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).
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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