Succession following fire: the 1916 fire
The occurrence
of many fires of different ages around Lake Duparquet provided a means of identifying
changes in forest composition over a period of 230 years after fire. Successions
on glacio-lacustrine clays and coarse till soils evolve following comparable
models (fig. 1;Leduc et al. 1995): starting with intolerant hardwoods (trembling
aspen, white birch), followed by mixed stands after 100 years (aspen, birch,
balsam fir, spruce), and finally by coniferous stands (primarily fir and cedar)
more than 150 years after fire. On rock outcrops and thin tills, jack pine
is replaced by black spruce.
Fig. 1. Changes in relative basal area of tree
species characterizing forest successional patterns
on three main site conditions. List of species
names: Bouleau blanc = Paper birch, Cèdre
= White cedar,
Épinette blanche = white spruce, Épinette noire = Black spruce,
Peuplier faux-tremble = Trembling aspen, Pin gris = Jack pine, Sapin baumier
= Balsam fir and Saules = Willows
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Stands originating from the
1916 fire (fire history map) constitute
mature post-fire populations. All canopy trees were recruited immediately after the fire
(fig. 2) while understory fir and spruces established gradually under
forest cover since 1916 (Bergeron and
Charron 1994). Old cedar trunks dating from the 1916 fire and survivor trees
showing fire scars are present on the site. The 1916 fire burned a coniferous
forest almost 200 years old, dating from the 1717 fire. In other words, the fire
replaced a conifer stand by an intolerant hardwood stand. A project currently
underway is evaluating the importance of this hardwood-softwood alternance to
site fertility maintenance. The study of the 1916 site drew our attention to
the importance of spruce budworm and forest tent caterpillar outbreaks in the
area. Successive forest tent caterpillar outbreaks partially explain the slow
growth of birch. Another project is evaluating the effect of gaps created by
spruce budworm on understory vegetation and softwood regeneration. Aspen in the
area attains heights >25 meters; biomass production for the species is the
highest reported in the literature in North America.
Fig. 2. Age structure of different species in the 1916 fire.
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