Forest Fuels Research Articles

Numerical Analysis of Effective Conditions of Chemical Reaction Suppression during Typical Forest Fuel Material Combustion

Three typical solution schemes of adjoint problems of heat transfer, phase transformations and chemical reaction at the forest fuel material surface were analyzed in this work. Characteristic times of thermal decomposition reaction suppression of forest fuel materials (needles of pine and fir-tree, leaves of birch) were presented for concerned heat transfer models. Effective heat exchange conditions which are characterized by minimal times of chemical reaction suppression in forest fuel materials and minimal extinguishing agent's expenditure were established.

Species composition influences management outcomes following mountain pine beetle in lodgepole pine-dominated forests

Mountain pine beetle outbreaks have killed lodgepole pine on more than one million hectares of Colorado and southern Wyoming forest during the last decade and have prompted harvest operations throughout the region. In northern Colorado, lodgepole pine commonly occurs in mixed stands with subalpine fir, Engelmann spruce, and aspen. Variation in tree species composition will influence structure, fuel profiles and fire hazard as forests recover from bark beetle outbreaks, and this diversity has implications for design and implementation of fuel reduction treatments. We used stand inventory data to predict forest structure and fuel loads starting after needle fall through one century after bark beetle infestation for three lodgepole pine-dominated forest types (pine, pine with aspen, pine with fir and spruce), and compared simulated effects of no-action and fuel reduction treatments (thinning, broadcast burning). In pine stands mixed with significant density of fir and spruce, the high canopy bulk density and low canopy base height increases passive and active crown fire hazards compared to stands with few shade tolerant trees. In contrast, stands of pine mixed with aspen had lower canopy bulk density and active crown fire hazard. All three forest types had high snag and coarse woody debris loads. Thinning and broadcast burning reduced canopy fuels in all forest types for several decades, but had the largest effect in forests with abundant fir. Burning temporarily reduced fine woody fuel, and caused a longer-term reduction in coarse wood and duff. Overall, these simulations indicate that management aimed at reducing canopy fuels in beetle-killed lodgepole pine forests should prioritize stands with high densities of overstory and understory fir and spruce. Forest growth following treatment requires frequent stand manipulation (as often as every 20years) to maintain reduced fuel loads, and since such treatments are expensive and likely not analogous to natural disturbances these activities are most appropriate where resource and infrastructure protection and human safety concerns are high.

Is tree growth in boreal coniferous stands on mineral soils affected by the addition of wood ash?

Increasing use of forest fuels for energy production is generating greater quantities of wood ash. In Sweden, it is recommended that this ash should be returned to the forest to counter soil acidification and avoid potential future nutrient deficiencies, but the effects on tree growth require clarification. Thus, 10 field experiments were established in Sweden in 1990–2006 to study the effects of adding wood ash of various origins, doses and combinations of both ash and nitrogen on stem growth in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) stands on mineral soil. Observations after 5–15 years show that growth responses were strongest when N was added, either alone or with wood ash. Growth responses to additions of wood ash without N were small and variable and statistically insignificant at all study sites. However, there were indications that adding wood ash may increase stem-wood growth at fertile sites and decrease it at less fertile sites. Hence, at fertile sites, it may compensate for the growth reductions that normally follow whole-tree harvests, at least temporarily, presumably due to its effects on soil N turnover. At less fertile sites, adding N is probably essential to counteract these growth reductions.

The influence of experimental wind disturbance on forest fuels and fire characteristics

Current theory in disturbance ecology predicts that extreme disturbances in rapid succession can lead to dramatic changes in species composition or ecosystem processes due to interactions among disturbances. However, the extent to which less catastrophic, yet chronic, disturbances such as wind damage and fire interact is not well studied. In this study, we simulated wind-caused gaps in a Pinus taeda forest in the Piedmont of north-central Georgia using static winching of trees to examine how wind damage may alter fuel characteristics and the behavior of subsequent prescribed fire. We found that experimental wind disturbance increased levels of fine and coarse woody fuels (but not leaf litter), increased spatial heterogeneity of fuels, and led to more complete consumption of leaf litter. These patterns led to changes in fire combustion characteristics in experimental gap plots within areas of downed tree crowns where we observed a large increase in fire radiative flux density (kWm−2) and its time integral, fire radiative energy density (MJm−2). These results suggest that wind disturbance may interact with fire not only through addition of fuel, but also through more subtle changes in fuel composition, consumption, and arrangement. More broadly, this study shows that disturbances can influence one another via a variety of mechanisms not all of which are immediately obvious. Understanding disturbance interactions can allow forest managers to make more informed decisions about how wind disturbance influences fuel heterogeneity, and how management processes, such as prescribed fire can interact with other prior wind disturbances to interactively shape plant communities.

Results of Forest Fuel Spatial Distribution Mapping for Fire Simulation Purposes – Case Study

In the paper we introduce an approach of mapping of surface forest fuel spatial distribution using the results of field survey and functions and tools of the ArcGIS environment. The analysis was provided for the Stare Hory locality, which was affected by a forest fire in April 2011. For classification of the surface forest fuel we used the terrain curvature features. Totally we identified 4 basic classes of terrain morphology (ridges and valleys with a low and high curvature). For those classes we did the field survey oriented to the investigation of the forest fuel volume in t.ha-1. To quantify the surface forest fuel volume as precisely as possible we established 21 test plots in the field. Using the tools of Spatial Analyst in ArcGIS we produced the map of surface forest fuel volume distribution in the locality of Stare Hory. Results of such analyses are required as input data to the fire modeling and simulation processes in Farsite and FlamMap environments.

A streamlined approach for the spatial allocation of fuel removals in wildland–urban interfaces

Major concerns are arising on the expansion of wildland–urban interfaces defined as zones where infrastructures and other man-made systems interact with undeveloped areas. Wildland–urban interfaces create an environment in which fire can easily spread from forest fuels to human settlements. In this context, there is a need to prevent fire spread by determining the sound allocation of fuel treatment (fuel removal). To this end, the Spatial Allocation Index was developed as a streamlined approach to determine where and what type of forest areas may be eligible for fuel removal in terms of fire suppression. This approach was developed as a case study example using forest landscapes located in the province of Taranto (Apulia region) in southern Italy. By using geostatistical techniques, we scaled up 210 data points of plot-level fuel load and developed maps for different forest types. These spatial predictions were combined with other landscape-level variables such as population density, urban density, and road density. Through our modelling approach we were able to determine the fuel model types and spatial allocations of wildland areas that are likely to be treated by fuel removal. Our results suggest that the predominant forest typology requiring treatment in the study area is the Mediterranean maquis (shrub-land), which covers 44 % of the wildland–urban interface landscape. The areas on the map where the Spatial Allocation Index reaches its maximum value are those with the highest priority in terms of fuel removal; i.e., the highest number of people, houses, and roads benefitting from wildfire suppression. By adopting this streamlined approach, forest managers and decision makers may avail of a fast and effective tool to improve efforts in landscape management and budgeting of financial resources.

Investigation of organic wastes from Mediterranean plants to produce biogas by anaerobic digestion

The University of Corsica is contributing to the research of both efficiency and integration of renewable energy in the main electrical grid. Since 2013, a scientific program concerning the valorization of biomass energy has been developed to investigate the methane potential through the anaerobic digestion process of lignocellulosic resources. In Corsica, due to the clearing brush policy to prevent forest fires, cellulosic wastes are generated. Besides, Corsica is an important producer of essential oil from Mediterranean species thanks to a process generating an important amount of dried vegetation as waste every year. The aim of this preliminary study on biomass as renewable energy was to characterize and to select the most appropriate substrates for the anaerobic digestion process. Fiber contents and Biochemical Methane Potential (BMP) were performed on five substrates. Heather, rockrose and strawberry tree were chosen as representative of forest fuels. Water distillation residues of laurel and immortelle were considered as natural resource wastes. On this work, we focus on the three species which had the best BMP. Rockrose, dry residue of immortelle and strawberry tree produced 139, 124 and 87 Nm3 CH4 per grams of volatile solids, respectively. The ratio holocellulose: lignin, thanks to the Van Soest method of fiber determination, was determined for those species: 3.8, 3.4 and 1.7. This parameter is a key factor to take into account for the correlation of the BMP with the compositional characteristics. Further work will be performed on these chosen substrates to optimize the anaerobic digestion process in 15 L-reactors.

Severity of an uncharacteristically large wildfire, the Rim Fire, in forests with relatively restored frequent fire regimes

The 2013 Rim Fire, originating on Forest Service land, burned into old-growth forests within Yosemite National Park with relatively restored frequent-fire regimes (⩾2 predominantly low and moderate severity burns within the last 35years). Forest structure and fuels data were collected in the field 3–4years before the fire, providing a rare chance to use pre-existing plot data to analyze fire effects. We used regression tree and random forests analysis to examine the influence of forest structure, fuel, fire history, topographic and weather conditions on observed fire severity in the Rim Fire, as estimated from an initial fire severity assessment based on the relative differenced normalized burn ratio (RdNBR). Plots that burned on days with strong plume activity experienced moderate- to high-severity fire effects regardless of forest conditions, fire history or topography. Fire severity was also highly negatively associated with elevation, with lower severity observed in plots over 1700m. Burning index (a composite index of fire weather), time since the last fire, and shrub cover had strong positive associations with fire severity. Plots that had experienced fire within the last 14years burned mainly at low severity in the Rim Fire, while plots that exceeded that time since last fire tended to burn at moderate or high severity. This effect of time since last fire was even more pronounced on days when the burning index was high. Our results suggest that wildfire burning under extreme weather conditions, as is often the case with fires that escape initial attack, can produce large areas of high-severity fire even in fuels-reduced forests with restored fire regimes.

Interactions among the Mountain Pine Beetle, Fires, and Fuels

Bark beetle outbreaks and wildfires are principal drivers of change in western North American forests, and both have increased in severity and extent in recent years. These two agents of disturbance interact in complex ways to shape forest structure and composition. For example, mountain pine beetle, Dendroctonus ponderosae Hopkins, epidemics alter forest fuels with consequences for the frequency and intensity of wildfires and, conversely, fire injury to trees can promote bark beetle attack and increase beetle populations. Given the great influence these processes have on forest ecosystems, a better understanding of how bark beetles and fires interact is needed to better manage forests and to predict and manage wildfires. Here we review current knowledge on how fire and bark beetles interact, focusing on the mountain pine beetle. We highlight research on how fuel reduction treatments and wildfires affect bark beetles and how bark beetles can affect wildfires by modifying the moisture content, chemistry, and structure of fuels. Last, we discuss the implications these findings have for fire management and firefighter safety.

Landscape‐scale modeling of reference period forest conditions and fire behavior on heavily logged lands

Forest conditions prior to extensive land clearing are often used as a point‐of‐reference by ecologists and resource managers for characterizing the historical range of variability in forest conditions shaped by intact disturbance regimes. Quantitative data on forest reference conditions can be developed from forest surveys and reconstructions using dendroecology; however, these methods lack the spatial resolution needed for landscape management. In this paper, we combine predictive vegetation mapping methods with reference forest conditions inferred from early forest surveys, dendroecology, and fire simulation models to develop landscape‐scale reference conditions for forest structure, forest fuels, fire frequency, and fire behavior using the Lake Tahoe Basin, California as an example.The dendroecological reconstruction method used for the Lake Tahoe Basin forests was not sensitive to variation in decomposition rates suggesting that our method provided robust estimates of reference period forest characteristics. The cluster analysis procedure identified five forest structure types (white fir, Jeffrey pine, red fir, lodgepole pine, and subalpine) and 15 subtypes. Each forest type had a characteristic composition, density, and basal area. Our random forests approach to classifying and mapping the spatial distribution of the five dominant reference forest structure types resulted in 51.5% classification accuracy using 14 physiographic and climatic variables. The random forests model to identify subtypes within each forest group had an average percent correct classification of 47.8%. The random forests model for fire intervals explained 67% of the variance in the point fire return interval estimates from fire‐scarred trees. Estimates of reference period fuels modeled from stand structure suggested moderate fuel loads for reference forests. The predicted potential fire type for forest subtypes under extreme weather was surface fire except for red fir and the lodgepole pine subtypes with potential for crown fire. By characterizing the reference forest composition, structure, and disturbance frequency with a range of variability, managers can develop a forested landscape more resilient to changes in disturbance regime and climate. Although our approach was developed for the Lake Tahoe Basin, California, it could be applied to a wide range of forest landscapes to identify forest reference conditions.

Bioenergy is a viable solution to BC's Wildland-Urban Interface fuels problem; however, a number of policy changes are needed first

We have an increasing wildfire risk to communities of the province that is not being effectively addressed by the current hazard reduction program. Existing planning and remediation efforts are a small fraction of what is required given the march of climate change, the steady accumulation of forest fuels in the WUI and the large number of affected communities. The greatest barrier to an adequate response is the high cost of initial and recurring treatments, dependent primarily on tax funds from senior governments, and the lack of a policy framework that makes it possible to earn offsetting revenues from remedial work. Continuing on this trajectory will bring the predictable results of increasingly frequent and increasingly severe interface fires. A solution to this impasse is a major departure from current policy and practice; it is an attempt to turn an economic barrier into an economic advantage by converting a fuel surplus from a costly burden to a commercially valuable energy source. Because the proposal affects the legislated jurisdictions of communities, the tenure rights of existing industry, the encouragement of a new energy industry, the revision of silvicultural requirements, the linked use of merchantable timber and lower value biomass, expanding the carbon offset regime and sensitivity to international timber pricing agreements it is a formidable challenge to our current forest administration. Such a bold transformation likely cannot be approached piecemeal nor can it be applied province-wide without practical trial.

Structure and composition of forest floor fuels in long-unburned Jeffrey pine–white fir forests of the Lake Tahoe Basin, USA

In spite of the mechanistic links between forest floor fuels and fire behaviour and effects, little information is available on their composition and structure. We collected fuels from well-developed forest floors in four long-unburned Jeffrey pine (Pinus jeffreyi)–white fir (Abies concolor) forests in the Lake Tahoe Basin in California and Nevada. We measured forest floor (litter, fermentation and humus, where present) load, depth, bulk density and mineral ash content at the base of each tree, near the crown drip line and beyond the crown in open gaps (n=40 Jeffrey pine, 40 white fir). We found substantial variability in composition between the two conifers’ forest floor fuels and across species. Forest floor was mounded near tree stems, with the majority of the depth (and mass) composed of fermentation fuels. Humus was present across spatial locations, but was patchier with increasing distance from trees. Ash content varied between trees (fir>pine) and with depth (humus>fermentation>litter). Results highlight the high spatial variation in forest floor fuels and underscore the need for building a greater understanding of forest floor fuels in long-unburned sites.

An Experimental Study Evaluating the Burning Dynamics of Pitch Pine Needle Beds Using the FPA

Pine needle litters, a key fuel in coniferous forest systems, are highly porous fuel beds. They provide a source of continuous fuel medium that can be easily ignited and will sustain flame spread on the ground during forest fires. This work represents an experimental study that is focused on the influence of the fuel moisture content on the burning dynamics and the flammability characteristics of forest fuel beds. The FM Global Fire Propagation Apparatus was utilized to obtain time to ignition, heat release rate, total heat released and CO/CO2 concentration data. The methodologies applied in previous studies were improved with new modifications. The results were analyzed with respect to the sample’s fuel moisture content as well as other test conditions, such as airflow condition (wind), sample holder openness and external heat flux. The importance of the fuel moisture content is critical to understand as the majority of fuels present in the natural environment have elevated moisture content compared to dead dry fuel. Samples studied are representative of wet ground fuels as well as live fuels which do burn when crowning conditions develop. The results presented here are a building block for developing an experimental database that can be used to understand the influence of environmental conditions on the flammability of porous forest fuels and assess the risks that comes with a wildfire. Furthermore, the data can also be used for fire behavior model validation.

Mathematical Simulation of Heat Transfer in Heterogenous Forest Fuel Layer Influenced by Heated Up to High Temperatures Steel Particle

Heterogeneity of forest fuel layer renders the important influence on forest fire occurrence processes. One of sources of the raised temperature on forested territories is metal particles heated up to high temperatures. Such particles can be formed as a result of welding of metals on forested territories. The present paper represents the heat transfer research in forest fuel at the influence of metal particle heated up to high temperatures. The heterogonous forest fuel layer with inclusions of small wooden branches and chips is considered. Such object research is urgent especially at fire forecasting on forest cutting. The technology of mathematical simulation is used. The two-dimensional problem of heat transfer in forest fuel layer structure with wood inclusions is solved.

Effect of Particle Size on Pyrolysis Kinetics of Forest Fuels in Nitrogen

Pyrolysis of forest combustibles is an elementary process in the ignition and spread of forest fires, and particle size is an important parameter which affects the pyrolysis kinetics. In this work, samples of pine needle (PN), pine branch (PBr) and pine bark (PB) were subject to thermogravimetric experiments, in order to examine the effect of particle size on pyrolysis characteristics. For all the samples, one peak and two shoulders are observed in all of the mass loss curves, at different positions for different levels of particle size. The observation of the mass loss curves and the analysis of peak temperatures by Kissinger method indicated that the major mass loss steps in different heating rates have consistent pyrolysis kinetics. For all the samples, the particle size has no obvious effect on the temperatures of the major peaks. Basically, the peak mass loss rate increases with increasing particle size for smaller particles, however the increased temperature gradient inside the sample may have a remarkable suppression on the mass loss rate when the particle size exceeds a certain level. The mass loss rates for the two shoulders show complex variations for different samples and particle sizes, which reflects the difference in chemical components. A kinetic model which includes three pseudo components was used to simulate the pyrolysis for different dimensions, and the obtained kinetic parameters were compared and discussed in details. By industrial analysis the products of ashes for different particle sizes were compared, and especially it was implied that to some extent the activation energy and ash content involve negative correlation.

Experimental confirmation of the MWIR and LWIR grey body assumption for vegetation fire flame emissivity

The temperature and emissivity of forest fire flames play a key role in understanding fire behaviour, modelling fire spread and calculating fire parameters by means of active fire thermal remote sensing. Essential to many of these is the often-made assumption that vegetation fire flames behave as grey bodies in the infrared (IR). Although the emissivity of flames and its relationship to flame depth has been measured experimentally using thermal imagers working in the long-wave IR (LWIR, 8–12µm), no published study has yet demonstrated relationships in the important mid-wave IR (MWIR, 3–5µm) spectral region, nor conclusively demonstrated that assumptions about grey body behaviour across these two important IR atmospheric windows fit well with reality. Our study explores these issues using measurements of boreal forest fuels burned with flame depths ranging from 0.2 to 4.2 m. Observations of two stable black body sources made through the differing flame depths were used to explore flame spectral emissivities and their relationship to flame depth. We found essentially the same relationship between flame emissivity and flame depth for both spectral regions, (extinction coefficient K=0.7 m–1), confirming that the grey body assumption for forest fire flames in the MWIR and LWIR atmospheric windows appears valid for the fire conditions encountered here.

黑龙江省温带森林火灾碳排放的计量估算研究

As global climate change continues to accelerate,the frequency and intensity of forest fires continue to grow.Forest fires,which play an important ecological role in forest ecosystems,have a very significant effect on carbon emissions and carbon sinks,and also play an important role in the carbon cycle. Although the impact of forest fires on carbon emissions has been analyzed in detail,studies that scientifically and accurately measure carbon and carbonaceous gas emissions from forest fires are lacking. Carbon dioxide( CO2) emissions from temperate forest fires are usually calculated based on Intergovernmental Panel on Climate Change guidelines( IPCC 1997) and only include direct effects of burning.Forest fires have been shown to release significant amounts of carbon into the atmosphere and play a significant role in theglobal carbon cycle and carbon balance. In this study,we estimated the level of emissions from forest fires for carbon and carbonaceous gases including CO2,carbon monoxide( CO),methane( CH4),and non-methane hydrocarbons( NMHC)from 1953 to 2012 in Heilongjiang Province,China. We used a geographic information system based modeling approach to simulate emissions using a two-step procedure. First,we calculated total carbon released from forest fires in Heilongjiang for selected years between 1953 and 2012 by merging and analyzing measurements of several parameters. Second,we calculated the amounts of four carbonaceous gases released during the burn,CO2,CO,CH4,and NMHC,using several different experimentally derived emission factors. The origin of each of the inputs used in our models was based on a combination of analysis of forest fire inventory,forest resources inventory,field research,and laboratory experiments.Direct total carbon emissions from forest fires in Heilongjiang during 1953—2012 were about 5. 88×107t,and mean annual carbon emissions were about 9. 80 ×105t per year,accounting for 8. 66% of the direct total carbon emissions from forest fires in China. Carbon emissions of four trace gases,CO2,CO,CH4and NMHC,from forest fires were 1. 89×108,1.06×107,6.33×105and 4. 43×105t,respectively; mean annual emissions of CO2,CO,CH4and NMHC were 3. 15×106,1.77×105,1.05×104and 7. 38×103t,respectively,accounting for 7. 74%,6. 52%,9. 42% and 6. 53% of the amounts of CO2,CO,CH4and NMHC released from forest fires in China,respectively,during that period. Our results indicate that combustion efficiency of coniferous broad-leaved mixed forest is lower than other forest types. The mean annual burned area for this type of forest accounts for 57. 54% of China's total burn area,while this area's fires account for only 38. 57% of carbon total emissions from forest fires. We propose the following forest fire management strategy. First,our studies show that the area's mean annual forest fire carbon emissions have an important impact on the regional carbon balance. So,we suggest strengthening the management of forest fuels( fine fuels,heavy fuels,etc.) as part of the regional forest fire management strategy. Fuels on the ground do not decompose easily in Heilongjiang's cold and dry temperate forests. Land managers should implement a reasonable prescribed burning plan designed to reduce the accumulation of combustible fuels.A policy for conducting periodic prescribed burning will reduce the incidence of forest fires. Prescribed burning should help land managers to control and limit the incidence and intensity of wildfires while allowing them to improve the condition of the ecosystem. Finally,we should give full consideration to the role of forest fires in maintaining the ecological balance of forest ecosystems.

Convection Ignition of Live Forest Fuels

Convection Ignition of Live Forest Fuels

Evaluating the Effects of Projected Climate Change on Forest Fuel Moisture Content

Understanding how live and dead forest fuel moisture content (FMC) varies with seasonal weather and stand structure will improve researchers’ and forest managers’ ability to predict the cumulative effects of weather on fuel drying during the fire season and help identify acute conditions that foster wildfire ignition and high rates of fire spread. No studies have investigated the efficacy of predicting FMC using mechanistic water budget models at daily time scales through the fire season nor have they investigated how FMC may vary across space. This study addresses these gaps by (1) validating a novel mechanistic live FMC model and (2) applying this model with an existing dead FMC model at three forest sites using five climate change scenarios to characterize how FMC changes through time and across space. Sites include post-fire 24-year old forest, mature forest with high canopy cover, and mature forest affected by the mountain pine beetle with moderate canopy cover. Climate scenarios include central tendency, warm/dry, warm/wet, hot/dry, and hot/wet.

An Exploratory Assessment of a Smartphone Application for Public Participation in Forest Fuels Measurement in the Wildland-Urban Interface

Wildfire management in the wildland-urban interface (WUI) protects property and life from wildland fire. One approach that has potential to provide information about the amount and location of fuels to forest managers and, at the same time, increase public knowledge and engagement in reducing wildfire threats is public participation in scientific research (PPSR)—also known as citizen science—where members of the public participate in the research process. In this exploratory study, residents of a wildfire-affected community tested a smartphone application to collect data about forest fuels and answered questions about wildfire, their community, and experiences using the application. In this paper, the application is introduced, the volunteers’ motivations, attitudes, and behaviors are considered, and the potential of using a PPSR approach for wildfire management discussed. Although there are practical challenges to applying PPSR approaches to wildfire hazard management, the participants in this study demonstrated the potential of PPSR to increase awareness and understanding of actions that can reduce the threat of wildfire. Wildfire managers may consider utilizing PPSR approaches to engage the community in wildfire preparedness.