Forest Fuels Research Articles

Emission Factors for Polycyclic Aromatic Hydrocarbons from Biomass Burning

Emission factors for 19 polycyclic aromatic hydrocarbons were measured during wind tunnel simulations of open burning for agricultural and forest biomass fuels including cereal grasses, agricultural tree prunings, and fir and pine wood (slash). Yields of total PAH varied from 5 to 683 mg kg-1 depending principally on burning conditions and to a lesser extent on fuel type. Barley straw and wheat straw loaded at 400−500 g m-2 emitted much higher levels of PAH, including benzo[a]pyrene, than other cereal and wood fuel types burning under more robust conditions. As anticipated, total PAH emission rates increased with increasing particulate matter emission rates and with declining combustion efficiency.

Estimating ratio of surface area to volume for dead needles

A method for estimating the ratio of surface area to volume for dead needles was developed. The method is based on the simplification proposed by Brown (1970), but the requested values (surface area and perimeter) have been obtained, on micrometrical cross sections, through an image analyzer. The propopsed method gather the necessary conditions of accuracy and rate. The ratio of surface area to volume (σ) is closely related to the fire behaviour in the different forest fuels. Therefore, this physical characteristic has been determinated for fine dead fue particles that taje part, frecuently, in forest fires. The values obtained for Pinus pinaster Ait., P. pinea L. and P. halepensis Mill. are, respectively, 48.24, 57.80 and 79.93 cm-1. The results show variations among species. Nevertheless, differences due to sampling areas have not been founded.

Dynamic models of moisture content of forest fuels

The fuel moisture content is an integral part of any workable fire danger-rating system. This paper presented dynamic models for estimating 1-h, 10-h, 100-h and 1000-h timelag fuels, that were developed by multiple regression and stepwise variable selection of statistics. The variables include both meteorological factors and moisture contents observed prior to the day correspondingly. The analysis revealed that the fuel moisture content are correlated positively with the precipitation of 24 hours prior to the observation time, and negatively with air temperature at observing height of 1.5 meter in forest.

Fire‐Regime Disruption and Pine‐Oak Forest Structure in the Sierra Madre Occidental, Durango, Mexico

AbstractFire is a common but poorly understood disturbance in the forested ecosystems of the Sierra Madre Occidental of Mexico. In this study, fire history, forest structure (density, species composition, regeneration, forest floor fuels, herbaceous cover, and age of pines), and the dendrochronological tree‐ring record were measured at two unharvested 70‐ha pine‐oak sites near Ojito de Camellones, Durango, Mexico. Study sites were matched in slope, aspect, elevation, slope position, and plant composition, but they differed in fire history since 1945 and in forest structure. The long‐term mean fire intervals (MFI) for all fires at both sites up to 1945 were similar—4.0 years at Site 1 (1744–1945) and 4.1 years at Site 2 (1815–1945)—but Site 1 burned only three times at the site margins since 1945 while Site 2 had 9 fires that scarred two or more sample trees and 15 total fires since 1945. Density measurements and age and diameter distributions showed that Site 1 was dominated by numerous, younger, smaller trees (mean total basal area of 23.4 m2/ha and 2730 trees/ha), while Site 2 had fewer, older, larger trees (basal area of 37.2 m2/ha, 647 trees/ha). Large, rotten fuel loading and duff depth were also greater at Site 1. Because regeneration averaged 6200 stems/ha at Site 1 and 8730 stems/ha at Site 2 (no significant difference), forest density at Site 2 was not limited by regeneration capability. The distributions of overstory diameter and pine age at both sites indicate that tree establishment occurred in pulses, with the largest cohort of trees establishing at Site 1 following the 1945 fire. The dense regeneration and heavy fuel accumulation at Site 1 are likely to support a switch from the former low‐intensity fire regime to a high‐intensity, stand‐replacing fire across the site when the next suitable combination of ignition and weather occurs. Baseline quantitative information on fire frequency and ecological effects is essential to guide conservation or restoration of Madrean forests and may prove valuable for restoration of related fire‐dependent ecosystems that have experienced extended fire exclusion elsewhere in North America.

The estimate of the effective fuel combustion value of forest community in the Daxingan Mountain

Under the condition of absolute dry, more than thirty forest fuel parameters, ash content, extract and burning point were measured. By the method of regression step by step, we found an experience formula which can estimate effective fuel high combustion value of forest community from the Daxingan Mountain, and then, By means of modifying moisture content, we gave an approximate formula about actual heat releasing of forest fuels in the forest fire behavior.

Dynamic models of aquiferous content of living fuels

Forest fire occurrence is closely relative with fuel water content. There are a lot of research about dead fuels, but forest fuels consist of both dead fuels and living fuels. Each large fire occurrence has a good relationship with living fuels. Especially living fuels can influence the production and development of big forest fire, so, we selected Tahe, in Daxingan Mountains, as observation site. According to actual data, we can establish a set of models of different living fuel water content variation with linear-regression method.

Predicting the Height to Live Crown Base in Plantations of Four Boreal Forest Species

A critical parameter for the initiation and propagation of a crown fire in the boreal forest is the height to the base of the live crown. The initiation of a crown fire requires that the surface fire intensity must be sufficient to ''jump'' the gap between the forest floor and the live crown and ignite crown fuels. The greater the height of the live crown base, the more intense the surface fire must be to induce a crown fire. Plantation forest fuels tend to be more structured and have less variability than naturally regenerated areas, allowing prediction of the height of the live crown base to be made from commonly available stand parameters. Plantations of four commonly planted boreal forest species were sampled over a variety of age classes to determine a predictive relationship for height to live crown base. Height to live crown base can be predicted from stand height and density for Pinus banksiana (jack pine), Pinus resinosa (red pine), Picea mariana (black spruce), and Picea glauca (white spruce). In addition to predicting the height to live crown base, parameters within the equations lead to other observations. Crown foliar fuel loading does not change with stand height following crown closure in red pine but in the other three species crown fuel load increases as the stand grows taller.

Comparative analysis of the thermokinetic constants for drying and pyrolyzing forest fuels

Thermogravimetric measurement in an inert medium and the simplest kinetic equations are used to obtain thermokinetic constants for drying and pyrolizing typical forest fuels. The adequacy of the model is demonstrated experimentally. Materials are identified for which a single value of the kinetic constants can be used. Methods are suggested for using these values in a general mathematical model of forest fires.

Moisture Diffusivity in Forest Fuels

Abstract. Apracticalmeans of quanmingthe diffusivities of forest fuels from fielddata is presented. The mathematics of this method is explored for four fuel shapes: a litter layer, a hardwood leaf, a twig and a square fuel moisture analogue stick, which are represented geometrically by a semi-infinite solid, a slab, a cylinder and a square prism, respectively. Theresults are presented graphically. Analyses of two published sets of field data indicate defusivities of 4.1 x 10-12m2 s-1 and 1.3 x 10-10m2 s-1 for Eucalyptus leaves and twigs, respectively, and 2.9 x 10-9m2 s-1 for a lodgepole pine litter layer.

Moisture Content of Fine Forest Fuels and Fire Occurrence in Central Portugal

Moisture content of ten fine fuels frequent in the forests of CentralPortugal and in other Mediterranean areas was measured daily since 1986. Average monthly results are presented for the period of 1987-1990. Pinuspinaster sticks were used as a predictor of dead fuel moisture content. A reasonable correlation was obtained with the moisture content of Pinus pinaster dead needles and Eucalyptus globulus dead leaves. Two options of the MOISTURE module of BEHAVE system were also tested to predict the daily minimum value of fine dead fuel moisture content. Predicted values were always lower than direct measurements, specially when only meteorological data was used. A better agreement was obtained when known moisture content of the previous day was introduced. Using statistical data of oily fire occurrence in some districts around the site where the tests were made, for the same period of time, the probability of fire occurrence, the average number of daily fires and the average area burned each year was analysed as a function of dead pine needles moisture content. Three distinct zones, around and adjacent to the test site showed a very similar behaviour.

US 4,966,942 Impact modifier for polycarbonate

Suppressant chemicals are often added to water for use in the direct attack of wildfires to extend the longevity and suppression effects of the water. There are a range of suppressants available, however there has been limited testing to determine which are the most effective. This paper presents an experimental methodology designed to enable the comparison of the relative effectiveness of wildfire suppressants applied in direct attack to fires in forest fuels. The method involves suppressants being applied onto the flaming fronts of standardised laboratory fires burning in uniform forest litter fuels within a wind tunnel through a pressurised system mounted above the burning fuel. The minimum volume of suppressant required to extinguish a standard fire is determined and used to quantify suppressant effectiveness. Examples of the method are presented for plain water and water with three types of wildland fire suppressant. Results show that repeated tests conducted with the same suppressants have low variability (coefficient of variation ~10.8%) and thus high reliability. In order to minimise effects of non-controlled variation in fire behaviour between tests, results can be normalised to produce relative values for comparison across datasets.

Moisture diffusivity and response time in fine forest fuels

Fine forest fuels, such as grasses, hardwood leaves, and conifer needles, vary greatly in response times and mean moisture diffusion coefficients when exposed to desorption and adsorption conditions. Results are reported for tests made with recently dead and weathered dead fine forest fuels and small woody samples. Test conditions were 26.7 °C (80°F) with changes in relative humidity from 90 to 20% and back, in an environmental chamber. Moisture diffusivities of fine forest fuels were found to be smaller than diffusivities of woody samples. The diffusivities of the foliage and grass fuels tested ranged from near 1.0 × 10−10 to 1.0 × 10−8 cm2/s, whereas the woody fuels ranged from 1.5 × 10−7 to3.0 × 10−5 cm2/s. Weathered fine fuels had faster response times and higher diffusivities than recently cast materials. Adsorption response times were longer and diffusivities lower than for fuels in desorption. Response times of various recently dead fine fuels ranged from 0.2 to 37 h and weathered fuels from 0.5 to 10 h. Therefore, specific fuel types need to be tested to assign more precise response times. Under the drying conditions of 26.7 °C and 20% relative humidity, fine forest fuels had lower diffusivities and longer response times than anticipated in the United States National Fire Danger Rating System. As a result, predicted fire danger during or after a weather change may be overestimated because fuels are responding more slowly than anticipated. Equations are presented for making first estimates of response time and (or) diffusivity if certain physical properties are known: surface area-to-volume ratio, packing ratio, and bed depth.

Woody fuel structure and fire in subalpine fir forests, Olympic National Park, Washington

The fuel structure and flammability of subalpine fir (Abieslasiocarpa (Hook.) Nutt.) stands were studied to determine the relationship between these forests and fire. It has long been known that subalpine fir forests burn catastrophically, but the contributions of fuel structure and fuel moisture to this pattern of burning have been relatively unstudied. This investigation discovered two relationships. First, over twice as much fuel in subalpine fir forests accumulated around the bases of the fir trees than in the forest as a whole, and the many dead branches on the lower trunks may allow fire to travel up into the canopy. Second, the fuels in subalpine fir forests were more flammable at the end of the summer than at the beginning, and maximum flammability was achieved in early August when the fuel moisture was between 16 and 22%. We also found that the fuel structure of subalpine fir was different from that of fire-stable ponderosa pine (Pinusponderosa Laws.) forests. The fuel around the bases of the trees in ponderosa pine forests was not significantly different from that in the entire forest, and there were few branches on the lower trunks.

Chemical composition of forest fuels affecting their thermal behavior

Flaming combustion is dependent upon the production of flammable volatiles that originate from the heating of the fuel materials. The thermal reactions that take place during this heating are determined by the chemical composition of the fuel. A knowledge of fuel chemistry and thermal reactivity can be useful in understanding and predicting fire behavior. Four plant materials were studied because their thermal decomposition curves showed unusually strong peaks from unknown combustible volatiles. The objective was to isolate and identify the chemical source of these volatiles. The tissues were methodically fractionated by following previously published techniques. Effects of each fractionation were carefully monitored by thermogravimetric analysis before and after treatment. Arabinogalactan was identified as the source of 325–350 °C volatiles from western larch (Larixoccidentalis Nutt.) wood. The major component of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) bark that decomposed above 400 °C was suberin. Foliage from gallberry (Ilexglabra (L.) Gray) and ponderosa pine (Pinusponderosa Laws.) contained cutin, which was responsible for their volatiles produced above 400 °C. The thermal behaviors of suberin and cutin reflect their similar chemical composition. The presence of these chemical components may produce similar thermal behavior in numerous other plant tissues.

Absorption properties and graphitic carbon emission factors of forest fire aerosols

Data on the optical absorption properties (expressed as a specific absorption, Ba) of the smoke emissions from fires with forest fuels have been determined for a series of low‐intensity field fires and a series of laboratory scale fires. The Ba data have been used to estimate the emission factors for graphitic carbon [EF(Ce)] for these test fires to provide data needed for regional visibility studies, tropospheric air chemistry studies, and studies evaluating nuclear winter scenarios.

Validating a Simplified Determination of Benzo[a]pyrene in Particulate Matter from Prescribed Forestry Burning

A high performance liquid chromatographic (HPLC) method for determining the concentration of trace amounts of benzo[a]pyrene (B[a]P) in particulate matter from combustion of forest fuels was validated. Particulate matter was prepared for analysis by a small-scale (1 mg), simplified preparation followed by HPLC with fluorescence detection. The chromatographic system had a limit of detection of 2.67 ng/mL, a precision of 6.4 percent relative standard deviation, and a working range of 2.67 to 100 ng/mL. The complete method gave a mean recovery of 100.6 percent across its working range with an 8.3 percent relative standard deviation. With National Bureau of Standards' Standard Reference Material 1649 (urban particulate matter), a mean recovery of 93.2 percent of the certified B[a]P content was obtained with a 9.9 percent relative standard deviation. After storing loaded filters for 4 months under refrigeration, the B[a]P content of the particulate matter from forest fire smoke had not significantly changed.

Simulation of Growth Curves from Periodic Increment Data

Alexander, M. E. 1982. Calculating and interpreting forest fire intensities. Canadian Journal of Botany 60:349-357. Byram, G. M. 1959. Combustion of forest fuels. Pages 6189 in K. P. Davis, editor. Forest fire: control and use. McGraw-Hill, New York, New York, USA. Cave, G H., III. 1982. Ecological effects of fire in the upper Sonoran Desert. Thesis. Arizona State University, Tempe, Arizona, USA. McLaughlin, S. P., and J. E. Bowers. 1982. Effects of wildfire on a Sonoran desert community. Ecology 63:246-248. O'Leary, J. F., and R. A. Minnich. 1981. Postfire recovery of creosote bush scrub vegetation in the western Colorado desert. Madrono 28:61-66. Rogers, G. F., and J. Steele. 1980. Sonoran desert fire ecol? ogy. Pages 15-16 in M. A. Stokes and J. H. Dieterich, technical coordinators. Proceedings ofthe fire history workshop. United States Forest S rvice General T chnical Re? port RM-81. Shreve, F. 1964. Vegetation ofthe Sonoran Desert. Pages 1-186 in F. Shreve and I. L. Wiggins, editors. Vegetation and flora ofthe Sonoran Desert. Stanford University Press, Stanford, California, USA. Steenbergh, W. F, and C. H. Lowe. 1977. Ecology of the saguaro: II, reproduction, germination, establishment, growth, and survival ofthe young plant. United States Na? tional Park Service Scientific Monograph Series 8. Steenbergh, W. F., and C. H. Lowe. 1983. Ecology ofthe saguaro: III, growth and demography. United States Na? tional Park Service Scientific Monograph Series 17. Wright, H. A. 1980. The role and use of fire in the semidesert grass-shrub type. United States Forest Service General Technical Report INT-85. Zedler, P. H., C. R. Gautier, and G. S. McMaster. 1983. Vegetation change in response to extreme events: the effect of a short interval between fires in California chaparral and coastal shrub. Ecology 64: 809-818.

A method for describing equilibrium moisture content of forest fuels

The isothermal adsorption and desorption of water vapor by forest fuels is represented with a two-parameter model based on an exponential relationship between Gibbs free energy change and equilibrium moisture content. The model is applied to five sets of sorption data in the literature to illustrate goodness of fit. Two of the data sets are well reproduced by the model; description of the remaining data is less satisfactory. Whether the deviations are due to experimental factors or a deficiency in the model is not determined. At constant temperature, hysteresis ratios tend to increase as percent relative humidity increases.

Differential Scanning Calorimetry of Forest Fuels

Previous investigations for developing fire spread models in wildland forest fuels have not adequately assessed the heat-sink characteristics of the different fuels. This research uses differential scanning calorimetry to determine the total heat required to change the temperature of a sample of forest fuel from 25/sup 0/ to 500/sup 0/C. The incremental heat input is recorded for 10/sup 0/C increments. Thermogravimetric analysis data are given for equivalent samples. Significant differences are noted between major fuels in the total heat required at 500/sup 0/C. Generally, the heat required for pyrolysis of these fuels is as important as that for evaporating moisture from the fuel.

Characterization of the thermal properties of forest fuels by combustible gas analysis

The thermal decompositions of forty-three typical forest fuels have been characterized up to 500 degrees C. The fuels studied include foliage, wood, small stems, and bark. Evolved gas analysis gave quantitative measurements of the oxygen stoichiometry for combustion of volatile pyrolysis products. Oxygen consumption by the volatiles is highly correlated to their calculated heats of combustion. Char heats of combustion were also determined and found to be very similar for the fuels studied. These data were used to partition total heat of combustion into flaming and glowing components. Addition of combustible gas analysis to other thermal analysis techniques provides a more complete comparison of thermal behavior over a wide temperature. (Refs. 30).