Historical Fire Cycles in the Canadian Rocky Mountain Parks

The subject of this article is the fire history of seven contiguous national and provincial parks in the Canadian Rocky Mountains, four to the east of the continental divide and three to the west. Seven centuries of time-since-fire data were combined and arrayed in three sets: all seven parks together, then the east-side and west-side groups separately. Fire cycles were estimated by four different methods: two of them statistical and two deterministic. Statistical evidence of distinct changes in fire regime, always toward a lower burning rate, was uncovered, with transitions in 1760 and 1940 on the east side, and in 1840 on the west side. The principal conclusions were: The seven parks as a unit supported a fire cycle of 60-70 yr for nearly five centuries before 1760. The burning rate then dropped sharply and a longer cycle of about 175 yr prevailed until 1940. Fire history in the combined large parks on the east side was similar to the above. By contrast, the smaller west-side parks group sustained a fire cycle of about 90 yr for at least five centuries before 1840; the burning rate then decreased irregularly to 2000. On the east side, the near absence of burned area after 1940 was attributed to the onset of effective fire protection. Possible prior causes of the earlier transitions on east and west sides include changes in climate or aboriginal fire practices, but this issue is left unresolved.