As a kid, I read lots of stories in the “Bambi” genre, tales of young creatures growing up in the forest. All those books seemed to feature a forest fire at some point, which terrified both their animal heroes and me.
With people living in and exploiting forests more and more, forest fires have begun to threaten humans, too–which is why we devote vast resources to fighting them.
Maybe it’s the least we can do, considering the majority of forest fires are started by humans. Here in Saskatchewan, for instance, more than 60 percent of forest fires are human-caused.
Fires require fuel, oxygen and heat. Obviously, fuel and oxygen are no problem in a forest, so to start a forest burning, just add heat. The dryer the forest, the easier that is. A moist piece of wood is hard to start burning because the water it contains heats up and boils away first, taking heat with it. But a dry piece of wood can catch fire almost instantly.
Forest fires can be ground fires, which burn the humus layer of the forest floor but don’t burn appreciably above the surface (and can therefore smolder along for days, undetected); surface fires, which burn forest undergrowth and leaf litter; and crown fires, the most spectacular and dangerous, which advance through the tops of trees or shrubs.
Before a forest fire can be fought, it must be spotted, by personnel stationed in fire towers, from patrol aircraft, or by members of the public. John Cook, information officer at the Saskatchewan forest fire management centre in Prince Albert, told me that in the last few years, technology has made spotting fires easier. Computers combine information from lightning detectors with a vast database of geographical and environmental information to help officials decide where to send patrol aircraft to look for fires and even to model the likely behavior of fires, which helps in forming strategy.
Strategy is the ideal word, too, because fighting forest fires is akin to fighting a war. As of June 5, for instance, Saskatchewan was using 2,691 fire fighters, 60 helicopters, 19 tanker aircraft, 81 bulldozers and 14 swamp tractors to fight 65 fires.
Each type of fire is fought differently, although the goal is always to deprive the fire of fuel, oxygen or heat. Ground fires are very difficult to extinguish. If the humus layer isn’t very deep, dumping water or sand on them may do the trick (by depriving the fire of oxygen and heat), but the best bet is usually to dig a trench around the area and let the fire burn itself out (because it runs out of fuel.). Surface fires are controlled by clearing the surrounding area of low vegetation and litter, or, again, digging emergency furrows and letting the fire burn itself out.
The most difficult fires to contain are crown fires. Bulldozers cut firebreaks to stop the advance of the fire, but in a strong wind, flaming brands can easily be carried across firebreaks. That’s why trees in the path of a fire are often doused with fire-retardent chemical from tanker aircraft.
The chemical used in Saskatchewan, Cook said, is mostly (93 percent) plain old ammonium phosphate fertilizer. Six percent is a type of clay, and there’s a bit of iron oxide (rust) to colour it orange and a little anti-corrosion chemical to keep it from eating through the skin of the airplane.
Some provinces, like Saskatchewan, fight all fires, giving first priority to those threatening human lives or property. Some jurisdictions, however, have a controversial policy of letting lightning-caused fires burn themselves out . It’s controversial because we tend to see all fires outside of a fireplace as bad, but the fact is, forests need the occasional fire. Burning releases nutrients, removes weeds, reduces soil acidity and enhances the growth of shrubs on which moose and other species browse. Fire-killed trees provide nesting cavities and insect foraging sites for birds. Fallen trees provide cover for small mammals. The seeds of some species won’t even germinate until they’ve been “cooked” by a fire.
Like it or not, our forests will burn from time to time–in fact, they have to. The best we can do is limit the damage and protect property and lives. In the long run, the forest itself will recover and thrive.
Of course, it’s hard to take the long view when the flames are breathing down your neck.
Just ask Bambi.
