Description

Canadian mixedwood forests have a high compositional and structural diversity. It includes both hardwood (aspen, balsam poplar, and white birch) and softwood (balsam fir, white spruce, black spruce, larch, and white cedar) species that can form pure stands or mixed stands. This heterogeneity results in a variety of vertical structural strata that can potentially interact with fire behaviour. Fourteen fire impact maps including information on preburn stand composition and structure were gathered in a Geographical Information System. The relative influence of prefire forest composition, stand density, and surficial deposits on postfire forest cover attributes (such as variation in proportion of green/red/charred trees) was analyzed using contingency tables. Many attributes of postfire forests (fire legacy) can be related to preburn forest composition and structure. Highest fire impact was observed in coniferous stands. At the other end of the spectrum, aspen stands and wetlands contributed to most of the fire skips. Within coniferous stands, there was a difference between species with regard to their susceptibility to windthrow following fire. Jack pine stands had less severe windthrow allowing for an abundance of snags, whereas windthrow is common in balsam fir stands. Impacts vary with regard to fire severity, suggesting that observed differences between stand types may be less important when fires are very intense. These results have consequences on the maintenance of the diversity of the forest mosaics through time as well as our capability to predict fire behaviour and impacts.