Forest Fuels Research Articles

Method for Optimizing the Kinetic Parameters for the Thermal Degradation of Forest Fuels Based on a Hybrid Genetic Algorithm

Method for Optimizing the Kinetic Parameters for the Thermal Degradation of Forest Fuels Based on a Hybrid Genetic Algorithm

Unraveling the relative importance of factors driving post-fire regeneration trajectories in non-serotinous Pinus nigra forests

In the Mediterranean, non-serotinous pinewoods are suffering an increasing occurrence of high-severity crown fires that usually drive vegetation shifts to fire-adapted communities and a decrease in pine-dominated area. Here we used a case-study approach on a large area dominated by Pinus nigra Arn. ssp. salzmannii burned in 1998 to gain further understanding of the relative importance of different factors related to local topography (elevation, aspect, slope, curvature), pre-fire vegetation (land-use history, canopy cover) and fire behavior (burn severity, presence of unburned patches) as drivers of post-fire regeneration dynamics. The results find that pine shows locally resilient responses driven mainly by factors related to fire effects (presence of unburned patches) and the characteristics of the pre-fire vegetation (i.e. stable forest areas). When fire-induced changes from pine dominance to other types of vegetation occurred, landscape 15years post-fire was dominated by woody vegetation, with some rare grassland communities emerging under very specific conditions (mountain ridges, hilltops and rocky sites). Conversion from forest to shrubland occurred mainly in the most xeric sites (south-facing areas, in some cases with steep slopes) and areas dominated by young pine stands prior to the fire. We found manageable factors such as the pre-fire structure and composition of the vegetation strongly determine the occurrence of post-fire regeneration trajectories dominated by tree species regeneration. This knowledge can be used to define preventive management strategies oriented to direct regeneration dynamics in anticipation of fire occurrence. At landscape level, managing forest fuels to favor the occurrence of unburned patches and modify their spatial distribution along the burned landscape will favor a more resilient pine response. At stand level, adjusting silvicultural interventions to favor the natural establishment of late-successional tree species will favor post-fire oak regeneration.

Finding balance between fire hazard reduction and erosion control in the Lake Tahoe Basin, California–Nevada

The 2007 Angora Fire served as a stark reminder of the need for fuel reduction treatments in the Lake Tahoe Basin, California–Nevada, USA. Concerns exist, however, that the corresponding removal of forest floor fuels could increase erosion rates, negatively affecting the clarity of Lake Tahoe. To quantify trade-offs between fuel reduction and erosion, we conducted field-based snowmelt runoff simulation experiments at 16 sites within the Lake Tahoe Basin that had received mechanical mastication or prescribed fire treatments. Erodibility was measured to determine if thresholds of litter, duff, and woody fuel cover could be established that are sufficient for trapping sediment and increasing infiltration, without contributing to fire hazard. Field snow-melt simulations revealed that as little as 25% of the ground surface covered with masticated fuels over duff was sufficient to mitigate erosion. The post-prescribed fire environment characterized by heterogeneous patches of exposed bare mineral soil interspersed with unburned patches mitigated erosion by increasing infiltration. Considerable increases in sediment yield were observed in plots with >35% of ground area burned; the highest total sediment yields (values) occurred in plots where between 66% and 100% of the soil surface burned. Our field results suggest that erosion and wildfire severity can be simultaneously mitigated through the use of masticated fuel reduction treatments or prescribed fire treatments that leave sufficient organic matter to trap sediment but have sufficiently low fuel loading and/or enough fuel discontinuity or patchiness to limit fire spread.

Ignition of low-density expandable polystyrene foam by a hot particle

Insulating materials are ubiquitous in modern buildings for improving energy efficiency, but their high flammability becomes a significant fire safety issue. Many large fires in high-rise buildings were caused by the ignition of insulating materials by hot particles from fireworks and welding processes. Such ignition event is fundamentally different from the traditional flame or radiation driven ignition assumed in the literature, and still presents significant knowledge gaps. In this work, we study experimentally the ignition of a widely used insulation materials, expandable polystyrene (EPS) foam, by a hot steel particle under different conditions. In the experiments, a small spherical particle (6∼14 mm in diameter) was heated to a high temperature (>900 °C), and then placed on a bench-scale low-density (18 or 27 kg/m3) foam sample. It was observed that flaming ignition could only occur on the foam surface during its rolling process (rolling ignition) or before it was fully embedded (embedding ignition). The measurements suggested that larger particles held lower critical temperatures for ignition, which decreased from 1030 to 935 °C for diameters increasing from 6 to 14 mm. Compared to higher-density forest fuels in the literature, the critical particle temperature of EPS foam is much higher, with a narrower transition region for ignition probability of 5–95% and has a weaker dependence on the particle size. Results also show that both the sample density and thickness have a negligible influence on the ignition probability and mass-loss ratio. Theoretical analysis suggested that the hot particle acts as both heating and pilot sources, and the ignition of EPS foam is controlled by the competition between the gas mixing time and the particle residence time.

Chip truck utilization for a container handling chipper truck when chipping logging residues and the effect of two grapple types on chipping efficiency

Most forest fuels harvested in Swedish final fellings are forwarded to a landing, and chipped before transport to the end user. Chipping on landing is usually done with a large chipper mounted on a forwarder, an alternative is to use a chipper truck which combines chipping and chip transport. These are an economically viable alternative where transport distances are short. Container handling chipper trucks (CCTs) were introduced 10 years ago, and their advantages include better utilization of the chipper and more economical road transport of the chips than ordinary chipper trucks. A CCT was studied to evaluate its utilization and to determine if the choice of grapple on the CCT or the preceding forwarder influenced chipping productivity. Results showed that average productivity varied between 9.3 and 13.5 odt PMH0 depending on choice of grapple. A standard residue grapple was the better choice for the CCT, while residues forwarded with an asymmetrical grapple increased chipping efficiency. One-sixth of the work time consisted of delays and half of that time was spent waiting for empty containers. By careful planning of operations and adjustments of the number of container trucks in the system total waiting costs can be reduced.

Evaluating primary forest fuel rail terminals with discrete event simulation: A case study from Austria

Biomass rail transport is a useful alternative to unimodal truck transport for medium or long transport distances, if only a short road pre-haulage is required. Up to now primary forest fuels (PFF) are rarely transported on the rail network in Austria and rail terminals able to tranship notable volumes are not established yet. The objective of this study is to investigate the potentials of existing transhipment infrastructure for introducing and operating PFF terminals. Such PFF terminals enable a regular PFF supply to bioenergy plants and additionally provide opportunities for buffer storage and production processes like comminution. Three existing railway sidings in South, Central and Western Austria were chosen to serve as a multimodal transhipment hub with a road pre-haulage and a rail main-haulage for this case study. The logistic potential of these terminals was investigated, modelling the specific PFF supply chains, by means of a discrete event simulation. Simulation results provide daily and annual transhipment capacities and revealed bottlenecks in the terminal layout under different supply scenarios.

Tools for Assessing the Impacts of Climate Variability and Change on Wildfire Regimes in Forests

Fire is an intrinsic element of many forest ecosystems; it shapes their ecological processes, determines species composition and influences landscape structure. However, wildfires may: have undesirable effects on biodiversity and vegetation coverage; produce carbon emissions to the atmosphere; release smoke affecting human health; and cause loss of lives and property. There have been increasing concerns about the potential impacts of climate variability and change on forest fires. Climate change can alter factors that influence the occurrence of fire ignitions, fuel availability and fuel flammability. This review paper aims to identify tools and methods used for gathering information about the impacts of climate variability and change on forest fires, forest fuels and the probability of fires. Tools to assess the impacts of climate variability and change on forest fires include: remote sensing, dynamic global vegetation and landscape models, integrated fire-vegetation models, fire danger rating systems, empirical models and fire behavior models. This review outlines each tool in terms of its characteristics, spatial and temporal resolution, limitations and applicability of the results. To enhance and improve tool performance, each must be continuously tested in all types of forest ecosystems.

Potential savings and cost allocations for forest fuel transportation in Sweden: A country-wide study

Bioenergy is becoming a more important energy source. An important bioenergy assortment in Sweden is given by primary forest fuels. These account for about 14% of the biofuels or about 4% of Sweden's total energy. There are large volumes of forest fuel available. However, it is a low-value commodity and it is very sensitive to logistic cost to make it profitable. In this article, we analyse alternatives to lower the logistic costs. This includes the scheduling of the harvest and chipping operations in relation to transportation, delivered mix of assortments to customers and collaboration. We study these alternatives in a case that accounts for all operations in Sweden, involving 200,000 registered transports of about 6.1 million tons of forest biomass, equivalent to 17.4 TWh of energy consumption. We define a number of instances for these alternatives and formulate an optimization model based on linear programming. The solution is obtained by using a decision support system. We identify savings potential of about 22% from changing the operations. These savings can have a large impact on the industry and, more importantly, increase the use of bioenergy. We also test cost allocation methods to spread the savings based on cooperative game theory concepts.

Analysis of the use of biomass as an energy alternative for the Portuguese textile dyeing industry

The energy efficiency and the development of environmentally correct policies are current topics, especially when applied to the industrial sector with the objective of increasing the competitiveness of the enterprises. Portuguese textile dyeing sector, being a major consumer sector of primary energy, needs to adopt measures to improve its competitiveness. Biomass appears to be a viable and preferred alternative energy source for the sector, while simultaneously develops an entire forest industry devoted to the supply of forest solid fuels. This work carries out a comprehensive PEST (political, economic, social and technological) analysis, which analyses Political, Economic, Social and Technological aspects of the replacement of the fossil fuels traditionally used in this sector by biomass, providing a framework of environmental factors that influence the strategic management of the companies. The main advantages are the reduction of external dependence on imported fuel due to the use of an endogenous renewable resource, the creation and preservation of jobs, the increased competitiveness of the sector by reducing energy costs, the use of national technology and the reduction of greenhouse gases emissions.

Experimental Study of Forest Fuel Ignition by the Source of Limited Energy Capacity

During the experimental study we examined the ignition of the litter of hardwood species by the particle heated up to high temperatures. Our study involved conducting tests, using a carbonic particle and samples of typical forest fuels, formed of birch leaves. We determined a mechanism for litter ignition by a local heating source, and obtained the dependence of ignition delay of birch leaves on the particle's initial temperature.

Mapping forest fuels through vegetation phenology: the role of coarse-resolution satellite time-series.

Traditionally fuel maps are built in terms of ‘fuel types’, thus considering the structural characteristics of vegetation only. The aim of this work is to derive a phenological fuel map based on the functional attributes of coarse-scale vegetation phenology, such as seasonality and productivity. MODIS NDVI 250m images of Sardinia (Italy), a large Mediterranean island with high frequency of fire incidence, were acquired for the period 2000–2012 to construct a mean annual NDVI profile of the vegetation at the pixel-level. Next, the following procedure was used to develop the phenological fuel map: (i) image segmentation on the Fourier components of the NDVI profiles to identify phenologically homogeneous landscape units, (ii) cluster analysis of the phenological units and post-hoc analysis of the fire-proneness of the phenological fuel classes (PFCs) obtained, (iii) environmental characterization (in terms of land cover and climate) of the PFCs. Our results showed the ability of coarse-resolution satellite time-series to characterize the fire-proneness of Sardinia with an adequate level of accuracy. The remotely sensed phenological framework presented may represent a suitable basis for the development of fire distribution prediction models, coarse-scale fuel maps and for various biogeographic studies.

Conceptual Framework for Assessing the Sustainability of Forest Fuel Reduction Treatments and Their Adaptation to Climate Change

Applying fuel reduction treatments (FRTs) to forested landscapes can alleviate undesirable changes in wildfire benefits and costs due to climate change. A conceptual framework was developed for determining the preferred FRTs across planning periods, adapting FRTs to future climate change, assessing the sustainability of adaptive responses to climate change, and evaluating the validity of the two premises motivating this issue of Sustainability. The conceptual framework: (1) accounts for uncertainty about future climate change and its effects on management objectives for FRTs; (2) employs biophysical simulation and mental models to estimate the management objectives for FRTs; (3) uses fuzzy TOPSIS to determine the preferred FRTs for climate futures; (4) employs the minimax regret criterion to identify the preferred FRT for each planning period; (5) determines the best strategy for adapting FRTs to future climate change; and (6) assesses landscape sustainability when using the preferred FRTs. The framework is demonstrated with constructed examples for adapting FRTs to climate change for privately- and publicly-owned forested landscapes. Based on the conceptual framework, current knowledge does not allow determining with certainty whether managers’ adaptations of FRTs to future climate change are sustainable or unsustainable due to type I and II decision errors.

Area burned in the western United States is unaffected by recent mountain pine beetle outbreaks

In the western United States, mountain pine beetles (MPBs) have killed pine trees across 71,000 km(2) of forest since the mid-1990s, leading to widespread concern that abundant dead fuels may increase area burned and exacerbate fire behavior. Although stand-level fire behavior models suggest that bark beetle-induced tree mortality increases flammability of stands by changing canopy and forest floor fuels, the actual effect of an MPB outbreak on subsequent wildfire activity remains widely debated. To address this knowledge gap, we superimposed areas burned on areas infested by MPBs for the three peak years of wildfire activity since 2002 across the western United States. Here, we show that the observed effect of MPB infestation on the area burned in years of extreme fire appears negligible at broad spatial extents. Contrary to the expectation of increased wildfire activity in recently infested red-stage stands, we found no difference between observed area and expected area burned in red-stage or subsequent gray-stage stands during three peak years of wildfire activity, which account for 46% of area burned during the 2002-2013 period. Although MPB infestation and fire activity both independently increased in conjunction with recent warming, our results demonstrate that the annual area burned in the western United States has not increased in direct response to bark beetle activity. Therefore, policy discussions should focus on societal adaptation to the effects of recent increases in wildfire activity related to increased drought severity.

An experimental assessment of the ignition of forest fuels by the thermal pulse generated by the Cretaceous–Palaeogene impact at Chicxulub

A large extraterrestrial body hit the Yucatán Peninsula at the end of the Cretaceous period. Models suggest that a substantial amount of thermal radiation was delivered to the Earth’s surface by the impact, leading to the suggestion that it was capable of igniting extensive wildfires and contributed to the end-Cretaceous extinctions. We have reproduced in the laboratory the most intense impact-induced heat fluxes estimated to have reached different points on the Earth’s surface using a fire propagation apparatus and investigated the ignition potential of forest fuels. The experiments indicate that dry litter can ignite, but live fuels typically do not, suggesting that any ignition caused by impact-induced thermal radiation would have been strongly regional dependent. The intense, but short-lived, pulse downrange and at proximal and intermediate distances from the impact is insufficient to ignite live fuel. However, the less intense but longer-lasting thermal pulse at distal locations may have ignited areas of live fuels. Because plants and ecosystems are generally resistant to single localized fire events, we conclude that any fires ignited by impact-induced thermal radiation cannot be directly responsible for plant extinctions, implying that heat stress is only part of the end-Cretaceous story.

Integrating volunteered smartphone data with multispectral remote sensing to estimate forest fuels

Volunteered data sources are readily available due to advances in electronic communications technology. For example, smartphones provide tools to collect ground-based observations over broad areas from a diverse set of data collectors, including people with, and without, extensive training. In this study, volunteers used a smartphone application to collect ground-based observations. Forest structural components were then estimated over a broader area using high spatial resolution RapidEye remote sensing imagery (5 spectral bands 440–850 nm, 5 m spatial resolution) and a digital elevation model following a three nearest neighbor approach (K-NN). Participants with professional forestry experience on average chose high-priority fuel load locations near buildings, while nonprofessional participants chose a broader range of conditions over a larger extent. When used together, the professional and nonprofessional observations provided a more complete assessment of forest conditions. A generalized framework is presented that utilizes K-NN imputation tools for estimating the distribution of forest fuels using remote sensing and topography variables, ensuring spatial representation, checking attribute accuracy, and evaluating predictor variables. Frameworks to integrate volunteered data from smartphone platforms with remote sensing may contribute toward more complete Earth observation for Digital Earth.

Integrating forest fuels and land cover data for improved estimation of fuel consumption and carbon emissions from boreal fires

Estimating carbon emissions from wildland fires is complicated by the large variation in both forest fuels and burning conditions across Canada’s boreal forest. The potential for using spatial fuel maps to improve wildland fire carbon emission estimates in Canada’s National Forest Carbon Monitoring, Accounting and Reporting System (NFCMARS) was evaluated for select wildfires (representing a transect across western Canada) occurring in 2003 and 2004 at four study areas in western Canada. Area-normalised emission rates and total emissions differed by fuels data source, mainly as a function of the treatment of open fuels in the higher resolution spatial fuel models. The use of spatial data to refine the selection of stand types that probably burned and the use of fire weather conditions specific to the fire increased the precision of total carbon emission estimates, relative to computational procedures used by Canada’s NFCMARS. Estimates of total emissions from the NFCMARS were consistent with the regional and national data sources following the spatial approach, suggesting the two approaches had equivalent accuracies. Though it cannot be said with certainty that the inclusion of this detailed information improved accuracy, the spatial approach offers the promise or potential for more accurate results, pending more consistent fuel maps, especially at finer scales.

Californians must learn from the past and work together to meet the forest and fire challenges of the next century

Outlook Californians must learn from the past and work together to meet the forest and fire challenges of the next century Susan Kocher, Forestry/Natural Resources Advisor, UC Cooperative Extension Central Sierra I The fire-suppression stalemate n 1920, forester Charles Ogle issued a warning about the emerging consensus that all wildfires in forests should be suppressed. “Under natural fire conditions,” Ogle wrote in the July 1920 issue of The Timberman, “a proper amount of thinning was effected and the remaining trees were thereby given a better chance to mature.” He predicted that trying to extinguish all wildfires would crowd the woods with small trees and leave forests prone to major fires and disease and warned that “a complete destruction of our standing timber of today and the elimination of possible second growth of practical value may be the result” (Ogle 1920). UC U.S. Forest Service Ogle and other prescribed-fire advocates lost the argument. Today their concerns seem prescient. After a century of fire suppression, California for- ests are denser and have fewer large trees. Severe fires are increasing in frequency and size through- out the Sierra Nevada. And regeneration is not a given for severely burned forests where seed trees have been killed across large areas. How have we gotten to this moment of crisis? Though land managers have understood for more than 40 years that fire has an important role in a functioning forest ecosystem, the use of fire to man- age forests has remained limited. Fire suppression has led to dramatic increases in forest fuels, and let- ting wildfires burn now for ecological benefits and hazard reduction is considered too risky in most forests and weather conditions. Thinning forests of small trees and brush can reduce the severity of fires that burn there; however, paying for the work required to get those materials out of the forest is increasingly difficult as the number of mills and biomass-burning facilities has waned in the last decade. Additionally, biological, legal, operational and administrative constraints significantly limit where thinning can be carried out in the 10 national forests in the Sierra Nevada (North et al. 2015). Decades of successful fire suppression lulled regulators of residential and commercial develop- ment into permitting new construction without regard to fire risk. These developments now reduce our ability to use fire to lessen future fire hazard. Attempts to get out of this predicament are made more challenging by political polarization over public land management, the uncertainties of a warming climate and concerns about the impacts of forest thinning on wildlife and the public health ef- fects of smoke from prescribed fires. Moving toward a healthier role for fire in California forests will be difficult. One area where there is opportunity, however, is in post-fire land- scapes. Because today’s wildfires tend to be so large and destructive, post-fire areas provide a large landscape on which to try to design a for- est that will incorporate wildfire concerns from the beginning. Reforestation can be developed to incorporate fire and warming climate concerns. Restoration sites can also serve as an ongoing labo- ratory for experimentation, so that forest managers The Rim Fire began in the Stanislaus National Forest on Aug. 17, 2013 and burned 257,314 acres. More than 100,000 acres burned at high severity, meaning nearly all trees were killed. http://californiaagriculture.ucanr.edu • JANUARY–MARCH 2015 5

Determination of Characteristic Peroids of Suppression of Thermal Decomposition Reaction of Forest Fuel Material by Specialized Software

Experimental studies determining periods of suppression of thermal decomposition reaction of forest combustible materials was carried out by high-speed, cross-correlation cameras and panoramic techniques PIV and IPI under influence of water steam. Conditions and characteristics of reaction termination of thermal decomposition of forest combustible materials under reaction with steam cloud were defined.

Forest structure and fuels dynamics following ponderosa pine restoration treatments, White Mountains, Arizona, USA

Southwestern ponderosa pine forest ecosystems have become uncharacteristically dense as a result of intensive livestock grazing, logging, and fire exclusion, which have contributed to a buildup of fuels and increased vulnerability to high-severity, landscape-scale crown fires. In 2002, we implemented a replicated ecological restoration experiment to (1) quantify site-specific reference conditions, (2) analyze effects of elevation on forest structure, surface fuels, and canopy fuels, (3) test responses to three treatments: control, full treatment, and burn-only, and (4) evaluate effectiveness of treatments for restoring attributes to near historical reference conditions. Reconstructed reference conditions showed that basal area (BA) averaged 9.2m2ha−1 and tree density averaged 86.2treesha−1 across the site in 1880 prior to widespread fire exclusion, with the highest tree density values occurring at the two upper elevation sites. In 2002, prior to treatment, BA averaged 28.9m2ha−1 and density averaged 927.9treesha−1, representing three- and ten-fold increases, respectively, compared to 1880 values with a higher proportion of the increase coming from mesic species at higher elevations. By 2013 (5-years post-treatment), the full treatment showed BA was reduced by 52% compared to pre-treatment values from 31m2ha−1 to 15m2ha−1 and density was reduced by 85% from 998treesha−1 to 153treesha−1. In the burn-only treatment, BA increased by 6% from 27.5m2ha−1 to 29.1m2ha−1 although density was reduced by 25% from 837treesha−1 to 625treesha−1 between 2002 and 2013. Canopy fuels dynamics were similar to forest structure responses: low values prior to fire exclusion, a marked increase by the pre-treatment measurement, substantial reductions following thinning plus burning, and minor reductions following burn-only treatments. Post-treatment diameter distributions in the full treatment closely resembled reference conditions; minor reductions occurred in the lower diameter classes in the burn-only. Mortality of trees established before European settlement circa 1880 varied by treatment: 25% of presettlement trees alive in 2002 died by 2013 in the full treatment, 31% died in the burn-only treatment, and 15% died in the control. Of the treatments tested, the full treatment was the only one that rapidly shifted forest structure, diameter distributions, and canopy fuels values to levels near or within the historical reference conditions. Results from this study showed that managers will have to consider tradeoffs between alternative treatments in the context of climate-induced, landscape-scale forest fires.

Modifying the Canadian Fine Fuel Moisture Code for masticated surface fuels

Mechanical mastication is a fuel management technique that disrupts the vertical continuity of forest fuels by shredding of trees and understory vegetation into a highly compacted surface fuel bed. Despite the increasing application of mastication to manage wildfire risk, there is little information to date on fuel moisture in masticated fuels and optimal ignition patterns for prescribed burning. We investigated the applicability of the Fine Fuel Moisture Code (FFMC), a component of the Canadian Fire Weather Index (FWI) System, in tracking the diurnal and day-to-day changes in masticated surface fuel moisture, and developed a calibration of the standard conversion between moisture content and FFMC via regression modelling. We also proposed several modifications to the FFMC model (including a solar radiation driven fuel temperature) to better estimate the fuel-specific parameters of small diameter (<1 cm) masticated surface fuels. Model validation was performed using destructive moisture content observations from a mastication treatment in west-central Alberta, Canada. A calibrated form of the moisture content to FFMC conversion produced mean error of –2.3% moisture content, and closely resembled previous FWI System calibrations for fast drying surface fuels. Our modified FFMC-based model fit well with field observations, and was capable of producing mean error of 1.0% moisture content. The fast drying that we observed highlights the need to better understand moisture dynamics of masticated fuel beds.