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    妙峰山林场主要针叶林冠层特征及潜在火行为

    Canopy characteristics and potential crown fire behavior of main coniferous forest in Miaofeng Mountain Forest Farm in Beijing

      摘要
    • 摘要:
      目的树冠火是一类对森林生态系统特别是针叶林造成严重损害的森林火灾。了解针叶林冠层特征, 探究树冠火发生、蔓延机制, 估测潜在冠层火行为是预防和扑救树冠火的关键。
      方法本研究以妙峰山地区主要的针叶林, 油松林和侧柏林作为研究对象, 调查灌木、草本和地表枯落物负荷量, 采用分段标准枝法对冠层可燃物负荷量进行了分层调查与测算, 研究冠层特征(冠层密度、冠层可燃物负荷量)的垂直分布规律; 并利用树冠火发生和蔓延模型以及火焰高度和强度模型, 按照树冠火类型划分标准, 研究针叶林树冠火发生的概率、类型和潜在火行为。
      结果油松林平均冠层密度为0.192kg/m3, 侧柏林为0.127kg/m3, 油松林冠层平均有效可燃物载量为1.21kg/m2, 侧柏林为0.619kg/m2; 油松林和侧柏林的下层(0~3m)垂直分布差异性较大, 油松林下层可燃物负荷量占整体负荷量10.5%, 而侧柏林则高达21.1%;在中等和高的燃烧情况下, 2种林分均表现出较高的潜在火行为指标, 油松林最高蔓延速度、火线强度和火焰高度分别为:91m/min、45281kW/m、23m, 侧柏林为85m/min、19911kW/m、16m。
      结论冠层密度和冠层可燃物负荷量随树高变化趋势相似; 林分树冠火发生概率和类型与林分冠层可燃物和冠层密度的垂直分布关系密切; 2种林分的连续型树冠火的潜在火行为估算指标具有蔓延速度快, 火焰强度大, 火焰高度高的特点, 一旦发生树冠火, 人为处置困难。

       

      Abstract:
      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.

       

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