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How Controlled Burns Work

        Science | Matter

Flames of the Future
Firefighter Elizabeth Ferolito keeps an eye on a controlled backfire in Irvine, California, set to protect homeowners as a wildfire rages.
Firefighter Elizabeth Ferolito keeps an eye on a controlled backfire in Irvine, California, set to protect homeowners as a wildfire rages.
Ann Johansson/Getty Images

Southern California is always in the news for devastating wildfires torching whole neighborhoods to the ground, so surely the state could benefit from controlled burning, right? That's what fire managers thought for a long time. In their efforts to control the annual blazes, they frequently set fire to the chaparral, a dense, thorny, shrubby tangle of vegetation that covers the canyon-sides.

All that burning did absolutely nothing to lessen wildfires or mitigate the damage they caused. Now researchers are beginning to understand why that is. Controlled burns help reduce the prevalence and impact of wildfires in certain kinds of forests where, if left to themselves, the woodlands will ignite every 10 to 15 years.

But chaparral isn't that kind of vegetation. When experts studied the geological record, they realized that, on its own, chaparral goes up in flames only once every 100 years or so. And when it does, it regenerates very slowly. So by regularly burning the chaparral, fire managers had inadvertently rid the landscape of natural, fire-resistant species and let invasive, more flammable vegetation take its place [source: Oskin]. In this particular case, in other words, controlled burning was counterproductive.

There is no general rule for how (and whether) controlled burning is beneficial. It all depends on the region. Local species and weather determine what works best and where. Take, for instance, the computer modeling about carbon capture mentioned earlier. Those simulations were conducted in a northern Arizona ponderosa pine forest. The results don't necessarily apply elsewhere.

In fact, a forestry expert in Oregon doubts that a northeastern forest that's managed with controlled burning would hold more carbon than one that wasn't. While it seems that controlled burning carried out in southeastern woodland helps the atmosphere, the same cannot necessarily be said of other forests.

Nevertheless, controlled burns help the environment in other ways. By maintaining open canopies, fire can improve a forest's structure and variety, making it more resilient to climate change [source: Gearin]. Paradoxically, it seems we might be able to use this great, destructive force to mitigate the damage we've done to the ecosystem.