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Succession following fire : the 1923 fire

The stands originating from the 1923 fire are mature. All trees forming the tree layer were recruited immediately following the fire either by root suckers (aspen), stump sprouts (white birch), seeds from serotinous cones (black spruce and jack pine) or from seed sources that were preserved from the fire (white spruce and balsam fir). This phenomenon is well illustrated by the age structure of the different species issued from the 1923 and 1916 fires (Gauthier et al., 1993; Bergeron and Charron, 1994; fig. 1). The abundance of advanced fir and spruce regeneration will contribute to the creation of mixed stands following mortality of the cohort established following the fire. Although all the species may be present in the cohort following fire, composition will vary according to site conditions and distance to seed sources. Aspen is find on deep, fresh soils on lower slopes, birch on tills situated on mid slopes, and black spruce and jack pine on outcrops and shallow tills associated with upper slopes and outcrops. The 1923 fire is characterized by an abundance of jack pine, explained by the presence of seed trees - (some partially burnt snags are still standing) - which, at the moment of the 1923 fire, were around 169 years old (Dansereau and Bergeron, 1993). We sporadically find red maple, a species situated at the northern limit of its distribution. These stands are generally isolated in higher elevations where the frost-free period is longest. Moreover, compared to southern populations of red maple, seeds are generally dormant in order to protect seedlings against the shorter growing season (Tremblay et al., 1996).

fig14.gif (182411 octets)
Fig. 1. Age structure of selected populations of Pinus banksiana. Arrows indicate the occurence of a non-lethal fire within a particular age class.



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