基于森林可燃物空间分布特征及调控基础的树冠火发生机制研究

Forest fuel is the fundamental of forest fire occurrence. The fuel type, loading and distribution characteristics are important condition which affect the forest fire occurrence. The spatial distribution of forest fuel (horizontal and vertical distribution) directly impact the potential of crown fire occurrence and spread. Through the fuel management measures such as pruning, cutting shrubs, and thinning, the forest fuel loading and distribution characteristics can be effectively modified, and decrease the potential probability of crown fire occurrence, reduce the potential fire intensity, as well as the negative effect of forest fire on natural resources and environment. This project will be conducted in the Beijing Xishan Experimental Forest Farm, the typical forest types in North China will be selected, including Pinus tabulaeformis, Platycladus orientalis and Robinia pseudoacacis forests, based on the fuel distribution characteristics and fuel management measures in different stands, by taking the methods including field investigation and lab experiments, the theoretical derivation combined with the modelling approach, the mechanism of crown fire occurrence and propagation in different stands were comparatively studied. The main research contents including (1) The mechanism of surface fire transition to the crown fire in different studied stands; (2) The condition and mechanism of crown fire spreading in different stands; (3) the influence of different fuel management measures on the potential crown fire occurrence and prevention; (4) Develop the assessment model for crown fire occurrence potential in different stands. The expected results will provide scientific basis on the forest fuel management and the crown fire prevention in the studied area, has the significant theoretical meaning and practical application value.

森林可燃物是森林火灾发生的物质基础，可燃物空间分布特征，直接影响到树冠火发生和蔓延的可能性。通过对森林可燃物进行调控（如修枝、割灌和疏伐等），可有效地改变林分可燃物负荷量及空间分布特征，减少树冠火发生的潜在风险，降低潜在火强度，减少林火对自然资源和环境造成的危害。项目拟在北京市西山试验林场，选择华北地区典型林分-油松林、侧柏林和刺槐林为研究对象，基于不同林分可燃物分布特征及调控措施，采用野外调查和室内实验、理论推导和模型拟合的方法，对比研究不同林分树冠火发生和蔓延的关键机制问题，研究内容包括：1、不同林分地表火蔓延到树冠火的发生机制；2、不同林分树冠火连续蔓延的机制和条件；3、不同调控措施对树冠火发生和蔓延的影响；4、构建不同林分树冠火发生潜在可能性评价模型。预期研究结果可为研究地区的可燃物管理，树冠火的有效防控提供科学依据，具有重要的理论意义和实际应用价值。

森林可燃物是森林火灾发生的物质基础，可燃物空间分布特征，直接影响到树冠火发生和蔓延的可能性。通过对森林可燃物进行调控（如修枝、割灌和疏伐等），可有效地改变林分可燃物负荷量及空间分布特征，减少树冠火发生的潜在风险。本项目拟选择油松林、侧柏林等华北地区主要林分，探讨冠层可燃物的空间分布特征并进行模型构建；模拟地表火行为，分析地表火向树冠火蔓延的机制；基于不同可燃物调控措施下，系统地开展树冠火发生及蔓延机制研究。重要结果包括：（1）人工侧柏林冠层可燃物模型构建研究。构建侧柏地上及各器官的一元、二元和多元可燃物负荷量模型，研究认为多元模型的预估精度最高，其地上总量与树干可燃物负荷量的预估精度超过93%，树冠、树枝和树叶模型的预估精度均在85%以上。（2）八达岭林场油松林树冠火蔓延机制研究。林冠底层（0-1m）可燃物占冠层总可燃物比例最大，为54.03%，在中度燃烧条件下，春季（3-5月份）风速较大，均存在发生连续型树冠火的可能；在极端干燥的高燃烧条件下，2-5月连续型树冠火的潜在火行为指标较高，4月份发生的连续型树冠火，表现出最高的潜在火行为指标，蔓延速度为46m/min，火线强度为8062kW/m，火焰高度为15m。（3）北京市十三陵林场油松林地表火行为模拟。结果表明油松林在低含水率的条件下，风速会显著增加地表火蔓延速度，难以人为扑灭，需清理地表可燃物，降低火险。（4）不同林分地表火蔓延到树冠火的发生机制。树木的第一枝下高和树木的绝对含水率对树冠火的发生具有重要影响，第一枝下高越高，树木的绝对含水率越大，越容易发生树冠火。刺槐林较难发生树冠火，可作为主要的防火树种。（5）抚育间伐对侧柏林冠层火发生和蔓延的影响。中度间伐（26%~35%）强度对冠层可燃物特征和树冠潜在火行为指标影响显著。预期研究结果可为研究地区的冠层可燃物管理，调控措施的选择、技术规程的制定、潜在火行为预测，以及树冠火的有效防控提供科学依据，具有重要的理论意义。