森林抚育对滇中地区潜在树冠火的影响

Effects of Forest Tending on Potential Crown Fires in Central Yunnan

通过实地测量和试验室测定,比较森林抚育前后枝下高及火行为的差异,定量分析森林抚育前后发生潜在树冠火的可能性,为定量评价森林抚育效果提供依据。在云南森林自然中心选择5个林班,根据林班森林可燃物分布情况,采取不同森林抚育方式进行森林可燃物调控。通过对5个林班中39个小班森林抚育前后枝下高、可燃物载量等调查,计算出森林抚育前后地表可燃物的热值、林火强度、林火蔓延速度和火焰高度。对比分析结果表明,1)森林抚育前柏木(Cypress)林和华山松(Pinus armandii)林平均枝下高分别为0.30 m和1.43 m,模拟的地表火火焰高度分别为0.34 m和0.67 m。抚育前柏木林和华山松林有很大的树冠火发生隐患;2)抚育后的柏木林,枝下高1.50 m左右,与地表火焰间的距离由-0.04 m增加到1.34 m,较大地降低了高强度树冠火发生的隐患;3)抚育后的华山松林,枝下高2.02 m左右,与地表火焰间的距离增加到1.68 m,高强度树冠火发生的隐患也得到了很大程度降低。通过森林抚育,有效减少了地表可燃物载量和提高枝下高的高度,从而有效降低了发生树冠火的可能性。

Through field measurement and laboratory measurement,the difference of height of lowest branch of tree and fire behavior before and after forest tending was compared,and the possibility of potential canopy fire before and after forest tending was quantitatively analyzed,which provided a basis for quantitative evaluation of forest tending effect.Five compartments were selected in Yunnan Forest Nature Center,and different forest tending methods were adopted to regulate and control forest fuel according to the distribution of forest fuel.The heat yield,fire intensity,fire spreading speed and flame height of surface fuel before and after forest tending were calculated by investigating the height of lowest branch and fuel load of 39 small classes in 5 compartments before and after forest tending.Through comparative analysis,the results showed that:1)the average height of lowest branch of Cypress forest and Pinus armandii forest was 0.30 m and 1.43 m,respectively,and the simulated surface flame height was 0.34 m and 0.67 m,respectively.Pretending Cypress forest and Pinus armandii forest had a great canopy fire hazard.2)The average height of lowest branch of Cypress forest after forest tending was about 1.50 m,and the distance between the surface flame was increased from-0.04 m to 1.34 m,which significantly reduced the hidden danger of high intensity canopy fire.3)The average height of lowest branch of Pinus armandii forest after forest tending was about 2.02 m,and the distance between the surface flame was increased to 1.68 m,and the hidden danger of high intensity canopy fire was greatly reduced.Forest tending could effectively reduce the surface fuel load and increase the height of lowest branch,thus effectively reducing the possibility of crown fire.