The kind of forest that grows up after a forest fire depends on a variety of factors, including such apparently minor things as the time of day the fire began to burn, says Al Beaver, Supervisor of Fire Management Planning for the Department of Indian Affairs and Northern Development's Forest Resources Branch. You can set out the stages of regeneration in general terms, but in detail the process is highly variable. Two of many factors that determine how a forest recovers are the intensity and severity of the fire. And both those factors depend, to some extent, on the time of day when the fire starts burning, Beaver says. Both terms, intensity and severity, have special meaning for forest managers.
Intensity is the amount of heat energy released by the fire.
Severity is a measure of the area burnt and the depth of the burn. Fires that start in the morning are generally less intense than fires that start in the afternoon because the air and fuel temperatures are lower in the morning. A fire that burns with high intensity, Beaver says, kills most trees in its path and burns off the duff layer, exposing the mineral soil beneath. A less intense fire might pass through an area quickly, scorching some trees without killing them and leaving much of the duff layer intact. A severe fire that burns a large area might leave parts of the burnt-out forest exposed to full sunlight and many kilometres away from the nearest living plants.