Understanding Pyrodiversity

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Ah, climate science. What a messy and divisive subject. And with events like “snowmaggedon” and “climategate” taking the media by storm, there seems to be no shortage of controversy to fuel the fire.

A new study from Oregon State University does just that. Researchers suggest that previous calculations of forest fires’ carbon dioxide contribution grossly overestimate the impact of flaming foliage on the atmosphere.

Previous research on the climatic effects of fires has suggested that forests, though often touted for their carbon-storage abilities, emit a significant amount of greenhouse gases when they go up in flames. And contrary to what Smokey the Bear might have you believe, the issue isn’t if a forest will burn, but when.

David Bowman says that by trying to prevent fire in nature, humans have actually made wildfires that much worse. It’s a vicious cycle: While fires may contribute to climate change, climate change has also affected their behavior, and humans are complicit. Bowman and Jennifer Balch argue in “Deforest Fires Fan Global Warming” that intentionally burning down forests accounts for up to one-fifth of mankind’s carbon dioxide emissions post-Industrial Revolution. And the impact of these fires on the atmosphere ultimately increases the likelihood of unintentional fires, which further add to the problem.

Balch suggests that instead of trying to control fires, we should try to manage the climate change that has made them so unpredictable. Both she and Bowman believe that humans need to accept fire, and the Oregon State findings may make that that much easier.

The OSU scientists conducted their research in the Metolius River Watershed in the central Oregon Cascade Range, where four large fires in 2002-03 consumed about one-third, or 100,000 acres, of the area. Previous studies of the area have estimated that fires took about 30 percent of the mass of living trees, but the OSU team found that only 1 to 3 percent was consumed.

Previous estimates of the atmospheric damage of the B & B Complex fire in 2003 (one of the four Metolius fires) suggested that it released 600 percent more carbon emissions that year than all other energy and fossil fuel sources in the state put together. But the OSU research suggests that all four fires combined produced about 2.5 percent of the annual statewide carbon emissions.

With numbers that vary so widely, it’s easy to wonder if they’re even talking about the same forest.

The OSU research team says there are some serious misconceptions about how much of a forest actually burns during a fire (which is also the focus of much of Balch’s work in the Amazon). Previous estimates of the carbon released during forest fires have been based on Canadian forests, which, they say, are very different from many of the forests in the United States.

Garrett Meigs, a research assistant in the Department of Forest Ecosystems and Society at OSU, calls for an appreciation of “pyrodiversity” — the diverse range of effects a fire can have. He says that more studies should take into account the varying responses of forests to fire.

Beverly Law, a professor of forest ecosystems and society at OSU, points out that most of the initial carbon emissions in a fire are from the burning of the tinder on the forest floor or below ground – not from the trees themselves.

Also, the scientists say, even if a severe fire kills almost all the trees in one area, the trees remain standing. They don’t fall, decay and release carbon immediately; the process goes on for decades. And in the meantime, grasses and shrubs pop up quickly, offsetting some of the carbon released by the trees.

Since fire events are episodic and the increase in greenhouse gas emissions is steady, the researchers argue that strategies to mitigate climate change should focus on human-caused emissions, not wildfires. They add that if scientists do want to estimate the carbon impact of fires, they need to take into account burn severity, non-tree responses and belowground processes to be accurate.

Ultimately, they echo Bowman: Although suppressing fires has reduced greenhouse gas emissions in the short term, in the long run, fires are here stay. And reducing human consumption of fossil fuels would be a much more effective way to cut atmospheric carbon emissions than trying to stop forest fires.

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