Forest Fuels Research Articles

Equilibrium moisture content of dead fine fuels of selected central European tree species

Fine fuel moisture content is a key parameter in fire danger and behaviour applications. For modelling purposes, equilibrium moisture content (EMC) curves are an important input parameter. This paper provides EMC data for central European fuels and adds methodological considerations that can be used to improve existing test procedures. Litter samples of Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) were subjected to three different experiments using conditioning in a climate chamber and above saturated salt solutions. Climate chamber conditioning yielded the best results and can generally be recommended, however saturated salt solutions are able to produce lower relative humidities, which are relevant to forest fire applications as they represent the highest fire danger. Results were within the range of published sorption isotherms for forest fine fuels. A fairly clear gradation was present with higher EMC values in leaf litters than in needle litters. These differences are in accord with values from the literature and suggest general differences in the sorption properties of leaves and needles, which may be caused by differing chemical and physical properties. The influence of temperature on EMC described in the literature could be confirmed.

Fire spread prediction for deciduous forest fires in Northern Thailand

Predicting fire spread rates is essential in planning and deciding whether to conduct prescribed fires or suppressing forest fires. This study was conducted with the objective of developing a fire spread model for deciduous forest fires by using a simple statistical model. Test fires were conducted under a range of weather and fuel conditions to gather quantitative data on fire spreading. A series of 80 experimental fire plots were set in deciduous forests in the Northern Thailand during the forest fire seasons from 2008-2009. The factors influencing the fire spread rate, i.e., weather, fuel, and topography conditions, were measured to model the fire spread. According to the burning experiments, the fire spread rate was 0.51-2.55 m/min. Multiple nonlinear regression analyses of slope terrain, fuel load, and moisture content of fuels were found to be able to accurately predict the fire spread rate at a confidence level of 25-88%. The developed model can be applied to deciduous forest fuels in other regions of Thailand. However, its use should be restricted to typical weather conditions.

Pre-wildfire fuel reduction treatments result in more resilient forest structure a decade after wildfire

Increasing size and severity of wildfires have led to an interest in the effectiveness of forest fuels treatments on reducing fire severity and post-wildfire fuels. Our objective was to contrast stand structure and surface fuel loadings on treated and untreated sites within the 2002 Rodeo–Chediski Fire area. Data from 140 plots on seven paired treated–untreated sites indicated that pre-wildfire treatments reduced fire severity compared with untreated sites. In 2011, coarse woody debris loading (woody material>7.62cm in diameter) was 257% higher and fine woody debris (woody material<7.62cm) was 152% higher on untreated sites than on treated sites. Yet, in spite of higher levels of coarse woody debris on untreated sites, loadings did not exceed recommended ranges based on published literature and many treated sites fell below recommendations. By 2011, basal area and stand density on treated sites and stand density on untreated sites met management guidelines for ponderosa pine forests, but untreated sites had basal areas well below recommendations. Snags declined over this period and only three plots had snags that met minimum size and density requirements for wildlife habitat by 2011. The effects of pre-wildfire treatments are long-lasting and contribute to changes in both overstorey and understorey fuel complexes.

Forest Fuel Reduction and Biomass Supply: Perspectives from Southern Private Landowners

Removing excess biomass from fire-hazardous forests can serve dual purposes: enhancing the health and sustainability of forest ecosystems and supplying feedstock for energy production. The physical availability of this biomass is fairly well-known, yet availability does not necessarily translate into actual supply. We assess the perception and behavior of private forestland owners in the southern United States with respect to thinning overstocked forests for bioenergy production. Landowner perception is then integrated with the USDA Forest Service's Fuel Treatment Evaluator to estimate the biomass supply from fuel treatments on non-industrial private timberlands in the region. Due to competing uses for lumber and pulp/paper products, only about one-third of this biomass could be used as bioenergy feedstock. Between 6 and 66% of landowners would consider thinning overstocked forests for bioenergy purposes depending upon whether financial incentives and technical assistance are provided. Accounting for competing uses, landowner willingness, accessibility, and recovery loss, annual feedstock supply from Southern private treatable timberlands is estimated between 0.9- and 11-million dry tonnes (dt). The average production cost is proximately $48/dt. Government cost shares, biomass market development, and technical assistance could significantly stimulate private landowners to procure biomass from fire-hazardous forests while mitigating wildfire risk.

Modelling fuel terminals for supplying a combined heat and power (CHP) plant with forest biomass in Finland

A model to decentralise the procurement of forest fuels using terminals is considered for sustainable energy production. Problems include the scheduling of a number of procurement chains to an energy plant during different periods. In Finland roadside terminals are commonly used for forest fuel inventories in the procurement chains of energy plants. However, due to the complex nature of the decentralised procurement problems, the use of roadside terminals has recently been considered as an inefficient supply chain. Therefore, a terminal model was developed and tested using district and plant terminal technologies changing forest fuel buffer decisions to better describe the combinatorial complexity of energy flows. The examples achieved global optimality as a result of adding the terminal technologies to the model. The resulting objective function value (total operating costs of the procurement schedule) decreased by 18.3% from 7.1 to 5.8 million €. The properties of the model are discussed and five examples are presented of how the model works based on real-world data. Examples analyse the sensitivity of the model to buffer constraints based on different district and plant terminal technology rates (100, 300, 500 and 1000%).

Radionuclide activity concentrations in forest surface fuels at the Savannah River Site

Background/objectiveA study was undertaken at the United States Department of Energy's Savannah River Site (SRS), Aiken, South Carolina to investigate radionuclide activity concentrations in litter and duff from select areas at SRS. Litter (i.e. vegetative debris) and duff (i.e. highly decomposed vegetative debris) can often be the major fuels consumed during prescribed burns and have potential to release radiological contaminants into the environment. MethodsRepeated samples from 97 locations were collected systematically across SRS and analyzed for radionuclide activity. Radionuclide activity concentrations found in litter and duff were compared. As spatial trends were of interest, spatial distributions of radionuclide activity concentrations found in litter and duff and spatial dependency amongst the data were explored. Results7Be, 40K, and 137Cs showed statistically significant proportional differences between litter and duff samples. Duff sample concentrations for 137Cs (p < 0.0001) and 40K (p = 0.0015) were statistically higher compared to litter samples. 7Be activity concentrations were statistically higher in litter as compared to duff (p < 0.0001). For 40K litter and duff samples, spatial correlation tests were not significant at p = 0.05 and the maps did not indicate any apparent high concentrations centered near possible radionuclide sources (i.e. SRS facilities). For 7Be litter samples, significant spatial correlation was calculated (p = 0.0085). No spatial correlation was evident in the 7Be duff samples (p = 1.0000) probably due to small sample size (n = 7). 137Cs litter and duff samples showed significant spatial correlations (p < 0.0001 and p < 0.0001, respectively). ConclusionsTo date, few studies characterize radionuclide activity concentrations in litter and duff, and to our knowledge none present spatial analysis. Key findings show that across SRS, 137Cs is the primary radionuclide of concern, with the highest number of samples reported above MDC in litter (51.4%) and duff samples (83.2%). However, 137Cs litter and duff spatial trends in the maps generated from the kriging parameters do not appear to directly link the areas with higher activity concentrations with SRS facilities. The results found herein provide valuable baseline monitoring data for future studies of forest surface fuels and can be used to evaluate changes in radioactivity in surface fuels in the southeast region of the U.S.

Greenhouse Gas Emissions, Energy Use, and Costs—Case Studies of Wood Fuel Supply Chains in Scandinavia

Use of bioenergy based on woody biomass has become increasingly important in recent years, especially in European countries. In three case studies from Scandinavia, we conducted life cycle assessment (LCA) of alternative wood fuel supply chains (WFSCs) with respect to greenhouse gas (GHG) emissions, energy use, and costs. Case study 1 is a local Norwegian supply chain, while case studies 2 and 3 are international WFSCs, where woody biomass is exported to Sweden from respectively lowland and mountain forests in Norway. The GHG emissions and energy use in the case of wood chip exportation from Norway to Sweden were lower than in the local alternative use of the biomass. The emissions were 31.7 kg CO2e/m3 solid over bark (67.4 kg CO2e/MWh) for case study 1; 22.2 kg CO2e/m3 solid over bark (47.2 kg CO2e/MWh) for case study 2; and 23.9 kg CO2e/m3 solid over bark (50.8 kg CO2e/MWh) for case study 3. From a GHG point of view, WFSCs with relatively long transport distances were best when transportation was by railway and the combustion plant had high efficiency. The highest GHG emissions occurred in the truck transportation and chipping operations. Energy input-output ratios show that for case studies 1, 2, and 3, respectively, the fossil fuel energy inputs were 4.5%, 3.4%, and 4% of the bioenergy produced. Forest fuels from mountain forests in Norway seem promising for filling the high demand for wood fuel in Sweden, where bioenergy use is relatively high. In all case studies, the GHG balance was positive, especially when wood fuel plants substituted energy production from coal and oil plants. The cost analysis showed that wood chip import from Norway to Sweden was economically feasible.

The Psychology of Environmental Attitudes: Conceptual and Empirical Insights from New Zealand

EcopsychologyVol. 4, No. 4 Original ArticlesAttitudes, Behaviors, and ConservationThe Psychology of Environmental Attitudes: Conceptual and Empirical Insights from New ZealandTaciano L. MilfontTaciano L. MilfontSearch for more papers by this authorPublished Online:31 Jan 2013https://doi.org/10.1089/eco.2012.0058AboutSectionsView articleView Full TextPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View articleFiguresReferencesRelatedDetailsCited byPredicting Sustainable Consumption Practices by Value-Attitude-Behavior Theory16 October 2022Environmentally friendly urban development: changes in decision-makers’ attitudes, problem perceptions and policy preferences over three decades16 December 2022 | Journal of Environmental Planning and Management, Vol. 4Perceptions and attitudes of tertiary level students towards wood and non-wood furniture and energy fuels in BangladeshTrees, Forests and People, Vol. 10Urban ‘Prosumers’ of Solar Energy: Exploring the Mediating Role of Government Initiatives26 November 2022 | Vision: The Journal of Business Perspective, Vol. 120ESD in school: Understanding French-speaking Swiss pupils’ representations of sustainability27 September 2022 | Environmental Education Research, Vol. 82Environmentalism as an independent dimension of political preferences25 August 2022 | European Journal of Political Research, Vol. 78The Theory of Reasoned Action as a predictor of environmental behavior: A cross-cultural comparison between college students from Texas, Louisiana, and Honduras31 May 2022 | Journal of Human Behavior in the Social Environment, Vol. 22Self-construals and environmental values in 55 culturesJournal of Environmental Psychology, Vol. 79The environmental attitude of the urban population living in Macapá City, Brazilian Amazon region18 February 2021 | Environment, Development and Sustainability, Vol. 23, No. 10The differential psychology of environmental protection/exploitation ( La psicología diferencial de la protección/explotación medioambiental )27 September 2021 | PsyEcology, Vol. 12, No. 3Reexamining the Measurement of Pro-Environmental Attitudes and Behaviors to Promote Sustainable Development: A Systematic ReviewEurasia Journal of Mathematics, Science and Technology Education, Vol. 17, No. 9The role of national identity in collective pro-environmental actionJournal of Environmental Psychology, Vol. 72Exploring the Factor Structure of Environmental Attitudes Measure in a Sample of Indonesian College Students28 May 2020 | CES Psicología, Vol. 14, No. 1Do Environmental Prompts Work the Same for Everyone? A Test of Environmental Attitudes as a Moderator5 February 2020 | Frontiers in Psychology, Vol. 10Validation française de l’Inventaire d’Attitudes EnvironnementalesEuropean Review of Applied Psychology, Vol. 66, No. 6Who Cares? Measuring Environmental Attitudes22 April 2016Proximity to Coast Is Linked to Climate Change Belief21 July 2014 | PLoS ONE, Vol. 9, No. 7Ecopsychology in the Antipodes: Perspectives from Australia and New Zealand Elizabeth Bragg and Joseph Reser31 January 2013 | Ecopsychology, Vol. 4, No. 4 Volume 4Issue 4Dec 2012 InformationCopyright 2012, Mary Ann Liebert, Inc.To cite this article:Taciano L. Milfont.The Psychology of Environmental Attitudes: Conceptual and Empirical Insights from New Zealand.Ecopsychology.Dec 2012.269-276.http://doi.org/10.1089/eco.2012.0058Published in Volume: 4 Issue 4: January 31, 2013PDF download

ЗАЖИГАНИЕ ТИПИЧНЫХ ЛЕСНЫХ ГОРЮЧИХ МАТЕРИАЛОВ ОПАДА ЛИСТВЕННЫХ ПОРОД ЛОКАЛЬНЫМ ИСТОЧНИКОМ ЭНЕРГИИ

ЗАЖИГАНИЕ ТИПИЧНЫХ ЛЕСНЫХ ГОРЮЧИХ МАТЕРИАЛОВ ОПАДА ЛИСТВЕННЫХ ПОРОД ЛОКАЛЬНЫМ ИСТОЧНИКОМ ЭНЕРГИИ

Determining landscape fine fuel moisture content of the Kilmore East ‘Black Saturday’ wildfire using spatially-extended point-based models

Fuel moisture is the most dynamic component of bushfire fuels. It varies rapidly both spatially and temporally and plays a significant role in determining the behaviour and spread of bushfires, particularly through combustibility and ease of ignition of dead fine fuels (i.e. particle diameter <6 mm). The Kilmore East fire in Victoria, Australia, on 7 February, 2009 (“Black Saturday”) was the most destructive bushfire in Australia's history. Its behaviour was characterised by mass spotting (the launch, transport and landing of burning firebrands that ignited new fires downwind of the main fire), an indication of low fine surface fuel moisture content (FMC). However, no direct measurements of FMC were taken during the run of the fire.Existing point-based models of dead fine FMC of grass and forest litter fuels were used in conjunction with historical weather, topographic and fuel data for the fire area to investigate the likely spatial and temporal variation in landscape FMC during the event for the purpose of reconstructing the fire's propagation. To assess model performance, output was compared with the only suitable fuel moisture data collected in the region of the fire, measured at two locations ten days after the event. The model was found to be within 1% under adsorption conditions at one location and within 33% under desorption conditions at the other. The model was also used to study the effect of an intensive five day heatwave in the week prior to the fire event on FMC. In the absence of the heatwave, predicted FMC was 2.5 times higher than with the heatwave, however the effect of increased FMC was short-lived and would not have had a direct impact on the fine FMC during the fire event a week later, although it may have affected live fuels or larger dead fuels.

Managing forest fuels using prescribed fire – A perspective from southern Australia

Prescribed fire has been used in a coordinated manner to manage fuels in eucalypt forests of southern Australia since the 1950s. The impetus for planned use of fire arose from the need to reduce the impact of extensive, high intensity fires on life, property and commercial forest values. Prescribed fire is increasingly recognised as also playing an important role in mitigating undesirable effects of high intensity fires on environmental values including soil, water and biodiversity. Critical elements for an effective prescribed fire program include a sound understanding of fire behaviour, an experienced and flexible workforce, and organisational commitment to adaptive management involving planning, monitoring and applied research. Implementation of prescribed fire programs has been closely linked with, and dependent upon, the development of burning guides for particular forest types through empirical field research. The contribution of prescribed fire to mitigating the effects of extensive, high intensity fires can be quantified in a variety of ways using basic combustion science, well-documented case studies, analysis of fire statistics, and simulation. Fuel reduction can improve the safety, efficiency and effectiveness of fire suppression, although these effects may be subtle and difficult to measure. Social and political factors can significantly influence the conduct and effectiveness of prescribed fire programs, and effective engagement with the community during planning, implementation and post-fire monitoring phases is essential to ensure that the role of prescribed fire in land management is properly recognised and understood.

Flammability studies for wildland and wildland–urban interface fires applied to pine needles and solid polymers

This paper presents flammability studies related to wildland fires that have been conducted at the University of Edinburgh and at WPI over the last 5 years. This is the first time that all of the contributions have been put together to present a consistent set of studies geared towards a better understanding of how wildland and solid fuels ignite and burn in the context of wildland and wildland–urban interface fires. The whole approach is based on experiments conducted with the Fire Propagation Apparatus. This experimental device was used due to its versatility, allowing for testing over a wide range of conditions applied to different forest fuels. To simplify the approach, well-characterized fuels were used in the form of dead pine needles and solid polymers. The different sets of results show that this approach enhances our understanding of wildland fire behavior and impact in general but also, more specifically, at the wildland–urban interface. These experimental data, along with the models developed to describe ignition, represent a successful application and extension of approaches and techniques developed for fire safety studies to the topic of wildland fires.

A new bench-scale methodology for evaluating the flammability of live forest fuels

The present study proposes a new method in order to evaluate the flammability of live plant parts at bench-scale. Flammability parameters were estimated by the use of a mass loss calorimeter, and fuel moisture content was evaluated by the use of moisture analyser. Forest fuels ( Pinus pinaster, Cistus laurifolius, Lavandula stoechas and Daphne gnidium) were monitored under field conditions to detect the changes in the fuel moisture contents during the fire risk season. The combination of two different bench-scale devices (moisture analyser and mass loss calorimeter) guarantees fixed conditions for carrying out laboratory tests (constant bulk density and constant sample dry mass), thus resolving problems detected with other devices and methodologies.

Development of Vegetation and Surface Fuels Following Fire Hazard Reduction Treatment

In dry western Unites States forests where past resource management has altered the ecological role of fire and stand characteristics alike, mechanical thinning and prescribed burning are commonly applied in wildfire hazard abatement. The reduced surface fuel loads and stand structures resulting from fuels modifications are temporary, yet few studies have assessed the lifespan of treatment effects. We sampled forest fuels and vegetation following fuels reduction in a chronosequence of time since treatment in the northern Sierra Nevada and southern Cascade regions of California. Treatments altered overstory characteristics including stand density, basal area, and species composition. These effects were still present on the oldest treatment sites (8–15 years post-treatment). Other stand characteristics, particularly timelag fuel loads, seedling density, and shrub cover, exhibited substantial variability, and differences between treatment age classes and between treatment and control groups were not statistically significant.

ЗАЖИГАНИЕ ЛЕСНЫХ ГОРЮЧИХ МАТЕРИАЛОВ ОДИНОЧНЫМИ, НАГРЕТЫМИ ДО ВЫСОКИХ ТЕМПЕРАТУР ЧАСТИЦАМИ

ЗАЖИГАНИЕ ЛЕСНЫХ ГОРЮЧИХ МАТЕРИАЛОВ ОДИНОЧНЫМИ, НАГРЕТЫМИ ДО ВЫСОКИХ ТЕМПЕРАТУР ЧАСТИЦАМИ

Characteristics of lightning related to wildfire ignitions in Catalonia

What are the characteristics of lightning that influence the probability that an individual stroke will ignite a wildfire? It is generally accepted that long continuing current following some return strokes is the cause of ignition in forest fuels. However, because these low-level currents are not detectable with operative Lightning Location Systems, other lightning characteristics correlating with its occurrence have been proposed and used to estimate ignition probability. These variables are typically: flash multiplicity, stroke polarity, stroke peak current and flash interstroke interval. The region of Catalonia is prone to forest fires, and to set a probability of ignition to each cloud-to-ground flash could be useful in wildfire management. A set of more than 500 lightning-ignited wildfires that occurred in Catalonia between 2004 and 2009 was analyzed, in order to find which flash/stroke characteristics are related to ignition. Lightning activity was gathered by the Lightning Location System of the Meteorological Service of Catalonia. Lightning related to these wildfires were selected from the lightning database using a proximity index. The statistical analysis has shown that the sample of lightning causing ignition does not present any characteristic that differentiates it from the overall population. Polarity percents, multiplicity and peak current frequency distributions in the lightning causing ignition set are similar to the climatological ones. Besides this analysis, a high-speed video field campaign of natural lightning recordings was conducted, to obtain new insight into the characteristics of lightning bearing a continuing current. Video analysis has shown that almost each kind of cloud‐to‐ground (CG) flash (negative, positive, single or multiple stroke) can have a continuing current component. Only negative strokes with peak currents above 20kA were not followed by long continuing current. These results are similar to studies carried out in other regions.

Long‐term responses of Mediterranean birds to forest fuel management

Summary1. Mechanical management of forest fuels is increasingly used in the Euro‐Mediterranean region in response to the abandonment of traditional agroforestry and the concurrent increase in fire hazard. Although fuel management may have positive side effects for biodiversity, its long‐term impacts remain largely unknown.2. We used a 70‐year post‐management chronosequence to investigate the influence of time since fuel management and management frequency on bird assemblages in cork oak Quercus suber forests.3. Fuel management strongly affected bird species richness, abundances and assemblage composition, with rapid changes often occurring during the first 10–20 years, followed in the next decades by a slow convergence to pre‐management levels.4. In winter, overall species richness and abundance, and that of frugivores and shrub foragers, were negatively affected by recent and recurrent management, only recovering in stands unmanaged for &gt;50 years. In spring, insectivore abundance and the richness and abundance of shrub foragers declined immediately following management, increased to a maximum about 20 years later, and declined thereafter. Breeding granivores and ground foragers were the only groups that benefitted from fuel management. There were no overall effects on species of conservation concern, although a few species with unfavourable status benefitted from fuel management.5. Synthesis and applications. Our study confirmed that mechanical fuel management has positive effects on some early‐successional bird species of conservation concern, although its effects were limited. These benefits should be compared with the strong negative impacts on key bird species such as wintering frugivores, which play a pivotal role in ecosystems by promoting seed dispersal. To reconcile the positive and negative aspects, fuel management should be used to create heterogeneous mosaics of forest patches encompassing a range of sizes (10–100 ha) and successional stages of understorey vegetation, including stands undisturbed for &gt;50 years. This management strategy will likely maintain conditions for a wide range of species with contrasting ecological requirements while also reducing fire hazard.

Fuel variability following wildfire in forests with mixed severity fire regimes, Cascade Range, USA

Fire severity influences post-burn structure and composition of a forest and the potential for a future fire to burn through the area. The effects of fire on forests with mixed severity fire regimes are difficult to predict and interpret because the quantity, structure, and composition of forest fuels vary considerably. This study examines the relationship between fire severity and post-burn fuel characteristics in forests with mixed severity fire regimes. We sampled live and dead canopy and surface fuels across four fire severity classes on three wildfires that occurred on the east side of the Cascade Range, USA, in 2007 and 2008. We used empirical fuels data and stand structure and composition characteristics to calculate potential surface fire behavior for the four fire severity classes. Post-burn average canopy cover is 25–30% in the low severity class and <10% in the high severity class and ranges from 0 to 50% for all fires. All variables representing post-burn canopy fuels differ by fire severity class. The average loading of dead and down woody fuels <7.6cm diameter and litter is 0.9–1.1kgm−2 in the low severity class and 0.6–0.8kgm−2 in the high severity class. Values for fuel loading variables span a wide range of values within and among fires, and substantial overlap exists among severity classes. Fire severity generally does not influence post-burn dead and down woody fuel loading. Estimates of potential fire behavior also cover wide ranges of values, particularly among fires. Flame lengths average 0.4–0.8m in the low severity classes and 0.3–1.1m in the high severity classes. The range of potential flame length values, modeled with a 16.1kmh−1 midflame wind speed, varies by up to 2.0m within a single severity class (0.6–2.6m). Fire severity does influence potential fire behavior, but typically just one severity class differs from the other three classes. These results indicate that fire severity influences immediate (2–3years) post-burn canopy fuels and potential fire behavior but does not influence dead and down surface fuel loading for the three fires studied. The wide ranges of values for the fuel components analyzed demonstrate the variability that is characteristic of forests with mixed severity fire regimes and emphasize the need to consider the natural heterogeneity of these forests in fire and fuels management. Quantification of post-burn fuel variability is critical for understanding the ecological significance of mixed severity fires and developing restoration strategies that emulate characteristics of the historical fire regime.

Piloted ignition of live forest fuels

The most unpredictable and uncontrollable wildfires are those that burn in the crowns of live vegetation. The fuels that feed these crown fires are mostly live, green foliage. Unfortunately, little is known about how live fuels combust. To understand how live fuels burn, piloted ignition experiments were performed with lodgepole pine and Douglas-fir. The thermal behavior (thick versus thin) of both live and dead needles was explored. Both live and dry needles were shown to behave as thermally intermediate solids in this apparatus. Additionally, samples were collected throughout the growing season to take advantage of the natural variation in moisture content and chemical composition. This data set was then compared to several correlations found in the literature to determine whether live fuel ignition can be predicted by moisture content alone and to test the applicability of these models to the wildland fire problem. Many of the correlations from the literature for ignition time with moisture content fail to capture the trends with live fuels. A linear regression of the ignition time with moisture content only predicts 74–80% of the variability suggesting that there is another mechanism controlling ignition time of live fuels. Based on the hypothesized difference in water storage between live and wet dead fuels, the chemical composition of the live needles was included in an empirical model for ignition time. Including chemical composition improved the prediction accuracy for Douglas-fir needles only. Because the thermal properties of live foliage are largely unknown, it is possible that the predictions from more physically-based models would show improvement with more accurate values of density, thermal conductivity, and specific heat.

Effects of ungulate herbivory on aspen, cottonwood, and willow development under forest fuels treatment regimes

Herbivory by domestic and wild ungulates can dramatically affect vegetation structure, composition and dynamics in nearly every terrestrial ecosystem of the world. These effects are of particular concern in forests of western North America, where intensive herbivory by native and domestic ungulates has the potential to substantially reduce or eliminate deciduous, highly palatable species of aspen (Populus tremuloides), cottonwood (Populus trichocarpa), and willow (Salix spp.). In turn, differential herbivory pressure may favor greater establishment of unpalatable conifers that serve as ladder fuels for stand-replacing fires. The resulting high fuel loads often require silvicultural fuels reductions to mitigate fire risk, which in turn may facilitate additional recruitment of deciduous species but also additional herbivory pressure. Potential interactions of ungulate herbivory with episodic disturbances of silviculture, fire, and other land uses are not well documented, but are thought to operate synergistically to affect forest dynamics. We evaluated individual and joint effects of ungulate herbivory and fuels reduction treatments in grand fir (Abies grandis) and Douglas-fir (Psuedotsuga menziezii) forests that dominate large areas of interior western North America. We applied fuels reduction treatments of mechanical thinning and prescribed fire and then evaluated the responses of aspen, cottonwood, and willow species to these treatments (N=3) versus areas of no treatment (N=3), and to exclusion from ungulate herbivory versus areas subjected to extant herbivory by free-ranging cattle (Bos taurus), elk (Cervus elaphus), and mule deer (Odocoileus hemionus). Densities of deciduous species were >4 times higher in response to fuels reduction treatments (84.4individuals/ha) compared to areas of no treatment (19.7individuals/ha). Additionally, when ungulates were excluded from fuels treated sites, the density of cottonwood was >5 times higher (122.5individuals/ha) than fuels treated sites subjected to extant herbivory (24.3individuals/ha). Similarly, densities of Populus spp. and Salix spp. were >3 times higher (211.6individuals/ha) on fuels treated sites excluded from ungulate herbivory versus fuels treated sites subjected to extant herbivory (66.1stems/ha). Deciduous species subjected to extant ungulate herbivory also were significantly lower in height, canopy surface area, and canopy volume than the same species inside the ungulate exclosures. Recruitment and long-term survival of aspen, cottonwood, and willow species in coniferous forests of interior western North America require a combination of episodic disturbances such as silviculture and fire to facilitate deciduous plant recruitment, followed by reductions in grazing pressure by domestic and wild ungulates during the time intervals between episodic disturbances to facilitate plant establishment, growth and survival.