Fire behavior in the boreal forest (Figure 1.1) has at least four characteristics which are important in understanding the dynamics of its populations: crown fires, the size of the area burnt, the frequency with which areas burn, and the amount of the forest floor which is ashed.

More precisely, fires in the boreal forest have high frontal intensity (heat output in kWm−1) or flame length at the flaming front. The high intensity results in a crown fire regime shared by only a few other North American ecosystems e.g. grasslands, chaparral and montane conifer forests. Some of the largest fires in the world have been reported in the boreal forest. Murphy and Tymstra (1986) give the size of a 1950 free-burning fire in northern British Columbia and Alberta as 1.4 million hectares. Fires greater than 100 000 ha are common with the interval between fires being on average about every 100 years. The forest floor of upland boreal forest has a depth, moisture content and bulk density which makes it very flammable so that large amounts of mineral soil are exposed.

These four fire behavior characteristics affect the population processes of recruitment and death. The high frontal fire intensity causes crown scorch and cambial death which results in both canopy and understory tree mortality. Rapid rates of fire spread lead to large areas burnt and greater dispersal distances for trees that do not have serotinous cones and must seed-in from outside the burn or from unburned patches within the burn. The frequency of fire is about half the trees' non-fire life span.