Study On The Combustibility Of Forest Fuels And Fire Behavior In Central Yunnan Province, China

Central Yunnan is a region with frequent and strong forest fires, both within the provinceand within China. The area is located on a low latitude plateau, with a large elevationdifference, complex and diverse topography, and clear three-dimensional climate. The uniquecharacteristics of climate, topography, forest type, and diverse fire sources produce acomplexity of forest fire behaviors and the difficulty of fire prevention. Research oncombustibility of forest fuel and fire behaviors can provide a basis for an understanding of theforest fire occurrence pattern and comprehensive fire management in the area. The mainresearch content, methods and conclusions in this paper are as follows:①Study on combustibility using ordering and sorting of living leaves from commonnative woody species. To compare the combustibility difference of plant species, combustionexperiments of live leaves from11common native woody plant species were conducted withan oxygen index measuring instrument under high oxygen concentration during the peak forestfire season. Moisture content, mass per unit area, burning rate, and damage extent of the liveleaves were measured and calculated. The combustibility orders based on factor analysis fromstrong to weak were: Rhododendron spinuliferum> Cinnamomum glanduliferum> Micheliayunnanensis> Ternstroemia gymnanthera> Rhododendron decorum> Lithocarpus mairei>Rhododendron siderophyllum> Viburnum cylindricum> Castanopsis orthacantha> Camelliapitardii> Illicium simonsii. The results showed that the live leaves of11species could bedivided into four categories:1was very inflammable,4were inflammable,3were combustible,and3were difficultly inflammable.②Study oncombustibility ordering and sorting of live branches of main forest woodyspecies. To understand the combustion characteristics of15common native woody plantspecies, a thermal radiation ignition experiment with small and medium size branches and anoxygen index experiment with small size branches were conducted during peak forest fire season. Based on the sample’s diameter, moisture content, time to ignition, quenching time offlaming combustion, smoking temperature， and weight loss, an integrated combustionparameter (S) reflecting the combustion characteristics was proposed. According to thecalculated S, the combustion order of the test tree species was Pinus yunnanensis<I. simonsii <Pinus armandii <Cyclobalanopsis glaucoides <Pinus yunnanensis var. pygmaea <C.glanduliferum <T. gymnanthera <R. decorum <R. spinuliferum <M. yunnanensis <R.siderophyllum <Lyonia ovalifolia <L. mairei <C. orthacantha <C. pitardii. The oxygen indexexperiment indicated that the small size live branches of the15tree species all had obviousflame-retardant characteristics, of which4(R. decorum, I. simonsii, T. gymnanthera and L.oralifolia) were difficultly inflammable，7(M. yunnanensis, P. yunnanensis，P. yunnanensis var.pygmaea，P. armandii，C. glaucoides，C. glanduliferum，and C. pitardii) were combustible，and4(R. siderophyllum，R. spinuliferum，L. mairei，and C. orthacantha) were inflammable.The reasons for the difference between the classifications derived by the two experiments wereanalyzed.③Study on the smoke density rating of3main coniferous species. In order to analyzeand compare the smoke density rating of conifers in burning, experiments using old and newconifers, litter from P. yunnanensis, P. armandii, P. yunnanensis Franch.var. pygmaea Hsuehwere conducted. The results showed that the smoke density rating of these3species increasedwith mass, but were not proportional. The smoke density rating of the litter increased withmoisture content, as with the case of a similar mass of dry matter.④Simulation study on forest fire behavior based on Fire Dynamics Simulator (FDS). Thepaper modeled forest fuel with FDS, and studied the forest fire behaviors, including the initialspread rate of forest burning under certain conditions of fuel and environment, the affect ofenvironment factors on forest burning and heat release rate. The result showed that the forestsurface fire spread rate calculated with FDS was similar to the initial spread rate of litter of P.yunnanensis and P. armandii measured by the burning experiment, and thus FDS modelpredictions are likely to provide a close approximation to actual conditions, at least in this regard.