Forest Fuels Research Articles

Fuel quality changes during seasonal storage of compacted logging residues and young trees

Abstract Forest fuel procurement creates logistical problems, as large stocks are accumulated along the supply chain. The purpose of this study was to examine fuel quality (moisture content, ash content and calorific value) of compacted young trees (mainly downy birch) and both uncompacted and compacted logging residues (LR) (mainly Norway spruce). The materials were examined before and after storage, with and without cover, and effects of handling were considered. Dry matter losses from compacted LR during storage and handling were determined. Fuel quality and mass were determined before and after storage and handling. The moisture content of LR dropped to 28.6% when stored in small piles after fuel adapted logging at the clear felling site for 3 weeks in May. Drying continued after compaction into cylindrical bales (length 3.4 m, diameter 0.7 m) and during storage in windrows (9 and 12 months), the moisture content falling to 18.2–20.7% for the covered and 18.8–24.9% for the uncovered material. The windrow of loose LR remoistened to 40.8% (by snow contamination) resulted in a 6% lower net calorific value as received, compared to cylindrical bales. Ash contents were in the range 1.6–2.2% for LR and 1.0–1.2% for young trees. Dry matter losses ranged from 8.4% to 18.1% on compacted LR. Remoistening during the winter is higher for loose than for compacted LR. Early summer in northern Sweden provides favourable conditions for drying forest fuels.

Measurement repeatability of a large-scale inventory of forest fuels

An efficient and accurate inventory of forest fuels at large scales is critical for assessment of forest fire hazards across landscapes. The Forest Inventory and Analysis (FIA) program of the USDA Forest Service conducts a national inventory of fuels along with blind remeasurement of a portion of inventory plots to monitor and improve data quality. The goal of this study was to evaluate the measurement repeatability/biases of FIA's national inventory of fuels and suggest opportunities for improving data quality and application of sampling protocols. Results indicated that more than half of the attributes did not attain the desired levels of repeatability and about one-third exhibited a non-zero measurement bias. However, the bias generally had little affect on plot-level estimates. A number of factors that contributed to these results were examined and a holistic approach that considers all aspects of inventory was suggested to improve measurement repeatability.

Informed multi‐objective decision‐making in environmental management using Pareto optimality

Summary Effective decision‐making in environmental management requires the consideration of multiple objectives that may conflict. Common optimization methods use weights on the multiple objectives to aggregate them into a single value, neglecting valuable insight into the relationships among the objectives in the management problem. We present a multi‐objective optimization procedure that approximates the non‐dominated Pareto frontier without the use of weightings, allowing for visualization of the trade‐offs among objectives. The non‐dominated Pareto frontier is approximated by the simultaneous optimization of a vector objective function; two vector objective functions are defined as non‐dominated if improvement with respect to one objective is at the detriment of another objective. We demonstrate the method with a case study for the optimum distribution of forest fuels treatments that reduce the impact of fire on a forest. The multiple objectives are to protect habitat of an endangered species, protect late successional forest reserves and minimize the total area treated. In the comparison of three optimization searches, the number of non‐dominated solutions increases with the dimensions of the objective space, but with only two objectives the search is ineffective in minimizing fire impact in the different landscape types. Key challenges include the extensive computation time required to approximate the non‐dominated set, and reducing the number of solutions that are analysed in detail. Synthesis and applications. The multi‐objective optimization program presented can be adapted to other environmental management problems, and easily incorporates a wide range of quantifiable objectives. This tool provides decision‐makers with a set of alternatives that estimates the full range of trade‐offs among multiple objectives and provides a common ground from which dialogue can come to an informed compromise and decision in environmental management problems.

Forest Fuel Inventory in 5 and 9-Year-Old Acacia Mangium Plantations

This study was conducted to determine the fuel components on forest floor of two different age stands and to estimate the fuel loading of the various fuel components. This study was carried out at Bukit Tarek Forest Reserve, Hulu Selangor, Selangor Darul Ehsan, at two stand age of Acacia mangium of 5 and 9-year-old. Fuel components of downed woody material and duff were sampled along transects lines. Shrubs, litter, herbaceous and small trees ( 1 of total fuel (downed woody material, litter and herbaceous), 1.73 cm of duff depth, 37,030 stem haG 1 of shrubs density and 2,175 tree haG 1 of small trees. The 9 year-old stand showed 17.42 Mg haG 1 of forest fuel, 3.03 cm of duff depth, 39,151 stem haG 1 shrubs density and 3,515 tree haG 1 of small trees. Downed woody material made up of 89 and 74% of the total fuel weight for 5 year and 9-year-old stands, respectively. Comparison between two different age stands, showed that 5 year old stand has higher quantity of downed woody materials than 9 year-old stand with 20.66 and 12.82 Mg haG 1 , respectively. Based on diameter class interval, the weight of downed woody material, diameter class of 0-7.6 cm were higher compared to diameter class of >7.6 cm. The fuel weight for 0-7.6 cm diameter class was 12.48 and 9.94 Mg haG 1 for 5 and 9-year-old stands, respectively. Statistical analysis showed that the loading of downed woody material on 5-year-old stand was significantly greater than the 9 year-old stand. However, litter loading was greater on the 9-year-old stand than the 5-year-old stand. The study concludes that in terms of fuel loading, 5-year-old stand has higher fire risk than 9-year-old stand. This is due to the silviculture activities in the 5-year old stand

A hierarchical approach for scaling forest inventory and fuels data from local to landscape scales in the Davis Mountains, Texas, USA

This study combined hierarchical cluster analysis and classification and regression tree algorithms to quantify vegetation and fuel characteristics and to generate spatially explicit vegetation and fuels maps for forest and fire management in the Davis Mountains of west Texas, USA. We used field data, landscape metrics derived from digital elevation models, and spectral information from remotely sensed imagery to (1) determine recent changes in forest stand structure in relation to historical fire exclusion, (2) quantify the effects of fire exclusion on fuel accumulation patterns, and (3) develop predictive vegetation and fuels maps for our study area. Four vegetation types were identified by cluster analysis including: mesic woodlands, pinyon pine forests, alligator juniper forests, and gray oak forests. Vegetation types varied by elevation, landform type, potential relative radiation (PRR), and spectral signature. Age data suggested that the majority of pines in the Davis Mountains established near 1920, just after the widespread 1916 fire and favorable climatic conditions in 1919. Three fuel types were identified that also varied by elevation, landform type, PRR and spectral characteristics, although the importance of these variables in distinguishing fuel types differed from the environmental variables that discerned the vegetation types. Forest stand densities and fuel accumulations were high in the Davis Mountains, which was probably the result of fire exclusion from grazing activities beginning in the early 1900s. Results from this study will be used to implement forest and fire management activities directed toward ecosystem restoration and maintenance.

Using simulated historical time series to prioritize fuel treatments on landscapes across the United States: The LANDFIRE prototype project

Canopy and surface fuels in many fire-prone forests of the United States have increased over the last 70 years as a result of modern fire exclusion policies, grazing, and other land management activities. The Healthy Forest Restoration Act and National Fire Plan establish a national commitment to reduce fire hazard and restore fire-adapted ecosystems across the USA. The primary index used to prioritize treatment areas across the nation is Fire Regime Condition Class (FRCC) computed as departures of current conditions from the historical fire and landscape conditions. This paper describes a process that uses an extensive set of ecological models to map FRCC from a departure statistic computed from simulated time series of historical landscape composition. This mapping process uses a data-driven, biophysical approach where georeferenced field data, biogeochemical simulation models, and spatial data libraries are integrated using spatial statistical modeling to map environmental gradients that are then used to predict vegetation and fuels characteristics over space. These characteristics are then fed into a landscape fire and succession simulation model to simulate a time series of historical landscape compositions that are then compared to the composition of current landscapes to compute departure, and the FRCC values. Intermediate products from this process are then used to create ancillary vegetation, fuels, and fire regime layers that are useful in the eventual planning and implementation of fuel and restoration treatments at local scales. The complex integration of varied ecological models at different scales is described and problems encountered during the implementation of this process in the LANDFIRE prototype project are addressed.

Designing a regional forest fuel supply network

New regulations on bioenergy lead to increasing demand for forest fuel. This paper describes a new approach to configure a wood biomass supply network for a certain region, a federal state of Austria. The network consists of several forest areas and a number of energy plants with a total demand of 1.2 million loose cubic meter (lcbm) wood biomass and 502,000 lcbm forest fuels. Starting with the regionally available forest fuel and the potential number of heating and energy plants we evaluate the different supply lines for the woody biomass from forest to plants by calculating the system cost for a number of alternative configurations. Especially, we compare central chipping against a local approach. The main contribution of this paper is to provide an evaluation method of forest fuel supply network design for a whole region.

Science Information for Informing Forest Fuel Management in the Dry Forests of the Western United States

Abstract Land managers need timely and straightforward access to the best scientific information available for informing decisions on how to treat forest fuels in the dry forests of the western United States. However, although there is a tremendous amount of information available for informing fuels management decisions, often, it is in a form that is difficult to use or of limited applicability. To improve access, interpretability, and use of the full body of research, a pilot project was initiated by the USDA Forest Service to synthesize relevant scientific information and develop publications and decisions support tools that managers can use to inform fuels treatment plans. This article provides an overview of the project and briefly discusses key lessons learned as an introduction to a series of articles, to be published in future Journal of Forestry issues, on different topic areas addressed by the project.

Managing Forest Structure and Fire Hazard—A Tool for Planners

Abstract Fire planners and other resource managers need to examine a range of potential fuel and vegetation treatments to select options that will lead to desired outcomes for fire hazard and natural resource conditions. A new approach to this issue integrates concepts and tools from silviculture and fuel science to quantify outcomes for a large number of treatment options in dry forest stands in the western United States. Five silvicultural options (thinning from below to 50 trees per acre [tpa]; 100, 200, and 300 tpa; or no thinning) are considered in combination with three surface fuel treatments (pile and burn, prescribed fire, or no treatment), resulting in a range of alternative treatments for each representative stand. The Fire and Fuels Extension of the Forest Vegetation Simulator (FFE-FVS) was used to calculate (1) immediate effects of treatments on surface fuels, fire hazard, potential fire behavior, and forest structure (including visualizations); and (2) a 50-year time series of treatment effects at 10-year increments. These fuel treatment scenarios can be used as a starting point for examining alternatives for National Environmental Policy Act documents and other applications that require scientifically based information to quantify the effects of modifying forest structure and surface fuels. Forest managers also can develop customized treatments for specific locations and resource objectives. Scenarios and output can be used to inform ecological, economic, and sociological evaluations of the effects of fuel and vegetation treatments.

Dwarf mistletoe effects on fuel loadings in ponderosa pine forests in northern Arizona

Southwestern dwarf mistletoe ( Arceuthobium vaginatum (Willd.) J. Presl ssp. cryptopodum ) infests about 0.9 million ha in the southwestern United States. Several studies suggest that dwarf mistletoes affect forest fuels and fire behavior; however, few studies have quantified these effects. We compared surface fuel loadings and predicted fire behavior among four levels of dwarf mistletoe infestation (none, light, moderate, and severe) in a total of 239 plots on 11 sites on basaltic soils in northern Arizona. In each plot we measured tree attributes, dwarf mistletoe rating and surface fuel loading. Stands severely infested by dwarf mistletoe had lower (P < 0.05) tree density and higher snag density, but higher (P < 0.05) total surface fuel loadings and total fuel loadings >7.62 cm and <7.62 cm, than non-infested stands. However, there were no statistical differences in any canopy fuel variables among infestation classes. Predicted fire behavior indicated that the wind speed required to promote the spread of a surface fire into the canopy was lower in severely infested stands than in non-infested stands. These results suggest that stands in northern Arizona that are severely infested with dwarf mistletoe should be priority areas for fuels treatments.

Modeling forest fire spread and spotting process with small world networks

The small world network model is extended to study fire spread through forest fuels. The proposed model includes the short-range radiative and convective effects from the flame as well as the long-range “spotting” effect of firebrands. It uses a weighting procedure on network sites based on the characteristic times of thermal degradation and combustion of a flammable site. First the model is validated against nonspotting fire experiments in homogeneous media. It is then applied to heterogeneous media to illustrate its ability to provide realistic fire patterns. It is found that the concentration of flammable sites, p, is a good measure of local small world network properties. Front propagation exhibits two thresholds delimiting the spreading/nonspreading transition: the first corresponds to a geometric second-order phase transition line and is inversely proportional to the fire impact length, l c , according to p c rn = 0.5 l c −1 , and the second is a dynamic threshold resulting from the weighting procedure. The p-dependence of the fractal dimension of the burned area confirms the percolation transition line behavior. Second, firebrands are considered by introducing a characteristic spotting distance. For homogeneous systems, the effect of firebrands on spread rate and burned area is strengthened when the fire impact length decreases and the characteristic spotting distance increases. The head fire goes forward by jumps, especially for small values of the fire impact length. However, the development of spotfires can slow down the overall propagation process. For heterogeneous systems, spread rate and burned area are significantly reduced as the degree of disorder increases. The influence of firebrands then becomes weaker and smoother. The model underlines the existence of critical channels of the propagation cluster, allowing to stop the propagation of fire if they are cut off.

Modelling the probability of sustained flaming: predictive value of fire weather index components compared with observations of site weather and fuel moisture conditions

We investigated the likelihood that short-duration sustained flaming would develop in forest ground fuels that had direct contact with a small and short-lived flame source. Data from 1027 small-scale experimental test fires conducted in field trials at six sites in British Columbia and the North-West Territories between 1958 and 1961 were used to develop logistic regression models for ten fuel categories that represent unique combinations of forest cover, ground fuel type, and in some cases, season. Separate models were developed using two subsets of independent variables: (1) weather variables and fuel moisture measurements taken at the site of the test fire; and (2) Canadian Fire Weather Index (FWI) system components calculated from weather observations recorded at a nearby station. Results indicated that models developed with FWI system components were as effective as models developed with site variables at predicting the probability of short-duration sustained flaming in most fuel categories. FWI system components were not useful for predicting sustained flaming in spring grass fuels and had limited usefulness for modelling the probability of sustained flaming in aspen leaf ground fuels during summer conditions. For all other fuel categories, FWI system components were highly effective substitutes for site variables for modelling the probability of sustained flaming.

Combustion characteristics of north-eastern USA vegetation tested in the cone calorimeter: invasive versus non-invasive plants

In the north-eastern United States, invasive plants alter forest fuels, but their combustion characteristics are largely unknown. We assessed unground samples of foliage and twigs in the cone calorimeter for 21 non-invasive, native species, paired with 21 invasive species (18 non-native). Variables included sustained ignition, peak heat release rate, total heat release, and especially average effective heat of combustion, which is independent of initial sample mass. Heat of combustion was overall slightly lower for invasive species than for counterpart non-invasive species, and was significantly lower for Norway maple, black locust, and glossy buckthorn than for three non-invasive trees. It was low for invasive Japanese stiltgrass, sheep sorrel, and glossy buckthorn, and for non-invasive whitegrass, interrupted fern, grape, sphagnum moss, and three-lobed bazzania. Heat of combustion was high for invasive roundleaf greenbrier (native), scotchbroom, tree-of-heaven, Japanese honeysuckle, Japanese barberry, swallow-wort, and garlic mustard, and for non-invasive plants of fire-prone ecosystems: black huckleberry, pitch pine, bear oak, northern bayberry, and reindeer lichen. Heat content of twigs and foliage interrelates with other factors that affect fire behaviour, yet the cone calorimeter results enabled comparison of combustion properties among many species. These data have potential application as improved inputs for fire behaviour modelling.

Empirical models of forest fire initial attack success probabilities: the effects of fuels, anthropogenic linear features, fire weather, and management

Canadian fire managers seek to contain fires below some target size (here 3 ha) by initial attack (IA). Suppression failures occur when fire size at IA exceeds this target (a response failure) or if an initially small fire cannot be contained below it (a containment failure). We examined the effects of cause, season, forest fuels, anthropogenic linear features, weather, and fire management (response time, size at IA) on the probability of these two types of suppression failures, using multiple logistic regression on 1196 fires that occurred within the boreal mixedwood forest of northeastern Alberta during 1995–2002. The frequencies of containment (7%) and response failures (10%) were similar, but the latter accounted for 85% of the area burned. Response failure probability was greater for fires caused by lightning than those caused by humans and increased with longer response times, local abundance of black spruce in summer, and pine fuel under severe fire weather. We found no effect of linear features or other fuel types. Containment failure probability was related to size at IA and fire weather conditions. Our models suggest that a reduction in area burned might be possible if additional fire-specific factors affecting response failure probability could be incorporated into operational decisions.

Thermal degradation of ligno-cellulosic fuels: DSC and TGA studies

The scope of this work was to show the utility of thermal analysis and calorimetric experiments to study the thermal oxidative degradation of Mediterranean scrubs. We investigated the thermal degradation of four species; DSC and TGA were used under air sweeping to record oxidative reactions in dynamic conditions. Heat released and mass loss are important data to be measured for wildland fires modelling purpose and fire hazard studies on ligno-cellulosic fuels. Around 638 and 778 K, two dominating and overlapped exothermic peaks were recorded in DSC and individualized using a experimental and numerical separation. This stage allowed obtaining the enthalpy variation of each exothermic phenomenon. As an application, we propose to classify the fuels according to the heat released and the rate constant of each reaction. TGA experiments showed under air two successive mass loss around 638 and 778 K. Both techniques are useful in order to measure ignitability, combustibility and sustainability of forest fuels.

Ash properties of Pinus halepensis needles treated with diammonium phosphate

The ash properties of Pinus halepensis (Aleppo pine) needles before and after treatment with diammonium phosphate (NH 4) 2HPO 4 (DAP) have been investigated, using thermogravimetric analysis (TG), differential thermal analysis (DTA), titrimetry, inductively coupled plasma-emission spectrometry (ICP-ES), X-ray diffraction (XRD) and scanning electron microscopy (SEM). DAP is extensively used as active component in wildland fire retardants. The following crystalline compounds have been identified in ashes prepared at 600 °C before treatment with DAP: KCl, Ca(OH) 2, MgO, (CaMg)CO 3, K 2CO 3·CaCO 3, K 2CO 3, K 2SO 4, CaO and CaCO 3, whereas CaO, MgO, K 2SO 4, K 2CO 3, CaCO 3, KCl and CaO, MgO, K 2SO 4 and K 2CO 3 at 800 and 1000 °C, respectively. The presence of DAP alters the composition of ashes converting, almost completely at high temperatures, the metallic oxides into phosphate salts. Thus, decreasing their alkalinity. The micrographs obtained by SEM indicate that pine needles ashes contain large porous particles of carbon compounds and several inorganic particles of irregular shape <1.0 mm, whereas after treating the needles with DAP an amorphous rigid structure was formed. To facilitate our investigation model mixtures of CaCO 3 + DAP, MgCO 3 + DAP, K 2CO 3 + DAP were heat treated under the same conditions used for preparing the ashes. The chemical transformations taken place during heating were studied by analysing the reaction products using thermal analysis and XRD. The physical, mineralogical and chemical forest ash properties determined could be used to evaluate the environmental risk of the use of fire retardants on soils, plants and aquatic systems as well as to investigate the mechanism of combustion of forest fuels in the presence of DAP.

The relation between the moisture content of fine forest fuels and several forest fire related aspects

The relations between the forest fuels moisture content and the meteorological data (or their derived indices), the fire occurrence or the burned area, are very important in terms of forest fire research. The measurement of the moisture content of the living and dead tree foliage from Pinus pinaster and Eucalyptus globulus was performed i n Viseu (Central Portugal), between April and June 2005. The samples were collected in a south - facing slope, between 12.00 and 13.00 Local Standard Time and their moisture content was obtained following an oven drying period of 24 h ours . A good empirical r elation was obtained between the moisture content of both species dead samples. The moisture content of the studied species was compared with the three fuel moisture indicators of the Canadian Forest Fire Danger Rating System (Fine Fuel Moisture Code, Duff Moisture Code and Drought Code) concerning the Viseu meteorological station, with good relations being obtained for the dead samples. The dead samples moisture content also showed good relations when compared with the statistical data, concerning the dail y fire occurrence and burned area in the Viseu d istrict during the same period. The indicators of the Canadian Forest Fire Danger Rating System concerning the Viseu meteorological station were compared with the statistical data, concerning the daily fire o ccurrence and burned area in the Viseu d istrict. The obtained empirical relations showed good results for the Fine Fuel Moisture Code, the Initial Spread Index and the Fire Weather Index.

Moisture content of fine forest fuels in the Central Portugal ( Lousã) for the Period 1996–2004

The moisture content of forest fuels is very important in terms of forest fire research given its implication in many aspects of fire risk, fire spread and fire ecology. In the present research program, living and dead tree foliage from Pinus pinaster and Eucalyptus globulus and living shrub foliage and extremities from Calluna vulgaris and Chamaespartium tridentatum (very common in the forests of Central Portugal) moisture content were measured by field sampling throughout the year from 1986 to present date. Samples were collected daily at Lousa (Central Portugal) during the Summer months and once a week during the rest of the year. In this paper the available values for the period 1996-2004, were systematized and analysed. In this program, moisture content was determined by oven-drying the fuel samples for 24 hours at 105oC. This methodology was compared with that of using an electronic balance that controls automatically the sample heating and the overall drying process. Seasonal moisture content patterns were analysed, as well as the relations between the moisture content values for the different studied species and the rainfall measured in the meteorological station from the Water Institute, located in Lousa. The obtained empirical relations show good results for dead tree species. During the period of 1996-1999 samples were collected at three sites located in the same region: Lousa, Silvares (Ponto Intermedio) and Olho Marinho. The relations between the moisture content values for the different species measured in these sampling sites were analysed. These relations enable the assessment of spatial moisture content patterns. The obtained empirical relations show good results for dead tree species and live shrub species. The relations between the moisture content values with fire occurrence for the different studied species were also analysed. These relations were systematized considering alternatively all data for the period 1996-2004, considering only the data corresponding the period of AprilSeptember, the period of October-March and considering only the data corresponding to moisture content values for dead tree species below 20%. The obtained empirical relations show good results for dead tree species and live shrub species. Dead tree species moisture content evolution after a summer precipitation episode was studied with the purpose of establishing a safe time period regarding the occurrence of forest fires.

Characterization and modeling of forest fuels in Araucaria angustifolia plantations

Characterization and modeling of forest fuels in Araucaria angustifolia plantations

Role of Foliar Moisture Content in the Silvicultural Management of Forest Fuels

Abstract In combination with measured stand data and assumed environmental conditions, reasonable estimates of foliar moisture content (FMC) are necessary to determine and justify silvicultural targets for canopy fuels management strategies. FMC often is overlooked in fuels planning, with default values substituting for more precise estimates, but its role is operationally significant in the selection of silvicultural targets even at modest surface fire intensities. This article discusses the role of FMC in canopy ignition and summarizes the results of 11 studies on the FMC values and trends for 16 North American conifers. FMC values ranged from 73 to 480% but varied by species, foliage age, and season. The information presented here will be helpful to managers engaging in canopy fuels planning with the use of popular fire behavior and fuels management software (e.g., NEXUS, Fuels Management Analyst, and the Forest Vegetation Simulator's Fire and Fuels Extension). West. J. Appl. For. 21(4):228–231.