计划火烧对区域森林燃烧性的影响

Influences of Prescribed Burning on Regional Forest Burning Probability

[目的]利用燃烧概率模型模拟计划火烧前后两种情景下的森林燃烧概率,在景观尺度上定量评估计划火烧在林火预防中的作用。[方法]利用SPOT6卫星数据提取大兴安岭部分区域在2016年火险期前进行计划火烧处理的可燃物状况,基于研究区附近地面气象观测数据利用R软件计算2016年火险期每日的火险指数,通过BURN-P3模型分别模拟计划火烧前后的森林燃烧性,评估计划火烧对森林燃烧概率和火行为的影响。[结果]2016年火险期前该区域进行计划火烧的面积为44 931 hm^2,占区域总面积的20.8%。计划火烧后,研究区平均燃烧概率从0.016 4降到0.012 4,落叶针叶林、常绿针叶林、针阔混交林、草地和落叶阔叶林平均燃烧概率分别降低4.2%、3.5%、5.9%、2.3%和0.6%。计划火烧前研究区的平均火烧强度和平均蔓延速度分别为548.9 kW·m^-2和2.2 m·min^-1,通过计划火烧处理,火烧强度和蔓延速度分别降低17.9%和24.3%。落叶针叶林和针阔混交林是发生树冠火的主要类型,火强度高、火蔓延速度快。计划火烧处理后研究区的树冠火比例降低了11.7%。[结论]火险期前的计划火烧减少了区域内草类可燃物的空间分布,降低了草类可燃物载量,也有效降低了区域内的森林燃烧性,平均火强度、蔓延速度和树冠火发生比例均显著降低。计划火烧区附近2 500 m范围内的燃烧概率明显降低。

[Objective]Burning probability model was used to simulate fire burning on the landscape scale and the impacts of prescribed burning on forest flammability were assessed quantitatively.[Method]The data about fuel conditions of some areas of Daxing’anling after prescribed burning before the fire season of 2016 were extracted from SPOT6 satellite data.The daily weather indices in the fire season were calculated with the weather observation data near the study area by using R-software.The burning probability and fire behavior indices of the forest were simulated with BURN-P3 model for the scenarios with and without prescribed burning.[Result]The areas treated with prescribed burning in 2016 were 44,931 hm^2,accounting for 20.8%of the total area.The average burning probability was 0.0164 and 0.0124 for the scenarios with and without prescribed burning.The average burning probability for each fuel type respectively decreased by 4.2%for deciduous coniferous forest,3.5%for evergreen coniferous forest,5.9%for coniferous and broad-leaved mixed forest,2.3%for grass,and 0.6%for broad-leaved forest after prescribed burning.The average fire intensity and spread speed were 548.9 kW/m^2 and 2.2 m/min under the scenario with prescribed burning.The average fire intensity and spread rate decreased by 17.9%and 24.3%due to prescribed burning.Deciduous coniferous forests and mixed forest showed high fire intensity and spread speed,and are easy to occur crown fires.The proportion of crown fire reduced by 11.7%after prescribed burning.[Conclusion]The prescribed burning could decrease the distribution areas of grass fuel and fuel loadings.The burn probability,fire intensity,rate of spread and crown fire fraction of the region decrease after prescribed burning.The burning probability will drop obviously in the buffer areas with 2500 m wide around the prescribed burning regions.