By Patricia Robertson
It’s hard for most of us - with images in our heads of Bambi fleeing the forest fire that kills his mother - to think of forest fires as a beneficial force.
But since ancient times fire has symbolized both purification and destruction, and today it’s the job of Yukon’s wildland fire management division to find a balance between the two.
“Fire management in the Yukon is a balancing act between the negative impacts of fire on society versus the positive result of having fire on a landscape to rejuvenate forests and provide different habitats,” explains wildland fire management officer Dave Milne.
In fact, there’s enough natural fire in the Yukon to take care of what Milne calls the forest’s need to “reset the clock” for ecological change. “Yukon has the luxury of allowing fire on the landscape rather than only suppressing it,” he says.
In the Yukon, weather is the main driver of forest fires, followed by the fuel or forest type. Sixty-two per cent of fires in the territory are caused by lightning, on average, with the remaining 38 per cent human-caused. Those humans are mainly locals, not tourists - homeowners burning debris, kids playing with matches, campfires not properly put out.
But the area burned each year is highly variable. The 2009 fire season saw 118 fires that burned approximately 290,000 hectares (an average fire year is approximately 150 fires with 180,000 hectares burned). Despite the warm, dry weather through much of May, June and July - July, in fact, was one of the warmest and driest on record - a lower number of lightning strikes meant fewer fires than usual. The largest area burned since records began was in 2004, when 1,720,300 hectares burned (65 per cent of the Canadian total for that year).
Still, the boreal forest is designed to burn. “When it comes to fire, the two species that readily burn and are found through much of the Yukon are white spruce and lodgepole pine,” says Milne. “The spruce in particular has a structure that promotes fire. The spruce boughs go right to the ground - that promotes crown fire because the fire travels along the forest floor and it gets to those lower branches and then it wicks right up the tree.”
Yukon fires are typically crown fires that destroy the whole forest. These stand-replacing fires set the stage for the growth of new forest over time. But it’s depth of burn - determined by the intensity of the fire - that triggers that growth.
“Depth of burn is very important from an ecological perspective,” says Milne. “Exposure of the mineral soil is needed for new tree seeding.”
All forest fires in the Yukon are monitored, though not all are fought. Yukon’s fire managers still rely on the public for the majority of reports, as well as fire towers situated around the communities. When there’s lightning, they also call in aircraft that fly fire-detection patterns (mainly along highways and areas with infrastructure). The department has a full-time meteorologist who provides two briefings a day throughout the summer. All that information is fed into computer models to help determine how dry the fuels are, where lightning might occur and where the department has to place its resources.
Today’s fire managers do have a new weapon in their arsenal, though - the use of satellites to detect and monitor fires. The MODIS Active Fire Mapping Program, maintained by the US Department of Agriculture’s Forest Service, draws on NASA satellites to provide daily mapping of active fires in North America, which is delivered via the web. (The website’s address is http://activefiremaps.fsfed.us/canada/).
Dealing with forest fires is a labour-intensive proposition.
“The only thing that really puts out a fire is a firefighter on the ground,” says Milne. Retardant - that reddish-coloured cloud blooming from air tankers - is used as a holding action to prevent the fire spreading until crews arrive. The retardant itself is a thickened, non-toxic slurry of water and fertilizer, coloured to make it visible, and dropped on a fire in a certain location and pattern. “A small fire crew or a large group of firefighters, depending on the size of the fire, with shovels and pumps and hose is what extinguishes a fire,” adds Milne. “There’s no point in using retardant without crews.”
With a small fire, helicopters and buckets are used. Helicopters are mainly used to transport the crew to the fire, but once there, the helicopter can hook up its bucket and scoop water out of a nearby water source to help speed up the firefighting process. “But once again, helicopter bucketing is not going to put a fire out,” Milne notes. “There always have to be crews. That’s our key resource.”
As for what climate change might bring in the future, “the common thought is that we are going to see more fire and the fire seasons are going to be more intense and it will change the forests,” says Milne. Those changes will include shifting ranges, new species composition, invasive species, insects and disease.
In fact, they’re already occurring.
As an example, Milne points to Alaska, where they’ve had three of their most dramatic fire seasons in the past six years. With more frequent and intense fires in the future, the result may be a lot of young forest. And that may make the job of finding the balance between forest rejuvenation and negative consequences for humans a whole lot harder.
This column is co-ordinated by the Northern Research Institute at Yukon College with financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.