Post-fire succession was reconstructed for a sector located in the southern part of the Quebec boreal forest. Forest composition for different periods since fire was evaluated using a stand initiation map together with ecological maps representing both site conditions and stand types. Nine fires covering at least 100 ha and representing a chronosequence of more than 230 yr were used. Although a relatively clear successional pattern from deciduous to coniferous composition relating to time-since-fire was observed, Pinus banksiana stands showed an erratic distribution not related to succession but possibly to the pre-fire stand composition. A comparison with forest cover maps produced after a recent spruce budworm outbreak, showed that succession toward coniferous dominance appeared to be interrupted by spruce budworm (Choristoneura fumiferana) outbreaks which, by killing Abies balsamea, lead to a mixed deciduous forest composition. A simple empirical model based on a negative exponential distribution of age classes was developed to evaluate how changes in the fire cycle would affect the composition of the forest mosaic. The transition between deciduous dominance and coniferous dominance occurs in a fire cycle gt 200 yr. Although pure deciduous stands tend to disappear during long fire cycles, the proportion of mixed stands remains relatively constant. Prediction of the forest composition for longer fire cycles is complicated by the interaction between post-fire composition and stand vulnerability to spruce budworm outbreaks.

Age determination of post-fire forests and the analysis of fire scars on surviving tree have allowed for the historical reconstruction and mapping of fires in a forest area of 11,175 ha in northwestern Quebec, south of Lake Abitibi (Canada). Most of the study area was burnt by two large fires ( gt 1000 ha) in 1760 and 1923. All the other fires recorded (1797, 1823, 1870, 1907, 1919) were smaller in extent and occurred in a restricted part (1984 ha) of the study area, characterized by the fragmentation of the forest landscape by water bodies. The compilation of data concerning are burnt per type of surficial material confirms that the physical environment exerts a stronger control on the delimitation of these smaller fires. The data do not allow for the estimation of the fire cycle owing to the small size of the study area and possible temporal changes during the observation period. However, methodological observations are formulated for future studies covering a larger area in the bioclimatic region. ©1993 NRC Canada