The Nuance in Fire Research Reporting

A recent announcement from UC Davis proclaimed, “Less Severe Forest Fires Can Reduce Intensity of Future Blazes,” and got plenty of play in regional newspapers. But like so many scientific papers, the piece has more nuance than the breathless publication might suggest.

The study used remote sensing to review 700 reburns across the West. According to one of the researchers, Claire Tortorelli: “Some previous fires can have moderating effects on future fire behavior. It’s important to understand how past wildfires will affect what happens in the future.”

The article promotes natural and human ignitions as a potential fuel reduction policy, but fails to acknowledge that not all high severity blazes should be reduced. I have no problem with more wildfire on the landscape.

However, the paper has numerous qualifiers not stated in the brief press announcement, presenting an entirely different picture of fuel reductions and their ability to reduce future wildfire severity and size.

PROBABILITY THAT FIRES WILL ENCOUNTER FUEL REDUCTIONS IS LOW

One of the findings is that there was a reduction in high severity fires that could last up to 20 years in some systems, but even that the effect lessened over time.

The key word in this statement is “could” because other research has shown that most fuel reductions, whether by past fires, prescribed burning, or thinning, have a limited time regarding their effectiveness. As the authors note, there are: “decreases in magnitude (of wildfire) over time as understory fuels recover following fire.”

As the authors recognize, “Severe fire weather can blunt moderating fire effects (Parks et al., 2015) (Figure 1c), especially in ecosystems with higher productivity where fire is more strongly constrained by fuel moisture and weather conditions than fuel amounts.”

The numerous clearcuts (essentially fuel reductions) along the Mckenzie River in Oregon failed to halt the wind driven Holiday Farm fire. Red is high severity, yellow moderate, and green low severity.

Another factor that influences the value of prescribed burning and thinning is vegetation regrowth. Both fires and logging reduce competition for light and water, often stimulating rapid plant regrowth. The authors noted that understory and ladder fuels far exceeded prefire levels 8 years after a low-severity prescribed fire in Sierra mixed conifer forests.

This rapid regrowth of vegetation raises the question of probability, or what is the likelihood that a fire will encounter one of these “fuel reduction” areas that are potentially effective? As Rhodes and Baker point out, fuel reductions cannot limit fires if a fire does not encounter a fuel reduction. Less than 1-2 %  of wildfires encounter a fuel treatment.

This limited probability of a fire encountering a fuel reduction is an essential consideration since fuel treatments can have severe negative impacts on forest ecosystems, including, but not limited to, the spread of weeds, disruption of natural mortality agents (e.g., pine beetles, or drought), increased human access to roads, loss of genetic variability, and other well-documented impacts.

The 1910 Big Burn charred more than 3 million acres. This fire occurred long before anyone suggested “fuel reductions” were effective. Portions of the 1910 burn reburned in 1919.

The paper is also predicated upon the notion that high-severity blazes are uncharacteristic, harmful to ecosystem integrity, and desirable to reduce or eliminate.

Even so, these authors recognize that “Despite the focus of media headlines on mega fire events that burn at uncharacteristically high severity, most of the burned area across the Western United States occurs at low- to moderate severity.”

The fact that most blazes are small and burn at low to moderate severity is critical to understanding an effective forest management policy. The vast majority of all wildfires burn at low to moderate severity. Most of these fires will self-extinguish and/or are easily controlled. It is the 1% or less of all wildfires that burn significant acreage annually, and the focus of wildfire policy aims to reduce such blazes with logging and prescribed burning.

A study of 1500 fires found that fewer acres burned at high severity in protected landscapes such as Yosemite seen here, even though they presumably have more fuel. Photo George Wuerthner

Numerous politicians and Forest Service officials advocate for logging and other fuel treatments under the assumption that prohibiting such treatments leads to larger high-severity blazes. However, a review of 1500 blazes in dry and mixed conifer forest regimes has found that areas protected from such treatments, like national parks and wilderness areas, even though they have higher levels of “fuel” (i.e., wildlife habitat), have fewer acres of high severity blazes.

So, the question as to whether logging and prescribed burning reduce high-severity blazes is critical.

One problem with researchers who suggest that thinning and prescribed burns can moderate large high-severity blazes is that all studies on fire severities are combined. Since logging and thinning can sometimes modify fire behavior, including these blazes can skew results.

ARE FUELS DRIVING WILDFIRES

Another issue with the paper is that the authors repeat the familiar canard that the elimination of Indian cultural burning and 100 years of fire suppression have led to “abnormal” fuel accumulations. Both of these ideas have been challenged. If the starting assumptions are incorrect, the rest of the paper may be in error.

There are numerous reasons to doubt these assertions, not the least of which is that there is almost no evidence that tribal burns influenced large areas. This is supported by the evolutionary evidence that numerous low-elevation ecosystems inhabited by Native Americans, like sagebrush, chaparral, and others, do not burn frequently.  

Another fundamental problem with the assertion that human ignitions are critical for “healthy” forest ecosystems is that it fails to recognize that tree species like ponderosa pine, which some assert require human ignitions to remain healthy, have existed for 50+ million years. Human presence in North America is roughly 15,000 years old. This naturally leads to the question of how ponderosa pine and other dry forest species survived all the millions of years before humans arrived to ensure their survival.

SHIFTING BASELINE

The idea that fire suppression has been successful for a hundred years ignores the dominant influence of climate on wildfire acreage charred. The middle portion of 1900-2000 was cooler and moister than at present, with fewer wildfires.

The paper suggests that “restoring historic” fire regimes is possible and desirable. However, this fails to note that all fire regimes are a consequence of climate. Change the climate, and you change the fire regime. The ongoing climate warming is likely increasing the frequency and severity of wildfires in some places. Still, there is disagreement over whether we are experiencing more high-severity blazes than in the past.

What dates you use for your baseline affect the perception. For example, during the last century, a warm period between the 1900s and 1930s, we had the 1910 Big Burn, which charred 3-3.5 million acres in Idaho and Montana and other significant fires. In 1929, more than 50 million acres burned, compared to the present, when 10 million acres burned in a season is considered a “record.”

This warm period was followed by a cold, moist period during the 1940s-1970s, when glaciers grew in the West, with fewer fires and few large blazes. In the late 1980s, the climate began to warm and dry again, increasing fire frequency.

Most advocates of more forest manipulation compare the 1970s with the present to show that there are more large wildfires and that fuel reductions are the solution.

Using the 1970s as your comparison is the shifting “baseline” effect. We indeed have larger fires today, but the explanation is not that there is suddenly more fuel due to “fire suppression”. Nature was suppressing fires, and now climate warming is facilitating larger blazes.

SNAG FORESTS CRITICAL TO HEALTHY ECOSYSTEMS

The paper acknowledges that high-severity blazes create more dead and downwood, but it notes that they may contribute to subsequent blazes. But what is fuel to many fire researchers is “wildlife habitat” to others. Indeed, high-severity blazes are among the major sources of dead snags and downwood critical to numerous fish, amphibians, birds, mammal species, and plants.

CONCLUSION

Their findings recounted in the paper are not that remarkable. Essentially, the paper concludes that reburns may limit the spread of fire immediately because it contributes to fuel reduction, but the effect of any fuel reduction is often short-lived. The authors recognize the limitations of fuel reductions, but the press release tends to suggest a different conclusion.