ObjectiveCrown fire is a type of forest fire that causes serious damage to forest ecosystems, especially to coniferous forests. Understanding the canopy characteristics, exploring the occurrence and propagation mechanism of crown fire, and estimating the potential crown fire behavior are the key points to prevent and save crown fire.
MethodIn this paper, the main coniferous forests (Pinus tabuliformis and Platycladus orientalis) in Miaofeng Mountain Forest Farm were selected as research objects. The load of shrubs, herbs and surface litter were investigated. The article used the segmented standard branch method to carry on the stratified investigation to the canopy combustible load for understanding the vertical distribution of canopy characteristics (canopy bulk density (CBD), available canopy fuel load (CFL)). According to the type of crown fire classification criteria and the model of occurrence and spread of crown fire and the model of flame height and intensity were used to calculate the probability, types and potential fire behavior of crown fire.
ResultThe results showed that, the average CBD of Pinus tabuliformis forest was 0.192kg/m3, and that of Platycladus orientalis forest was 0.127kg/m3, and the average CFL was 1.21kg/m2 for Pinus tabuliformis and 0.619kg/m2 for Platycladus orientalis forest; The vertical distribution of the lower layer (0-3m) of Pinus tabuliformis forest and Platycladus orientalis forest was quite different, the amount of CFL in the lower layer of Pinus tabuliformis forest stands was 10.5% of the total load, while that of Platycladus orientalis was 21.1%. Under medium and high burning conditions, both stands showed higher potential fire behavior indicators. The highest spreading rate, fire line intensity and flame height of Pinus tabuliformis forest were 91m/min, 45281KW/m and 23m, and 85m/min, 19911kW/m, 16m in Platycladus orientalis forest.
ConclusionCanopy density and canopy combustible load were similar with tree height. The occurrence probability and type of canopy fire were closely related to the vertical distribution of CFL and CBD. The estimation of potential fire behavior of continuous canopy fire with two types of forest had the characteristics of rapid spread, large flame intensity and high flame height. Once the crown fire occurs, it is difficult to handle manually.