Effects of vegetation type and fire regime on flammability of undisturbed litter in Southeastern France

To assess the effect of vegetation types and of fire regime on the flammability of dead fuels, samples of litter were collected undisturbed (i.e. keeping the structure of litter layers) in 29 study sites spread over the limestone-derived soils of Provence. The sampling plan comprised the most representative ecosystems of the study area: pure Pinus halepensis stands, mixed pine-oak stands and shrublands. Three classes of litter depth were studied (low, medium and high) to account for the variability existing in the field. Sampling also included the number of fires in each site since 1960 (no fire, 1 or 2 fires and ≥3 fires) and the time interval since the last fire (≤15 years, 15-45 years and >45 years). Flammability experiments were carried out in laboratory using a glowing firebrand and a 10 km h⁻¹ wind. The main variables recorded were: ignition frequency, time-to-ignition, flaming duration, flame rate of spread, flame propagation, mean flame temperature, maximum flame height and rate of consumption.Results showed that the ignition frequency was higher in mixed stands than in pure pine stands whereas the time-to ignition, flaming duration and rate of consumption were the highest in pure pine stands. The maximum flame height and the flame propagation decreased with the increase of the number of fires and the time-to-ignition was the highest when the interval since the last fire was the shortest. Increases in litter depth resulted in increased mean flame temperature, maximum flame height and flame propagation. These results can be explained, in part, by the proportions of the different litter components.     

迎面火与主地表火相互作用的实验研究

为了研究地表火卷吸作用的范围和迎面火与主火相互作用的机理 ,在大空间室内实验室进行了实验研究 .在该实验室实验可以避免环境风和环境温度变化的影响 .研究结果表明 :(1)在火头前方有明显的逆风区存在 .在逆风区下部的逆风风速要比上部的大 ,而且当高度达到某一数值时 ,逆风就不明显了 ;(2 )迎面火与主火之间即使相距较远也存在相互作用 .当它们相互接近到一定程度时 ,彼此相互吸引 .这使得火的蔓延速度显著升高 .对于火线火强度为 16 0kW·m-1地表火来说 ,蔓延速度增加2 7% .     

Canopy fuel characteristics and potential crown fire behavior in Aleppo pine (Pinus halepensis Mill.) forests

Canopy fuel characteristics that influence the initiation and spread of crown fires were measured in representative Aleppo pine (Pinus halepensis Mill.) stands in Greece. Vertical distribution profiles of canopy fuel load, canopy base height and canopy bulk density are presented. Aleppo pine canopy fuels are characterized by low canopy base height (3.0–6.5 m), while available canopy fuel load (0.96–1.80 kg/m²) and canopy bulk density (0.09–0.22 kg/m³) values are similar to other conifers worldwide. Crown fire behavior (probability of crown fire initiation, crown fire type, rate of spread, fireline intensity and flame length) in Aleppo pine stands with various understory fuel types was simulated with the most updated crown fire models. The probability of crown fire initiation was high even under moderate burning conditions, mainly due to the low canopy base height and the heavy surface fuel load. Passive crown fires resulted mostly in uneven aged stands, while even aged stands gave high intensity active crown fires. Assessment of canopy fuel characteristics and potential crown fire behavior can be useful in fuel management and fire suppression planning.     

Moisture content thresholds for ignition and rate of fire spread for various dead fuels in northeast forest ecosystems of China

Fuel moisture content is one of the important factors that determine ignition probability and fire behaviour in forest ecosystems. In this study, ignition and fire spread moisture content thresholds of 40 dead fuel were performed in laboratory experiments, with a focus on the source of ignition and wind speed. Variability in fuel moisture content at time of ignition and during fire spread was observed for different fuels. Matches were more efficient to result in ignition and spread fire with high values of fuel moisture content compared to the use of cigarette butts. Some fuels did not ignite at 15% moisture content, whereas others ignited at 40% moisture content and fire spread at 38% moisture content in the case of matches, or ignited at 27% moisture content and spread fire at 25% moisture content using cigarette butts. A two-way ANOVA showed that both the source of ignition and the wind speed affected ignition and fire spread threshold significantly, but there was no interaction between these factors. The relationship between ignition and fire spread was strong, with R2 = 98% for cigarette butts, and 92% for matches. Further information is needed, especially on the density of fuels, fuel proportion(case of mixed fuels), fuel age, and fuel combustibility.     

西非Sudanian稀树草原森林在旱季火烧温度、持续时间及对种子萌发的影响

Prescribed fire is used in the Sudanian savanna-woodland of West Africa as a forest management tool. An experiment was carried out to assess the effects of season of burning, and different vertical probe positions on maximum fire temperature and temperature residence time above 60°C which is considered lethal for plant tissues. Seasons of burning considered were: an early season fire set at the beginning of the dry season (beginning of December), mid-season fire set at the peak of the dry season (mid-January), and a late season fire at the end of the dry season (end of March). The effects of these fires on the germination of buried seeds of three socio-economically valuable tree species were also examined. Results indicated significant differences in maximum fire temperature and residence time with respect to season of burning and vertical probe position (p < 0.001). The highest and longest lasting temperatures were observed at 20 cm above ground during early fire and at the soil surface during mid-season and late fires. This, in turn, affected germination responses of seeds buried at different soil depths. Implications of these findings in the current management practices are discussed.     

Nomographs for predicting crown fire initiation in Aleppo pine (<Emphasis Type="Italic">Pinus halepensis</Emphasis> Mill.) forests

Nomographs that calculate the threshold values of surface fire parameters which lead to crown fire initiation were created by linking two separate fire behavior models: Van Wagner’s crown fire ignition criteria and Byram’s surface fire model. The nomographs were also based on the existing surface (fuel load, fuel heat content) and canopy (foliar moisture content, live crown base height) fuel models of Aleppo (Pinus halepensis Mill.) pine forests of Mediterranean Greece. The most important fire parameters for crown fire initiation that are calculated by the nomographs are the critical flame length and the forward spread rate of the surface fire. These parameters are readily observable in the field during fires. The nomographs provide a judicious way to assess whether a crown fire is likely to occur in a conifer forest stand. Although the fire behavior models used had limited testing and are based on certain assumptions, yet they are widely applied in forestry practice worldwide, as a basis for justified fire prevention and suppression planning.     

Forest Fire Risk Zone Modeling Using Logistic Regression and GIS: An Iranian Case Study

Forest fires are an important environmental concern worldwide, affecting the soil, forests and human lives. During the process of burning, soil nutrients are depleted and the soil is subsequently more vulnerable to erosion. Nowadays it is necessary to identify the factors influencing the occurrence of fire and fire hazard areas, in order to minimize the frequency of fire and avert damage. Logistic regression was used to study the forest fire risk and identify the most influential factors in the occurrence of forest fires. Climatic variables (temperature and annual precipitation), human factors (distance from streams and farmland) and physiography (land slope and elevation) were considered and their correlation with the occurrence of fires investigated. Results of model validation and sensitivity of various areas to fire were examined with the ROC coefficient and Hosmer–Lemeshow test. The estimated coefficients for the independent variables indicated that the probability of occurrence of fire is negatively related to land slope, site elevation and distance from farmlands, but is positively related to amount of annual precipitation.     

Soil nutrients and microbial activity after early and late season prescribed burns in a Sierra Nevada mixed conifer forest

Restoring the natural fire regime to forested systems that have experienced fire exclusion throughout the past century can be a challenge due to the heavy fuel loading conditions. Fire is being re-introduced to mixed conifer forests in the Sierra Nevada through both early season and late season prescribed burns, even though most fires historically occurred in the late season. We assessed the impact of early and late season prescribed fires on soil biogeochemical and microbiological parameters that are important for ecosystem recovery. We found that the late season burns had more dramatic short-term effects on soil abiotic conditions (temperature, moisture and pH), mineral soil carbon levels, total inorganic nitrogen, and microbial activity than the early season burns, relative to unburned sites, suggesting a higher severity burn. However, the total soil nitrogen pools and fluxes and soil respiration rates were not differentially impacted by burn season. These burn season effects suggest that soil variables may be regulated more strongly by fire severity than by the season in which the prescribed fire is conducted.     

王正非林火蔓延模型改进研究

王正非林火蔓延模型是目前国内比较先进的森林火灾蔓延模型,但是由于林火行为的复杂性,此模型在准确率和普适性方面仍存在许多不足。本文结合已有的成果进一步改进王正非模型,增加了可燃物湿度对林火蔓延速度的影响,改进了林火初始速度的计算方式。针对各种坡度对林火蔓延行为的影响给出了一个计算公式。与改进前相比,改进后的模型使其对林火蔓延情况的预估更为精准。     

Summer Forest Fire Meteorological Environment in the North of Daxingan Mountains

In recent years, especially in the summer of 2002, the most serious forest fires occurred in the Daxingan Mountain of Heilongjiang province and Inner Mongolia. There has been long time serious forest fire environment in summer in Daxingan Mountain. The grass in the forest is scorched for long time drought and the moisture content of litter and turf layer decrease rapidly. The accumulation and dryness of fuel build the summer forest fire environment, which are major caused by Meteorological environment. Human are lack of the right recognition of summer fires, and can not achieve the goal of detecting and fighting in time. Also summer fires have the tendency to increase in some areas of the world and human have to pay much more attention to how to prevent and control summer fires.     

桉树扦插育苗轻基质试验

试验结果表明：在１２种不同配方基质中,各组合基质间的干、湿重达极显著差异,扦插生根率和杯期苗木高生长达显著或极显著差异。以容积比为２：１的炭化木糠＋黄心土基质的平均每扦插杯干重和湿重都最轻,分别为４０．９ｇ和５２．１ｇ;扦插平均生根率最高的为泥炭土＋黄心土基质,生根率最低的为容积比１：１的炭化栲胶渣＋黄心土基质,分别为８５．％和６．７％;从基质改良角度考虑,容积比为２：１：１的木糠＋黄粘土＋黄心土     

The ecology of mixed severity fire regimes in Washington, Oregon, and Northern California

Forests characterized by mixed-severity fires occupy a broad moisture gradient between lower elevation forests typified by low-severity fires and higher elevation forests in which high-severity, stand replacing fires are the norm. Mixed-severity forest types are poorly documented and little understood but likely occupy significant areas in the western United States. By definition, mixed-severity types have high beta diversity at meso-scales, encompassing patches of both high and low severity and gradients in between. Studies of mixed-severity types reveal complex landscapes in which patch sizes follow a power law distribution with many small and few large patches. Forest types characterized by mixed severity can be classified according to the modal proportion of high to low severity patches, which increases from relatively dry to relatively mesic site conditions. Mixed-severity regimes are produced by interactions between top-down forcing by climate and bottom-up shaping by topography and the flammability of vegetation, although specific effects may vary widely across the region, especially the relation between aspect and fire severity. History is important in shaping fire behavior in mixed-severity landscapes, as patterns laid down by previous fires can play a significant role in shaping future fires. Like low-severity forests in the western United States, many dry mixed-severity types experienced significant increases in stand density during the 20th century, threatening forest health and biodiversity, however not all understory development in mixed-severity forests increases the threat of severe wild fires. In general, current landscapes have been homogenized, reducing beta diversity and increasing the probability of large fires and insect outbreaks. Further loss of old, fire tolerant trees is of particular concern, but understory diversity has been reduced as well. High stand densities on relatively dry sites increase water use and therefore susceptibility to drought and insect outbreaks, exacerbating a trend of increasing regional drying. The need to restore beta diversity while protecting habitat for closed-forest specialists such as the northern spotted owl call for landscape-level approaches to ecological restoration.     

Effect of recurrent fires on soil nutrient dynamics in a tropical dry deciduous forest of Western Ghats,India

The role of forest fires in the soil dynamics and global carbon cycle has not been comprehensively studied in tropical forests as the effects of fire on tropical forest soils can be extremely variable. This study was aimed to understand how repeated fires affect physical and chemical properties of soil in a tropical dry deciduous forest and alter soil fertility and health. The study was carried out in the dry deciduous forest of Mudumalai Tiger Reserve. Soil samples were collected from unburned (B0) to six-time burned (B6) plots. Samples were collected from each plot from three different depths viz. 0–10 (Top), 10–20 (Middle), and 20–30 cm (Bottom) and analyzed for soil physical and chemical properties. Soil pH, EC, WHC decreased with increasing fire frequencies while bulk density increased. Organic Carbon, Total N, and available P decreased with increasing fire frequencies whereas extractable K initially increased but decreased with the very high frequency of fires. NO₃^?N slightly decreased with high fire frequencies but NH₄^?N decreased significantly with increasing fire frequency. These results provide a new insight regarding the influence of repeated fires on soil that will be valuable to understand the effect of fire on the recovery of soils and nutrient dynamics.     

Litter Decomposition in Three Plantation Species in Semi-Arid and Sub-Humid Regions of Central India

Abstract

The forest floor litter decomposition rate followed in the order: Tectona grandis(teak) > Madhuka indica (mahua) > Butea monosperma (palas). Higher decomposition rates were observed during rainy season and lowest during winter. The decay rate was significantly correlated with rainfall and soil moisture, and with population densities of earthworms. The lumbricid distribution under three plantations of semi-arid and sub-humid regions of central India in relation to several environmental factors including climate, soil moisture and litter quality was studied. Native species of earthworms and their densities were not abundant in this forest due to less moisture content in soil and accidental forest fires. Eight earthworms were identified and three of them were epigeic earthworms, viz., Eisenia fetida (Savigny), Perionyx excavatus (Perrier) and Dichogaster bolaui (Michaelsen), which were predominant throughout the year.     

Analysis of the seasonal characteristics of forest fires in South Korea using the multivariate analysis approach

For efficient forest fire management, special precautions are required in dry and strong-wind seasons vulnerable to severe forest fires. To extract the seasonal characteristics of forest fires in South Korea, the statistics over the past 16 years, 1991 through 2005, were investigated. The daily records of the number of fire occurrences, the total area burned and the average burned area per occurrence were examined to identify the seasonal patterns of forest fires using cluster analysis and principal component analysis; the risk of daily fires was also assessed using the ordered logit model. As a result, the fire patterns were classified into five clusters and a general danger index for forest fires was derived from the first principal component, showing relatively large-scaled fire regimes in spring, and frequent small-scaled fire regimes in autumn and winter. In connection with the ordered logit model, the probability for the five ranks of forest fire risk was calculated and the threshold for high-risk fires was detected. As an implementation of the results above, the proper forest fire precautionary period in South Korea was estimated, and consequently October 21 through May 17 was recognized as a dry season at a high risk of forest fires. This period began 10 days earlier in autumn and extended into midwinter (late December and January) as opposed to the existing precautionary period, indicating the need of more cautious forest fire management earlier in autumn and continuing through midwinter.     

Spatial heterogeneity of dead fuel moisture content in a Larix gmelinii forest in Inner Mongolia using geostatistics

Spatial heterogeneity of fuel moisture content determines the spread rate and direction of a forest fire.Research on the spatial heterogeneity of the moisture content of dead fuel of Larix gmelinii Rupr.showed that:(1) fuel moisture content in litter layer semi-humus layer humus layer,and the coefficient of variation decreased with sampling depth;(2) the sill value of the semi-humus layer was highest,the humus layer moderate,the litter layer the smallest,overall,the spatial heterogeneity of the semi-humus layer was the highest.The humus layer in the slant direction and three layers in a vertical direction showed strong spatial correlation with the lowest nugget coefficient of 0.0968;(3)the fuel moisture content of the humus layer showed strong spatial anisotropy;and,(4) estimating the total moisture content of the sampling site by stimulated sampling reasonable control of the sampling interval,and increasing the sampling intensity can reduce the error.When the sampling intensity is increased to more than 16 and the sampling interval 3 m,the standard error is 15%.The spatial heterogeneity of fuel moisture content is best revealed by increasing sampling density,sampling in different fire seasons,and in different slope directions and positions.The results can provide a scientific basis for forest fire prediction and prevention.     

Mulch type and moisture level affect pupation depth of <Emphasis Type="Italic">Rhagoletis mendax</Emphasis> Curran (Diptera: Tephritidae) in the laboratory

Mulching can be beneficial for organic highbush blueberry production, but its effects on insect pests have received little attention. For pests that pupate in soil, depth may affect pupation success due to differences in temperature and moisture, mortality factors such as predation, or efficacy of controls such as insecticidal soil drenches. We examined how mulch type and moisture affect pupation depth for Rhagoletis mendax Curran (blueberry maggot), an important pest of blueberries. In laboratory studies, pupation depth was measured in wood waste compost, uncomposted pine needles, soil and sand, each at dry, field moisture levels and wet, 99% water holding capacity conditions. Pupation occurred more deeply but with greater variability in pine needle mulch compared to compost mulch, soil, or sand. Approximately 50% of maggots pupated on the surface of wet soil, however, maggots burrowed more deeply in wet than in dry pine needles. Moisture level did not significantly affect pupation depth in compost or sand. Some larvae unexpectedly escaped the stacks of cups used to assess pupation depth or died before forming a puparium. Less than 70% of stacks with dry pine needles contained pupae, and fewer pupae were recovered from wet than dry compost and soil. These results suggest that mulch material and/or moisture levels can have significant impacts on R. mendax pupation depth with potential implications for its management.     

Fire-vegetation interplay in a mosaic structure of Quercus suber woodlands and Mediterranean maquis under recurrent fires

We examined the effects of fire recurrence on a mosaic structure of Quercus suber and Erica-Cistus shrubland communities of Southeastern France in order to improve the understanding of fire-vegetation interplay. Plant communities that were similar in 1959 (woodlands on shrublands called maquis on acidic soils) were compared along a gradient of fire recurrence, from 0 to 4 fires, with different time intervals between fires. The results showed that understory cover increased roughly with fire recurrence, whereas tree height, cover, density, stand basal area and litter depth decreased. Different fire recurrences along the past decades led to different vegetation types. High fire recurrence corresponded to maquis and sparse cork-oak woodlands while pure oak woodlands established in the absence of fire during the same period. In all, the diversity of tree diameter decreased with fire recurrence. High fire recurrence (3 or 4 fires in 50 years) led to a simple vertical structure of vegetation with a mono-layered shrub cover and few Quercus suber trees. In contrast, spatial connections between plants were maximal at longer time intervals, leading to a multi-layered vegetation. We finally discuss the potential implications of past fires on the behavior of future fires in the perspective of a sustainable management of these Mediterranean ecosystems.     

华山松人工林凋落物层细小可燃物含水率预测模型研究

在防火期2~5级火险天气条件下,在华山松人工林测定了153组林内气温(x1)、相对湿度(x2)、凋落物表面温度(x3)、腐殖质层表面温度(x4)、凋落物层厚度(x5)、可燃物含水率(y)数据,建立了华山松林细小可燃物含水率预测的多元线性回归模型。分析表明,影响华山松林凋落物上层易燃可燃物含水率的因子依次为:x3>x2>x4>x1。应用该模型,可以用易于获取的火环境和可燃物因子来预测可燃物的含水率,为合理开展林火预测预报、计划火烧、营林用火等提供依据。     

Analysis of Original Causes of Reed Fires in Zhalong Nature Wetland Reserve in Heilongjiang Province

Zhalong Nature Reserve is located in the border areaof Qiqihaer City, Fuyu County, Lindian County andTailai County of Heilongjiang Province. The area ofthe reserve is 210 000 ha. The reserve is the firstnature reserve for protecting wetland and crane inChina. There were more than 300 red-crownedcranes here at the very most. Zhalong Nature Reserveis situated at the Songnen Plain, the lower stream ofthe Wuyuer River. It is the biggest nature reserve inChina that takes crane and wetland …