A new study offers a prescription to increase carbon storage in western U.S. forests: Use more controlled burns to prevent a completely scorched earth.
Increasingly, forest managers are setting so-called "prescribed" fires to clear out underbrush and small trees that, if left to accumulate, can quickly escalate a single spark into a catastrophic blaze.
Prescribed practices mimic the natural, smaller burns, caused by lightning or set by Indians, that were all but eliminated by decades of unnatural fire suppression. Today, in many Western forests, piles of fuels are just waiting for a spark.
Wildfires can also contribute to climate change. Because they are much more intense than prescribed fires, they often kill many old-growth trees that store the most carbon, a consequence that hazardous-fuel reduction programs are meant to avoid. No one before, however, has measured the carbon savings of better fire management on any large scale, according to Christine Wiedinmyer, the study's lead author.
"We know that prescribed fire can burn less fuel than a large, stand-replacing wildfire. The question was how much? Is it enough that it should be a management technique worth perusing if you want to store more carbon?" asked Wiedinmyer, an atmospheric chemist at the National Center for Atmospheric Research.
The study, published in Environmental Science and Technology, found that widespread prescribed burns might have slashed fire-related carbon dioxide emissions in 11 Western states by an average of 18 to 25 percent between the years 2001 and 2008, and by as much as 60 percent in some forest systems.
Huge CO2 emissions from major fires
The actual carbon dioxide emissions from fires during those years averaged anywhere from 22 million to 103 million metric tons a year, the study estimates. The latter figure is about double the emissions produced by California's entire electric power sector, according to recent U.S. Energy Information Administration data. The total amount of emissions from wildfires is still being debated, however. One other recent study claimed that earlier emissions estimates were likely too high (ClimateWire, Jan. 28).
Wiedinmyer cautioned that the emissions savings present an "upper limit" scenario in which prescribed burning is used in all suitable forest types, such as dry Douglas fir and ponderosa pine.
The real world is not as ideal. Prescribed fire use is often more limited because it can be controversial, prohibitively expensive, impractical and even dangerous.
An incident about a decade ago gave prescribed fires their most well-known black eye. On May 4, 2000, National Park Service managers set a burn in New Mexico's Bandelier National Monument. It quickly ran out of control when extreme winds and dry conditions pushed the fire into the surrounding area. Within a week, the wildfire spread into nearby Los Alamos, threatening the famous nuclear energy lab, forcing 20,000 people to evacuate their homes, and ultimately consuming 48,000 acres.
Prescribed burns can be costly and risky
The projects can also be expensive, especially when they are in remote areas. Most are lit and managed by hand using a drip torch, which pours out a small stream of burning fuel, according to the Forest Service. Managers have to wait for the right weather conditions and also advertise their plans well in advance to avoid panic in nearby towns as smoke rises.
In its fiscal year 2011 budget, the Forest Service is proposing to direct $349 million to overall programs that reduce hazardous fuels and hopes to treat a total 1.6 million acres in high-priority zones where wildlands meet communities.
Officials say prevention activities, though expensive, save money in the long run. By comparison, the fiscal 2011 budget request for fire suppression is $2.4 billion, with some funds dedicated to new contingency funds meant to prevent the service from raiding the rest of its budget as it has in past years.
As wildfires intensify, a trend of the past decade, the issue will become more pressing. According to a federal report in 2008, wildfires could soon begin consuming 10 million to 12 million acres a year. For comparison, in 2007, the worst of the last five years, 9.9 million acres burned nationwide.
"Fires are going to burn in the forests in the western United States. It's partly up to us to decide how we want that to occur. Carbon is just one piece of the puzzle," Wiedinmyer said.