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林火灾变是失去人为控制、自由蔓延的森林燃烧，破坏了原有森林的结构与功能，并在相当时间内难以恢复原有林的结构，带来一定的经济损失。本文提出６个林火灾变的生态指标，３个火行为指标，并提出林火灾变的阈值：短期内发生频度为两次以上的森林火灾，或虽发生一次林火但紧接着又引发其它灾害（如严重病虫害、水土流失等）。林火（面积１公顷以上）为树冠火，或地下火，或高强度地表火（火强度３０００ｋｗ／ｍ）。５０％以上林木被烧死，或火后森林发生明显的次生演替，或火后林地形成草地、秃山裸地
The forest fire change is the loss of artificially controlled and freely spread forest burning, destroying the structure and function of the original forest, and it is difficult to restore the original forest structure within a certain period of time, resulting in some economic losses. In this paper, six ecological indicators of forest fire change and three indicators of fire behavior are proposed, and the threshold of forest fire disaster is proposed: a forest fire frequency of more than twice in the short term, or a forest fire, Disasters (such as serious pests, soil erosion, etc.). Forest fire (area of more than 1 hectare) is the crown fire, or underground fire, or high-intensity surface fire (fire intensity 3000kw / m). More than 50% of forest trees are burned to death, or obvious secondary succession occurs in the forest after fire, or the grassland after fire is formed,