Biologist Ileene Anderson with the Center for Biological Diversity, an environmental organization, said burn permits should be difficult to get because of the potential damage to air quality. Clearing chaparral by hand or machine must be closely scrutinized because it can hurt native species.
"Our air quality, for a variety of factors, doesn't need to be further reduced by these controlled burns," she said.
Setting pre-emptive fires can be especially risky near heavily populated urban areas like Los Angeles because of the danger of flames burning out of control. Last month, a 90-acre prescribed burn near Foresta, on the edge of Yosemite National Park, jumped fire lines and consumed more than 7 square miles in the park.
Angeles National Forest Supervisor Jody Noiron defended the agency's efforts to reduce the fire risk. "The Angeles Forest has been pretty aggressive about implementing fuels-reduction projects with the funds we are given," she said.
She said that it is extraordinarily difficult to get the right weather conditions to pull off a prescribed burn. "This year with the weather and the drought and all of that, the last couple of years actually, we've had very few days that we can do prescribed burning," she said.
Los Angeles fire Capt. Steve Ruda said that pre-emptive fires were used more frequently in the region in the 1980s. But a growing backcountry population and increasingly complicated environmental rules have made them less frequent.
Conducting a prescribed burn requires a detailed study of wind, terrain, temperature and humidity and reviews by a host of government entities, including air-quality regulators.
Max Moritz, co-director of the Center for Fire Research and Outreach at the University of California at Berkeley, said there is wide discussion about the need to do more prescribed burns to reduce the fire hazard. But "you have this difficult needle you have to thread to find the right place, the right conditions, to pull it off," Moritz said.
Ultimately, he said, the answer is to stop building in fire-prone areas instead of spending huge sums on firefighting.
Steve Brink, a vice president with the California Forestry Association, an industry group, said as many as 8 million acres of national forest in California are overgrown and at risk of wildfire. He said that too few days provide the conditions necessary for larger, prescribed burns and that the Forest Service needs to speed up programs to thin forests, largely by machine.
"Special interest groups that don't want them to do it have appeals and litigation through the courts to stall or stop any project they wish. Consequently, the Forest Service is not able to put a dent in the problem," Brink said.