Forest Fuels Research Articles

Strata-based forest fuel classification for wild fire hazard assessment using terrestrial LiDAR

Fuel structural characteristics affect fire behavior including fire intensity, spread rate, flame structure, and duration, therefore, quantifying forest fuel structure has significance in understanding fire behavior as well as providing information for fire management activities (e.g., planned burns, suppression, fuel hazard assessment, and fuel treatment). This paper presents a method of forest fuel strata classification with an integration between terrestrial light detection and ranging (LiDAR) data and geographic information system for automatically assessing forest fuel structural characteristics (e.g., fuel horizontal continuity and vertical arrangement). The accuracy of fuel description derived from terrestrial LiDAR scanning (TLS) data was assessed by field measured surface fuel depth and fuel percentage covers at distinct vertical layers. The comparison of TLS-derived depth and percentage cover at surface fuel layer with the field measurements produced root mean square error values of 1.1 cm and 5.4%, respectively. TLS-derived percentage cover explained 92% of the variation in percentage cover at all fuel layers of the entire dataset. The outcome indicated TLS-derived fuel characteristics are strongly consistent with field measured values. TLS can be used to efficiently and consistently classify forest vertical layers to provide more precise information for forest fuel hazard assessment and surface fuel load estimation in order to assist forest fuels management and fire-related operational activities. It can also be beneficial for mapping forest habitat, wildlife conservation, and ecosystem management.

Efficient forest fuel supply systems: Research, development and dissemination of knowledge in Sweden

Efficient Forest Fuel Supply Systems (ESS) was run as a collaboration program, financed by the forestry sector, the energy sector, and the Swedish Energy Agency. The objective was to enable a long-term, sustainable and greatly increased use of forest fuel by supporting the development of a more efficient production system. The financial framework of ESS was SEK 130 million (approximately CA $ 19.5 million) over eight years, and the program supported approximately 150 research and development projects. Skogforsk administered the program, and was responsible for coordination and disseminating information to the stakeholders. A program board made formal decisions, and a fuel technology collaboration group helped to identify R&D areas. A project pilot was linked to each project to ensure that the focus was on sector needs and interests, and to help the project manager with relevant study objects, networks and updated information. In and around the program, valuable expertise and networks were built up in each sector and in research organisations, both nationally and internationally. Great emphasis was placed on practical demonstration, implementation and communication, in order to disseminate knowledge about new technology and methods and to influence attitudes toward forest fuel harvest. The forestry sector and its contractors gradually strengthened the supply system through improved skills, better organisation, and advanced equipment. The goals were largely attained, and practical aspects relating to forest fuel were implemented, incorporating many of the results.

Fire whirls in forest fires: An experimental analysis

This work presents a study on the formation of fire whirls with vertical axis on wildfires at laboratory scale. A particularity of the study is the use of typical forest fuels instead of fossil fuels as seen in some of previous studies on this topic. The forest fuels tested in the experiments were dead needles of Pinus pinaster, straw of Avena sativa, dead leaves of Eucalyptus globulus and a mix of shrubs mainly composed by heather (Erica australis) and gorse (Pterospartum tridentatum). The experimental results of the tests with and without forced flow inside a fire whirl generator were compared with tests in similar conditions out of the generator. It was possible to evaluate the effects of fuel bed size, bulk density and external vorticity on several parameters like flame height and diameter, mass decay and heat release rate. The results show that forced flow increases dramatically the burning rate and reduces the time needed to achieve a high rate of energy release. Comparison with results of other sources show that the flames that are generated in the present fire whirl generator are in a transition from fire whirl to pool fire regime and that it is possible to scale up some flow and thermal properties of field scale fire whirls and to derive predictive models on the basis of laboratory scale experiments.

Future demand for forest-based biomass for energy purposes in Sweden

This paper assesses the potential changes in the demand for forest-based biomass for various energy purposes in Sweden in 2030 and 2050, respectively. The assessment is based on a review of scenarios and predictions of how the Swedish energy system may develop, taking into account techno-economical conditions. It includes potential changes in district heating, electricity production in combined heat and power plants, industrial process energy, and production of biofuel for road transportation. In addition, the potential demand for forest-based feedstock in the chemical and petrochemical sector, replacing current use of fossil feedstock, is analysed. The assessment suggests that Sweden may see an additional demand for forest fuels at about 30TWh in 2030 and 35–40TWh in 2050. This can be compared with the current use of biomass for energy in Sweden at 130TWh per year, and the estimated potential increase of sustainable harvest of logging residues (slash and stumps) at some additional 20TWh per year, based on current conditions. If also potential demand for forest-based feedstock in the chemical and petrochemical industry is included, another 10–15 and 25–30TWh of biomass per year may be needed in 2030 and 2050, respectively. The future demand is sensitive to the pace and magnitude of energy efficiency improvements and electrification in the various sectors. If far-reaching energy efficiency improvements and electrification are realised, the total additional demand for biomass as energy and industry feedstock may be about 20 and 30TWh per year in 2030 and 2050, respectively, thus roughly corresponding to the sustainable harvests of logging residues. If, however, efficiency improvements and electrification are only marginal, then the additional demand for biomass as industry and energy feedstock may reach 70TWh and 100TWh per year in 2030 and 2050, respectively. In these cases, the use of logging residues will not suffice and additional biomass would be needed. A combination of regulations and incentives is recommended to accelerate the fuel and feedstock switch, especially in the transportation and industrial sectors, and incentives promoting a substantial improvement in energy efficiency and electrification in all sectors.

Physics of suppression of thermal decomposition of forest fuel using surface water film

The paper presents results of an experimental study of the suppression of thermal decomposition of forest fuel (FF) due to formation of a thin surface water film (3 mm thick). The investigations were carried out with birch leaves, as well as a mixture of birch leaves, pine needles, and twigs of aspen. The experiments involved model bases of fire of the above FFs in the form of cylinders. The cylinders were 20 mm to 60 mm in diameter and 40 mm to 100 mm high. The effect of water on the FFs was monitored via high-speed (up to 105 frames per second) video recording and fast (a thermal lag of less than 1 s) thermal transducers. The times of termination of FF thermal decomposition and the minimum (required) volumes of water were determined. The feasibility of complete suppression of the FF thermal decomposition process due to formation of a thin surface water film (10–15 times thicker than the reacted material) was experimentally supported. The foundations of the physical model of a complex of processes that occur owing to the water film effect on the forest fuel heated to a high temperature (well above the point of thermal decomposition) were formulated.

Duration of fuels reduction following prescribed fire in coniferous forests of U.S. national parks in California and the Colorado Plateau

Prescribed fire is a widely used forest management tool, yet the long-term effectiveness of prescribed fire in reducing fuels and fire hazards in many vegetation types is not well documented. We assessed the magnitude and duration of reductions in surface fuels and modeled fire hazards in coniferous forests across nine U.S. national parks in California and the Colorado Plateau. We used observations from a prescribed fire effects monitoring program that feature standard forest and surface fuels inventories conducted pre-fire, immediately following an initial (first-entry) prescribed fire and at varying intervals up to >20years post-fire. A subset of these plots was subjected to prescribed fire again (second-entry) with continued monitoring. Prescribed fire effects were highly variable among plots, but we found on average first-entry fires resulted in a significant post-fire reduction in surface fuels, with litter and duff fuels not returning to pre-fire levels over the length of our observations. Fine and coarse woody fuels often took a decade or longer to return to pre-fire levels. For second-entry fires we found continued fuels reductions, without strong evidence of fuel loads returning to levels observed immediately prior to second-entry fire. Following both first- and second-entry fire there were increases in estimated canopy base heights, along with reductions in estimated canopy bulk density and modeled flame lengths. We did not find evidence of return to pre-fire conditions during our observation intervals for these measures of fire hazard. Our results show that prescribed fire can be a valuable tool to reduce fire hazards and, depending on forest conditions and the measurement used, reductions in fire hazard can last for decades. Second-entry prescribed fire appeared to reinforce the reduction in fuels and fire hazard from first-entry fires.

The potential role of forest management in Swedish scenarios towards climate neutrality by mid century

Swedish climate policy targets net zero greenhouse gases (GHG) by mid-century, with road transport independent of fossil fuels by 2030, requiring far-reaching changes in the way energy is used. Forest management is expected to support carbon sequestration and provide biomass for various uses, including energy. In this paper, we combine two energy scenarios with four forest scenarios and quantify GHG balances associated with energy-use for heat, electricity, and road transport, and with forest management and production, use, and end-of-life management of various forest products, including products for export. The aggregated GHG balances are evaluated in relation to the 2-degree target and an allocated Swedish CO2 budget. The production of biofuels in the agriculture sector is considered but not analyzed in detail.The results suggest that Swedish forestry can make an important contribution by supplying forest fuels and other products while maintaining or enhancing carbon storage in vegetation, soils, and forest products. The GHG neutrality goal is not met in any of the scenarios without factoring in carbon sequestration. Measures to enhance forest productivity can increase output of forest products (including biofuels for export) and also enhance carbon sequestration. The Swedish forest sector can let Sweden reach net negative emissions, and avoid “using up” its allocated CO2 budget, thereby increasing the associated emissions space for the rest of the world.

Forest fuel treatment detection using multi-temporal airborne lidar data and high-resolution aerial imagery: a case study in the Sierra Nevada Mountains, California

ABSTRACTTreatments to reduce forest fuels are often performed in forests to enhance forest health, regulate stand density, and reduce the risk of wildfires. Although commonly employed, there are concerns that these forest fuel treatments (FTs) may have negative impacts on certain wildlife species. Often FTs are planned across large landscapes, but the actual treatment extents can differ from the planned extents due to operational constraints and protection of resources (e.g. perennial streams, cultural resources, wildlife habitats). Identifying the actual extent of the treated areas is of primary importance to understand the environmental influence of FTs. Light detection and ranging (lidar) is a powerful remote-sensing tool that can provide accurate measurements of forest structures and has great potential for monitoring forest changes. This study used the canopy height model (CHM) and canopy cover (CC) products derived from multi-temporal airborne laser scanning (ALS) data to monitor forest changes following the implementation of landscape-scale FT projects. Our approach involved the combination of a pixel-wise thresholding method and an object-of-interest (OBI) segmentation method. We also investigated forest change using normalized difference vegetation index (NDVI) and standardized principal component analysis from multi-temporal high-resolution aerial imagery. The same FT detection routine was then applied to compare the capability of ALS data and aerial imagery for FT detection. Our results demonstrate that the FT detection using ALS-derived CC products produced both the highest total accuracy (93.5%) and kappa coefficient (κ) (0.70), and was more robust in identifying areas with light FTs. The accuracy using ALS-derived CHM products (the total accuracy was 91.6%, and the κ was 0.59) was significantly lower than that using ALS-derived CC, but was still higher than using aerial imagery. Moreover, we also developed and tested a method to recognize the intensity of FTs directly from pre- and post-treatment ALS point clouds.

Rapidly evolving ultrafine and fine mode biomass smoke physical properties: Comparing laboratory and field results

AbstractCombining field and laboratory results, we present biomass smoke physical properties. We report sub‐0.56 µm diameter (Dp) particle sizing (fast mobility particle sizer, FMPS) plus light absorption and scattering at 870 nm (photoacoustic extinctiometer). For Dp < 200 nm, the FMPS characterized sizing within ±20% compared to standards. As compared to the traditional scanning mobility particle sizer, the FMPS responded most accurately to single‐mode polydispersions with mean Dp < 200 nm, which characterized the smoke sampled here. Smoke was measured from laboratory fresh emissions (seconds to hours old), the High Park Fire (hours to < 1 day), and from regional biomass burning (several days). During a High Park Fire episode, light extinction rapidly reached a maximum of σep = 569 ± 21 Mm−1 (10 min) with aerosol single scattering albedo peaking at ω = 0.955 ± 0.004. Concurrently, number concentration and size peaked with maximum Dp = 126 nm and a unimodal distribution with σg = 1.5. Long‐range transported smoke was substantially diluted (Ntot factor of 7 lower) and shifted larger (maximum Dp = 143) and wider (σg = 2.2). We compared ambient data to laboratory burns with representative western U.S. forest fuels (coniferous species Ponderosa pine and Alaska black spruce). Smoldering pine produced an aerosol dominated by larger, more strongly light scattering particles (Dp > 100 nm), while flaming combustion produced very high number concentrations of smaller (Dp ~ 50 nm) absorbing particles. Due to smoldering and particle growth processes, Dp approached 100 nm within 3 h after emission. Increased particle cross‐sectional area and Mie scattering efficiency shifted the relative importance of light absorption (flaming maximum) and light scattering (smoldering maximum), increasing ω over time. Measurements showed a consistent picture of smoke properties from emission to aging.

Supercritical extracts of forest fuels in Great Xing’an Mountains

Extracts are important components of fuels. Fatty-extracts with high heating value (HV) are hypothesized by researchers as positively related to the HV of fuels. The Soxhlet extractor is typically used to extract fatty-extracts but it has shortcomings, including long processing time (8–10 h) and the requirement for large amounts of organic solvent. Supercritical extraction is an alternate and useful technique for extraction of natural products. However, published studies rarely discuss the relationship between extracts and HV. In this study, we assessed the supercritical extracts (SuE) of forest fuels in the Great Xing’an Mountains. Our results indicated that the optimum conditions for extraction of SuEs were 40–60 mesh, 40–50 MPa, 45 °C, 80 min and a CO2 flow rate of 1.5–2.0 dm3/min. The Soxhlet extracts contents and the SuE contents were all related to HV. However, R 2 of the coniferous samples (0.8499) and needle samples (0.9722) demonstrated that the correlation between HV and the SuE content was closer. We conclude that supercritical fatty-extracts provide a useful index of the HV of fuels, especially coniferous fuels. SuE data can be used in fire management, for example to estimate the rate of fire spread or fire intensity.

Patterns and Trends in Burned Area and Fire Severity from 1984 to 2010 in the Sierra de San Pedro Mártir, Baja California, Mexico

Yellow pine (Pinus spp. L.) and mixed conifer (YPMC) forests of California, USA (Alta California), have been negatively affected since Euro-American settlement by a century or more of logging, fire exclusion, and other human activities. The YPMC forests in northwestern Mexico (northern Baja California) are found in the same climate zone as those of Alta California and support mostly the same dominant species, yet they are much less degraded, having suffered little logging and only 30 years of fire suppression. As such, the Baja California forests are believed to more closely approximate pre-Euro-American settlement conditions, and they have been proposed as reference ecosystems for restoration and management of Alta California forests. We studied fire severity trends in the Sierra de San Pedro Martir National Park (SSPMNP), which supports the largest area of YPMC forest in Baja California, to determine whether fire severity is rising over the last three decades in the same manner that it is rising in the Sierra Nevada of Alta California. We used LANDSAT data to identify 32 fires that burned 26 529 ha in the Sierra de San Pedro Martir National Park in the period 1984 to 2010. Of this, 1993 ha burned in YPMC forest types in 17 fires. We found no temporal trends in forest burned area or in the proportion of high severity fire, but we did find that the mean size of high severity patches within fires is rising. In the SSPMNP, the overall proportion of fire area burned at high severity averaged 3 % in both yellow pine and mixed conifer forests. We found no significant autoregressive effects of year in any of our analyses, but the year with the most burned area occurred after drier-than-average periods. In the SSPMNP data, there was no correlation between burned area and proportion of high severity fire; we interpreted this to mean that differences in fuels in SSPMNP were more important to fire behavior than weather conditions. The SSPMNP continues to burn at very low severities, even after 30 years of effective suppression of lightning-ignited fires. This is in stark contrast to similar forests in Alta California, which are experiencing fires of sizes and severities that fall far outside the historical range of variation. Current fire severities in the SSPMNP are very similar to the levels of severity described for Alta California YPMC forests before Euro-American settlement. Nonetheless, fire suppression policies in Mexican national parks in northern Baja California are causing increases in forest fuels and may be the cause of recent increases in high severity patch size. Current wildfire trends in YPMC forests in Alta California should serve as a warning to Mexican managers that continued fire exclusion in the Baja California YPMC forests is a recipe for ecological disaster in these unique and important ecosystems.

Mapping regional patterns of large forest fires in Wildland–Urban Interface areas in Europe

Over recent decades, Land Use and Cover Change (LUCC) trends in many regions of Europe have reconfigured the landscape structures around many urban areas. In these areas, the proximity to landscape elements with high forest fuels has increased the fire risk to people and property. These Wildland–Urban Interface areas (WUI) can be defined as landscapes where anthropogenic urban land use and forest fuel mass come into contact. Mapping their extent is needed to prioritize fire risk control and inform local forest fire risk management strategies. This study proposes a method to map the extent and spatial patterns of the European WUI areas at continental scale. Using the European map of WUI areas, the hypothesis is tested that the distance from the nearest WUI area is related to the forest fire probability. Statistical relationships between the distance from the nearest WUI area, and large forest fire incidents from satellite remote sensing were subsequently modelled by logistic regression analysis. The first European scale map of the WUI extent and locations is presented. Country-specific positive and negative relationships of large fires and the proximity to the nearest WUI area are found. A regional-scale analysis shows a strong influence of the WUI zones on large fires in parts of the Mediterranean regions. Results indicate that the probability of large burned surfaces increases with diminishing WUI distance in touristic regions like Sardinia, Provence-Alpes-Côte d'Azur, or in regions with a strong peri-urban component as Catalunya, Comunidad de Madrid, Comunidad Valenciana. For the above regions, probability curves of large burned surfaces show statistical relationships (ROC value > 0.5) inside a 5000 m buffer of the nearest WUI. Wise land management can provide a valuable ecosystem service of fire risk reduction that is currently not explicitly included in ecosystem service valuations. The results re-emphasise the importance of including this ecosystem service in landscape valuations to account for the significant landscape function of reducing the risk of catastrophic large fires.

Spatial point process modeling applied to the assessment of risk factors associated with forest wildfires incidence in Castellón, Spain

During the last decades the Mediterranean zone in Europe has experienced an increment in the incidence of forest wildfires. This increase is partly explained by higher mean temperature and lower relative humidity, while socioeconomic change has lead to the abandonment of farms, resulting in an increase in an unusual accumulation of forest fuels, increasing the risk of wildfires. Mapping wildfire risk is highly important because wildfires are known to potentially lead to landscape changes and to modify fire regime by inducing potential changes in vegetation composition. Also, they pose a hazard to human property and life. Maps of wildfire risk based on statistical models provide a measure of uncertainty for the inferences derived from such risk maps, leaving a quantitative error margin for managers and decision takers. Further, some of the model parameters often have a physical or a biological interpretation which can give ecologists and forest engineers answers about scientific questions of interest. In this paper, we analyze the incidence of wildfires in the province of Castellón in Spain in order to identify risk factors associated with wildfire incidences during the years 2001–2006. We used the discrete nature of wildfire events to build such models using point process theory and methods and included information about elevation, slope, aspect, land use and distance to nearest road as covariates in our modeling process. Our results show that wildfire risk in Castellón is associated with all the covariates considered and that three land-use categories have the highest risk of wildfire incidence. Also, wildfire incidences are not independent and some degree of interaction exists, which indicates that the commonly used Poisson point process models are not applicable in this case, but instead area-interaction models should be considered.

Characterization of gas and particle emissions from laboratory burns of peat

Peat cores collected from two locations in eastern North Carolina (NC, USA) were burned in a laboratory facility to characterize emissions during simulated field combustion. Particle and gas samples were analyzed to quantify emission factors for particulate matter (PM2.5), organic carbon (OC), elemental carbon, light absorbing carbon, absorption Angstrom exponent, metals, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated dibenzodioxins/dibenzofurans (PCDDs/PCDFs). CO from the smoldering burns, up to 7 h in duration, contributed approximately 16% of the total carbon emitted. Emission factors for black carbon (BC) and light absorbing carbon (UVPM) were considerably lower than those found for forest litter burns. Emission factors for PCDDs/PCDFs were near published values for forest fuels, at 1–4 ng toxic equivalents (TEQ)/kg carbon burned (Cb). Total PAH concentrations of ≥12 mg/kg were higher than published data from biomass burns, but roughly the same in terms of toxicity. Application of these emission factors to the noteworthy 2008 “Evans Road” fire in NC indicates that PM2.5 and PCDD/PCDF emissions from this fire may have been 4–6% of the annual US inventory and 5% of the annual OC amount.

Seeing forests as fuel: How conflicting narratives have shaped woody biomass energy development in the United States since the 1970s

This article provides an historical analysis of arguments for and against using forests for fuel since the 1970s energy crises, and explores the relationship between public narratives and the implementation of renewable energy technologies. I argue that different ideas about the use of forest resources created narrative conflict between stakeholder groups, and this conflict influenced the development of biomass energy systems by limiting private investment and shaping public policy. Promoters and opponents of forest fuels both worked to achieve political goals as well as economic and environmental ones, and debates about biomass energy reflected these different views. Although this paper focuses on public perceptions about wood energy in the US, biomass advocacy in the US was influenced by efforts in other countries, particularly by innovation in Sweden and Finland. By providing an historical investigation of the cultural barriers to developing decentralized renewable energy systems in the US, and explaining how this experience compared with biomass development in other countries, this research demonstrates how conflicting narratives have shaped energy and environmental policy since the 1970s. This historical perspective contains valuable lessons about how different social groups’ values and beliefs have affected – and continue to affect – decisions about new energy technologies.

Climatic and structural comparison of yellow pine and mixed-conifer forests in northern Baja California (México) and the eastern Sierra Nevada (California, USA)

Effects of fire suppression policies on semi-arid yellow pine and mixed conifer (YPMC) forests in the western US have been well documented, and restoration of forest structure and natural fire regimes are high management priorities to ensure the health and resilience of such forests. However, determining reference conditions for ecological restoration is difficult due to the near absence of undegraded forests in the US. YPMC forests of the Sierra de San Pedro Mártir (SSPM) in northern Baja California, Mexico, are highly similar to forests of the Eastern Sierra Nevada, California, USA, have experienced little to no logging, and until relatively recently supported a natural fire regime. As such, these Mexican YPMC forests are thought by many to represent reference ecosystems for restoration and resource and fire management in the US. However, to this point there has been no direct climatic comparison to determine to what extent SSPM is validly compared to California YPMC sites, nor a direct statistical comparison of forest conditions to see in what ways northern California forests might differ from SSPM. We compared climatic data from SSPM with 17 meteorological stations in the range of Jeffrey pine in Alta and Baja California. Based on this comparison, we determine that SSPM clearly belongs to the general class of Jeffrey pine-dominated YPMC forests found along the eastern edge of the California Floristic Province. We used field sampling to measure forest structure, fuels, and vegetation and ground cover in SSPM and in multiple National Forests along the eastern slope of the Sierra Nevada. Live tree density was nearly twice as high in the eastern Sierra Nevada as in SSPM, and dead tree density was 2.6 times higher. Basal area was about 30% higher in the eastern Sierra Nevada, even though average tree size was larger in SSPM. Fuel loads and coarse woody debris were very similar between the two sites, and fine fuels (1-hour fuels) were actually higher in SSPM. Logging and fire suppression have resulted in denser YPMC forests dominated by smaller trees in the US, but our results suggest that fire suppression in SSPM over the last 30years has increased fuel loads. Nonetheless, the Baja California forests still retain an overstory structure created and maintained by centuries of frequent fire. This study provides important reference information for the management of eastern Sierra Nevada forests, and indicates that continued full fire suppression in SSPM carries significant ecological risks.

Forest Fuels and Wildfire Hazard in Two Fire-Excluded Old-Growth Ponderosa Pine Stands: Contrasting Stand-Average Calculations with Measures of Spatial Heterogeneity

Forest managers in the northern Rocky Mountains are charged with conducting restoration treatments that will enhance the resilience of fire-dependent old-growth stands, and reduce their susceptibility to stand-replacing fire. Yet, stand-average metrics that are routinely used for prescription development poorly characterize the typically heterogeneous stand structure and forest fuels that are associated with old-growth forests. We conducted a proof-of-concept study to compare stand-average calculations of forest fuels and associated wildfire hazard to the within-stand spatial heterogeneity of those properties. We analyzed two fire-excluded old-growth ponderosa pine stands in western Montana, encompassing the moisture gradient across which the forest type occurs in this region. At one site, we also analyzed the effect of a restoration prescription to reduce fuels and abate wildfire hazards. Fixed-area plot sample data were analyzed to describe within-stand heterogeneity by analyzing the distributions of current and anticipated post-treatment plot conditions, and contrasting these with conventional stand-average calculations. Distributions of overstory structures, fuel loads, and modeled fire behaviors were typically non-normal, skewed, and varied widely. Generally, standaverage calculations poorly represented the range of within-stand conditions. The study’s findings highlight the heterogeneity of stand structure, forest fuels, and wildfire fire hazard in old-growth ponderosa pine stands, and reveal the shortcomings of analytical methods that simplify spatially heterogeneous stand data.

Forest fuels and potential fire behaviour 12 years after variable-retention harvest in lodgepole pine

Variable-retention harvesting in lodgepole pine offers an alternative to conventional, even-aged management. This harvesting technique promotes structural complexity and age-class diversity in residual stands and promotes resilience to disturbance. We examined fuel loads and potential fire behaviour 12 years after two modes of variable-retention harvesting (dispersed and aggregated retention patterns) crossed by post-harvest prescribed fire (burned or unburned) in central Montana. Results characterise 12-year post-treatment fuel loads. We found greater fuel load reduction in treated than untreated stands, namely in the 10- and 100-h classes (P = 0.002 and 0.049 respectively). Reductions in 1-h (P < 0.001), 10-h (P = 0.008) and 1000-h (P = 0.014) classes were greater in magnitude for unburned than burned treatments. Fire behaviour modelling incorporated the regenerating seedling cohort into the surface fuel complex. Our analysis indicates greater surface fireline intensity in treated than untreated stands (P < 0.001), and in unburned over burned stands (P = 0.001) in dry, windy weather. Although potential fire behaviour in treated stands is predicted to be more erratic, within-stand structural variability reduces probability of crown fire spread. Overall, results illustrate trade-offs between potential fire attributes that should be acknowledged with variable-retention harvesting.

Technologies of Physical Monitoring and Mathematical Modeling for Estimation of Ground Forest Fuel Fire Condition

Description of new experimental installations for the control of parameters of environment with a view of monitoring of forest fires presented in article. Stationary and mobile variants developed. Typical results of operation of installations during a fire-dangerous season of 2015 in vicinities of Ulan-Ude (Republic Buryatiya, Russia) presented. One-dimensional mathematical model of forest fuel drying which can be used for monitoring of forest fire danger with attraction of environmental parameters data during fire-dangerous season offered. Verification of mathematical model with use of known experimental data spent.

Visual assessments of fuel loads are poorly related to destructively sampled fuel loads in eucalypt forests

Fire managers around the world commonly use visual assessment of forest fuels to aid prediction of fire behaviour and plan for hazard reduction burning. In Australia, fuel hazard assessment guides also allow conversion of visual assessments to indicative fuel loads, which is essential for some rate of spread models and calculation of fireline intensity or emissions. The strength of correlation between fuel hazard and destructively sampled (directly measured) fuel load was tested using a comprehensive dataset of >500 points from across a range of eucalypt forests in Australia. Overall, there was poor correlation between the assigned fuel hazard rating and measured biomass for surface, near-surface and elevated fuel components, with a clear tendency for these systems to under-predict fuel load at low hazard ratings, and over-predict it at high hazard ratings. Visual assessment of surface fuels was not statistically different from a random allocation of hazard level. The considerable overlap in fuel load between hazard ratings at higher ranges suggests the need to reduce the number of hazard classes to provide clearer differentiation of fuel hazard. To accurately assess forest fuel condition, improvements in fuel hazard descriptions and calibration of visual assessment with destructively measured fuels is essential.