THE INFLUENCE OF MAN AND CLIMATE ON FREQUENCY OF FIRE IN THE INTERIOR WET BELT

(1) The effects of man and climate on fire frequency have been studied using historical data and a fire-history model in Glacier National Park in British Columbia, Canada. (2) Glacier National Park experienced a change in fire cycle in the 1760s, which could be related to the occurrence of the Little Ice Age. Before 1760, the fire cycle was 80 years and after 1760 it was 110 years. The longer fire cycle after 1760 was clearly related to the cooler, moister climate which also resulted in the advance of glaciers at that time in the Park. (3) The construction of the Canadian Pacific Railroad through the Park corresponded to a period in which the area burnt by man increased (1883, 1885 and 1886) and many lightning fires occurred. There has not been a decrease in the fire frequency since the establishment of Glacier National Park in 1888, despite a fire-suppression policy. (4) Large, high-intensity, rapidly spreading fires caused by lightning are associated with a characteristic synoptic weather pattern which consists of two parts: (i) intense fuel drying associated with a stationary high-pressure system blocking access of moist Pacific air, and (ii) one or more periods of breakdown of the high-pressure system into low-pressure systems, which create lightning and high winds. (5) To have supplanted climate as a major determinant of fire frequency, man must either have used regular management burning or suppressed fires during critical weather periods. Because this has not occurred in Glacier National Park, the present fire regime is largely natural