Public Release: 

Without thinning the worst is yet to come for fire-prone forests

University of Washington

Some Washington and Oregon eastside forests are crowded with as many as 3,000 trees per acre, putting them at high risk for wildfire. Photo credit: University of Washington

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When fires turn eastern Washington and Oregon forests into wastelands, valuable wildlife habitat is lost and it costs between $1,300 and $2,100 per acre in fire-fighting costs, lost buildings, economic suffering by nearby communities and degraded waterways, say University of Washington researchers in a recently published report.

The report attempts for the first time to tally the cost per acre of letting the worst wildfires - the crown fires - burn. It's a needed perspective when considering thinning overly dense stands - work that could cost nearly $600 an acre in some places. So say UW researchers who are offering land owners, wildlife advocates and policy makers a newly tested software package that weighs how much fire danger is reduced against how much it costs to thin out fuels.

The new software integrates several computer programs offered by the U.S. Forest Service - including one that models the way fire can tear through a forest - with a program called the Landscape Management System developed at the UW that predicts such things as how a forest grows and habitat changes after thinning or other forest operations.

On the Okanogan National Forest in Washington and the Fremont National Forest in Oregon, where some of the region's worst fires have occurred in recent years, the most effective treatment tested using the computer software preserved ponderosa pine and western larch, while taking the smallest trees of other species until a targeted density was achieved. This approach typically left between 40 and 100 of the largest trees per acre. The trees removed rarely included any larger than 12 inches in diameter.

Unfortunately, markets are weak or nonexistent for the small diameter trees removed under this scenario. They can't, for instance, be used for lumber. The new software package helps weigh the economics of thinning in such cases to develop the most cost-effective approaches.

"The challenge of developing long-term strategies to reduce wildfire risks across tens of millions of acres of inland west forest is daunting. The information to be considered is complex and the planning process may be formidable," says Larry Mason, lead author of "Investigation of Alternative Strategies for Design, Layout and Administration of Fuel Removal Projects," published by the UW's College of Forest Resources as part of its Rural Technology Initiative.

"We've tried to make the Landscape Management System and its support applications user-friendly so that the general public, as well as professionals, can use it. There is less confusion and distrust if everyone can analyze the various choices for themselves."

The report is available at or by calling 206-543-8684. The Landscape Management System software is available for download at no charge at

With the UW software, a stand of trees can be "thinned" in various ways and "grown" on a computer. Simulated fires can be "set" to see if the fire remains on the forest floor or finds its way into "ladder" fuels, short trees, shrubs and trees with low-hanging branches. Once a fire makes its way into treetops it can explode into a difficult-to-fight and destructive crown fire.

The most over-all effective treatment as determined by the case studies of the Okanogan and Freemont forests, kept all the ponderosa pine and western larch and then thinned the smallest trees until reaching the target density of 45 square feet of "basal area" per acre. Foresters have long used basal area per acre rather than wood volume or number of trees to describe density. Basal area is determined by calculating the area of the surface across the diameter of every tree at chest height, and then summing the total.

The UW software then analyzed the economics. Where costs of harvesting and hauling are highest - possibly because the wood must be hauled long distances - a contractor could lose an average of $170 per acre. Add the typical $205 an acre the Forest Service says it costs to prepare a thinning contract and the cost per acre is $380.

That's not as prohibitive as Mason and his colleagues expected, but other higher-cost strategies for thinning may cost more than $580 an acre, $375 for harvesting and hauling and $205 to prepare the contract. Where revenue from thinned material isn't enough to cover costs, other forms of support will be needed, the researchers say, which could include:

  • More funding for the fledgling Stewardship End Result Contracting, a federal program where it's understood that revenues won't cover the full costs of some restoration projects.
  • Greater Forest Service flexibility to package restoration jobs so the contractor makes some money.
  • Development of new infrastructure to use small-diameter forest biomass to generate electricity.

"We are attempting to deal with a problem that has taken a century to create," says Bruce Lippke, UW professor and director of the Rural Technology Initiative.

"Before Europeans arrived there were typically 30 to 60 large trees per acre in the Okanogan and Fremont national forests. Today the average is 1,000 trees per acre and in some places it's as high as 3,000 trees. More than three-fourths of these two national forests are considered at high to moderate risk for crown fires, and both are fairly representative of forests in the Intermountain West from Canada to Arizona and New Mexico. Selected forest management activities can return forests to prior healthy conditions while providing economic opportunities for rural communities."

While UW researchers totaled up the costs of such things as fire-fighting and lost buildings and timber for this study, they weren't able to put a price tag on environmental costs that include loss of wildlife habitat and the release of tons of carbon dioxide, a greenhouse gas, to the atmosphere as a forest burns.

"While the cost of acting may be high; the cost of doing nothing is greater," Lippke says. "Even an upper-end cost of $580 an acre for difficult-to-treat forests pales compared to the cost of a fire."


The research was funded by a Multi-Agency National Fire Plan Grant administered by the USDA Forest Service. For more information:
Mason, 206-543-0827,
Lippke, 206-543-8684,

-- Costs and benefits of reducing fire risks by thinning are considered
-- See section 4.6.12, "Market and non-market values of fire risk reduction," in full report at

-- Some Washington and Oregon eastside forests are crowded with as many as 3,000 trees per acre, putting them at high risk for wildfire. Photo credit: University of Washington

-- Changes in fire risk in coming years are modeled for stands on the Okanogan National Forest under scenarios ranging from doing nothing to allowing wildfires to burn. ("With regen" means the model took into account how the forests are likely to regenerate in each scenario. The most effective risk reduction is the one "Below, Leave 45sqft Basal Area," which included removing the smallest diameter trees until a tree density of 45 square feet of basal area is reached.

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