ObjectiveForest combustion is the difficulty degree of igniting a forest and the characteristics of fire behavior after a fire. Analysis of combustible fire behavior and combustion can provide a scientific basis for the forest fire prevention management and fire zoning under the forest of Miaofeng Mountain Forest Farm.

MethodThrough the investigation of surface combustibles of 12 major forest types in farm, combined with the continuous forest resources, this paper selects four categories of indicators: surface fire behavior, fire environment, flammable physical properties and bed structure to calculate the combustibility of 104 small class surface fuels by principal component analysis and cluster analysis, and the surface combustibles combustion index (CI) and ranking were calculated.

Result(1) In 104 small classes, the potential fire behavior of each dominant tree species in small classes was from large to small: coniferous forests was generally larger and the surface fire intensity reached 2 000 kW/m, the spread speed was above 3 m/min, and the flame height was over 1.5 m. The shrub was second, and its surface fire intensity was 700−2 000 kW/m, the spreading speed is 1.5−3 m/min, and the flame height is 1−1.5 m. The broadleaved was the lowest and it had a surface fire intensity of 700 kW/m or less, a propagation speed of 1.5 m/min or less, and a flame height of 1 m or less. (2) Principal component analysis showed that, the fire behavior index was directly proportional to the combustion, and the altitude factor was inversely proportional to the combustion. The water content was inversely proportional to the combustion. The effective load and the bed height were directly proportional to the combustion. (3) Cluster analysis showed that, the small class surface fuel combustion index (CI) was divided into five grades: high combustion (Ⅰ), higher combustion (Ⅱ), combustion (Ⅲ), lower combustion (Ⅳ), low combustion (Ⅴ). Small-shift dominant species of each flammability class, such as Pinus tabuliformis, Larix gmelinii and Platycladus orientalis, distributed in the southeastern and northwestern of the forest farm. Mixed forest of the Pinus tabuliformis, Platycladus orientalis and Quercus variabilis, Acer monoMaxim. mainly located in the northwestern corner of the forest farm. Broadleaved pure forest, such as cork oak, Quercus variabilis, Phellodendron amurense, Acer mono, which were concentrated in the southeastern and northwestern of the forest farm. Mountain peach and shrubs such as Vitex negundo and a few broadleaved mixed forests, such as Quercus variabilis, Juglans mandshurica, which were distributed in the northwestern forest farm. The shrubs such as Vitex negundo, Armeniaca sibiricat, Rhamnus davurica and Spiraea salicifolia, mainly located in the southwestern and central forest farm.

ConclusionThe potential fire behavior of small-scale of Pinus tabuliformis and Larix gmelinii forests is generally large, and it is easy to form high-intensity surface fires, which are prone to canopy fires. Combustibility is affected by fire environment, fire behavior and combustibles, especially combustible payload, bed height, altitude and moisture content factors. Small classes of the higher-combustion and high-combustion are located in the north and northwest of the forest farm. It is necessary to pay attention to the small-class classification management and scientific patrol of different combustion levels.