Woodland Fires Research Articles

Overview of some radiative transfer issues in simulation of unwanted fires

Fire is an extremely complex phenomenon that is responsible for loss of human life and considerable property and environmental damages every year around the world. Significant progress during the last few decades in modeling of pool, compartment (enclosure), urban and outdoor (i.e., forest and woodland) fires has manifested in improved understanding of fire phenomenology, fire-safety regulations and fire-fighting techniques. Recent research efforts to develop numerical CFD (computational fluid dynamics) models for simulating fire phenomena from first principles are discussed. Since both thermal and oxygen-limited feedback processes can affect fire dynamics, quantitative description of fire development requires understanding of materials, turbulence, chemical kinetics, heat and mass transfer, radiation, and other important physical processes. Focus in the discussion is on radiative transfer (one of the most complex and time consuming process) in numerical simulation of large pool, compartment, urban and outdoor fires. The overview discusses current trends and identifies the outstanding problems requiring research attention.

The Allerød/Younger Dryas transition in Wolin Island, northwest Poland, as reflected by pollen, macrofossils, and chemical content of an organic layer separating two aeolian series

A palaeoecological study including pollen, macrofossils, and chemical analyses of an organic sediment separating two series of aeolian cover sands has enabled us to reconstruct environmental changes during the Allerod/Younger Dryas transition in Wolin Island, northwest Poland. The Allerod woodland dominated by Pinus sylvestris became more open at the beginning of the Younger Dryas, when aeolian (wind) activity resulted in instability of the soil. During the early phase of the Younger Dryas the water level in the local basin distinctly raised, indicating a change to a wetter climate. This short-lasting phase was followed by an increased frequency and intensity of aeolian processes. However, the main aeolian event took place before the major expansion of Juniperus, not later than 10,780±120 b.p. Frequent woodland fires, probably due to the activities of Palaeolithic people, have been documented both for the Allerod and the Younger Dryas periods. Macrofossils of Alnus sp. found in the Allerod layer are of special interest in showing the presence of alder trees in northwest Poland as early as the Late-glacial.

Radial growth responses of singleleaf pinyon ( Pinus monophylla) to wildfire

Dendroecological methods for quantifying and dating historical canopy disturbance events have been widely applied for temperate forests, but may not be useful for semi-arid woodlands, where growth is more strongly influenced by drought cycles. Our study focuses on the potential utility of dendroecological methods for reconstructing historical fire in woodlands of the Nevada Great Basin, USA, which are dominated by singleleaf pinyon pine ( Pinus monophylla Torr. and Frem.). We assess growth responses to a historical fire of known date, and compare different analytical methods involving radial-growth averaging approaches. Despite the strong influence of climate on radial growth of trees growing in semi-arid woodlands, most pinyon pines sampled in this study exhibited profound growth releases in response to fire. The growth releases could be detected using radial-growth averaging criteria, even given thresholds of percent growth change that effectively eliminated responses to climatic variability. The most conservative dendroecological method was radial-growth averaging with a 10 yr moving window and a percent growth change (PGC) threshold of at least 125%. This method detected the known fire for nearly one in three surviving trees, with very minimal occurrence of false positives in control trees or in the historical record. Results suggest that such approaches may be useful for identifying and approximately dating historical fires that burned adjacent to living pinyon trees. However, these methods will likely not be able to separate historical wildfire from other disturbance types, such as pinyon ips ( Ips confusus) or root rot fungi, which could be expected to cause growth releases in surviving trees. Also, the year of growth release following the known burn was delayed until years of good precipitation, resulting in a lagged response that can confound the ability of growth release methods to accurately pinpoint the year of disturbance.

A Method of Detecting Fire Smoke by Using Optical Flow

In this paper, the authors propose a method for detecting fire smoke by using the optical flow. This method is not influenced against the image obtainment environment. About 60,000 fires have occurred every year in Japan. To be most important to the fires is an early period fire fighting. At present, the automatic devices of detectiong fires is needed. The alarms which can detect smoke and heat are utilized to house fires. However, these alarms are not useful for the outside of house such as the incendiary or woodland fire. This method is able to detect such a flame that becomes a fire is the early period. First, the region of the flame in the images obtained from the observation camera is detected. Next, the characteristic quantity that expresses the smoke is extracted. This characteristic is not influenced to the motion such as the cloud, leaf and moving objects. In other words, the only smoke can be detected, from the range which looks like the flame in the image.

Seasonal variation and ecosystem dependence of emission factors for selected trace gases and PM2.5 for southern African savanna fires

In this paper we present the first early dry season (early June‐early August) emission factor measurements for carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), nonmethane hydrocarbons (NMHC), and particulates with a diameter less than 2.5 μm (PM2.5) for southern African grassland and woodland fires. Seasonal emission factors for grassland fires correlate linearly with the proportion of green grass, used as a surrogate for the fuel moisture content, and are higher for products of incomplete combustion in the early part of the dry season compared with later in the dry season. Models of emission factors for NMHC and PM2.5 versus modified combustion efficiency (MCE) are statistically different in grassland compared with woodland ecosystems. We compare predictions based on the integration of emissions factors from this study, from the Southern African Fire‐Atmosphere Research Initiative 1992 (SAFARI‐92), and from SAFARI‐2000 with those based on the smaller set of ecosystem‐specific emission factors to estimate the effects of using regional‐average rather than ecosystem‐specific emission factors. We also test the validity of using the SAFARI‐92 models for emission factors versus MCE to predict the early dry season emission factors measured in this study. The comparison indicates that the largest discrepancies occur at the low end (0.907) and high end (0.972) of MCE values measured in this study. Finally, we combine our models of MCE versus proportion of green grass for grassland fires with emission factors versus MCE for selected oxygenated volatile organic compounds measured in the SAFARI‐2000 campaign to derive the first seasonal emission factors for these compounds. The results of this study demonstrate that seasonal variations in savanna fire emissions are important and should be considered in modeling emissions at regional to continental scales.

Rodent Populations Recovering from Fire in an East Mediterranean Woodland*

Fire in woodlands causes a dramatic decrease in rodent populations. The aim of this study was to detect rodent succession in three different management regimes of a post-fire habitat on Mount Carmel: (1) a control area of mixed woodlands of burnt pine and oak; (2) a mixed burnt woodland in which the burnt pine trees were cut and left in situ; and (3) a mixed burnt woodland in which burnt pines were cut and removed from the plot. Two plots in an unburnt mixed woodland were used as controls. The first invader species observed in the post-fire habitats were Mus macedonicus, which was the most abundant species in all burnt plots, Gerbillus dasyurus, which was mainly trapped in plots where the burnt pine trees were removed, and Meriones tristrami, which was mainly trapped in plots where the burnt pine trees were left in situ. The highest species diversity was recorded in the control plots of the burnt pine and oak woodland. In these burnt control plots the field mice (Apodemus) of both species reappeared. However, the numbers of trapped A. flavicollis were rather higher than of A. mystacinus. It is thus assumed that the invading species will be replaced by the originial woodland rodent species through resilience. *This study is dedicated in the memory of our colleague Mr. D. Banin.

Fire and man in post-glacial woodlands of Eastern England

Abstract It has for long been suggested that English early post-glacial woodlands, particularly those dominated by hazel, were a fire-climax vegetation type. This conflicts with the evidence of fire frequency in present-day woodlands. Charcoal and pollen analyses of post-glacial lake sequences in East Anglia, England, suggest that early post-glacial woodlands were not fire-climax types. The pre-5000 BP charcoal record can be best interpreted as a record of intensity of occupation beside lake shores. After 5000 BP, charcoal deposition may reflect increasing use of fire as an agent in land clearance.

Influence of Fire and Edaphic Factors on Germination of the Arid Zone Shrubs Acacia aneura, Cassia nemophila and Dodonaea Viscosa

The germination of some shrub species may be enhanced following fire in shrublands and woodlands. This paper reports the germination response of Acacia aneura, Cassia nemophila and Dodonaea viscosa - common shrub species in semi-arid and arid woodlands - to laboratory fires over a range of intensities and durations. Seeds were subjected to fires of different intensities in the controlled environment of a glasshouse. Depth of seed placement in the soil, soil moisture level and amount and type of fuel influenced the percentage of seeds that germinated. Amounts of shredded paper fuel, equivalent to typical grass fuel levels in semi-arid woodlands did not enhance the germinability of seeds of any of the species, except for A. aneura on a moist or wet soil surface. A high, dense fuel load (simulating slow burning, low- intensity litter fires) either increased or decreased the germinability of surface and buried seeds of all species, depending upon soil moisture level and depth of seeds. The germination response to the heat of fires differed significantly between species: A . Aneura germination increased substantially at low levels of peak temperature up to 60°C whereas germination of C. nemophila increased to a lesser extent and D. viscosa was not affected at all over this low temperature range. Seeds of all species were killed by slow burning litter fires when the temperature exceeded 80°C. These results confirm the view that fire- promoted germination does not result from the burning of fine fuels per se but occurs only where there is litter buildup and when the soil temperature does not exceed the lethal threshold of 70-80°C.

A laboratory study of postfire nutrient redistribution in subarctic spruce–lichen woodlands

The redistribution of nutrients after fire was examined by igniting samples of spruce needles, birch leaves, and lichen and leaching the ash through a soil column, under laboratory conditions. Nitrogen was lost from the tissue samples at temperatures above 200 °C. Up to 40 kg/ha can be lost from the woodlands during a fire. Leaching of the plant tissue ignited at 500 °C for 2 min removed about a third of the cations, as well as 10% of the phosphorus, but very little ammonium or nitrate. The cations were adsorbed by the organic and subsoil horizons, so that losses from the soil column were small (10–15 kg/ha). Ninety percent of the phosphorus removed from the ash and the organic horizons was absorbed by the subsoil horizons. The leachates of the lichen ash were acid and low in nutrients, promoting nutrient removal from, or redistribution within, the soil column. The nutrient flush from subarctic woodland fires is small compared with the flush from other ecosystems.

Forest Fires

LEAFLET No. 9 issued by the Forestry Commission (H.M.S.O., 1931) deals with this subject, which is of growing importance in Great Britain. The type of forests most subject is the coniferous; outside tropical regions, fires in forests of broad-leaved trees are less dangerous. Woodland fires are not new in Great Britain, and in dry seasons they have been only too prevalent on commons. The Forestry Commission attributes twenty-five per cent of the fires occurring nowadays in its new forests to carelessness on the part of picnickers and wayfarers. Since the advent of the Forestry Commission and the large coniferous planting campaign which has been inaugurated under its auspices during the past twelve years, the forest fire problem has entered upon a new phase. The most common form of danger is the surface or ground fire, burning dead leaves, etc., on the forest floor. The stem and crown fire is rarer in Great Britain. Newly planted areas are in greatest danger during March and April, although a dry February produces the same conditions. During a summer drought the danger reappears. The grass, under the influence of dry east winds or a summer drought, becomes as dry as tinder, and a cast-away lighted match or burning cigarette-end will start a fire which will quickly get out of control of the perpetrator of the act. After pointing out the various dangers to plantations situated under differing conditions, the leaflet deals with various methods of control, such as lay-out of plantations, order of felling, removal of debris, patrolling, equipment of tool depots, clearance of growth outside plantations, importance of immediate action, counterfiring, and the measures to be taken after the outbreak.