Fires on islands and the northern limit of red pine

While some islands have not burned for a very long time, certain have experienced very high fire frequencies. As an exemple, one island in Lake Duparquet has burned five times during the last 200 years (fig. 1; Bergeron and Brisson, 1990). Many fires, however, were of low intensity, scarring trees but not killing them. This fire regime appears to favour red pine by maintaining an open forest floor environment while sparing seedtrees (fig. 2). Presence of the lacustrine fire regime on islands, compared to major fires on the mainland, explains why red pine populations are found on islands at its northern limit of distribution. This limit appears to be ecological rather than climatic, as growth and reproduction of pines appear to be very good in this region. Common juniper is another species that is restricted to islands that have had low intensity fires, while being virtually absent in similar sites on the mainland (Diotte and Bergeron, 1989).

Fig. 1. Area of island affected by the last five fires. Zones correspond to different fire-intensity boundaries: L= low, M= medium, and H= high. Some boundaries remain uncertain (? and ---) for the 1849 and 1881 fires. For the 1799 fire, --- encircles the area where fire indicators were found; however, it can reasonably be assumed that the fire burned the entire island. The arrows represent time-of-fire wind direction.

Fig. 2. Age structure of red pine (Pinus resinosa) and jack pine (Pinus banksiana) populations on island A. fire years are indicated by arrows beneath the abscissa axis.

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