dry branches,and fire resistance of leaves parts were better during combustion process. |
