Large forest regions in Canada are about to experience increased risks of wildfires due to climate change according to new models that show there are threshold values for wildfires just as there are for epidemics.

Large areas of Canada are apparently approaching this threshold value and in the near future may exceed it due to climate change. As a result both the area burnt down annually and the average size of the fires  would increase, according to researchers of the Helmholtz Centre for Environmental Research (UFZ) and the University of Michigan.

Writing in the December 2011 issue of the journal The American Naturalist, the study authors suggest strategies for  combating wildfires in large parts of Canada should be reconsidered.

Citing media reports about forest and scrubland fires in British Columbia the authors questioned whether such events were the result of climate change, a question that is being hotly debated by ecologists all over the world.

In July a group of US researchers led by Anthony Westerling of the  University of California forecasted that climate change might result in a dramatic increase in the threat of wildfires in Yellowstone National Park and that forests in those areas might disappear in the 21st century.

Fires are an important factor in many terrestrial ecosystems. They are a result of the interaction of the weather, vegetation and land use, which makes them very sensitive to global change.

'Changes in the wildfire  regime have a significant impact on a local and global scale and therefore on the climate as well. It is therefore important to understand how the mechanisms which shape these wildfires work in order to be able to  make predictions on what will change in future,' explains PD Dr. Volker Grimm of the UFZ.

Left: Dead trees destroyed by forest fire in British Columbia. Photo: © Scott Latham, Fotolia.com Zoom (473.6 KB)

For their model, the scientists evaluated data from the Canadian Forest Service, which had recorded fires greater than 200 hectares between 1959 and 1999, and sorted these by ecozone.

This showed that three of  these ecozones in Canada are close to a turning point: the Hudson Plains south of the Hudson Bay, the Boreale Plains in the Mid-West the Boreale Shield, which stretches from the Mid-West to the East coast and is  therefore the largest ecozone in Canada.

The closest to a turning point is apparently the Boreale Shield. In order to check their model and the theory of a threshold value for wildfires, the scientists looked at the  fires in this region more closely.

Around 1980 the average size of the fires in this part of the provinces of Alberta, Saskatchewan and Manitoba tripled rapidly. 'In our opinion this is a sign that there are also  threshold values for forests above which the wildfire regime drastically changes,' reports Volker Grimm.

'It is likely that the Boreale Plains have in recent decades, particularly around 1980, experienced a change  to a system characterised by wildfires. This has fundamental repercussions for the environment and the combating of wildfires. Small changes in the fire propagation parameters have a great impact on the size of the  fires.'

The scientists were also interested in the parallels with disease propagation. Prevention strategies, which reduce combustible material, are in a way similar to the vaccinations which are used against the spread  of diseases such as the measles.

Here too there is a threshold value above which a disease spreads and below which it falls. Other modellers from the UFZ were therefore able to turn this theoretical threshold value into a practical value.