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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.

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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


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.

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Fig. 2. Age structure of different species in the 1916 fire.


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