【作者】 牛树奎；

【导师】 贺庆棠；

【作者基本信息】 北京林业大学 ， 生态学， 2012， 博士

【摘要】 本研究以北京市山区主要森林类型为研究对象,采用可燃物分类、野外林内空间单元可燃物种类负荷量调查、统计分析、模型计算等方法,通过研究不同树种、灌木、草本以及地表枯枝落叶等可燃物负荷量在空间上的分布规律,探讨不同森林空间单元上的可燃物属性、结构和潜在火行为特征。在对针叶林可燃物负荷量空间分布与树冠火发生关系分析的基础上,建立了可燃物连续性指数模型,对不同针叶林类型的树冠火发生和蔓延的危险性进行估测和分析,并提出了阻滞树冠火发生和蔓延的科学调控措施。本文在可燃物连续性模型及等级的建立、可燃物临界负荷量的确定、可燃物定量调控等方面具有创新性。本文得出如下主要结论：(1)通过对侧柏林、油松林、元宝枫林的组成树种和枝叶负荷量的研究,比较了不同森林类型及各层次之间可燃物负荷量的差异,分析了不同树种组成及可燃物负荷量的空间分布对树冠火发生与蔓延的影响。结果显示,侧柏林的可燃物负荷量最高,油松林居中,元宝枫林最低；三个森林类型灌木层负荷量差异显著,灌木层的负荷量集中在荆条、胡枝子和紫穗槐等少数几个种,占90%以上；森林中针叶树的存在和组成比例是树冠火发生与蔓延的基本条件。(2)通过不同树种和可燃物种类的理化性质分析和基于Rothermel火蔓延模型的火行为特征估测,比较了不同森林类型的地表可燃物的反应强度和蔓延速度,分析了可燃物负荷量、含水率、坡度、风速对反应强度和蔓延速度的影响。结果表明,可燃物负荷量与火反应强度正相关；侧柏林的火反应强度最高,其次是油松林,元宝枫林最低；相同含水率情况下的火反应强度,油松林>侧柏林>元宝枫林；在坡地上,油松林的火蔓延速度高于其他两个类型；相同风速下,油松林火蔓延速度最快,其次是元宝枫林,最慢的是侧柏林。(3)基于Byram火线强度和火焰长度模型,根据无风条件下火焰高度、可燃物层次和针叶树树冠下沿所在层次高度,建立了可燃物垂直连续指数(C)及等级；应用C对侧柏林和油松林的垂直连续性进行了评估；采用修枝、稀疏灌木、枯枝平铺等措施定量调控可燃物垂直连续性,.降低了针叶林树冠火发生的危险性。(4)根据北京地区防火季节月最大风速和火焰水平伸展距离以及样方面积,构建了可燃物水平连续指数(D)；应用D评估了侧柏林和油松林的树冠可燃物的水平连续性；采用在坡度和风速影响下调整林分针叶树种组成比例等方法,初步对侧柏林的可燃物水平连续性进行了定量调控。(5)依据火焰高度等级,提出了可燃物连续性临界负荷量(WD)及计算公式,得出了侧柏林和油松林不同垂直连续性等级的临界负荷量,可作为针叶林可燃物连续性调控的基础。更多还原

【Abstract】 This dissertation studied the fuel spatial distribution and characteristics and structure and potential fire behavior in forest space combustible units using fuel classification, fuel loading survey, statistics analysis, calculation model and other methods, through analyses of fuel loading distributions among tree, shrub, grass and litter/duff in major forests in the mountainous area of Beijing. The relation between the spatial distribution of fuel and crown fire was quantified by using the vertical and horizontal continuity indices and ratings. Based on the continuity models of forest fuel, the hazard of crown fire was evaluated and precautions to prevent the formation and spread of crown fires were proposed for major coniferous forests. The innovation of this paper was fuel continuity model and ratings, fuel loading threshold and fuel quantitative control. The major results are as follow:(1) By studying tree species composition and branches loadings of Pinus tabulaeformis, Platycladus orientalis, and Acer truncatum forests, the difference of fuel loadings for the various forest types and all levels were compared, and the influences of different species composition and fuel loading spatial distribution on the occurrence and spread of crown fire were analyzed. The results showed that fuel loading between forest types varied obviously, Platycladus orientalis forest (61.1t/hm2)> Pinus tabulaeformis forest (47.0t/hm2)> Acer truncatum forest (22.9 t/hm2); the differences of fuel loadings for shrub layer of three forest types were significant, and 90% of shrub layer loading was concentrated on several shrub species including Vitex negundo var. heterophylla, Lespedeza bicolor, Amorpha fruticosa and so on; the existence and the proportion of conifers in forest stands were basic conditions of the occurrence and spread of the crown fire.(2) Through the analysis of physical and chemical properties of different species and fuel categories and the estimates of fire behavior characteristics based on the Rothermel model of fire spread, the reaction intensities and spread speeds for different forest types were compared, and the impacts of fuel loading, moisture content, slope, wind speed on the reaction intensity and spread speed of fires were analyzed. The results indicated that fire reaction intensity was positively correlated with fuel loading; the reaction intensity in Platycladus orientalis forest was highest, Pinus tabulaeformis forest was mediate, and Acer truncatum forest was lowest; under the same moisture content, the order of fire reaction intensities (from high to low) was Pinus tabulaeformis> Platycladus orientalis> Acer truncatum; on the slope, fire spread speed of Pinus tabulaeformis forest faster than that of Acer truncatum and Platycladus orientalis forests; under the same wind speed, the rate of fire spread took the order (from high to low) of Pinus tabulaeformis> Acer truncatum> Platycladus orientalis.(3) Based on Byram’s fireline intensity and flame height models, vertical fuel continuity index (C) and the rating system were established based on the flame height under calm condition, the levels of fuel and the height of the base of coniferous crown. The fuel vertical continuities of Platycladus orientalis and Pinus tabulaeformis forests were evaluated using C. The measures of pruning, thinning shrub, scattering dead wood and branches can control fuel vertical continuity and decrease the risk of crown fire occurrence in the coniferous forests.(4) Fuel horizontal continuity index (D) and the rating system were founded according to sampling area, flame horizontal length and the monthly maximum windspeed in fire seasons of Beijing; D was used to evaluate the fuel horizontal continuity of Platycladus orientalis and Pinus tabulaeformis forests. Fuel horizontal continuity in Platycladus orientalis forest was quantitatively primary regulated using the methods such as adjusting the composition proportion of conifers under the influence of the slope and the wind speed.(5) A new concept of the loading threshold (WD) for fuel continuity was proposed and formulated mathematically on the basis of flame height ratings. WD of fuel vertical continuity rating for Platycladus orientalis and Pinus tabulaeformis forests can be computed and used as the basis of fuel vertical continuity regulation in coniferous forests.更多还原