Study finds thinning slows wildfires

Study finds thinning slows wildfires

26 August 2011

published by

USA — Local forest officials already knew what the Wallow Fire in Arizona so dramatically demonstrated recently: A treated forest does not burn as intensely or as quickly as one overgrown.

In the largest ever study of fuel treatment effectiveness, U.S. Forest Service researchers have found that intense thinning treatments that leave between 50 and 100 trees per acre are the most effective in reducing the probability of crown fires.

The study, the results of which are published in a recent issue of the Canadian Journal of Forest Research, provides a scientific basis for establishing guidelines for reducing stand densities and surface fuels, said the U.S. Forest Service. The total number of optimal trees per acre on any given forest will depend on species, terrain and other factors.

“This study proves once again that an ounce of prevention equals a pound of cure,” said U.S. Forest Service Chief Tom Tidwell. “Thinning dense forests reduces the impacts of the catastrophic wildfires we’ve already seen this year and expect to see more and more of in the future. This work helps protect communities, provides jobs and promotes overall better forest health.”

Brent Skaggs, Sequoia National Forest fire chief, said the local forest has several areas that have been treated, but he would like to see more.

Decades of excluding fire in forests have resulted in densely packed stands and a buildup of forest-floor fuels which can lead to large, continuous crown fires when wildfires do occur.Crown fires are of particular concern to managers because they are challenging to suppress and are capable of causing widespread destruction. Skaggs admits much of the Sequoia National Forest, including the Giant Sequoia National Monument, is overgrown with thicker forests than he would like to see. Still, he said the forest has made some progress.

“We have several success stories,” he said, admitting that most are where brush has been removed, not timber.

He explained one of the best examples was the 2002 McNally Fire that burned into a treatment area. “It kept it from impacting a Giant Sequoia grove (on the west side),” he said of the area where both brush and timber had been removed six years before the fire.

Removing brush does not generate the controversy that cutting trees does. Timber sales — the method used to thin forests or to harvest timber — are not favorites with environmental groups who continuously challenge such actions, but Skaggs said both treatments are beneficial to a forest.

“You tell me. What would you want, a forest crown fire where not even seeds survive or a thinned forest that’s still green,” he asked.

The importance of thinning was illustrated by the Wallow fire in Arizona this year, which burned more than 538,000 acres. Although 38 structures burned, a system of fuel treatments developed cooperatively by federal, state and local governments, as well as private citizens, successfully reduced fire behavior and allowed firefighters to protect thousands of structures and, in many places, halt the spread of the fire, the forest service reported.

“Most forest managers understand that dry Western landscapes need to be heavily thinned to significantly reduce the threat of crown fires, and our findings now give a sense of just how much thinning is required,” said Morris Johnson, the study’s lead and a research fire ecologist based at the station’s Pacific Wildland Fire Sciences Laboratory. “We found that thinning at this level reduced tree density, raised the canopy base height, and reduced canopy density.”

To test how effective fuel treatments in the Western states are in reducing the probability and severity of crown fires, Johnson, along with University of Washington researcher Maureen Kennedy and station research biologist David L. Peterson, used the Fire and Fuels Extension of the Forest Vegetation Simulator to simulate the effects of four types of thinning and surface fuel treatments in dry forest types in 11 Western states.

By inputting information on weather and fuel conditions into the simulator — which is the standard computer model used by most federal, state, and tribal agencies — they generated simulations in 45,162 forest stands that depicted crown fire hazard and potential fire behavior based on thinning densities leaving 300, 200, 100, and 50 trees per acre.

“This kind of simulation modeling allows us to evaluate multiple treatment types across a large number of forest stands and conditions in diverse geographic areas,” Johnson said. “It would be almost impossible to conduct a study like this on the ground.”

Their simulations suggested that the effectiveness of fuel treatments in the West depends on thinning intensity, with the most intense treatments they studied, which leave 50 to 100 trees per acre, being more effective in reducing the threat of crown fires than less-intense treatments. Thinning to this level, along with the removal of post-treatment debris known as “slash,” made conditions unfavorable for crown fire initiation and reduced the probability of active crown fire, the researchers found.

Skaggs said the goal of “treating” an area of the forest is to try to mimic what a fire would do. He said such treatments are needed every eight to 15 years.

He said brush treatments near Camp Nelson will make that area “much easier to defend.” Similar treatments have been done around Sugarloaf, Hume Lake and Alta Sierra.

He said a final agreement on the Giant Sequoia National Monument management plan would allow officials to move forward on plans to thin the forest, of course, depending on what the plan includes. That plan is now 10-years in the making and environmentalists have objected to any timber plans.

He said when you look at the entire forest, “we really haven’t done a whole lot. To get us a little more protection, you need a buffer around a community.”

He also said thinning a forest is good for the health of the forest, but as fire chief, it is more an issue of safety.

“When you see a fire, you always wonder if the fuel break is wide enough,” he said.

Print Friendly, PDF & Email
WP-Backgrounds Lite by InoPlugs Web Design and Juwelier Schönmann 1010 Wien