Media Misinterpretation of Wildfire Ecology

Giant sequoia at Sequoia National Park, California. Photo George Wuerthner

One significant problem with explaining complex ecological stories is that many journalists are unprepared to interpret scientific research. A recent report in the Washington Post on a University of California Irvine study of wildfire fuels in California’s Sierra Nevada is a classic example of a misleading summary.

The study, Evidence for multi-decadal fuel buildup in a large California wildfire from smoke radiocarbon measurements, published in Environmental Research Letters, is a case in point. The article reports that one of the chief fuels of wildfires in California’s Sierra Nevada mountains is the decades-old remains of large trees.

The researchers tested the smoke from the KNP Complex Fire that burned almost 90,000 acres in California’s Sequoia and Kings Canyon National Parks. The researchers analyzed the air samples for their radiocarbon content, which was used to calculate the age of burnt material.

“Our findings support the idea that large-diameter fuel buildup is a strong contributor to fire severity,” said Audrey Odwuor, a Ph.D. candidate in the UCI Department of Earth System Science and the new study’s lead author.

The majority, 86%, of the 90,000 acre KNP Complex blaze burned at low to moderate severity where most large trees survived the fire. Photo George Wuerthner

Here’s the problem. What exactly is “large diameter fuel”?

Most people when they read about “large diameter fuels” envision down logs as seen in this photo. However, as defined by this study, something as small as 3 inches, including shrubs, small trees, and branches qualifies as “large diameter fuel”. Photo George Wuerthner

Most people are likely to envision that large-diameter fuel means big down logs. However, as defined by the study authors, anything larger than 3 inches is a “large diameter.” In other words, much of the debris, such as small branches, shrubs, and small trees, is what they suggest is the dominant fuel in wildfires—not big logs as one might expect from the description of “large diameter fuels.”

Another issue with the study is that researchers only took smoke measurements for one day—a tiny sample from which to generalize about overall fire fuels.

However, there are other problems with the study and media characterization.

Bryant Baker, Director of Conservation & Research at Los Padres ForestWatch, has reviewed the original study and has numerous qualifications about the interpretation of the study.

The biggest problem is the researchers did not test the size and kind of fuel that burned. Instead, they made assumptions about what was burning. For instance, soil organic matter could have been burning rather than woody debris.

The idea that most wildfires are burning at higher severity and killing many trees is part of the media and Forest Service narrative.

Much of the KNP Complex burned at relatively low severity and well within historical conditions. Photo George Wuerthner 

In keeping with this narrative, the researchers imply that the KNP Complex burned at high severity. Still, some 86% of the 90,000-acre blaze was charred at low to moderate severity, leaving only 14% scorched at high severity.

As Baker points out, this is well within the historical range of variability for low- to mid-elevation mixed-conifer and yellow pine forests in the Sierra Nevada. In other words, the KNP Complex burned within historical parameters.

The Washington Post article implied that the “large diameter fuels” were burning when researchers took air samples, contributing to sequoia’s high mortality.

However, the study did not analyze the size, type, or even age of charred fuels in KNP Complex giant sequoia groves, especially in the woodlands where most mature sequoia mortality was found. Baker’s review of the fire suggests that when researchers obtained smoke measurements, there was not a “single active fire front near a giant sequoia grove.” Ironically, the closest fire fronts were backfires set by firefighters.

So, here’s the take-home message. The mean combusted fuel age reported in the KNP Complex study represents one day. Furthermore, the fire on that day was nowhere near where the giant sequoia mortality occurred.

The Washington Post mischaracterized the study’s findings. The researchers never stated that down woody large-diameter logs drove the blaze—but “large diameter” as defined in the study could be anything from 3 inches or more extensive and include shrubs, small trees, and branches.

Sequoia regeneration is favored by high severity fires. Historically most of the existing large sequoia now found along the western slope of the Sierra Nevada, got their start after some ancient high severity blaze. Photo George Wuerthner 

Better media coverage of fire ecology is necessary if we hope to have well-informed public participation in federal forest policy. Unfortunately, most journalists do not have the scientific background to judge the validity of scientific research or to interpret the findings accurately. This is where independent researchers like Los Padres ForestWatch, John Muir Project, Wild Heritage, and other organizations can play an important role.

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