Girardin, M. P., Tardif, J. and Flannigan, M.D. 2006. Temporal variability in area burned for the province of Ontario, Canada, during the past 2000 years inferred from tree rings. Journal of Geophysical Research 111: 10.1029/2005JD006815.
The authors note that "human-induced climate change could lead to an increase in forest fire activity in Ontario, owing to the increased frequency and severity of drought years, increased climatic variability and incidence of extreme climatic events, and increased spring and fall temperatures," citing several references in support of this hypothesis. In addition, they say that such climate change "could cause longer fire seasons, with greater fire activity and greater incidence of extreme fire activity years," citing several more papers in support of this contention. Consequently, they decided that to provide a more rigorous test of these hypotheses than could be provided by the historical observational record, it should be placed in a much longer context.
What was done
In a study designed to provide that context, Girardin et al. inferred past area burned in Ontario by regressing various tree-ring chronologies against actual area burned data and developing transfer functions that they used "to estimate annual area burned at times during which there were no instrumental data."
What was learned
The tree-ring model revealed 1804 to be "the year of most extreme area burned," with the next most area burned years being, in descending order, 1910, 1821, 1907, 1792 and 1875. In addition, the three researchers’ results generally "showed higher mean area burned values prior to 1840 and through the 1860s-1880s and the 1910s-1920s," with "mean values during the mid-20th century [being] the lowest in the record [our italics]" in spite of the fact, in Girardin et al.’s words, that "humans during the past decades have been an important source of fire ignition."
What it means
That the findings of the Canadian scientists are robust is substantiated by their noting that "numerous studies of forest stand age distributions [which is a totally independent way of assessing the matter] across the Canadian boreal forest [which is an even larger area than Ontario alone] report lower fire activity since circa 1850 (Masters, 1990; Johnson and Larsen, 1991; Larsen, 1997; Bergeron et al., 2001, 2004a, 2004b; Tardif, 2004)." Hence, it is clear that over vast regions of Canada, the climate-alarmist concerns discussed in the Background section of this Journal Review are but hollow claims lacking true substance.
Bergeron, Y., Gauthier, S., Kafka, V., Lefort, P. and Lesieur, D. 2001. Natural fire frequency for the eastern Canadian boreal forest: consequences for sustainable forestry. Canadian Journal of Forest Research 31: 384-391.
Bergeron, Y., Flannigan, M., Gauthier, S., Leduc, A. and Lefort, P. 2004a. Past, current and future fire frequency in the Canadian boreal forest: Implications for sustainable forest management. Ambio 33: 356-360.
Bergeron, Y., Gauthier, S., Flannigan, M. and Kafka, V. 2004b. Fire regimes at the transition between mixedwood and coniferous boreal forest in northwestern Quebec. Ecology 85: 1916- 1932.
Johnson, E.A. and Larsen, C.P.S. 1991. Climatically induced change in fire frequency in the southern Canadian Rockies. Ecology 72: 194-201.
Larsen, C.P.S. 1997. Spatial and temporal variations in boreal forest fire frequency in northern Alberta. Journal of Biogeography 24: 663-673.
Masters, A.M. 1990. Changes in forest fire frequency in Kootenay National Park, Canadian Rockies. Canadian Journal of Botany 68: 1763-1767.
Tardif, J. 2004. Fire History in the Duck Mountain Provincial Forest, Western Manitoba. Sustainable Forest Management Network, University of Alberta, Edmonton, Alberta, Canada.
Reviewed 2 July 2008