| Forest fire is global,transnational,sudden natural disasters as a natural enemy of forest.It is one of the common forest disasters,whieh not only destroyed a large area of forest resources and forced ecological imbalance,but also a serious threat to the safety of human life and property.As a ecological factors,Forest fire is different from other ecological factors.Fuel combustion is the material foundation and important condition of combustible material,which directly determine the occurrence and spread of forest fires.Taking seven types of forest ecosystem included broad-leaf forest,mixed forest,Phyllostachys pubescens forest,Pinus massoniana forest which were young,middle-age,near-mature,mature as research object in the Wuyishan Scenery District which as the most essence part of the Nature and Culture World Heritage sites.Canonical correlation analysis was used to explored the characteristic of fuel loading and the relationships which were including the moisture of surface fuels and all factors between different seasons(summer and winter)and different types of forest based on the survey of meteorology,landform,soil,stand factors.In addition,the forest fire danger evaluation indicator system was set up to evaluate risk index in different forest types.the result will provide the theory reference and decision support to the forest fire prevention work for the world heritage sites of Wuyishan Scenery District.(1)the absolute moisture content influenced by all factors was more sensitive than the relative moisture content in every layer of fuels between summer and winter.Therefore,the absolute moisture content will be used to analyze in the following.In summer,the absolute moisture content of fuel were:young forest of P.massoniana(69.2%),broad-leaf forest of P.massoniana(67.2%),mixed forest(59.6%),mature forest of P.massoniana(50.7%),P.pubescens forest(47.5%),near-mature forest of P.massoniana(50.7%),medium age forest of P.massoniana(31.9%);the absolute moisture content of fuel in winter was lower than that of summer as a whole.The order in the absolute moisture content of every fuels among medium age forest,near-mature forest,mature forest of P.massoniana was:herb layer>shrub layer>half decomposition layer>decomposition layer>dead leaves and branch layer;the moisture content of dead leaves and branch layer was the lowest in winter among broad-leaf forest,P.pubescens forest,mixed forest,then that of summer was in the shrub layer,the second was dead leaves and branch layer.(2)Comparing the moisture of surface fuels(dead leaves and branch layer)with environmental factors,we found:?the moisture of dead leaves and branch layer in summer and winter was increasing when air humidity was 53.3%?72.3%and 67.1%?85.4%,more than 72.3%and 85.4%,it would decrease,less than 53.3%,67.1%,it would increase;?the moisture of dead leaves and branch layer in the two season was increasing when the air temperature was 3.7??15.9? and 29.4??32.3?,no matter more than 15.9??32.3? or less than 13.7??29.4?,it would decrease;?the soil temperature in winter was lower than that of summer,when it was 10.7??13.0?,the moisture of live combustible fuel increased basically,less thanl0.7?,it would decrease,the relationship between soil temperature and the moisture of live combustible fuel was not obvious.(3)Canonical correlation analysis was done among the moisture of surface fuels and environment,stand factors in different seasons.We found that there were certain correlations among the moisture of surface fuels and environment,stand factors.Correlation degree between the moisture of herb layer in broad-leaf forest and landform,stand factors in the two season was the greatest(?1.000**|?-0.850**).And correlation degree between the moisture of shrub layer in P.pubescens forest and lighting,and that of dead leaves and branch layer and slope persent in the two season was the greatest(0.998**?0.951**).And the greatest negative correlations degree in mixed forest between the two season were the moisture of decomposition layer and landform,stand factors(-0.991**),the moisture of decomposition layer and wind speed,landform(-0.952**).Correlation degree between the moisture of half decomposition layer in mature forest of P.massoniana and meantotal height in winter was the greatest(0.796**).And in summer the greatest negative correlations degree in medium forest of P.massoniana between the moisture of shrub layer and environment,stand factors(1.000**).And correlation degree between the moisture of shrub layer in near-mature forest of P.massoniana and environment,stand factors,the moisture of half decomposition layer and altitude in the two season were the greatest(1.000**,0.811**).And in the two season the greatest negative correlations degree in young forest of P.massoniana between the moisture of herb layer and lighting,and that of dead leaves and branch layer and slope(-0.790*?-0.930**).(4)The surface fuel loadings was different in 7 forest types.The surface fuel loading in winter were more than that of summer;the total surface fuel loading and that of dead leaves and branch layer was three varying from summer to winter,they were in the P.massoniana forest which were medium forest,young forest,near-mature.The most reduction in the medium forest of P.massoniana was(30724 kg/hm2),the second one was in the young forest of P.massoniana(an increase of 19012 kg/hm2);the three forest types in dead leaves and branch layer were also different,it was in the sequence of near-mature(an increase of 3769 kg/hm2)>young forest(an increase of 3664 kg/hm2)>medium forest(an increase of 4.3 kg/hm2)in P.massoniana forest.(5)Drawing on the local environment and combining with the stand factors,tourist disturbance intensity and other factors,the third-grade fire risk classification system in the Wuyishan Scenery District was established,including 3 first stage classification,5 second classification,12 third classification.The 21 forests were divided into 4 fire risk grade based on fire risk division standard,which was according to different seasons.The fire risk grade was different among all forests in the two seasons.The fire risk grade of mixed forest of shady slope in summer was first-grade,and that of winter was second-grade;The fire risk grade of P.pubescens forest of shady slope in summer was second-grade,and that of winter was second-grade,The fire risk grade of P.pubescens forest in sunny slope was third-grade in summer,and that of winter was second-grade;The fire risk grade of broad-leaf forest in sunny slope was third-grade in summer,and that of winter was first-grade;The fire risk grade of mature forest of P.massoniana in sunny slope was third-grade in summer,and that of winter was second-grade;The fire risk grade of medium forest of P.massoniana in sunny slope was fourth-grade in summer,and that of winter was third-grade. |
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