云南松林内可燃物与计划烧除火行为的相关分析

为了研究森林可燃物对林火的发生及发生后林火行为的影响程度,采用小样地调查方法对四川省西康磨盘林区的云南松(Pinus yunnanensisFranch)林内的可燃物及火行为进行调查,对标准地中的火蔓延速度、火强度、火焰高度进行相关性分析;对不同火强度下烧失率进行统计。试验结果表明:定期进行计划火烧,能减少可燃物积累,降低森林可燃性,具有良好的防火功能;在进行有计划的烧除林内枯枝落叶时,必须有效地控制火强度。     

油松辽东栎凋落叶可燃物载量对火行为的影响

林地可燃物火行为的研究是林火管理、林火预报、火灾扑救的理论基础,森林可燃物类型及特性对可燃物的火行为具有非常重要的影响。通过室内点烧试验,分析油松辽东栎凋落叶可燃物载量对火行为的影响。结果表明:载量对蔓延速度有显著影响,载量越大,蔓延速度越快;可燃物载量对蔓延速度、火线强度、火面强度、火焰高度都有显著影响,均呈正相关,对火线强度、火面强度、火焰高度有极显著影响。降低地表可燃物载量能够有效降低发生地表火的潜在危险性。     

林火行为和扑救技术研究进展

森林火灾会破坏森林资源，积极开展林火扑救研究对于保护森林资源具有重要意义。林火行为研究一直是林火研究领域的重点。文中针对地下火、地表火和树冠火3种类型，从火行为和扑救技术2个方面进行综述；认为通过研究林火发生与蔓延机理，建立基于燃烧物理机制的火增长模型，是发展林火扑救技术的科学基础。林火行为未来研究的重点是，探究自然条件下的地下火蔓延机制，发展地下火探测技术；完善地表火和树冠火蔓延的物理模型，确定地表火向树冠火转换的临界条件；提升火行为预报能力和开发扑救装备，增强扑救能力。     

森林火灾蔓延强度与能量释放表述

森林可燃物燃烧时整个火场热量释放速度称为林火强度(简称火强度)。火强度包括火线强度和发热强度,前者应用较为广泛,是林火行为的重要参数之一。在实际森林火灾中,火强度变化幅度相差极大,火蔓延速度是林火行为的一个重要指标。火持续时间是指山火在某一地点的驻留时间。在同等火强度条件下,火持续时间越长,火作用力越大。通过了解这些因素对火灾的影响以及控制措施,可以为扑救森林火灾做好必要准备。     

森林燃烧中的特殊火行为研究进展

在森林火灾中,当火强度达到一定程度时,具有特殊的火行为现象.森林燃烧中的特殊火行为研究是国内外研究难点和重点之一,特殊火行为的特征有:火强度急剧增加、可持续的火蔓延速度很快、空气对流十分容易、远距离飞火、火旋风或大片的水平火焰、风突然平静.特殊火行为的现象有火旋风、对流柱、飞火和火爆等.当火表现出以上这些特征和现象时,它的强度就已经达到了常规的扑灭方法进行扑救很少有效的程度.在这种情况下,扑救工作要在那些能够保证安全工作的部分火线上进行,采取措施去保护宝贵的财产或资源.     

森林火行为与特殊火行为研究进展

森林火灾主要包括地表火、地下火、树冠火3种蔓延形式.目前火蔓延模型主要关注于森林地表火的蔓延研究,对一些特殊的火行为,如树冠火、火旋风、飞火等研究极为薄弱,而这些火行为在特大森林火灾的蔓延传播中起着重要作用,往往加速火蔓延,并对扑火人员造成生命危险.我国森林大多集中在山区,火灾一旦发生,由于复杂的地形、不均匀的可燃物分布、多变的局地风和林火的相互作用,极易形成复杂的火行为.文中对森林火灾中的火行为和特殊火行为进行了论述,讨论了当前的研究进展和未来发展趋势.     

林分尺度上的森林火灾风险评估方法及应用

[目的 ]基于森林燃烧概率、潜在火行为和火影响评估一个区域的森林火灾风险是有效开展林火管理的基础。[方法 ]利用森林燃烧概率模拟软件(Burn-P3)模拟了北京九龙山林场的燃烧概率、潜在火强度、蔓延速度及火发生类型。根据林场内各林班的生态重要性、生态脆弱性和保护等级确定火影响,并考虑火对周围城镇和水源的潜在影响,利用层次分析方法建立了林分尺度上的森林火灾风险评估体系。[结果 ]结果表明,研究区的平均燃烧概率为0.035 1,燃烧概率高和很高的区域分别占研究区的10.3%和6.0%。火烧以地表火和间歇性树冠火为主,平均火强度及蔓延速度分别为2 140.9 kW·m~(-2)和3.7 m·min~(-1)。火行为指数高和很高的区域分别占17.8%和14.0%。[结论 ]研究区森林生态价值和火对环境的影响较高。森林火灾风险评估结果显示,火灾风险高和很高的区域占31.8%。西部、北部及南部的落叶松林和混交林的火灾风险较高,未来需要加强针对性的林火管理。     

应用线性方程确定林火强度

森林火灾作为燃烧系统,和森林可燃物的数量,含水量以及分布状态有关,也和当时的蔓延速度和可燃物的燃烧速率有关。按照不同的要素,包括初始燃烧速率,蔓延速度和地表杂草枯枝落叶层单位面积上的负荷量,以确定林火强度。火爬坡时,蔓延速度增加,火强度相应地增加;相反,下坡火的蔓延速度减缓,火强度也相应地变小。根据计算结果,林火强度不超过1×10~3千瓦/米~2是低强度,这时1立方米内的可燃物被烧掉的数量不超过3公斤,地表杂草枯枝落叶层的可燃物数量(W_0)不超过2.5公斤。即便地表可燃物保持在2.5公斤以下,蔓延速度大于3米/分时,火强度均将超过1×10~3千瓦/米~2。地被物数量大,火蔓延速度也大的林型中将产生最大的火强度,这和过去的经验是完全符合的。     

森林火灾中高能量火——飞火研究进展

森林火灾中高能量火的爆发伴随着突发性、随机性和不可抗拒性，会给森林火灾的扑救工作带来极大困难，并对扑火人员的生命安全造成严重威胁。飞火是一种较为常见的高能量林火行为，飞火的产生往往是林火行为愈演愈烈的唯一警告。文中结合国内外森林飞火行为相关研究进展，阐述了飞火的产生原因，并从飞火不同燃烧阶段以及不同火源引燃机理等方面总结飞火行为研究进展，分析飞火的形成机制，以期为提高森林火灾扑救效率、减少森林火灾扑救伤亡和进一步开展飞火研究提供参考。     

黑龙江省夏季林火火焰高度和火强度的研究

介绍了黑龙江省夏季森林火灾的种类,其包括地表火、地下火、树冠火三种.分析了这三种林火蔓延方式之间的相互演变关系,阐述了火强度的研究方法并给出了平均火强度值.     

Effects of fuel treatments on fire severity in an area of wildland–urban interface,Angora Fire,Lake Tahoe Basin,California

The Angora Fire burned 1243 ha of Jeffrey pine and mixed conifer forest in the Lake Tahoe Basin between June 24 and July 2, 2007. The Angora Fire burned at unusually high severity due to heavy fuels; strong winds; warm, dry weather; and unseasonably low fuel moistures. The fire destroyed 254 homes, and final loss and suppression cost estimates of $160,000,000 make the Angora Fire one of the ten costliest wildfires in US history. The Angora Fire burned into 194 ha of fuel treatments intended to modify fire behavior and protect private and public assets in the Angora Creek watershed. The fire thus provides a unique opportunity to quantitatively assess the effects of fuel treatments on wildfire severity in an area of wildland–urban interface. We measured fire effects on vegetation in treated and adjacent untreated areas within the Angora Fire perimeter, immediately after and one year after the fire. Our measures of fire severity included tree mortality; height of bole char, crown scorch, and crown torch; and percent crown scorch and torch. Unlike most studies of fuel treatment effectiveness, our study design included replication and implicitly controlled for variation in topography and weather. Our results show that fuel treatments generally performed as designed and substantially changed fire behavior and subsequent fire effects to forest vegetation. Exceptions include two treatment units where slope steepness led to lower levels of fuels removal due to local standards for erosion prevention. Hand-piled fuels in one of these two units had also not yet been burned. Excepting these units, bole char height and fire effects to the forest canopy (measured by crown scorching and torching) were significantly lower, and tree survival significantly higher, within sampled treatments than outside them. In most cases, crown fire behavior changed to surface fire within 50 m of encountering a fuel treatment. The Angora Fire underlines the important role that properly implemented fuel treatments can play in protecting assets, reducing fire severity and increasing forest resilience.     

Stand structure, fuel loads, and fire behavior in riparian and upland forests, Sierra Nevada Mountains, USA; a comparison of current and reconstructed conditions

Fire plays an important role in shaping many Sierran coniferous forests, but longer fire return intervals and reductions in area burned have altered forest conditions. Productive, mesic riparian forests can accumulate high stem densities and fuel loads, making them susceptible to high-severity fire. Fuels treatments applied to upland forests, however, are often excluded from riparian areas due to concerns about degrading streamside and aquatic habitat and water quality. Objectives of this study were to compare stand structure, fuel loads, and potential fire behavior between adjacent riparian and upland forests under current and reconstructed active-fire regime conditions. Current fuel loads, tree diameters, heights, and height to live crown were measured in 36 paired riparian and upland plots. Historic estimates of these metrics were reconstructed using equations derived from fuel accumulation rates, current tree data, and increment cores. Fire behavior variables were modeled using Forest Vegetation Simulator Fire/Fuels Extension.Riparian forests were significantly more fire prone under current than reconstructed conditions, with greater basal area (BA) (means are 87 vs. 29 m²/ha), stand density (635 vs. 208 stems/ha), snag volume (37 vs. 2 m³/ha), duff loads (69 vs. 3 Mg/ha), total fuel loads (93 vs. 28 Mg/ha), canopy bulk density (CBD) (0.12 vs. 0.04 kg/m³), surface flame length (0.6 vs. 0.4 m), crown flame length (0.9 vs. 0.4 m), probability of torching (0.45 vs. 0.03), predicted mortality (31% vs. 17% BA), and lower torching (20 vs. 176 km/h) and crowning indices (28 vs. 62 km/h). Upland forests were also significantly more fire prone under current than reconstructed conditions, yet changes in fuels and potential fire behavior were not as large. Under current conditions, riparian forests were significantly more fire prone than upland forests, with greater stand density (635 vs. 401 stems/ha), probability of torching (0.45 vs. 0.22), predicted mortality (31% vs. 16% BA), and lower quadratic mean diameter (46 vs. 55 cm), canopy base height (6.7 vs. 9.4 m), and frequency of fire tolerant species (13% vs. 36% BA). Reconstructed riparian and upland forests were not significantly different. Our reconstruction results suggest that historic fuels and forest structure may not have differed significantly between many riparian and upland forests, consistent with earlier research suggesting similar historic fire return intervals. Under current conditions, however, modeled severity is much greater in riparian forests, suggesting forest habitat and ecosystem function may be more severely impacted by wildfire than in upland forests.     

METHODS OF EVALUATING FOREST FIRE HISTORY

Forest fire history can be reconstructed over past centuries across a widevariety of forest types.Fire scars on living tress,and age classes of forest stands,are thetwo sources of information for these reconstructions.Point and area frequencies are usedto reconstruct fire history.Point frequencies are useful in forest types that burn withfrequent,low intensity fire so that many fire-scarred residual trees exist.A true point isa single tree,but more often point estimates are made by combining fire scar records fromseveral adjacent trees.Area frequences are applied where fires are infrequent but ofmoderate to high intensity,so that stand ages are used across wide areas to estimate firereturn interals.Proper selection and application of fire history methods are essential toderiving useful ecological implications from fire history studies.This review evaluates the common methods of determining fire history:what thetechniques are,where they are best applied,and how to interpret them in an ecologicalcontext.E     

FIRE IN NORTHEAST CHINA FORESTS

Fire plays an important role in Northeast China forests,The occurrence of fires isclosely related to the environmental characteristics.High temperature,drought,and strong wind inspring(March to July)and autumn(September to November)are common fire climatic character-istics in Northeast China.Based on the chemical and physical characters of fuels,fuel quantity dis-tribution,sites as well as fire potential behaviour,fourteen fuel types have been classified inNortheast China Forest area.The fire adaptation of several main tree species has been also analysedin this paper.These species are widely distributed and of great economic significance in NortheastChina.Fire use is paid much more attention recently.Fire have been employed in many silviculturepractice such as fireline creation,fuels reduction and seed bed preparation in Northeast China     

Changes in wildfire severity from maritime pine woodland to contiguous forest types in the mountains of northwestern Portugal

Large and severe wildfires are now widespread in the Mediterranean Basin. Fire severity is important to ecosystem properties and processes and to forest management but it has been neglected by wildland fire research in Europe. In this study, we compare fire severity between maritime pine (PS) woodland and other forest (OF) types, identify other variables influent on fire severity, and describe its variation. We sampled contiguous, paired stands of PS and OF cover types – including deciduous and evergreen broadleaves and short-needled mountain conifers – that burned under very high to extreme fire danger in northwestern Portugal. Data on stand characteristics and fire severity metrics were collected in plots along transects perpendicular to the PS–OF boundary. Fire severity was rated in separate for the tree canopy, understorey vegetation and forest floor layers, and then an average (composite) fire severity rating was calculated. Fire intensity inferred from stem char height (adjusted for the effects of other factors) was highest in PS, followed by deciduous broadleaved woodland and short-needled conifer forest. With a few exceptions, all fire severity ratings were significantly different between PS and OF at all sites. Most fire severity metrics and ratings were correlated. The distance for fire severity minimization did not differ between OF types (median = 21 m). Variation in composite fire severity was accounted for by a classification tree (R² = 0.44) based on cover type (contributing with 51% to the overall explanation), stand variables, aspect, distance to the PS–OF edge and fire spread pattern. Except for a more immediate decline in deciduous broadleaves, fire severity rating was not affected by OF type and tended to decrease in more mature stands and moister aspects. The fire severity moderation from PS to OF was compounded by a dominant pattern of down slope fire propagation into moister topographical positions, exacerbating the fuel effect implicit in the cover type change. The results are consistent with fire hazard and fire incidence studies and support conventional knowledge that advocates the expansion of broadleaved deciduous or evergreen forest as a means to achieve more fire-resilient ecosystems and landscapes.     

永安市森林火险等级区划研究

针对永安市森林火灾发生特点与规律 ,参照YL10 6 3 - 92《全国森林火险区划等级》 ,按照农业人口密度、路网密度、气温、风速、降水量、树种 (组 )燃烧类型的指标值与立木蓄积量和有林地、未成林面积等火险因子 ,求算两项综合得分值 ,确定火险等级。     

思茅松林的可燃物与火行为研究

通过野外调查,基于森林亚类型,以主要伴生树种或下层植被为基础,对思茅松林内可燃物进行划分,并在林内进行试验火烧,得到相应的火行为参数.结果表明,思茅松林的火行为强度比较弱,主要为中低强度的火,这与林内的可燃物有关,也和所处的生境和立地条件有关;火烧后的树木死亡率比较低,表明思茅松在长期的演替中已经适应了火烧.     

Historic and current fire regimes in the Great Xing’an Mountains,northeastern China: Implications for long-term forest management

Understanding both historic and current fire regimes is indispensable to sustainable forest landscape management. In this paper, we use a spatially explicit landscape simulation model, LANDIS, to simulate historic and current fire regimes in the Great Xing’an Mountains, in northeastern China. We analyzed fire frequency, fire size, fire intensity, and spatial pattern of burnt patches. Our simulated results show that fire frequency under the current fire scenario is lower than under the historic fire scenario; total area burnt is larger with lower fire intensity under the historic fire scenario, and smaller with higher fire intensity under the current fire scenario. We also found most areas were burned by high intensity fires under the current fire scenario, but by low to moderate fires under the historic fire scenario. Burnt patches exhibit a different pattern between the two simulation scenarios. Large patches burnt by high intensity class fires dominate the landscape under the current fire scenario, and under historic fire scenario, patches burnt by low to moderate fire intensity fires have relatively larger size than those burnt by high intensity fires. Based on these simulated results, we suggest that prescribed burning or coarse woody debris reduction should be incorporated into forest management plans in this region, especially on north-facing slopes. Tree planting may be a better management option on these severely burned areas whereas prescribed burning after small area selective cutting, retaining dispersed seed trees, may be a sound forest management alternative in areas except for the severely burned patches.     

广西大桂山区防火树种的选择研究

森林火灾是危害森林的一大主要自然灾害,采用生物防火可以有效地控制特大森林火灾的发生。本文对广西大桂山区的木荷、火力楠、杨梅等１０种常绿阔叶树种和杉木、马尾松两种针叶树种的叶、小枝和皮的燃烧性能及其组成成分进行了测定,结果表明：（１）各树种均以叶的抗火性能最差,阔叶树种比针叶树种的抗火性能强;（２）热值、含水量、燃点和灰分含量是影响叶的抗火能力的主要指标。木质素含量和苯乙醇抽取物与总发热量有线性相关关系;（３）由多目标决策方法对１２种树的抗火性能综合排序得知,木荷、红椎、杨梅的抗火性强,润楠、米老排、火力楠、大桂山荷和木莲的抗火性中等,稠木、观光木的抗火能力较弱,杉木、马尾松的抗火能力强。