Fire scientists fight over what Western forests should look like

  • Blackened stumps surround Cheesman Lake in Colorado 10 years after the 2002 Hayman fire, the largest in the state's recorded history, swept through the area. A controversial new study says severe fires like this one are more normal than previously thought.

    Peter Brown

Mark Williams and Bill Baker stand amid ponderosa pines in the mountains west of Fort Collins, Colo., holding a copy of a 19th century land survey. They're looking for a small pile of rocks with three notches on the east side, indicating that a General Land Office surveyor stopped here to describe the forest. Surveyors noted many things, says Baker, a professor at the University of Wyoming; they even discovered a gallows where two men had been hung. But generally the reports focus on forest type and structure -- less dramatic, perhaps, but more useful for modern researchers reconstructing historic Western forests and their fire patterns.

Over the past five years, Williams and Baker compiled thousands of hand-written descriptions and combined them with tree-ring data from the lines the surveyors walked. What they found surprised them. In each of their study areas -- mixed conifer and ponderosa forests in northern Arizona, Colorado's Front Range and eastern Oregon -- dense thickets of spindly trees and severe crown fires were common even before European settlement. In fact, the two scientists argue that the severity of many recent megafires, like Arizona's 2002 Rodeo-Chediski fire, which burned 190,000 acres, is actually pretty normal.

If that sounds counterintuitive, it is. Conventional wildfire wisdom is generally the opposite. Many scientists say that dry Western forests were once open and park-like, with large, widely spaced trees and little undergrowth.  Now, however, due to fire suppression and logging practices, they've become overgrown with small trees and shrubs. The result is that frequent low-severity fires have been replaced by a new era of megafires that are hotter and more severe than ever before.

That's true in some parts of the West, say Baker and Williams, a recent Ph.D. student, but not everywhere; many dry forests throughout the region historically were more dense and prone to severe fires. They also disagree with the idea that thinning and prescribed burns can prevent such fires.  That kind of treatment, applied in the wrong places, is not only misguided, they say, but could do more harm than good.

Naturally, those strong statements have met equally strong criticism from many pre-eminent fire ecologists. But Baker and Williams are not the first researchers to complicate fire ecology in the West. Unfortunately, the nuances in their and other scientists' perspectives are often oversimplified in the media and in policy-making, with damaging results. "A set of laws, policies and initiatives that aim to uniformly reduce fuels and fire severity is likely to (have) adverse effects on biological diversity," wrote Baker and Williams in  their recent paper in Global Ecology and Biogeography.

"It's very important that we take a more regional geographic approach and not apply what we know from one system to another," says Rosemary Sherriff, an associate professor of geography at California's Humboldt State University, whose work corroborates some of the Wyoming researchers' findings. But "it's hard to get that across, because the idea of park-like ponderosa pine is widespread."

One of the main researchers behind the traditional view is ecologist Wally Covington. When he began working at Northern Arizona University in 1975, many of the landscapes he encountered were choked with trees that had sprung up during decades of fire suppression. Covington wondered how the forests looked before widespread settlement.  His study results strengthened earlier findings that, in the past, Southwest ponderosa pine forests were kept open by frequent surface fires.

Subsequent recommendations to remove small trees and reintroduce surface fires became the basis for policies like the 2002 Healthy Forests Initiative, attracting the support of both lawmakers and environmentalists, since they would heal damaged ecosystems while reducing the risk of catastrophic fire.

The "Southwest model" gained support from other fire ecologists and began to be used as an explanation for forest problems elsewhere in the West -- even areas with vastly different historical fire regimes. Foresters in places like eastern Oregon, Montana and California's Sierra Nevada began thinning to make forests more park-like and reduce the risk of severe fires -- in the process jeopardizing wildlife such as black-backed woodpeckers and Kirtland's warblers, whose habitat is found in burn patches. Further research would reveal the situation's complexity; in reality, both surface and severe crown fires played an important role in many landscapes.

For example, the Sierra Nevada's ponderosa pine and mixed conifer forests are open and park-like on dry, south-facing slopes, with densely packed trees in creek beds and on northern aspects. Despite this variety, Malcolm North, a scientist with the U.S. Forest Service's Pacific Southwest Research Station, found in 2008 that fuel management officers were applying the Southwest model to an extreme, thinning the landscape into an "asbestos forest," rows of evenly spaced trees with no understory.

The Southwest model has also been used to justify thinning and prescribed burns in dry Montana and Idaho forests. But further study by The Wilderness Society's scientists and Dick Hutto, a University of Montana biologist, showed that those forests had a history of less frequent, more severe fires than did Southwestern forests.

Merrill Kaufmann, a retired Forest Service ecologist with the Rocky Mountain Research Station in Fort Collins, Colo., was one of the first to question the ideal of park-like, open forests. In the 1990s, while studying the Pike National Forest in south-central Colorado, he asked agency staffers where they got their forest-treatment information. "All they could come up with was the Southwest model," he says.

Kaufmann soon discovered that the area's old-growth ponderosa pine and Douglas fir forests didn't fit that model, though. Low-severity surface fires and open, park-like stands were not the dominant types over the past 500 years. Instead, the forest had many dense patches of trees that had grown up in areas burned by severe crown fires.

Few fire ecologists -- including those whose work supports the conventional wisdom -- dispute the idea that fire regimes and forest structure vary around the West. Tom Swetnam, who directs the tree-ring research lab at the University of Arizona, writes in an email, "No one that I know is arguing that all forests and all management solutions to fire problems are the same everywhere. … It is quite true that high severity, stand-replacing fires are not abnormal in some forest and shrub types."

Yet while scientists may be clear about which specific forests were park-like and subject to frequent, low-intensity fires, the complexities are often lost on politicians and the mainstream media, who prefer straightforward explanations.

Many news stories about Western wildfires perpetuate the Southwest model. "Historically, natural, smoldering fires thinned the forest floor every 15 to 20 years," a July 19 CBS News story asserts about all Western forests. A July 2 story in New Scientist makes a similar claim.

The 2002 Healthy Forests Initiative also assumes that all Western forests are more overgrown now than they were historically. "Today, the forests and rangelands of the West have become unnaturally dense. … When coupled with seasonal droughts, these unhealthy forests, overloaded with fuels, are vulnerable to unnaturally severe wildfires." The 2009 FLAME Act makes similar assumptions.

Covington himself may have inadvertently contributed to the problem:  Scientific papers with titles like "Helping western forests heal: the prognosis is poor for U.S. forest ecosystems" suggest his research has broad applications for all Western forests. And he says, "There is no 'Southwestern' model. That is horseshit. Everywhere you go, you find ponderosa pine that is open and park-like."

Baker and Williams are not the only researchers who say ponderosa and mixed conifer forests are not all prone to frequent, low-severity fires. Still, other fire ecologists have questioned their methods and data interpretation.

North and Kaufmann both criticized their reliance on and interpretation of the General Land Office surveys. "It's a very scant data set," North says. "The methods used in those papers are not at all appropriate for making the kinds of extrapolations" the team made.

And both Swetnam and Peter Brown, who runs the nonprofit Rocky Mountain Tree-Ring Research lab, questioned how ponderosa pines could regenerate if Baker and Williams are correct about severe fires having scarred Western landscapes for generations. Lodgepole pine seeds need heat to be released from their cones, but ponderosa seeds are destroyed by fire. Baker acknowledges their concerns, calling the regeneration question "a problem area" in fire ecology.

Normally, such critiques play out in scientific journals, but this has been a particularly public controversy, with researchers lashing out at Baker in newspapers. Swetnam told the Associated Press the paper was "deeply flawed in multiple ways, and I have yet to hear any knowledgeable forest or fire ecologist or forest manager say they are convinced by (its) main interpretations."

The passionate reaction is driven by fear that Baker's studies could undermine support for restoration work, according to Greg Aplet, a senior forest scientist at The Wilderness Society. Many researchers and fire managers think immediate action is needed to reduce fuels, and that not nearly enough thinning has been done, especially around communities, where reducing the risk of fire is as much of a priority as restoration. "We gotta get in there and we gotta restore these stands," Brown said, "and to my mind, Baker is just an anchor dragging us backwards."

But so far, Forest Service budget cuts have impacted restoration efforts more than studies, including Baker and Williams', that question the effectiveness of fuel treatments. More and more, the treatments that do occur are based on localized research rather than a blanket application of the Southwest model. A three-year old Forest Service initiative, the Collaborative Forest Landscape Restoration Program, is working on localized studies to influence forest management.

It's important to tailor treatment work to local conditions, says Hutto, the Montana biologist, because the federal government is spending money thinning forests that actually have a long history of dense stands and severe fires. "If they knew severe is natural, there's less justification for that kind of behavior," he says. "I think it's very important to taxpayers to be worried about whether we're going about things in a way that's kind of a waste."