Résumé - CAFD

The influence of Fire Weather and Land Use on the Fire Activity of the Lake Abitibi Area, Eastern Canada.

Patrick Lefort, Sylvie Gauthier, Yves Bergeron.

The fire history of two adjacent regions of the boreal forest, one characterized by fogging (Ontario-510,000 ha) and the other by small scale agricultural activities (Quebec-140,000 ha), was studied before and after these regions were opened up to settlement in 1916. From a review of provincial forest fire records and the assessment of the age of fire-initiated forest stands, it appears that large but rare fires occurred during the presettlement period on both sides of the border. After 1916, due to slash and burn activities, the agricultural region (Que) had proportionally about twice the burned areas and ten times more fires than the forestry region (Ont). Despite differences in population density, road network, and land use, fire size class occurrence did not differ between landscapes overtime. However,the occurrence of fires larger than 100 ha, considering three development phases (1916-1939; 1940-1969; 1970-1998), decreased in both regions from settlement to the present, particularly during the late phase (1970-1998) in the agricultural region. An analysis of fluctuations in the Canadian forest Fire Weather Index system (FWI), a rating of fire danger severity, showed major climatic stresses at the beginning of the century (1916-1924), followed by a decrease in the occurrence of extreme FWI values. Combined with the impact of climate, which affected the annual area burned and the number of large fires in both landscapes, the results suggest that the landscape fragmentation, the increase in the percentage of deciduous trees overtime and/or effective fire detection by residents led to a decrease in the number of fires larger than 100 ha on the agricultural side for the late phase (1970-1998).