Forest Fire

A forest fire is a moving combustion reaction, spreading outwards in a band from its ignition point, leaving burned out FOREST behind it.

Basic Facts

On average, about 9 100 forest fires occur annually in Canada. Of these, over 60% are started by people, most by accident, and 35% by LIGHTNING. Being generally less accessible, fires started by lightning are about 10 times as large as human-caused fires. The mean annual national burned area is 2.5 million ha, and 85% of it is accounted for by lightning fires. This total equals about 0.6% of Canada's forested area. Half of all recorded fires fail to reach 0.01 ha in size but occasional fires exceed 100 000 ha. In fact, 2% of fires account for 98% of total burned area. The number of fires is fairly steady from year to year, but annual burned area varies greatly. Since 1970, the smallest annual total has been 289 000 ha (1978) and the largest 7 560 000 ha (1989), a range of 25-fold. The BOREAL FOREST sustains the bulk of the burned area, most of which is thus not seen by the average citizen. About $300 million is spent annually across Canada in dealing with forest fires.

Fire Behaviour
Forest fires are classed mainly according to whether they remain on the ground surface or rise into the TREE crowns. Combustible matter in surface fires includes leaf litter, dry MOSS and LICHEN, dead grass, decomposing humus, dead or rotting wood, and live brush and herbs. Crown combustibles include live foliage, dead branches, and small twigs. In crown fires the surface and crown phases spread as a unit, and no appreciable part of the live tree is consumed. In Canada, only CONIFER forests will support crowning combustion.

A forest fire is described physically by its rate of advance downwind, by the weight of combustibles consumed, and by its frontal intensity. This latter is the rate of energy output per unit length of the fire's front, expressed in terms of kilowatts per metre (kw/m). Frontal intensities range up to 150 000 kw/m in crown fires, with flames of 50 m or so, but a gentle surface fire may produce less than 100 kw/m with flames no higher than 0.5 m. The maximum known downwind rate of advance is about 100 m/min (6 km/h), but few fires spread faster than 25m/min and most spread at less than 10 m/min. This immense variation in behaviour depends on the moisture content of the combustible matter as affected by past and present WEATHER; the current WIND speed; and the kind of forest. Similarly, the great swings in the annual burned area (nationally and from region to region) are primarily due to variation in the national pattern of spring and summer weather.

Canadian forest fire agencies prevent an immense amount of burning that would otherwise occur; nevertheless, after weeks without RAIN, on hot, dry, windy days it is impossible to prevent a few fires from becoming very large. The Canadian Forest Fire Weather Index (FWI) System is used throughout Canada to measure daily the susceptibility of the forest to fire. Based on its output, the Canadian Forest Fire Behaviour Prediction (FBP) System provides numerical estimates of spread rate and frontal intensity in specific forest types. All this information is used by the fire-control agencies to plan their day-to-day preparedness levels and fire-control operations.

Fire Management
Because most forest land in Canada is under provincial or territorial jurisdiction, fire management is the responsibility of their forestry agencies. The Canadian Interagency Forest Fire Centre, established in Winnipeg in 1982, provides daily information, keeps statistics, and co-ordinates inter-agency exchanges of fire-control forces and equipment. The federal government's Atmospheric Environment Service collects and processes daily weather data and provides fire-danger ratings to the various control agencies. The Canadian Forest Service, in co-operation with several universities, carries out most forest fire research in Canada, including the development of systems for danger-rating and management.

Fire detection in Canada is usually by aerial patrols along planned flight patterns; these have nearly superseded the traditional fire towers. Aerial patrols are backed up by systems of lightning detectors that pinpoint probable locations and expected numbers of lightning fires. Fire-control methods include aerial water-bombing (sometimes with fire-retardant additives) and, on the ground, the use of portable water pumps with hose lines, tank trucks, bulldozers, and hand tools. Burning out from a prepared line to stop an oncoming fire is sometimes feasible. All Canadian forest fire agencies are now well computerized, and utilize a range of programs based on the outputs of lightning-detection and REMOTE-SENSING equipment, the FWI and FBP Systems, historical fire-data analyses, and topographical forest-land maps. These programs guide resource deployment, design aerial patrol layout, predict fire occurrence, model fire growth, and back up fire-control strategy generally.

The practice of prescribed burning has a place in Canadian forest management. Prescribed fires, set deliberately by professionals to burn a specified area under chosen conditions to achieve a particular purpose, are used in site preparation following boreal forest clear-cuts, in connection with partial cutting in certain pine forests, and for various other purposes in vegetation management.

Fire Ecology and Economics
Fire, along with CLIMATE and SOIL, is one of the three primary natural factors that have shaped the present Canadian forest. Much of this forest is, in its natural state, ecologically dependent on recycling by random periodic fire for its long-term stable existence on the landscape. Exceptions to this pattern include the southeastern hardwood forest, forests in the wetter areas of the east and west coasts, and forested bogs and swamps in general. In the boreal forest, for example, the main tree species are black SPRUCE, jack PINE, lodgepole pine, trembling ASPEN, and white BIRCH, all of which are adapted to regenerate even after all individuals over a large area have been killed by fire. Aspen suckers directly from its root systems, while other hardwoods sprout from the base of dead trees. Jack and lodgepole pines and black spruce store live seed in their crowns for years, only shedding them after the cones are opened by heat from a fire.

Other prominent species, such as red and white pine, white spruce and DOUGLAS FIR, require ground that has been prepared and opened up by fire for optimum regeneration, but some individuals must survive to supply seed. In pre-European times ignition was mainly by lightning, and, without control, perhaps two to three times as much area burned annually as at present. Ecologically, then, fire is neither good nor bad, but simply an environmental necessity for the perpetuation of the forest in its natural state.

Economically, fire competes with the forest industry for the annual tree growth on which the industry is based. Some high-value fire-killed timber is recovered, but salvage is impractical on the large scale. Of the 2.5 million ha burned annually on the average, about 30% is classed as stocked, productive forest. However, no commonly accepted way of evaluating this economic loss directly has yet been devised. A better approach has been to analyse the indirect effect of forest fire on the annual timber supply from the whole forest; the fire-killed timber itself then turns out to be a red herring. Based on several such analyses, it is probable that, across the boreal forest, the current level of fire incidence depresses the potential ideal annual timber supply by about 15%. This effect would be somewhat less in our more southerly forests.

As fire-control efforts are increased, it costs more and more to reduce the annual burned area by any given amount. Theoretically, the ideal position would be the point at which the cost of further reduction in burned area just equalled the value of the corresponding increase in timber supply (see FOREST ECONOMICS). Other forest uses are also taken into consideration, and the safety of forest towns is a primary concern.

The ecological realities of fire create a dilemma in large natural parks and other unmanaged areas, because certain kinds of forests cannot be maintained in perpetuity in the absence of fire. The administrators of Canada's national PARKS are well aware of this problem, and are developing operational combinations of fire control and prescribed fire to cope with it. The interaction of ecological and economic factors complicates forest-fire management in general, and debate is continuous about the optimum level of fire-control effort. The Canadian Forestry Association along with the provincial forestry departments carry out fire-prevention programs aimed at educating people about their responsibilities toward the forest. Whatever the complexity of the forest fire picture, the rule "do not start forest fires" remains as valid as ever for the individual citizen.

See also FORESTRY.

Author CHARLES VAN WAGNER

Links to Other Sites
Canadian Bushplane Heritage Centre
Aviation enthusiasts will want to touch down at this website for the award-winning Canadian Bushplane Heritage Centre in Sault Ste. Marie, Ontario. Features photos and extensive documentation about float planes and other aircraft. Also covers forest fire suppression technology.

Saguenay
Historica’s acclaimed one-minute movies about Canadian history

Canadian Wildland Fire Information System
The Canadian Wildland Fire Information System creates daily fire weather and fire behavior maps year-round and hot spot maps throughout the forest fire season, generally between May and September.

The Evoloution of Waterbombing
A history of waterbombing technology used in forest fire suppression from the 1940's to the present day. From borealforest.org.

Ontario: Aviation Services
Click on the links on the right side of the page to access illustrated histories of bush flying and the use of waterbombers in the province of Ontario.