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1.
The Mediterranean basin is a fire-prone area and is expected to continue being so according to projected climate and socioeconomic changes. Sustainable exploitation of forest biomass could have a positive effect on wildfire hazard mitigation. A modelling approach was used to compare how four different Scenarios for biomass collection for energy use affect fire behaviour and potential burnt area at landscape level under extreme meteorological conditions in a typical Mediterranean Massif. A case study of Pinus halepensis stands in Valencia (Eastern Spain) was conducted. The FARSITE simulator was used to evaluate the burnt area and fire behaviour parameters. Simulations predicted a significant increase in the burnt area and the values of most fire behaviour parameters in a Scenario of rural abandonment, relative to the current situation. Biomass management through thinning reduced canopy bulk density; however, no differences in the values of the main fire behaviour parameters were detected. Thinning and understory clearing, including biomass collection in large shrub fuel model areas, significantly reduces fire hazard. Forest biomass sustainable harvesting for energy is expected to reduce fire hazard if management includes intense modification of fuel models, comprising management of shrub biomass at the landscape level. Strong modification of forest fuel models requires intensive silvicultural treatments. Therefore, forest biomass collection for energy in the Mediterranean basin reduces fire hazard only if both tree and shrub strata are managed at landscape level.  相似文献   

2.
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.  相似文献   

3.
Fire behavior modeling systems are important in predicting wildfire risk, fire growth, and fire effects. However, simulation software requires a new fuel modeling to include fuel treatments, prescribed fire and the transition to crown fire. The thirteen Rothermel models are insufficient in completely representing Mediterranean ecosystems. In this sense, the new American modeling includes five fuel types, requiring the acquisition of hybrid models made up of the mixture of grass and shrub and the grass or shrub mixed with litter from forest canopy. Respecting meteorological conditions and shrub characteristics, field studies have shown significant differences between American and Mediterranean models. As a consequence, the definition of new Mediterranean models requires the adjustment of specific parameters such as fuel load by category (live and dead) and particle size class (1-, 10- and 100-h time-lag), fuelbed depth and surface area-to-volume ratio. These new parameters were obtained in situ of sample itineraries, prescribed fires, and forest fires. The availability of this new modeling, validated on a field of regional scale, will facilitate preventive planning and management as well as an efficient application of suppression techniques, both ground and aerial operations, required in defending a territory against forest fires.  相似文献   

4.
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5.
Bark beetle-caused tree mortality in conifer forests affects the quantity and quality of forest fuels and has long been assumed to increase fire hazard and potential fire behavior. In reality, bark beetles, and their effects on fuel accumulation, and subsequent fire hazard, are poorly understood. We extensively sampled fuels in three bark beetle-affected Intermountain conifer forests and compared these data to existing research on bark beetle/fuels/fire interactions within the context of the disturbance regime. Data were collected in endemic, epidemic and post-epidemic stands of Douglas-fir, lodgepole pine and Engelmann spruce. From these data, we evaluated the influence of bark beetle-caused tree mortality on various fuels characteristics over the course of a bark beetle rotation. The data showed that changes in fuels over time create periods where the potential for high intensity and/or severe fires increases or decreases. The net result of bark beetle epidemics was a substantial change in species composition and a highly altered fuels complex. Early in epidemics there is a net increase in the amount of fine surface fuels when compared to endemic stands. In post-epidemic stands large, dead, woody fuels, and live surface fuels dominate. We then discuss potential fire behavior in bark beetle-affected conifer fuels based on actual and simulated fuels data. Results indicated that for surface fires both rates of fire spread and fireline intensities were higher in the current epidemic stands than in the endemic stands. Rates of spread and fireline intensities were higher in epidemic stands due, however, to decreased vegetative sheltering and its effect on mid-flame wind speed, rather than changes in fuels. Passive crown fires were more likely in post-epidemic stands, but active crown fires were less likely due to decreased aerial fuel continuity. We also discuss the ecological effects of extreme fire behavior. Information is presented on managing forests to reduce the impact of bark beetle outbreaks and the interplay between management, bark beetle populations, fuels and fire hazard and behavior.  相似文献   

6.
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.  相似文献   

7.
Crown fire occurrence and subsequent crown fire behaviour are strongly dependent on canopy fuel characteristics, especially canopy fuel load (CFL), canopy bulk density (CBD) and canopy base height (CBH). Therefore, quantification of such variables is required for the appropriate selection of silvicultural treatments aimed at reducing susceptibility to crown fire. Data from the IV Spanish National Forest Inventory and individual tree biomass dry weight equations were used to estimate the canopy fuel characteristics of four representative types of pine stands in north-western Spain. Probability of crown fire initiation and crown fire rate of spread were simulated by using the mean surface fuel load observed for each type of pine in this area and assuming different burning conditions. The results indicate that a 22.13 % of the sample plots analysed showed a rather high potential for active crown fire spread under moderate burning conditions, and this value increases to 69.27 % under extreme burning conditions. Equations relating the canopy fuel characteristics to common stand variables (stand density, basal area and dominant height) were fitted simultaneously for each pine, and weighting factors for heteroscedasticity were included. The models explained more than 93.90, 74.70 and 69.42 % of the observed variability in CFL, CBD and CBH, respectively. Basal area was the most important variable for estimating CFL and CBD while dominant height explained most of the observed variability in CBH. The use of the fitted equations together with existing dynamic growth models and fire management decision support systems will enable assessment of the crown fire potential associated with different silvicultural alternatives used in these types of pine stands.  相似文献   

8.
Due to increases in tree density and hazardous fuel loading in Sierra Nevadan forests, land management is focusing on fuel reduction treatments to moderate the risk of catastrophic fires. Fuel treatments involving mechanical and prescribed fire methods can reduce surface as well as canopy fuel loads. Mastication is a mechanical method which shreds smaller trees and brush onto the surface fuel layer. Little data exist quantifying masticated fuel beds. Despite the paucity of data on masticated fuels, land managers desire fuel loading, potential fire behavior and fire effects such as tree mortality information for masticated areas. In this study we measured fuel characteristics before and after mastication and mastication plus prescribed burn treatments in a 25-year old ponderosa pine (Pinus ponderosa C. Lawson) plantation. In addition to surface fuel characteristics and tree data collection, bulk density samples were gathered for masticated material. Regressions were created predicting masticated fuel loading from masticated fuel bed depth. Total masticated fuel load prior to fire treatment ranged from 25.9 to 42.9 Mg ha−1, and the bulk density of masticated fuel was 125 kg m−3. Mastication treatment alone showed increases in most surface fuel loadings and decreases in canopy fuel loads. Masticated treatment in conjunction with prescribed burning reduced both surface and canopy fuel loads. Detailed information on fuel structure in masticated areas will allow for better predictions of fire behavior and fire effects for fire in masticated fuel types. Understanding potential fire behavior and fire effects associated with masticated fuels will allow managers to make decisions on the possibility of mastication to create fuel breaks or enhance forest health.  相似文献   

9.
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.  相似文献   

10.
Each year, forest fires destroy about 500,000 ha of vegetation in Europe, predominantly in the Mediterranean region. Many large fires are linked to the land transformations that have taken place in the Mediterranean region in recent decades that have increased the risk of forest fires. On the one hand, agricultural fallows and orchards are slowly being colonized by vegetation, and on the other hand, the forest is not sufficiently used, both of which result in increased accumulation of fuel. In addition, urbanization combined with forest extension results in new spatial configurations called “wildland-urban interfaces” (WUI). WUI are commonly defined as “areas where urban areas meet and interact with rural lands, wildland vegetation and forests”. Spatial analyses were performed using a WUI typology based on two intertwined elements, the spatial organization of homes and the structure of fuel vegetation. The organization of the land cover in terms of representativeness, complexity or road density was evaluated for each type of WUI. Results showed that there were significant differences between the types of WUI in the study area. Three indicators (i) “fire ignition density”, derived from the distribution of fire ignition points, (ii) “wildfire density”, derived from the distribution of wildfire area and (iii) “burned area ratio”, derived from the proportion of the burned area to the total study area were then compared with each type of WUI. Assuming that the three indicators correspond to important aspects of fire risk, we showed that, at least in the south of France, WUI are at high risk of wildfire, and that of the different types of wildland-urban interfaces, isolated and scattered WUI were the most at risk. Their main land cover characteristics, i.e. low housing and road densities but a high density of country roads, and the availability of burnable vegetation such as forested stands and shrubland (garrigue) explain the high fire risk. Improving our knowledge of relationships between WUI environments and fire risk should increase the efficiency of wildfire prevention: to this end, suitable prevention actions and communication campaigns targeting the types of WUI at the highest risk are recommended.  相似文献   

11.
Dwarf mistletoes (Arceuthobium spp.) are a group of obligate, hemiparasitic plants that infect numerous species in the Pinaceae in North America. Wildland fire is considered to be the primary natural agent influencing the population and distribution of dwarf mistletoes across landscapes. Based on this understanding, prescribed fire has been suggested as a potential method for dwarf mistletoe sanitation and control; however, experimental work has primarily focused on prescribed surface fire. In this study, we report long‐term impacts of three experimental crown fires on dwarf mistletoe severity in infested lodgepole pine stands in Colorado 33 years post‐fire. The three fires achieved tree mortality rates ranging from 20% to 100%. Our results suggested a significant negative relationship between the amount of fire‐caused tree mortality and future dwarf mistletoe severity. These findings supported the presumed natural role of fire in altering dwarf mistletoe populations, which perhaps exhibits a linear relationship between fire‐caused host tree mortality and future dwarf mistletoe severity.  相似文献   

12.
森林火灾中的树冠火研究   总被引：5，自引：1，他引：4  
森林火灾按其燃烧物和燃烧部位的不同, 通常可分为地表火、树冠火和地下火3种。树冠火是指在林冠层燃烧和蔓延的火, 通常与地表火同时发生。树冠火发生数量不多, 但其燃烧温度高、火强度大、蔓延速度快, 对森林的破坏性极大。从树冠火的发生机制、蔓延模型、扑救方法、预防和减弱树冠火发生及蔓延危险性的措施几方面对当前国内外树冠火的研究进展进行了综述, 并对今后的研究方向进行了展望。  相似文献   

13.
Forest thinning and prescribed fires are practices used by managers to address concerns over ecosystem degradation and severe wildland fire potential in dry forests. There is some debate, however, about treatment effectiveness in meeting management objectives as well as their ecological consequences. The purpose of this study was to assess changes to forest stand structure following thinning and prescribed fire treatments, alone and combined, in the eastern Cascade Mountains of Washington State. Treatments were applied to 12 management units, with each treatment combination replicated three times (including untreated controls). Thinning modified forest structure by reducing overall tree density by >60% and canopy bulk density by 50%, and increased canopy base height by ∼4 m, thereby reducing susceptibility to crown fire. The prescribed fire treatment, conversely, did not appreciably reduce tree density or canopy fuel loading, but was effective at increasing the density of standing dead trees, particularly when combined with thinning (37 snags/ha increase). Prescribed fire effects were more pronounced when used in combination with thinning. Thinning was more reliable for altering stand structure, but spring burning was lower in intensity and coverage than desired and may have led to results that downplay the efficacy of fire to meet forest restoration goals.  相似文献   

14.
在全球变暖背景下森林火灾发生的危险性持续增加,可燃物是唯一可人为调控的火环境因子。与天然林相比,人工林结构简单,且以富含油脂的纯林为主,同时多为中幼龄林,易发生森林火灾。文中从人工林可燃物特点及其与林火引燃和火行为的角度出发,综述了人工林可燃物管理技术,对管理中存在的问题进行了分析,建议今后人工林可燃物管理在降低森林易燃性和燃烧性的同时,还须充分考虑管理技术对生态系统和林木生长的影响,优先选择对生态环境友好且促进林木生长的技术和措施。  相似文献   

15.
The severity of the 2000 Samcheok forest fire was classified by using Landsat TM images, and the effects of vegetation structures and topographic conditions on fire severity were analyzed. The estimated normalized difference vegetation index differences between the pre and post-fire Landsat TM images were used as the criteria in determining the levels of fire severity–low, moderate, and extreme. According to the results from fire severity estimation, of the 10,600 ha forest stands, 28% was severely damaged by crown fires, 38% was moderately damaged, and the remaining 34% was damaged slightly by surface fires. The overall accuracy of the fire severity classification was 83% (Kappa coefficient = 0.76). The results of χ 2-tests showed that fire severity differed significantly with the vegetation and topographic conditions as follows. The coniferous stands, compared with the mixed and broad-leaved, were more vulnerable to fire damage; the higher the slope of fire sites, the greater the fire damage; the south was the most vulnerable aspect; fire severity of coniferous forest stands increased with increasing elevation. However, in the study area it was found that fire severity of broad-leaved forest stands were negatively related to the elevation of the corresponding fire sites and affected more by vegetation conditions rather than by topographic conditions.  相似文献   

16.

The history of forest fires was studied in north-west Russia near the Finnish-Russian border on a total of 22 transects within a 3 x 4 km area, 100 m long and 20 m wide, bydendrochronological methods. In total, 25 fires were identified as having occurred in the area between 1400 and 1998. On average, a fire occurred somewhere within the area once every 23 yrs, and once every 13 yrs between 1650 and 1950. The fire frequency (proportion of the area burnt per time unit) broadly followed the changes in the number of fires, but there were also differences. The fire frequency was 1.87% from 1679 to 1872 and 0.40% from 1873 onwards. The mean fire interval was 62 yrs and the median interval 56 yrs. According to the tree-ring width chronology tree growth was significantly lower in the dated fire years than in other years. Forest fire history in north-west Russia is broadly similar to that in many parts of Scandinavia.  相似文献   

17.
Forest fire risk estimation constitutes an essential process to prevent high-intensity fires which are associated with severe implications to the natural and cultural environment. The primary aim of this research was to determine fire risk levels based on the local features of an island,namely, the impact of fuel structures, slope, aspects, as well as the impact of the road network and inhabited regions. The contribution of all the involved factors to forest fires ignition and behavior highlight certain regions which are highly vulnerable. In addition, the influence of both natural and anthropogenic factors to forest fire phenomena is explored. In this study, natural factors play a dominant role compared to anthropogenic factors. Hence essential preventative measures must focus on specific areas and established immediately. Indicative measures may include: the optimal allocation of watchtowers as well as the spatial optimization of mobile firefighting vehicles;and, forest fuel treatments in areas characterized by extremely high fire risk. The added value of this fire prediction tool is that it is highly flexible and could be adopted elsewhere with the necessary adjustments to local characteristics.  相似文献   

18.
A key challenge in modern wildfire mitigation and forest management is accurate mapping of forest fuels in order to determine spatial fire hazard, plan mitigation efforts, and manage active fires. This study quantified forest fuels of the montane zone of Boulder County, CO, USA in an effort to aid wildfire mitigation planning and provide a metric by which LANDFIRE national fuel maps may be compared. Using data from 196 randomly stratified field plots, pre-existing vegetation maps, and derived variables, predictive classification and regression tree models were created for four fuel parameters necessary for spatial fire simulation with FARSITE (surface fuel model, canopy bulk density, canopy base height, and stand height). These predictive models accounted for 56–62% of the variability in forest fuels and produced fuel maps that predicted 91.4% and 88.2% of the burned area of two historic fires simulated in the FARSITE model. Simulations of areas burned based on LANDFIRE national fuel maps were less accurate, burning 77.7% and 40.3% of the historic fire areas. Our results indicate that fuel mapping efforts that utilize local area information and biotic as well as abiotic predictors will more accurately simulate fire spread rates and reflect the inherent variability of forested environments than do current LANDFIRE data products.  相似文献   

19.

Key message

In the African rim of the Western Mediterranean Basin, cork oak forests and pine plantations coexist. Under similar fire regimes, cork oak forest is more resilient in terms of habitat structure (canopy, understory, and complexity of vegetation strata) than pine plantation. By contrast, both woodland types show similar resilience in plant species composition. Resilience in habitat structure varies between the two woodland types because of the resprouting and seeding strategies of cork oak and pine species, respectively. These differences can be relevant for the conservation of biodiversity of forested ecosystems in a future scenario of increased fire frequency and scale in the Mediterranean basin.

Context

Wildfires have major impacts on ecosystems globally. In fire-prone regions, plant species have developed adaptive traits (resprouting and seeding) to survive and persist due to long evolutionary coexistence with fire. In the African rim of the Western Mediterranean Basin, cork oak forest and pine plantation are the most frequently burnt woodlands. Both species have different strategies to respond fire: cork oak is a resprouter while pines are mostly seeders.

Aims

We have examined the hypothesis that pine plantations are less resilient in habitat structure (canopy, understory, diversity of vegetation strata) and plant composition than cork oak woodlands.

Methods

The habitat structure and plant species composition were measured in 30 burnt and 30 unburnt 700-m transects at 12 burnt sites from north-western Africa, where the two forest types can coexist. Habitat structure and plant species composition were compared between burnt and unburnt transects from cork oak and pine plantation woodlands with generalized linear mixed models and general linear models.

Results

The results showed significant interaction effect of fire and forest type, since cork oak forest was more resilient to fire than was pine plantation in habitat structure. By contrast, both forest types were resilient to fire in the composition of the plant communities, i.e., plant composition prior to fire did not change afterwards.

Conclusion

The higher structural resilience of cork oak forest compared to pine plantation is related to the resprouting and seeding strategies, respectively, of the dominant tree species. Differences in the responses to fire need to be considered in conservation planning for the maintenance of the Mediterranean biodiversity in a future scenario of changes in fire regime.
  相似文献   

20.
森林火行为与特殊火行为研究进展   总被引：4，自引：1，他引：3  
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。  相似文献   

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