VEGETATION CHANGES CAUSED BY RECENT FIRES IN THE NORTHERN BOREAL FOREST OF EASTERN CANADA

From 1980-1989, fires burned 32 440 km(2) of boreal forest, 200 km sou th of the forest-tundra border in northern Quebec, Canada. An assessme nt of the impact of fire on tree population densities was carried out by comparing the number of Pinus banksiana and Picea mariana in 83 sit es before and after the sites burned in 1981, 1983, 1988 or 1989. Age structure analysis of post-fire populations burned in 1972, 1976 and 1 983, along with the rapid exhaustion of the seed bank from burned tree s, suggest that the majority of seedlings were established within 3 to 10 yr after fire. Consequently, given the absence of nearby living se ed bearers, little (if any) further recruitment can be expected in the even-aged, regenerating populations. According to the tree density co mparison (pre-fire vs post-fire), a shift from Picea- to Pinus-dominat ed communities occurred in most of the sites burned in 1981 or 1983, a nd in some of the sites burned in 1988 or 1989. The 1988 fire reduced the tree population density by 95 % in 10 of the 15 sites; total tree density decreased by at least 75 % in 28 out of 40 sites burned in 198 9. This suggests that the areas burned in 1988 and 1989 will mainly re generate as very open forests or lichen-heath communities that are mor e commonly found in the forest-tundra zone, north of the study area. F ire intensity, short fire interval, and unfavorable climate during and after fires are three plausible mechanisms associated with these post -fire vegetation changes.