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Researchers: hotter fires may heat underlying soil less than cooler fires

Bill GabbertApril 30, 2013August 25, 2019Uncategorizedecology, Portugal, research1 Comment

Researchers studying a 22-acre prescribed fire in Portugal have concluded that fires which burn hotter do not necessarily produce higher soil temperatures. Below is an excerpt from an American Geophysical Union press release.

When scientists torched an entire 22-acre watershed in Portugal in a recent experiment, their research yielded a counterintuitive result: Large, hot fires do not necessarily beget hot, scorched soil.

It’s well known that wildfires can leave surface soil burned and barren, which increases the risk of erosion and hinders a landscape’s ability to recover. But the scientists’ fiery test found that the hotter the fire—and the denser the vegetation feeding the flames—the less the underlying soil heated up, an inverse effect which runs contrary to previous studies and conventional wisdom.

Rather, the soil temperature was most affected by the fire’s speed, the direction of heat travel and the landscape’s initial moisture content. These new findings could help forest managers plan when and where to ignite small controlled burns to reduce dry vegetation and restore the ecosystem in at-risk areas, said Cathelijne Stoof, the soil and water scientist who led this study as part of her PhD research at Wageningen University in the Netherlands.

A report about the experiment by Stoof, who is now at Cornell University in Ithaca, New York, and her colleagueshas been accepted for publication by Geophysical Research Letters, a journal of the American Geophysical Union.

To some people this may be “counterintuitive”, but many firefighters know the residence time, or how much time high temperatures exist at a location, is very important in determining how much heat is transferred into the soil or the organic material that is not consumed by the fire.

On a related subject…

In two previous fire management jobs I had the opportunity to assist researchers who were measuring the temperature at which wildland fires burn. Obtaining this data is not the easiest thing in the world.

In southern California I helped place thermocouples, which can measure very high temperatures, on brushy hillsides prior to a prescribed fire. Then, trying not to disturb the vegetation which could influence fire behavior when the site was burned, I crawled under the brush running asbestos-covered wires from the thermocouples to data loggers which were about the size of a football. Each one recorded information from several scattered thermocouples. Then we had to bury the data loggers so they could survive the fire. This was in the 1970s. The researchers in the Portugal study mentioned above used thermocouples and data loggers, but the data loggers were probably about the size of a package of chewing gum — much easier to bury.

On another project the temperature was measured using heat sensitive paint, a much less accurate system. About eight different paints were used which discolored at specific temperatures. A narrow strip of each paint was brushed onto a very thin strip of aluminum which was stapled onto stakes, sticking out to the side at various heights above the ground. After the fire burned through you would examine the strips and you might see, for example, that the 1,200 degree paint discolored but the 1,250 degree paint did not, so you could conclude that the temperature at that location was between 1,200 and 1,250 degrees. Sometimes it was a judgement call about which paints discolored and which ones did not.

At what temperatures do forest fires burn?

We’ve been asked a few times, “what is the temperature of a forest fire”, so we placed an entry on our Frequently Asked Questions page:

An average surface fire on the forest floor might have flames reaching 1 meter in height and can reach temperatures of 800°C (1,472° F) or more. Under extreme conditions a fire can give off 10,000 kilowatts or more per meter of fire front. This would mean flame heights of 50 meters or more and flame temperatures exceeding 1200°C (2,192° F). (Information provided by Natural Resources Canada.)

How hot is the sun?

On our Facebook page someone once wrote that forest fires burn hotter than the sun. He, of course, was badly and sadly mistaken. According to Space.com:

The temperature in the photosphere [near the surface] is about 10,000 degrees F (5,500 degrees C). It is here that the sun’s radiation is detected as sunlight.

The interior of the sun is much hotter and can reach more than 27 million degrees F (15 million degrees C).

Discovering more about how dormant seeds decide to sprout after a fire

Bill GabbertApril 30, 2013Uncategorizedecology, research

Scientists have known for years that some seeds after being dormant in the soil for years can be triggered to germinate and sprout after a wildland fire. But exactly how this happened was not clear.

Recent research by personnel at the Salk Institute for Biological Studies has shed some light on this process. Below are some excerpts from an article at Science Daily:

[Joseph P.] Noel’s co-senior investigator on the project, Joanne Chory, professor and director of Salk’s Plant Molecular and Cellular Biology Laboratory, says the team found the molecular “wake-up call” for burned forests. “What we discovered,” she says, “is how a dying plant generates a chemical message for the next generation, telling dormant seeds it’s time to sprout.”

[…]

In previous studies, scientists had discovered that special chemicals known as karrikins are created as trees and shrubs burn during a forest fire and remain in the soil after the fire, ensuring the forest will regenerate.

[…]

The chemical structures the team solved revealed all the molecular contacts between karrikin and KAI2, according to Salk research associate Yongxia Guo, a structural enzymologist and one of the study’s lead investigators. “But, more than that,” Gou says, “we also now know that when karrikin binds to the KAI2 protein it causes a change in its shape.”

The studies’ other lead investigator, Salk research associate and plant geneticist Zuyu Zheng, says this karrikin-induced shape change may send a new signal to other proteins in the seeds. “These other protein players,” he says, “together with karrikin and KAI2, generate the signal causing seed germination at the right place and time after a wildfire.”

A review of wildfire ignitions

Bill GabbertApril 23, 2013April 23, 2013Uncategorizedresearch

Researchers have released a report titled Wildfire Ignitions: A Review of the Science and Recommendations for Empirical Modeling. It summarizes the state of knowledge regarding the underlying causes and the role of wildfire prevention efforts on all major categories of wildfires, including findings from research that have sought to model wildfire occurrences over fine and broad spatial and temporal scales. The report also describes a conceptual model of wildfire ignitions, which is designed to provide a modeling framework for analysts who seek to better understand wildfire ignition processes or develop statistical models that can predict wildfire occurrences across any spatial or temporal scale.

Below is a chart from the report. (Click the image to enlarge.)

Myth of catastrophic fires, revisited

Bill GabbertApril 18, 2013November 21, 2018Uncategorizedbeetles, ecology, research4 Comments

Myrtle fire, South Dakota Black Hills, July 23, 2012. Photo by Bill Gabbert

In 2010 we told you about a paper written by Chad Hanson, Director of the John Muir Project. His point of view was that large stand-replacement fires are a necessary part of the forest ecosystem.

Brooks Hays has a recent article at his Government from the Ground Up blog that explores that premise and says the land management agencies should embrace high-intensity fires. Here is an excerpt:

It looks like this ecological truth is not yet understood by the general public. But the Forest Service also seems to be gripped by an old-fashioned view of fire’s functions. “It’s still a good old boy network,” says [Richard] Hutton, [forest ecologist and director of the Avian Science Center at the University of Montana], “full of rangers who honestly believe in their heart of hearts that their job is to keep trees green.” Their idea of a healthy forest is “no beetles, no fire,” he explains. “And they’ll thin and cut away trees to prevent fires or any other disruption that might prevent trees from being green.”

Making matters worse is the fact that the agency remains underfunded. And when the Forest Service is strapped for cash, Hutto points out, it’s the younger, better-educated, more ecologically-minded rangers that get the ax – and the trees follow.

“What’s missing,” says Hutto, “is ecology, in a word. There are too few ecologists in the forest service.”

Below we revisit the article we wrote in 2010.

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The Director of the John Muir Project, Chad Hanson, has written a paper about wildfire and its relationship to biodiversity and climate change, titled The Myth of ‘Catastrophic’ Wildfire. Here are some of his findings, as reported by New West:

There is far less fire now in western U.S. forests than there was historically.
Current fires are burning mostly at low intensities, and fires are not getting more intense, contrary to many assumptions about the effects of climate change. Forested areas in which fire has been excluded for decades by fire suppression are also not burning more intensely.
Contrary to popular assumptions, high-intensity fire (commonly mislabeled as “catastrophic wildfire”) is a natural and necessary part of western U.S. forest ecosystems, and there is less high-intensity fire now than there was historically, due to fire suppression.
Patches of high-intensity fire (where most or all trees are killed) support among the highest levels of wildlife diversity of any forest type in the western U.S., and many wildlife species depend upon such habitat. Post-fire logging and ongoing fire suppression policies are threatening these species.
Conifer forests naturally regenerate vigorously after high-intensity fire.
Our forests are functioning as carbon sinks (net sequestration) where logging has been reduced or halted, and wildland fire helps maintain high productivity and carbon storage.
Even large, intense fires consume less than 3% of the biomass in live trees, and carbon emissions from forest fires is only tiny fraction of the amount resulting from fossil fuel consumption (even these emissions are balanced by carbon uptake from forest growth and regeneration).
“Thinning” operations for lumber or biofuels do not increase carbon storage but, rather, reduce it, and thinning designed to curb fires further threatens imperiled wildlife species that depend upon post-fire habitat.

In addition to being the Director of the John Muir Project, Mr. Hanson is also a researcher at the University of California at Davis and was elected as one of the directors of the Sierra Club in 2000.

Transferring fire research results — to middle schools

Bill GabbertApril 14, 2013April 14, 2013Uncategorizedopen access, research4 Comments

State and federal governments spend millions of taxpayer dollars on research every year. If the knowledge gained through those efforts is kept locked away in for-profit journals or not made freely and easily available to the public, a person could argue — what is the point of paying for the research?

One avenue the U.S. Forest Service is using to transfer research results is through the “Natural Inquirer”, created so that scientists can share their research with middle school students. Each article on the site introduces scientific research conducted by Forest Service scientists.

Here is an excerpt from the web site:

…All of the research in this journal is concerned with nature, trees, wildlife, insects, outdoor activities and water. First students will “meet the scientists” who conduct the research. Then students read special information about science, and then about the environment. Students will also read about a specific research project, written in a way that scientists write when publishing their research in journals. Students become scientists when they do the Discovery FACTivity, learning vocabulary words that help in understanding articles.

This seems like a great idea, and deals with at least two issues. That of transferring research results, and helping to increase and improve the science programs in schools. It may also allow students to identify with scientists by linking research with individual employees in the USFS. Who knows, it might even encourage a middle school student to consider science as a profession.

Wildland fire is included as one of the many topics covered at the site, as you can see if you search for “fire” on their search page.

The Natural Inquirer has published a series of “Scientists’ Cards”. Below are the front and back of the card for Dr. Pepe Iniguez, a landscape fire ecologist:

Wildfire potential, for 2013

Bill GabbertApril 6, 2013August 25, 2019Uncategorizedpotential, research1 Comment

The map above is an attempt by the U.S. Forest Service to quantify by location the potential, this year, of wildfires that that would be difficult for suppression resources to contain. Areas with higher values have a higher probability of experiencing high-intensity fire with torching, crowning, and other forms of extreme fire behavior.

A much larger zoomable version of the map can be found here (1.5MB). (It becomes more interesting when you click to zoom in to see more detail.)

At their web site, the USFS does not describe in detail the criteria for developing the map but it appears to be primarily past fire occurrence, estimates of wildfire likelihood and intensity, vegetation, and probably topography. Recent weather, most likely not so much.

Below is an excerpt about the map from their web site:

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“Using the FPA FSim products as inputs, as well as spatial data for vegetation and fuels characteristics from LANDFIREand point locations of fire occurrence from FPA (ca. 1992 – 2010), we used a logical series of geospatial processing steps to produce an index of WFP for all of CONUS at 270m resolution. The final WFP map is presented here in two forms: 1) continuous integer values, and 2) classified into five WFP classes of very low, low, moderate, high, and very high. We don’t intend for the WFP map to take the place of any of the FSim products; rather, we hope that it provides a useful addition to the information available to managers, policy makers, and scientists interested in wildland fire risk analysis in the United States. On its own, WFP does not provide an explicit map of wildfire threat or risk, because no information on the effects of wildfire on specific values such as habitats, structures or infrastructure is incorporated in its development. However, the WFP map could be used to create value-specific risk maps when paired with spatial data depicting highly valued resources (Thompson et al. 2011a, Thompson et al. 2011b).”

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