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Can New Research Help Reduce the Impact of Wildfires?

In the last 15 years, scientific studies have overturned common knowledge about the behavior and consequences of wildfires. A leading researcher discusses how it can help guide future efforts to protect both people and forests.

The Bobcat fire, which started September 6, rages in Juniper Hills, California, on Friday, Sept. 18, 2020. (Irfan Khan/Los Angeles Times/TNS)
Wildfires in Oregon and California burned more than 3 million acres as of late September, according to data published by the National Interagency Fire Center. The U.S. total is over 7 million acres, well above the year-to-date average of 6 million seen over the last 10 years, but not as big as the numbers for five of those years.  

At this writing, about half of the 42 fires in these states are more than 50 percent contained, and 12,000 firefighters are currently battling them in California alone. Peak fire season extends through the end of October.
As first responders work relentlessly to protect homes and communities, some in government are considering strategies that could prevent, or at the very least mitigate, wildfire impacts to communities. Over the last 15 years or so, a new body of research has been building that could guide such efforts.

According to Chad Hanson, a researcher at the leading edge of this work, the “common knowledge” about forest fires shared by citizens, policymakers, and land managers can be out of step with what recent studies are finding. As papers began to accumulate in peer-reviewed journals, Hanson and his colleagues were surprised at what they reported.

“My field is like ‘opposite world,’ because most of the truths that are emerging from the data are seemingly counterintuitive, the polar opposite of what we thought we knew,” he says.

Hanson, who holds a Ph.D. in ecology from the University of California, Davis, first became concerned about forest health when he hiked the Pacific Crest Trail in 1989 and encountered the after-effects of logging in national forests in California, Oregon and Washington. He co-founded the John Muir Project in 1996, shortly after earning a law degree from the University of Oregon. 

His research focuses on fire history, fire ecology and forest ecology. Hanson has published dozens of papers on these topics in scientific journals and is the editor and co-author of The Ecological Importance of Mixed Severity Fires: Nature’s Phoenix, as well as the author of the upcoming book Smokescreen. In an interview with Governing, he discussed common ideas about fire that bear reconsideration.

Fire ecologist Chad Hanson, Ph.D., co-founder of the John Muir Project, is working with other scientists to improve understanding of fire behavior and fire ecosystems. (Photo courtesy of the John Muir Project)
The fires in Oregon and California are being described as “historically” large. Would you agree with that assessment?

You can’t use the 1960s or the 1970s as your baseline to compare to current fires. We do have more fire than we had then, but in the late 19th or early 20th century, 30 or 40 million acres burning in the U.S. in a year was a normal thing. Before fire suppression, three or four million acres in California was an average year. 

What most people don’t understand is that we’re actually on the low end of the natural range of variability with regard to forest. That doesn’t mean we want 150 million acres burning every year. We don’t want too much or too little; we want fire to occur within the natural range. 

Chaparral is a different story. We have too much fire in Southern California chaparral, but in forest and in many other vegetation types, we have significantly less fire than we used to.

Does coverage of these events omit anything important that scientists are now learning about fire behavior?

Three things come to mind. No. 1: fires are driven overwhelmingly by weather and climate, and therefore climate change. Logging in our forests does not stop fires, in fact it usually makes them burn hotter and faster.

The second thing is that we cannot address this problem in any meaningful way by doing more logging and fire suppression in remote wildlands and backcountry. 

The third thing is that we have to focus on communities. We should put resources on helping homeowners make their homes more fire safe, with ember-proof vents, fire resistant roofing, rain gutter guards, and defensible space. If this is done in conjunction with an evacuation plan it is extraordinarily effective. Case studies are telling us that over 95 percent of homes will survive even a very intense, weather-driven fire. 

It seems natural to see destruction in a burned forest — how could it not be an ecological disaster?

It’s been common knowledge for generations that if fires flare up and kill most all of the trees in a large patch of forest, it won’t regenerate. But it wasn’t until recently that anyone bothered to really study this. There’s been an almost vertical rise in research on this in the last 12 years.

Here’s what we know now, based on literally hundreds of published, peer-reviewed studies. Areas where fire kills most or all of the trees are some of the most ecologically important and biodiverse habitat types in the whole forest. A snag forest, a snag being a dead standing tree, is actually comparable to old growth forest in terms of native biodiversity and wildlife abundance. 

In many data sets, it actually exceeds old growth forest. Instead of being a loss, it is actually ecological treasure, and forests naturally regenerate vigorously after fires, including big ones. They don’t need to be artificially replanted. 

What happens in the forest after the smoke clears? Fire ecologist Chad Hanson describes the process of regeneration.

Do burned, dead or fallen trees act as fuel for the next fire?

The idea that a forest with a lot of dead trees is going to burn more intensely seemed obvious, but it hadn’t been tested. We did our first study, which was published in 2009, in the mountains of Southern California and we didn't see any relationship. If they had a bunch of dead trees, or if they had almost no dead trees, they didn't burn any differently. It was all governed by weather and, therefore, climate. Others said that can't be right, but different scientists looked at the same question and found the same thing. 

Other researchers have found that if you look at forests with a lot of dead trees, at more and more years after the trees die, what you see in most cases is reduced potential for intense fire and lower fire intensity when and if a wildland fire occurs. The real scientific debate is whether dead trees have no effects, or whether forests with more dead trees burn at lower intensity.

Are fires worse in forests that haven’t burned in a long time?

The assumption that a dense old forest is going to burn almost exclusively at high intensity because there is so much fuel was so intuitively obvious that no one bothered to test it scientifically for generations. My colleagues and I thought we should subject that assumption to the scientific method, and we published our first paper in 2006. Other ones have followed, and different groups of researchers have looked at the same question.

What we have all found is that the densest and oldest forests, the ones that haven’t burned in the longest period of time, burn mostly at low and moderate intensity, including in the middle of summer and high fire weather. 

A forest that had burned a few years earlier might burn again, at somewhat lower intensity, but beyond about 10 years after the last fire there’s really no difference. So the idea of a linear increase in potential for intense fire with more time, or decades, since the last fire is false. 

Why wouldn’t a denser old forest burn more? That does seem likely.

You do have more above-ground biomass, but we now know two key things that make it scientifically false, or even dangerous, to think of that as fuel. 

When a forest fire occurs, only a tiny percentage of the tree biomass is consumed, typically only two or three percent, even in a big, intense fire. That’s important to understand because that means that 97 to 98 percent of the wood removed in so-called thinning projects is literally non-combustible.

The other key thing is the countervailing factors. When you have dense forest, you also have high canopy cover. High canopy cover means more cooling shade and that means you have more moisture on the forest floor. It means you have less sunlight reaching the forest floor, so a lot of the combustible understory vegetation starts to die back and recede. The lower limbs on the mature trees start to self-prune. The higher density of tree stems acts as a wind break. Because of these countervailing factors, dense older stands typically burn at lower intensity. 

If density isn’t the problem, what can make fires burn at high intensity?

I was a co-author of a study published in Ecosphere in 2016. We looked at three decades of data from 1,500 fires involving over 23 million acres of fire areas in forests. We found that weather and climate variables were the primary drivers of fire behavior, fire intensity in particular. 

Forest management was a secondary factor, but it didn’t have the result that some politicians claim. It had the opposite effect. The more logging that occurred, the fewer environmental protections in a forest, the hotter and faster fires burned.

I’ve looked at the big Oregon fires using Google Earth imagery to see what those forests looked like before the fires occurred. These landscapes are predominantly dominated by heavily logged areas, clear cuts and commercial thinning. In the big current California fires, the areas that the fires have burned through fastest and most intensely were also heavily logged and postfire logged in previous years. 
Hanson examines regrowth following the Rim Fire, which started on Aug.17, 2013, in California's Stanislaus National Forest. It burned more than 250,000 acres and was the largest fire in the Sierra Nevada mountain range at the time. (Photo: Ed Struzik)
How do climate factors make fires worse?

Intense fires are driven by hot, dry, windy conditions and drought. Climate change affects all of those.  

Logging in the backcountry is making climate change worse. Only a very small percentage of the carbon in a tree that’s removed from the forest ends up in a lumber product. The rest ends up in the atmosphere.

What about carbon emissions from the fires?

It’s a short-term emission, but because only a tiny portion of the tree carbon is consumed in fires, carbon emissions from forest fires are far smaller than theoretical models have assumed in the past. After a surprisingly short period of time, it’s a net plus in regard to carbon. Fires create a nutrient-rich bed of mineral ash on the forest floor and this spurs growth and increases carbon sequestration. That lasts for many decades.

Actually, if you don’t have fires cycling nutrients this way and making them more available, the forest starts to become less productive, less vigorous. If it goes on long enough, for enough centuries, the forest will turn into a woodland and from a woodland into non-forest vegetation. You need fire to maintain the carbon in the forest, and to maintain forest biomass and biodiversity.

Most of the forests in the West are publicly owned and managed, largely by the federal government. Are there things these agencies should be doing differently?

People don't realize the No. 1 thing the U.S. Forest Service does is sell public timber to private logging companies and keep the revenue. The Forest Service should not be in the commercial logging business. 

They have changed the terminology, using “forest health treatment” or “fuel reduction project” rather than “logging.” Even a clear cut of an old growth forest on public land, sold to a logging corporation, is described this way. These terms are applied to post-fire logging as well. 

How is post-fire logging problematic?

The scientific community is wildly against post-fire logging. Entire landscapes are cleared under the guise of restoration, fuel reduction or even “reforestation.” Ecologically rich snag forest habitat is completely obliterated and the natural conifer regeneration that comes free of charge from Mother Nature is crushed under the treads of machinery. Herbicides are sprayed on the ground, and trees are planted artificially. 

If fires occur again, the artificially planted areas burn more intensely because the snags are removed. Highly combustible grasses like cheatgrass are spread by the logging operations, and they form dense mats across the logged areas that can whip flames through them. 

How do the fires that have just erupted in wine country, for the third time in recent years, reflect the climate change or forest management factors you have described?

The current and recent fires in Napa and Sonoma counties are occurring mostly in grassland and oak woodlands with grass understories. They are a combination of two key factors— accidental human ignitions and high fire weather - hot, dry, windy. Some areas that burned just a few years ago are burning again because they are mainly in grasslands, which can burn very frequently. 

I think these fires underscore the misleading nature of the current Congressional focus on national forests. Most of the area burned in a typical year in California is not in forests, and most of the communities at risk are not in the mountains. Legislative attempts, by Senators Feinstein, Daines, Wyden and others, to increase logging in remote areas of our national forests under the guise of community protection, are really just a cynical and opportunistic effort to benefit logging industry campaign contributors. These bills would not help protect communities. 

What should we keep in mind as we recover from recent events and begin to look at how we can do a better job of protecting both forests and people?

We have to decouple the conversations about the impact of fires on nature and their impact on people. These are not ecological disasters. They can be human disasters, but if we focus properly on human communities and human health and safety, the great majority of that is preventable.

We should not be doubling down on policies or laws designed to increase logging in remote forests under the guise of fuel reduction. We’ve got to protect the forest, keep the carbon in the forest and mitigate climate change.

We need to focus on saving homes and lives. We need to redirect resources, including logging subsidies, into creating fire-safe communities and evacuation assistance for communities that are vulnerable to wildland fires. 

We need more rangers to prevent unplanned human ignitions in foothill chaparral ecosystems. There’s almost no staffing at state, federal or local levels to do that right now, to stop people from building illegal campfires or shooting off fireworks. We need to put a lot of power lines underground. 

These things are where our focus should be.
Carl Smith is a senior staff writer for Governing and covers a broad range of issues affecting states and localities. He can be reached at or on Twitter at @governingwriter.
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