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A recent study at Oregon State University indicates that some past approaches to calculating the impacts of forest fires have grossly overestimated the number of live trees that burn up and the amount of carbon dioxide released into the atmosphere as a result.

Effects of forest fire on carbon emissions, climate impacts often overestimated


CORVALLIS, Ore. – A recent study at Oregon State University indicates that some past approaches to calculating the impacts of forest fires have grossly overestimated the number of live trees that burn up and the amount of carbon dioxide released into the atmosphere as a result.

The research was done on the Metolius River Watershed in the central Oregon Cascade Range, where about one-third – or 100,000 acres – of the area burned in four large fires in 2002-03. Although some previous studies assumed that 30 percent of the mass of living trees was consumed during forest fires, this study found that only 1-3 percent was consumed.

Some estimates done around that time suggested that the B&B Complex fire in 2003, just one of the four Metolius fires, released 600 percent more carbon emissions than all other energy and fossil fuel use that year in the state of Oregon – but this study concluded that the four fires combined produced only about 2.5 percent of annual statewide carbon emissions.

Even in 2002, the most extreme fire year in recent history, the researchers estimate that all fires across Oregon emitted only about 22 percent of industrial and fossil fuel emissions in the state – and that number is much lower for most years, about 3 percent on average for the 10 years from 1992 to 2001.

The OSU researchers said there are some serious misconceptions about how much of a forest actually burns during fires, a great range of variability, and much less carbon released than previously suggested. Some past analyses of carbon release have been based on studies of Canadian forests that are quite different than many U.S. forests, they said.

“A new appreciation needs to be made of what we’re calling ‘pyrodiversity,’ or wide variation in fire effects and responses,” said Garrett Meigs, a research assistant in OSU’s Department of Forest Ecosystems and Society. “And more studies should account for the full gradient of fire effects.”

The past estimates of fire severity and the amounts of carbon release have often been high and probably overestimated in many cases, said Beverly Law, a professor of forest ecosystems and society at OSU.

“Most of the immediate carbon emissions are not even from the trees but rather the brush, leaf litter and debris on the forest floor, and even below ground,” Law said. “In the past we often did not assess the effects of fire on trees or carbon dynamics very accurately.”

Even when a very severe fire kills almost all of the trees in a patch, the scientists said, the trees are still standing and only drop to the forest floor, decay, and release their carbon content very slowly over several decades. Grasses and shrubs quickly grow back after high-severity fires, offsetting some of the carbon release from the dead and decaying trees.

And across most of these Metolius burned areas, the researchers observed generally abundant tree regeneration that will result in a relatively fast recovery of carbon uptake and storage.

“A severe fire does turn a forest from a carbon sink into an atmospheric carbon source in the near-term,” Law said. “It might take 20-30 years in eastern Oregon, where trees grow and decay more slowly, for the forest to begin absorbing more carbon than it gives off, and 5-10 years on the west side of the Cascades.”

Since fire events are episodic in nature while greenhouse gas emissions are continuous and increasing, climate change mitigation strategies focused on human-caused emissions will have more impact than those emphasizing wildfire, the researchers said. And to be accurate, estimates of carbon impacts have to better consider burn severity, non-tree responses, and below-ground processes, they said.

“Even though it looks like everything is burning up in forest fires, that simply isn’t what happens,” Meigs said. “The trees are not vaporized even during a very intense fire. In a low-severity fire many of them are not even killed. And in the Pacific Northwest, the majority of burned area is not stand-replacement fire.”

Fire suppression has resulted in a short-term reduction of greenhouse gases, the researchers said, but on a long-term basis fire will still be an inevitable part of forest ecosystems. Timber harvest also has much more impact on carbon dynamics than fire. Because of this, forest fires will be a relatively minor player in greenhouse gas mitigation strategies compared to other factors, such as human consumption of fossil fuels, they said.

Global warming could cause higher levels of forest fire and associated carbon emissions in the future, the researchers said, although there are many uncertainties about how climate change will affect forests, and no indication that forest fire carbon emissions will become comparable to those caused by fossil fuel use.

This research was published recently in the journal Ecosystems, and funded by the U.S. Department of Energy.

Full Citation: Meigs, G.W., D.C. Donato, J.L. Campbell, J.G. Martin, and B.E. Law. 2009. Forest Fire Impacts on Carbon
Uptake, Storage, and Emission: The Role of Burn Severity in the Eastern Cascades, Oregon. Ecosystems 12: 1246–1267.

For more information, contact:
Beverly Law

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  1. Shoulda known you’d toot this horn, Matt.
    Bev Law is a political scientist more than a real one, a pure theoretician more interested in preventing the application of knowledge than anything else.

  2. Dave, Funny. Because I did post this for you…and Bearbait…and Mike D and the boys over at SOS Forests.

    Do you have any specific examples of how this new research is flawed or the findings inaccurate? Or do you just have a general “shoot the messenger” comment directed at Bev Law?

    BTW, I enjoyed your piece about Weyerhaeuser riding off into the REIT sunset with their pockets full of dough. You’ve done some good educational work on REITs. People should check out your piece…

  3. Bev Law was Donato’s thesis adviser. Rushed to publication, really said nothing new, ticked off everyone involved including the federal liaison, abused taxpayer funds, generated Congressional hearings —
    I suggest that folks take a look here:
    I did good work there…had I been wrong about any of it, I would have expected at least one or two libel/slander summonses.
    Yes, I’m biased, toward repeatable, defensible science that recognizes that society values scientists who work to improve the environment AND the human condition. The rest is just useless fluff.

  4. Uh Oh Dave

    looks like your claims that the fires release more emissions than any human generated mechanisms was just BS!

    How about that salvage logging being beneficial after fires?


  5. I’m seeing that they are ignoring many significant impacts, and especially, post-fire impacts that spread far beyond the boundaries of the fire. Erosion, soil degradation, increased bark beetle attacks and hazard trees are just a few of the impacts that add to the devastation of today’s wildfires. Following the big fires on the Groveland Ranger District of the Stanislaus National Forest during the “Siege of ’87”, bark beetle populations radically spiked and mortality skyrocketed on the Tahoe, the Eldorado and the Lake Tahoe Basin. Take a look at the Bitterroot, where unharvested timber produced a massive bloom of bark bettles that overcame all natural defenses. How about the massive bark beetle attacks on the LA Basin forests?? Ya think there’s a link there?!?!? Yes, “climate change” is playing a role but, the facts are that most National Forests are way overstocked compared to pre-European baselines.

    Are we going to set a new record this year, topping 10 million acres burned?? The idea that forests can be restored with uncontrolled wildfire is patently barbaric.

  6. Larry Harrell/Fotoware: Where do you get the idea that 10 million acres burned in a year would set a new record?

    The fact of the matter is that in 1930 over 50 million acres burned nationally, in 1931 over 50 million acres burned nationally and from the late 1920s to late 1930s at least 30 million acres burned every single year.

  7. Like in baseball records, forest fire totals should be compared to modern-day totals. It was a different world back then. There were no roads or fire suppression infrastructure. There were fewer (and smaller) towns that needed protection. There were no slash disposal practices.

    Why not compare that 10 million acres with the average of 2-3 million acres back in the 60’s and 70’s. How about comparing intensities and tree densities. You are talking apples and oranges.

    Yes, I won’t argue that those pure stands of lodgepole pines have a natural cycle that causes huge fires. There IS much that cannot (or should not) be treated. However, man’s recent policies have allowed lodgepole stands to radically expand, and intrude into formerly healthy, vigorous and resilient ponderosa pine forests. We should be eradicating lodgepoles that have invaded into our neglected yellow pine stands. We should be saviing those stands and perpetuating the endangered species they harbor.

    If we allow those forests to burn, we’ll be side-stepping the Endangered Species Act. When will those recovery plans address catastrophic wildfires that completely consume habitat?