Forest Fires

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Abstract

About 10 000 fires burn 2.5 million hectares of forest in Canada each year. This map focuses on two themes in fire science: monitoring the location and extent of fires (shown in the Hotspots map layer), and determining the fire danger based on weather conditions and vegetation types (shown in the Forest Fire Danger Rating map layer).

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Wildfires are a significant agent of change in Canadian forest ecosystems. 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 other fires are the result of human activities, which are more numerous but smaller.

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 on average approximately $400 million per year, and in terms of property damage (excluding lost timber value) over $10 million per year.

However, there are many positive impacts of 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).

For information on the two map layers on Forest Fires please see below:

• Fire Danger Rating in Canada
• Hotspots

Fire Danger Rating in Canada

Method

Fire danger rating is the process of systematically evaluating and integrating the factors that determine the ease of a fire starting and spreading, the difficulty of control, and the resulting impacts based on an assessment of ignition risk, the fire environment (fuels, weather, and topography) and values at risk. Fire danger rating systems produce indexes of fire potential that are used as a guide in a wide variety of fire management applications.

In Canada, fire danger is monitored using the Canadian Forest Fire Danger Rating System (CFFDRS) developed by the Canadian Forest Service. The CFFDRS comprises two primary subsystems: the Canadian Forest Fire Weather Index (FWI), which provides estimates of fire danger based on continuous records of weather observations taken daily at noon; and the Canadian Forest Fire Behaviour Prediction System (FBP) which uses fuel type and terrain (elevation, slope, aspect) data, along with the weather-based FWI system outputs, to make predictions of fire spread rate, fuel consumption, and fire intensity.

The FWI is probably best known from signs like this one that can be found in forested areas all over Canada.

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Fire Hazard Sign

Interpretation

In the fire danger rating layer, the FWI values have been classified into five groups. In a representative fuel type (a pine forest), the following fire behaviour can be expected:

• Low: smouldering or self-extinguishing fire. Flame height: less than 10 centimetres.
• Medium: creeping or gentle surface fire. Direct manual attack by firefighters with hand tools and water is possible. Hand-constructed fire guard should hold. Flame height: up to 1 metre.
• High: moderately vigorous surface fire. A hand-constructed fire guard will probably fail. Heavy equipment (bulldozers, pumpers, aircraft) is generally successful in controlling the fire. Flame height: up to 2 metres.
• Very high: intense surface fire. Frequent torching is possible. Control efforts at the fire's head may fail. Flame height: up to 3 metres.
• Extreme: crown fire. Control very difficult. Suppression action restricted to the fire's flanks. Indirect attack with aerial ignition (backfiring) may be effective. Flame height: 3 to 25 metres or more.

Hotspots

A hotspot is a pixel in an infrared satellite image that contains the "spectral signature" of burning vegetation. Each image pixel, and therefore each hotspot, represents a 1 squared kilometre on the ground. The fire within the hotspot may cover the entire area, or it may be as small as 0.001 kilometres squared (about 30 by 30 metres). A particular pixel can be hot for several days in a row, as different areas within the pixel are burned.

There is a national fire information system that automatically identifies, monitors and maps large forest fires on a daily basis using infrared satellite images. After the hotspots have been identified, fire danger ratings are calculated for the hotspot locations.

This system gives a spatially-explicit overview of forest fire activity in Canada on a daily basis. Hotspots and other satellite data are also used to estimate area burned. However, the satellite sensors cannot "see" through cloud cover. Fires burning under cloudy conditions will not show up as hotspots on the maps.

Interpretation

Most of the fires are found in the boreal forest, the broad band of mainly coniferous trees that stretches across the country from the Yukon to Newfoundland and Labrador. The boreal forest is prone to large, intense fires, especially in the west, because of its composition (needle-leaf trees), climate, and contiguity. Fire is a natural part of the boreal forest ecosystem, and plays a major role in nutrient and carbon cycling.