USA — Forest fires in the Sierra Nevada are bigger, hotter, more numerous and they are killing more trees than ever as a result of human fire suppression and climate change, according to data from a fire severity monitoring study released Wednesday.
The information, culled from 21 years of monitoring in the Sierra by U.S. Forest Service personnel, shows that recent fires have left gaping scars in the forest. The deforested portions of land often erode in subsequent rains, causing sedimentation and other environmental problems.
“We’re finding that the proportion of acres burning at high severity increased very rapidly from 1984 through 2004,” said Forest Service ecologist Hugh Safford, who presented the findings during an Ecological Society of America meeting in San Jose. “It is really the first solid quantitative data in the nation showing that fire severity across a major portion of the West is increasing across most of the major forest types in the area.”
The data, which included blazes in the Lassen and Modoc national forests, charts 197 large fires over the two decades starting in 1984 and then compares that information with the available data on fire behavior before Europeans settled in the region.
The research revealed that the average number of trees killed by fires has increased dramatically in the lower- and middle-elevation Sierra forests, generally located between 1,500 and 5,000 feet. This region, also known as the mixed conifer belt, is home to a wide array of wildlife, including the spotted owl, California fisher and goshawk. It is also where the vast majority of Sierra development is occurring.
The reason for the increase in fire severity, according to Safford, is a warmer climate – and consequently less snowmelt – along with more woody debris in the forest caused by a century of fire suppression.
The data are still considered preliminary, Safford said, because it is part of a larger report that won’t be released for at least a month. The results released Wednesday were not surprising to foresters or environmentalists, who have long been in agreement that overgrown forests have become a major fire danger.
Craig Thomas, the executive director of the Sierra Forest Legacy, said the issue is not whether fires are more intense but how the new data will be used by logging interests and the Bush administration to influence forest management policy.
“The Forest Service wants to cut a lot of the larger trees when the solution is to remove the smaller trees, the brush and the surface fuels,” said Thomas, whose coalition of 100 conservation advocacy organizations sued the federal government over its 2004 revision of the Sierra forest plan.
“The Forest Service is targeting the bigger trees because the Bush administration has put them in the position where the only way they can get funded is with the revenue from cutting larger trees,” he said.
For much of the 20th century, firefighters controlled wildland fires in California. Before that, fires were very common in the state, serving to cleanse the forests of excess underbrush. Back then, fire-resistant old-growth trees like Ponderosa pine dominated much of the Sierra, forestry experts say.
“Low- and moderate-severity fires generally leave much or most of the tree canopy alive yet clear out much of the surface fuels that we are concerned about,” Safford said. “That is the way we believe most of the fires burned throughout much of the Sierra Nevada before European settlement.”
Fire management has since become so effective that 98 percent of all fires are now put out, Safford said. As a result, vast quantities of brush and undergrowth have begun to choke the forests. As a result, experts agree, fires are more intense and cause more overall damage to the forest when they finally ignite.
The whole issue blew up in 2004 when Jack Blackwell, the California regional forester appointed by the Bush administration, scrapped the Sierra Nevada Framework, a Clinton-era plan implemented in 2001 that emphasized ecological restoration and halted most logging in the Sierra’s 11 national forests.
Blackwell’s Sierra Nevada Forest Plan Amendment, which has been policy for three years, emphasizes the need to thin out the vast quantities of “ladder fuels,” such as brush and thick stands of small trees. But it also authorizes logging some trees in the 20- to 30-inch-diameter range, a provision that was hailed by commercial foresters and attacked by environmentalists.
Ignoring the politics surrounding the various possible solutions, Safford argues that the new research validates the basic assumptions behind the Forest Service revision – that fires are becoming more numerous, larger and more severe.
Measurements of the various fires in the study showed that high-severity fires, in which large trees burn to their crowns, constituted 15 to 20 percent of fires at the beginning and greater than 25 percent by the end of the study period.
These crown fires, he said, increase fragmentation of forest stands and old-growth woodlands.
“Warming climates are clearly behind some of the increases we see in fire severity and fire size,” he said, “but increased fuels due to fire suppression and current fire management policies also play a role.”