Forest type and wildfire in the alberta boreal mixedwood: What do fires burn?

Two determinants of fire behavior are fire weather and spatial variation in fuels. Their relative importance in boreal forests has been unclear. I eva luated the effect of fuels on a similar to 74 000-km(2) landscape in the bo real mixedwood region of western Canada. My data were the compositions, or the proportional areas of different forest types, of 48 mapped lightning fi res and of their immediate surroundings. I measured areal compositions from forest inventory maps, using a five-way classification representing decidu ous forest, three types of coniferous forest, and wetlands. The fires burne d between 1980 and 1993. Fire sizes ranged from 70 ha to 70 000 ha. By mult ivariate linear regression, fire surroundings explain 57% of the variation in forest types within mapped fires. Fire compositions are not representati ve of the study area as a whole, or of a fire's surroundings, and are unrel ated to fire size and location within the study area. Using the model, I pr edicted the areas of the five types burned within all other lightning fires >200 ha in the study area during 1961-1996 and estimated type-specific mea n annual burn rates. These rates vary by an order of magnitude. Deciduous s tands burn at the lowest rate, and black spruce stands burn at the highest rate. Fires exhibit significant preferences between forest types at both lo cal and regional scales. Preference orderings are similar at both scales an d are generally consistent with the rank order of estimated burn rates. Pre ferential burning may result from between-class differences in vertical can opy structure and foliage characteristics. The statistical model and the po stulated variations in fire behavior between classes indicate that landscap e-scale fuels management may be feasible in this system. The rank ordering of burning frequencies and preferences is the inverse of the planned distur bance rates under forest management.