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Boreal Wildfires in a Warming World
Volume 16, Number 51: 18 December 2013

In a paper recently published in the journal New Phytologist, Girardin et al. (2013) write that many people have supposed - think Al Gore, for one - that "global wildfire activity resulting from human-caused climatic change is a threat to communities living at wildland-urban interfaces world-wide and to the equilibrium of the global carbon cycle." But is this really the case?

Implying that it might not be, the eight researchers note that "broadleaf deciduous stands are characterized by higher leaf moisture loading and lower flammability and rate of wildfire ignition and initiation than needleleaf evergreen stands," citing the work of Paatalo (1998), Campbell and Flannigan (2000) and Hely et al. (2001). And they therefore speculate that the introduction of broadleaf trees into dense needleleaf evergreen landscapes "could decrease the intensity and rate of spread of wildfires, improving suppression effectiveness, and reducing wildfire impacts," citing the studies of Amiro et al. (2001) and Hirsch et al. (2004). But to be more confident about this line of reasoning, they proceeded to conduct their own study of the subject.

This they did by integrating into a wildfire modeling scheme information about millennial-scale changes in wildfire activity reconstructed from analyses of charred particles found in the sediments of eleven small lakes located in the transition zone between the boreal mixed-wood forests and the dense needleaf forests of eastern boreal Canada. And what did they find?

Girardin et al. report that their assessment of millennial-scale variations of seasonal wildfire danger, vegetation flammability and fire activity suggests that "feedback effects arising from vegetation changes are large enough to offset climate change impacts on fire danger." But will such vegetation changes actually occur?

In answer to this question, the Canadian and French scientists note that the studies of McKenney et al. (2011) and Terrier et al. (2013) suggest that "future climate warming will lead to increases in the proportion of hardwood forests in both southern and northern boreal landscapes." And they say that this change in landscapes likely will have other benefits as well, such as "the higher albedo and summer evapotranspiration from deciduous trees, which would cool and counteract regional warming (Rogers et al., 2013), and the increase in the resilience of forests to climatic changes (Drobyshev et al., 2013)."

So, yes, it would indeed appear that both the frequency and ferocity of boreal wildfires in a warming world could well decline.

Sherwood, Keith and Craig Idso

Amiro, B.D., Stocks, B.J., Alexander, M.E., Flannigan, M.D. and Wotton, B.M. 2001. Fire, climate change, carbon and fuel management in the Canadian Boreal forest. International Journal of Wildland Fire 10: 405-413.

Campbell, I.D. and Flannigan, M.D. 2000. Long-term perspectives on fire-climate-vegetation relationships in the North American boreal forest. In: Kasischke, E.A. and Stocks, B.J. (Eds.). Fire, Climate Change, and Carbon Cycling in the Boreal Forests. Springer-Verlag, New York, New York, USA, pp. 151-172.

Drobyshev, Y., Gewehr, S., Berninger, F. and Bergeron, Y. 2013. Species specific growth responses of black spruce and trembling aspen may enhance resilience of boreal forest to climate change. Journal of Ecology 101: 231-242.

Girardin, M.P., Ali, A.A., Carcaillet, C., Blarquez, O., Hely, C., Terrier, A., Genries, A. and Bergeron, Y. 2013. Vegetation limits the impact of a warm climate on boreal wildfires. New Phytologist 199: 1001-1011.

Hely, C., Flannigan, M., Bergeron, Y. and McRae, D. 2001. Role of vegetation and weather on fire behavior in the Canadian mixed-wood boreal forest using two fire behavior prediction systems. Canadian Journal of Forest Research 31: 430-441.

Hirsch, K., Kafka, V. and Todd, B. 2004. Using forest management techniques to alter forest fuels and reduce wildfire size: an exploratory analysis. In: Engstrom, R.T., Galley, K.E.M. and de Groot, W.J. (Eds.). Fire in Temperate, Boreal, and Montane Ecosystems. Tall Timber Research Station. Tallahassee, Florida, USA, pp. 175-184.

McKenney, D.W., Pedlar, J.H., Rood, R.B. and Price, D. 2011. Revisiting projected shifts in the climate envelopes of North American trees using updated general circulation models. Global Change Biology 17: 2720-2730.

Paatalo, M.-L. 1998. Factors influencing occurrence and impacts of fires in northern European forests. Silva Fennica 32: 185-202.

Rogers, B.M., Randerson, J.T. and Bonan, G.B. 2013. High-latitude cooling associated with landscape changes from North American boreal forest fires. Biogeosciences 10: 699-718.

Terrier, A., Girardin, M.P., Perie, C., Legendre, P. and Bergeron, Y. 2013. Potential changes in forest composition could reduce impacts of climate change on boreal wildfires. Ecological Applications 23: 21-35.