Forest Fires

• Forest Fire Hotspots, 2005 Map | Read about this map
• Fire Danger Rating, 2005 Map | Read about this map
• Forest Fire Hotspots, 2004 Map | Read about this map
• Forest Fire Hotspots, 2003 Map | Read about this map
• Forest Fire Hotspots, 2002 Map | Read about this map
• Forest Fire Hotspots, 2001 Map | Read about this map

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Forest aflame

Wildfires are a significant agent of change in Canadian forest ecosystems. On average, 10 000 fires burn 2.5 million hectares of forest in Canada each year. The number of fires and area burned varies widely from year to year, with the highest area burned being 7.5 million hectares in 1989 (Figure 1). In comparison, Canada has a total of 400 million hectares of forested land, or about 10% of the world's forests. About 1 million hectares are harvested each year.

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Figure 1. Annual Variability of Forest Fires

There are two distinct causes of forest fires in Canada: people and lightning. On average, lightning causes one-third of the fires in Canada, yet results in 90% of the area burned. Typically these lightning-caused fires occur in remote areas of the country where detection is more difficult.

The Canadian Forest Service has been conducting forest fire research for over 75 years. The maps in this series focus on two themes in fire science: monitoring the location and extent of fires (in the Hotspots map), and determining fire danger based on weather conditions and vegetation types (in the Forest Fire Danger Rating map). The data are maintained by the Fire Management System group at the Northern Forestry Centre, part of the Canadian Forest Service of Natural Resources Canada. The Fire Management Systems group compiled this information and the associated maps.

Fire Characteristics

Not all fires are the same:

There are many types of fires, but they can be classed into three groups:

• Surface fires: fires burning in fuels near to the ground, such as dead leaves and twigs, fallen trees, grass and duff. (Duff is loosely-compacted organic material of moderate depth below the forest floor.)
• Intermittent crown fires: fires consuming the crowns of some of the trees
• Continuous crown fires: fires consuming the crowns of all or most of the trees

The images below show, top to bottom, a surface fire, an intermittent crown fire, and a continuous crown fire.

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Low intensity surface fire

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High intensity surface fire

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Crown fire

The type of fire depends on a large number of factors, but these can be classed into three groups:

• Weather (especially wind speed and temperature)
• Fuels (moisture content, amount of fuel, size and arrangement)
• Terrain (especially slope)

The moisture content of the fuel, in turn, depends on the current and recent weather, as well as the type of vegetation. For example, coniferous trees are generally much more flammable than deciduous trees because coniferous trees contain larger amounts of flammable chemicals (resins).

Fire is hot:

Depending on the moisture content, woody fuel ignites at around 350°C. The maximum temperature in forest fire flames is in the 800 to 1000°C range. However, temperature is not a good indicator of fire intensity. The standard measurement of fire intensity in the Canadian Forest Fire Behaviour Prediction System (FBP) is the energy release per unit length of fire front, measured in kilowatts per metre. Typical intensities for the three fire types are:

• Surface: 100 kilowatts per metre
• Intermittent Crown: 2000 kilowatts per metre, depending on fuel type
• Continuous Crown: 10 000 kilowatts per metre or greater. At these intensities, the heat is unbearable within 100 metres of the fire front.

The energy released by forest fires in Canada annually is enough to supply the electricity needs of the entire country for six months.

Fire moves:

A fire's spread rate and direction are largely determined by the fuel type, and the wind speed and direction. Typical spread rates in metres per minute are:

• Surface: 1 to 5 metres per minute (excluding surface fires which are primarily grass fires)
• Crown: 25 to 50 metres per minute
• Grass: 25 to 80 metres per minute

Crown fires can spread at up to 100 metres per minute. They also spread by throwing out fire brands, which can be carried by the wind to start new fires up to several kilometres from the fire front. The fastest fires are grass fires, which have been clocked at over 300 metres per minute.

Fire makes smoke:

The well-known link between fire and smoke can be summarized in different ways.

• Fire Researcher: Where there are visible vapors having their origin in ignited carbonaceous materials, the result is a large destructive fire
• Fire Fighter: Where there's smoke, there's fire

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Smoke plume - Vermilion Pass Fire, 1968

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Smoke plumes can be hundreds of kilometres long

Fire needs fuel:

Without combustible material, a fire cannot start or spread. A common fire suppression tactic is to steer the fire into an area where there is no fuel (a fire break) such as a river, lake or road. Attacking an intense fire directly is often ineffective. Where no fire breaks exist, they can be made using bulldozers or by burning ahead of the fire.

Fire is wild:

Predicting forest fire occurrence and behavior is like predicting the weather. Fire responds quickly to changes in fuels and in wind speed and direction: a fire can smolder for days, then flare up when conditions change; a fire can overwhelm extensive, high-tech suppression efforts.

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A crown fire can send up walls of flames high above the treetops

Fire Monitoring and Mapping

In Canada, fire detection and suppression are carried out by the provinces, territories and the federal government (in national parks). Fires are detected from fire towers, from air patrols, or by the public. The agency then decides how to respond. Some provinces have different priority zones, in which response to a fire is partly determined by where it occurs. Others try to suppress all fires.

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Fire Tower

Large-area fire monitoring can be carried out using infrared images taken from the air or from satellites. For examples of the latter, refer to the hotspots map or the Forest Fires in Canada Web site.

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Infrared Air Photo

Fire mapping is done to assess impacts, keep accurate statistics, and to maintain forest inventories. Frequently fire mapping is not a straightforward task because the fire perimeter may be indistinct and contain partially burned areas and unburned islands. Mapping methods include sketching, helicopter Global Positioning System, air photo interpretation, and satellite photo interpretation.

Fire Suppression

In some national parks and northern areas, fires are allowed to burn uncontrolled as long as they do not threaten communities, merchantable timber, or other values at risk. However, most fires are suppressed. Fire suppression costs in Canada average approximately $400 million per year, and property damage (excluding lost timber value) averages over $10 million per year. In comparison, forestry in Canada is a $60 billion industry.

Suppression of fire has an unwanted side effect in the accumulation of fuel. As the amount of combustible material (the fuel load) increases, the risk of large, intense fire increases. In recognition of fire's natural role in fuel regulation, some forestry companies are working to make their logging practices more closely mimic fire in order to avoid these large, uncontrollable fires.

Fire suppression activities bear some resemblance to war, with weapons varying from shovels and portable pumps to helicopters and air tankers.

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Fire fighters on the front line

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Air tankers can drop large amounts of water and fire-retardant foam

For more information, refer to the British Columbia Ministry of Forests Web site.

Impacts of Fire

Fire affects people, property, companies, and the environment in various ways. The level of impact depends largely on fire intensity and size. An extreme fire event can result in town evacuations, road closures, airport closures, property loss, timber loss (though this can be mitigated with salvage logging), habitat loss for some species (though this is usually temporary) and habitat creation for others, removal of the vegetation, and consumption of the forest floor.

There are also many positive impacts to fire. It is an important natural part of the boreal forest ecosystem. The boreal forest has been called fire-dependent because of the role of fire in recycling biomass and nutrients. Some species, such as jack pine, depend on fire to reproduce. Its cones open in the heat of the fire, and the seeds then fall onto soil that has been cleared of vegetation and fertilized by ash.

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Serotinous cones require the heat of fire to open

Fire maintains biodiversity and stand age diversity by opening gaps in the forest canopy, allowing more sunlight onto the forest floor. Fire also acts as a fire regulator: where a fire has burned, the amount of fuel is reduced and the fire hazard is decreased.

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The first species to grow in a burned area is frequently fireweed (Epilobium angustifolium).