Résumé - CAFD

Fire regime in red pine stands at the northern limit of the species range.

Yves Bergeron, Jacques Brisson.

In order to define more precisely the fire regime prevailing in red pine stands, and to evaluate its effect on the maintenance of marginal populations in the boreal forest, we documented the frequency, extent, and intensity of fires that affected red pine populations un northwest Quebec. We focused on two islands in Lake Duparquet, divided the islands into 5 X 5 plots, and recorded topography, soil moisture, and vegetation for each plot. We mapped stems and noted fire scars, took core samples and stem cross sections to determine the age of trees, and uses fire scars, post-fire regeneration, surviving trees, and changes in growth rates as indications of fire passage and intensity. Fire frequency was also estimated using fire history data from 13 stands.

Before 1906 the fire regime was characterized by: (1) a short but very irregular fire interval averaging 30 yr, (2) a large variation un burned area, including patches that were generally left unburned, (3) a low fire intensity, although some fires were locally very intense, and (4) the occurrence, roughly every 68 yr. of fires of sufficient intensity to kill most trees on the entire island. Since 1906 the frequency of fire has decreased dramatically.

The fire regime appears to be controlled by abiotic conditions. The high-frequency fires of variables intensity primarily affect the xeric habitats The less frequent, intense (possibly crown) fires that affect the entire island may depend on stand development from a less susceptible pine and hardwood forest towards a more typical spruce-fir boreal forest in more mesic habitats.

The fire regime described for these insular stands as the limit of the species' range is similar to that described for other parts of the range of red pine. We hypothesize that red pine is restricted to insular habitats at this northern limit of its range because of the particular fire regime that prevails there; the larger and more intense fires of the mainland here led to elimination if the species.