Canadian Wildland Fire Information System
FBP Fuel Type Descriptions
M4 - Dead Balsam Fir Mixedwood–Green
This fuel type (and its "leafless" counterpart, M3) is characterized by mixedwood stands in which balsam fir (Abies balsamea (L.) Mill.) grows, often as an understory species, in a heterogeneous mix with spruce (Picea spp.), pine (Pinus spp.), and birch (Betula spp.). These stands are found in the Great Lakes – St. Lawrence and Boreal Forest regions of Canada and are not to be confused with the pure balsam fir stands typical of Nova Scotia and New Brunswick. Repeated annual defoliation (due to spruce budworm (Choristoneura fumiferana Clemens) attack) causes balsam fir mortality, followed by peeling bark, draped lichen (Spanish moss or old man's beard, Usnea spp.) development, top breakage, and windthrow, peaking 5–8 years after mortality. The volume of down woody material is initially low but increases substantially with progressive stand decomposition following mortality. The forest floor is a mixture of feather mosses, conifer needles, and hardwood leaves. The organic layer is moderately compacted and 8–10 cm deep. Summer fires are hampered by the proliferation of green understory vegetation resulting from the opening of stand canopy. As sufficient surface fuel accumulates through stand decomposition (usually after 4–5 years), fires will spread through the fuel complex, although not as vigorously as in spring. Forest fire behavior potential is greatest 5–8 years after mortality, decreasing gradually as the suface fuels decompose and the understory vegetation continues to proliferate.
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