Reconstructing Fire Behaviour and Effects in a Subalpine Forest

Abstract

(1) The behaviour of the August 1936 Galatea fire in the foothills of the Canadian Rocky Mountains was reconstructed with respect to the rate of spread, frontal-fire intensity and fuel consumption, and illustrates that tree mortality, seed dispersal distance into the burn and condition of the seed bed can be understood from these fire behaviour variables. (2) The fire followed a dry period caused by a blocking high pressure system over Alberta. (3) Major fire runs occurred only three times in the duration of the fire. (4) Differences in fuel appeared to play a minor role in the pattern and behaviour of the fire because of small differences between fuel types and the extremely dry conditions. (5) Fire burned within one topographic basin and within a basin elevation appeared to have little effect. Wind speeds seem to be most important in determining fire behaviour. Fire effects were reduced in areas adjacent to water bodies and in valleys at right angles to, or upwind of, the fire spread direction. (6) Canopy mortality was almost complete due to the low moisture content in fuels and high frontal-fire intensity. (7) Although the fire size was greater than the mean dispersal distance of Engelmann spruce (Picea engelmanii), the composition of the forest does not appear to have changed. (8) The calculated moisture content of soil-surface organic matter and fallen boles was low enough to cause much of it to be consumed by the fire, thus creating surfaces suitable for conifer seed germination.