Study shows firefighters’ exposure to smoke increases disease risk

Depending on the type of work performed and the number of years of exposure, the increased risk can be 22 to 39 percent.

Above: Smoky conditions on the Legion Lake Fire in Custer State Park in South Dakota, December 12, 2017. Photo by Bill Gabbert.

Originally published at 6:02 p.m. MT, February 6, 2018.

After collecting data from wildland firefighters in the field, a group of researchers concluded that firefighters’ exposure to smoke can increase the risk of mortality from lung cancer, ischemic heart disease, and cardiovascular disease. In this first section we cover what is in vegetation fire smoke, and after that we have details about the additional mortality risk faced by firefighters who can’t help but breathe the toxic substances.

What is in the air that firefighters breathe?

There have been many studies about smoke dating back to the 1988 NIOSH project at the fires in Yellowstone National Park. Most of them confirmed that yes, wildland firefighters ARE exposed to smoke and in most cases they quantified the amount.

In 2004 Timothy E. Reinhardt and Roger D. Ottmar  found a witches’ brew of methyl ethyl bad stuff that firefighters are breathing. All of these are hazardous to your health:

  • Aldehydes (volatile organic compounds); can cause immediate irritation of the eyes, nose, and throat, and inhalation can cause inflammation of the lungs. Short-term effects include cough, shortness of breath, and chest pain. The most abundant aldehyde in smoke is formaldehyde. When formaldehyde enters the body, it is converted to formic acid, which also is toxic.
  • Sulfur dioxide (SO²); causes severe irritation of the eyes, skin, upper respiratory tract, and mucous membranes, and also can cause bronchoconstriction. It forms sulfuric acid in the presence of water vapor and has been shown to damage the airways of humans.
  • Carbon monoxide (CO); As CO is inhaled it displaces O2 as it attaches to red blood cells and forms COHb. COHb reduces the ability of the blood to carry oxygen and causes hypoxia (a condition in which the body does not receive sufficient oxygen). Due to their strenuous work, wildland firefighters often have increased respiratory rates, which will increase the amount of CO being inhaled when smoke is present. COHb has a half-life (the time it takes half of the COHb to dissipate from the body) of about 5 hours. Symptoms of CO exposure include headaches, dizziness, nausea, loss of mental acuity, and fatigue. Prolonged, high exposure can cause confusion and loss of consciousness
  • Particulate matter; Respirable particulates are a major concern as they can be inhaled into the deeper recesses of the lungs, the alveolar region. These particles carry absorbed and condensed toxicants into the lungs
  • Acrolein; may increase the possibility of respiratory infections. It can cause irritation of the nose, throat, and lungs. Long-term effects can include chronic respiratory irritation and permanent loss of lung function if exposure occurs over many years.
  • Benzene; can cause headaches, dizziness, nausea, confusion, and respiratory tract irritation. Although the human body can often recover and repair damage caused by irritants, prolonged exposure from extended work shifts and poorly ventilated fire camps can overwhelm the ability to repair damage to genes and deoxyribonucleic acid (DNA).
  • Crystalline silica; can cause silicosis, a noncancerous lung disease that affects lung function. But OSHA classifies it as a carcinogen.
  • Intermediate chemicals; have been shown to cause a variety of health problems including bronchopulmonary carcinogenesis, fibrogenesis, pulmonary injury, respiratory distress, chronic obstructive pulmonary disease (COPD), and inflammation.

One of the more recent research efforts, from 2009 to 2012, was led by George Broyles of the U.S. Forest Service, National Technology and Development Program, in Boise, Idaho. They collected data in 11 fuel models in 17 states on initial attack, prescribed burns, and large project fires. The group measured carbon monoxide (CO) with electronic datalogging dosimeters and particulate matter using air pumps and filters.

carbon monoxide exposure firefighters
Data from the 2009-2012 wildland firefighter study led by George Broyles. “TWA” stands for Time Weighted Average. CO is carbon monoxide. OEL is Occupational Exposure Limits.

Monitoring carbon monoxide (CO) can be important, and is also fairly easy to do and not terribly expensive. Researchers have found that it can be a surrogate for the primary irritants of concern in wildland smoke near the combustion source. If CO is present, it’s almost certain that the smorgasbord of nasty stuff is in the air.

wildfire smoke monitoring firefighters
Jon Richert displays the various devices the National Technology Development Center research crews use to measure the amount of smoke firefighters deal with during wildfire suppression. This equipment was used in 2016 in a different but similar study than the one described in this article.
Diffusion tube
Diffusion tube.

Electronic CO monitors are available for $100 to $300. Another option is the little disposable CO monitors called diffusion tubes. With the holder they are about the size of a dry erase marker. Many are made by Drager, and for eight hours can record the cumulative CO. You can’t get an instantaneous reading, but the total hourly exposure can be monitored. They cost about $13 each. If one or two people on the crew carry them it can provide a heads up if the air quality is really bad.

What are the health effects of smoke exposure on a wildland fire?

Employers in most if not all workplaces are required to minimize hazards and provide a safe working environment. But of course it is impossible to totally eliminate all risks to firefighters. A cynic might assume that leadership in the wildland fire community may be hesitant to ask the question if they don’t want to hear the answer.

In spite of numerous studies confirming that yes, there is smoke where wildland firefighters work, there has been little in the literature that quantifies the effects on a person’s health. A new study published in August, 2017 contains a preliminary analysis addressing that question.

It is titled Wildland Fire Smoke Health Effects on Wildland Firefighters and the Public – Final Report to the Joint Fire Science Program. The authors are Joe Domitrovich, George Broyles, Roger D. Ottmar, Timothy E. Reinhardt, Luke P. Naeher, Michael T. Kleinman, Kathleen M. Navarro, Christopher E. Mackay, and Olorunfemi Adetona.

They used the field data collected in the 2009 to 2012 George Broyles study to extrapolate the physical and health effects on humans. The authors actually came up with numbers that indicate firefighters’ relative mortality risk for lung cancer, ischemic heart disease, and cardiovascular disease.
Continue reading “Study shows firefighters’ exposure to smoke increases disease risk”

Fire Narratives: Are Any Accurate?

We may not know as much as we think we know about wildfires in the Wildland-Urban Interface

This article by Sarah McCaffrey, a Research Forester with the U.S. Forest Service, first appeared at Fire Adapted Communities Learning Network.


How you tell a story influences what conclusions people draw from it (think Aesop’s Fables). Over the past decade, the overarching American wildfire narrative has become fairly focused on three dynamics: fuels buildup due to suppression, climate change, and the expanding wildland-urban interface (WUI). But what are these narratives based on?

There is a fair bit of research and debate as to when and where fuel overloading and climate change will have the most influence, in fact too much to be easily citable here. However, according to research for a paper that I’m developing with Matt Thompson of the Rocky Mountain Research Station and Courtney Schultz of Colorado State University, few data support the WUI story. Specifically, only limited data support the arguments for why and how the WUI is contributing to the wildfire problem.

For instance, a commonly cited concern is that 50–95 percent of wildfire suppression costs can be attributed to the protection of private property in the WUI. However, when our team followed the citations for this statement, we found that they all led back to data from a single 2006 Office of Inspector General (OIG) report (PDF, 1.57 MB). Further, the report reached that particular conclusion using data that most social scientists would find problematic at best. Stay tuned for my team’s paper to learn more about that report’s limitations.* We have found a few studies that examine the breakdown of suppression costs in a more rigorous manner, using meaningful metrics (e.g., the number of homes near the fire perimeter and the percent of private land). But, while they do find a positive association between homes being located in the WUI and suppression costs, none demonstrate causality or conclude that the costs of protecting private property come close to the low end of OIG’s estimates. Nor can we find any study that tracks changes in the WUI with changes in suppression costs over time, even though a key perceived “problem” with the WUI is that its expansion will automatically increase wildfire suppression costs.

Similarly, although it is often stated that wildfire-related housing loss is increasing, it is hard to find any data that support or deny this claim, as wildfire-related housing loss hasn’t been tracked consistently until fairly recently. Further, even the existing data are problematic. For instance, the National Interagency Coordination Center (NICC) claims that 2,638 homes were lost nationally in 2015 (see page 9 of this NICC report, PDF, 830 KB); while CAL FIRE reports that 3,217 homes were destroyed in California alone that same year (see page 10 of this CAL FIRE report, PDF, 1.28 MB). Further, while it is too short of a time span to draw any solid conclusions, it is worth noting that both datasets suggest that higher losses are periodic and due to specific wildfire events. For example, the graph below, which I developed using NICC annual summary reports, illustrates that when excluding the state that lost the most residences in a given year — say Tennessee in 2016, the year of the Gatlinburg fires — home loss (shown in green) is relatively flat.

wildfire structure loss

Inaccurate Stories Are Unlikely to Lead to Effective Solutions
Accepting WUI narratives that lack sufficient supporting data can lead to developing solutions that are less likely to have the desired impact, because they may be targeting the wrong problem. Further, these proposed solutions may have unintended consequences because they don’t take existing data, or lack thereof, or the larger context into account. For instance, a common recommendation based on the WUI narrative is to limit development in fire-prone areas. However, while we do have fairly robust science concerning factors that make an individual home more fire resistant, we don’t have much information on what type of larger scale development is associated with improved wildfire outcomes. There are only a few relevant studies, and they offer conflicting “solutions.” For example, some studies suggest clustered housing would help with decreasing suppression costs, but others suggest clustered housing would lead to more losses.

Another common recommendation based on the WUI narrative is to form a national fire-insurance program similar to the National Flood Insurance Program, which appears to be seen as a means of ensuring that WUI residents bear the cost of living there. This recommendation ignores the significant evidence concluding that the National Flood Insurance Program has done little to shift the cost burden from federal taxpayers (and in fact has probably increased it) or to limit housing development in flood-prone areas. This argument also seems to assume that if individuals can’t obtain or afford insurance, then they will choose to not live in the WUI. However, there is no evidence that this is the case. It’s just as likely that individuals will continue to live there for a variety of reasons (e.g., amenities, affordability in other regards) and just take their chances, essentially making those with fewer resources even more vulnerable.

Further, insurance levers can raise an equity consideration: if insurance did have the desired effect, it is likely that only the wealthy would be able to live in the WUI since only they could afford to pay higher insurance premiums or to self-insure. It is worth asking whether that is an acceptable tradeoff.

Shifting Our Language
Through this process, I have begun to question whether the WUI is still a useful construct. While it may have been useful at one point to draw attention to the increasing intermingling of housing and natural vegetation, it now seems to create an artificial distinction that may be misleading. I doubt many of those who lost their homes in the recent California wildfires, particularly in Santa Rosa, thought of themselves as living in the WUI. Further, a preliminary analysis by the University of Wisconsin shows that regarding the Tubbs Fire, many of the losses were not technically in the WUI. Instead, the largest portions of homes lost were in areas considered either too dense or not dense enough to be classified as the WUI. Forest Schafer’s recent blog post about how Lake Tahoe partners are rethinking their WUI is another example of the limitations of drawing artificial lines when assessing wildfire risk.

And then there is the question of how limiting development in the WUI would work. Beyond equity issues and the fact that we don’t have strong evidence regarding what “better” land-use planning for wildfire looks like, I always wonder, “So, where are people supposed to live then?” As one recent newspaper headline stated: “All Californians Live in Fire Country Now.” Perhaps just thinking about how we can best live in fire-prone landscapes may be a more useful way to frame the discussion, rather than creating artificial distinctions based on housing density and natural vegetation.

*This blog describes initial findings from a paper that Courtney, Matt and I are working on. The articles referenced in this blog post will be identified in that paper, which will be available on Treesearch once it is published.

Sarah McCaffrey
Photo credit: Sarah McCaffrey

Sarah McCaffrey, Ph.D., is a research forester for the USDA Forest Service, Rocky Mountain Research Station. Her research focuses on the social aspects of fire management. This work has included projects examining wildfire risk perception, social acceptability of prescribed fire and thinning, characteristics of effective communication programs, and incentives for the creation and maintenance of defensible space. She has also initiated work examining social issues that occur during and after wildfires, including evacuation-decision making, agency-community interactions during fires, public perception of wildfire management overall, views on the Cohesive Strategy, and perceptions about what it means to be a fire adapted community. She received her Ph.D. in Wildland Resource Science in 2002 from the University of California at Berkeley.

Study concludes wildfire smoke causes lower infant birth weight

An economics researcher found that infants’ proximity to smoke pollution while in utero affects birth weight.

Above: Whitetail Fire in South Dakota

(Originally published at 6:17 p.m. MST January 22, 2018)

When researchers seek to determine a single or primary cause for a human health problem, they know they’re battling uphill. Our environments are complex, multifaceted, and permeated by a seemingly infinite number of factors that could shape us. Rare is the circumstance that is so ideal, at least from a researcher’s perspective, that one can sift through the noise and emerge with a definitive root of an issue.

That is, of course, unless nature is on your side — as was the case for UNLV economics professor Shawn McCoy and his University of Pittsburgh economics colleague Xiaoxi Zhao.

It’s hard to imagine anything positive coming out of wildfires. They’ve become six times more likely to occur and four times as large since the 1980s, McCoy said, due to climate and population changes. And yet for his research, which demonstrates that proximity to smoke pollution causes lower infant birthweight, wildfires proved to be a sort of equalizer.

“Wildfires are a meaningful topic to research in and of themselves, but they also help solve this causality problem that is difficult in our studies of pollution,” McCoy said. “Two features make fire pollution different from that of, say, an industrial plant: the random timing of fires and their random location, in that wind patterns on any given day drive the direction and concentration of smoke. This sets up a quasi-experimental research design wherein a fire happens randomly and by chance and randomly and naturally assigns treatment and control groups, because only a certain segment of the population will be exposed to the smoke.”

Several studies have established correlations between pollution sources and negative public health outcomes, McCoy said. However, prior research has faced difficulties demonstrating a direct causal relationship. One reason for this, according to McCoy, is the number of factors that could be involved in past research scenarios.

“Suppose we build an industrial plant,” McCoy said. “Once that plant is built, we need to think about the economics of that problem, which is that people don’t like to live next to plants. Holding everything else constant, home prices will drop in the surrounding area because of that, which could induce geographical sorting, wherein households with lower income might migrate into the areas surrounding the plant and households with higher incomes may leave. When that happens, it becomes harder to determine if changes in health outcomes occurred because of plant pollution, geographical sorting dynamics, or even something else.”

The random timing and location of wildfires mitigate these dynamics, making it ideal for McCoy and Zhao’s research. Wildfire smoke is similar to other sources of ambient air pollution; its particulate matter can be so small that it passes through the heart and lungs, disrupts fetal nutrition, and slows fetal growth. Within this framework, birthweight becomes a useful metric to track because of its link to short-term outcomes, such as one-year mortality rates, as well as long-term outcomes such as educational attainment and earnings, McCoy said.

McCoy and Zhao leveraged geographic information systems (mapping software) to identify ignition sources and smoke paths and plotted the home addresses of infants born during a time that would place them in the smoke’s path while in utero. They then compared the birthweight of those infants to a control group outside of the smoke’s path.

The researchers’ results indicate that wildfire smoke leads to a 4 to 6 percent reduction in birthweight, and these effects are most pronounced among mothers exposed to smoke during the second or the third trimesters of pregnancy. They also found that these effects attenuate (or diminish) with respect to distance to a wildfire, becoming ineffectual three miles and further from the burn source. In contrast, the researchers found that even if infants had been close to a wildfire while in utero, there was no statistically significant effect on their birthweight if they were outside the smoke’s path.

“One really neat thing about this research is that I can do more than tell you what the effect of being exposed to the smoke is or not,” McCoy said. “I can tell you how that effect varies based on where an infant is relative to the source of pollution. Beyond that, we now have the evidence that reinforces earlier findings on the effects of ambient pollution at large and can say that these effects are very likely real, not just loosely correlated or tied up with other economic issues like household migration dynamics.”

McCoy’s hope is that this research will help inform policymakers of the potential economic and health consequences of wildfires, the magnitude of this type of disaster, and the mechanism behind wildfires — all of which enable people to better target the problem.

“There’s a lot of evidence to suggest that homeowners don’t fully acknowledge the risks associated with natural disasters — in particular, the risks associated with wildfire,” McCoy said. “One way to address this problem is to inform the public of risks through information-based regulation, such as posting billboards of people standing on cars during floods to discourage them from attempting to drive through inundated areas in the future. The idea is, if you give people this information, it can affect how they evaluate disaster risks, and it will likely have a spillover effect in terms of how they manage those risks.” That being said, McCoy noted that a one-time exposure to this type of information likely won’t be enough to have a lasting impact, so regulators should share this type of messaging often.

McCoy and Zhao’s research findings have been detailed in their article “Wildfire and Infant Health: A Geo-Spatial Approach to Estimating the Health Impacts of Ambient Air Pollution and In-Utero Stress,” currently under review by a top industry journal.


Source: provided by University of Nevada, Las Vegas (UNLV). Original written by Sara Gorgon. University of Nevada, Las Vegas (UNLV). “Exposure to wildfire smoke in utero lowers birthweight.” ScienceDaily. ScienceDaily, 6 December 2017.

How does tree mortality caused by drought and insects affect forests accustomed to frequent fire?

Research results were published January 17, 2018

This week a group of nine scientists and researchers published the results of their work considering how unusually high tree mortality affects wildfires in California’s Sierra Nevada forests that over thousands of years have adapted to frequent fire. They point out that fire suppression-caused forest densification has increased competition among trees for water and other resources, destabilizing many frequent fire forests by making them prone to mortality from other agents such as bark beetles.

Authors

Scott L. Stephens, Brandon M. Collins, Christopher J. Fettig, Mark A. Finney, Chad M. Hoffman, Eric E. Knapp, Malcolm P. North, Hugh Safford, Rebecca B. Wayman

The abstract and conclusions are below. The entire paper can be accessed at BioScience. The illustrations are from the document.


Abstract

Massive tree mortality has occurred rapidly in frequent-fire-adapted forests of the Sierra Nevada, California. This mortality is a product of acute drought compounded by the long-established removal of a key ecosystem process: frequent, low- to moderate-intensity fire. The recent tree mortality has many implications for the future of these forests and the ecological goods and services they provide to society. Future wildfire hazard following this mortality can be generally characterized by decreased crown fire potential and increased surface fire intensity in the short to intermediate term. The scale of present tree mortality is so large that greater potential for “mass fire” exists in the coming decades, driven by the amount and continuity of dry, combustible, large woody material that could produce large, severe fires. For long-term adaptation to climate change, we highlight the importance of moving beyond triage of dead and dying trees to making “green” (live) forests more resilient.

Fire Responses Post Drought Beetle
A conceptual diagram showing fuel load and expected fire behavior in a mixed-conifer forest prior to and following a major bark-beetle-caused tree-mortality episode, with either (a) no follow-up-fuels treatment or (b) periodic prescribed fire to consume fuels. Surface-fire intensity is expected to roughly follow surface fuel load, whereas crown-fire potential is regulated by the amount of surface fuel (necessary to heat and dry live fuels to the point of combustion), as well as crown bulk density.

 

Forest Responses Severe Drought
Forest responses following a severe drought (1999–2002) in the Sierra de San Pedro Mártir (SSPM), Baja California, Mexico (a, drought and bark-beetle-caused tree mortality followed by wildfire; b, drought- and bark-beetle-caused tree mortality only) and in the southern California mountains (SCM), California, United States (c, drought- and bark-beetle-caused tree mortality at larger scales; d, drought and bark-beetle-caused tree mortality at stand scale. Note no wildfire in either SCM area). The SSPM and SCM photos were taken in 2004 and 2003, respectively. The SSPM site experienced a wildfire immediately following the multiyear drought (picture from 2003), with the photos capturing effects of both drought- and wildfire-related tree mortality. Pictures (a), (b), and (d) from SLS, (c) from G. Barley.

[…]

Conclusions

Unprecedented Sierra Nevada tree mortality has rapidly occurred after a severe drought with effects compounded by forest densification from decades of fire suppression. In the central and southern Sierra Nevada some areas have experienced more than 90% tree mortality, producing extensive landscapes of standing dead trees. This differs from mortality resulting from stand-replacing wildfire because bark beetles do not reduce surface fuels or jumpstart succession of shade-intolerant, fire-resistant pines. Forest managers have been struggling to determine whether these new postmortality conditions will increase wildfire intensity and/or severity, what the near- and long-term effects on forest communities will be, and what the appropriate intervention measures are.

In the first decade, wildfire severity in bark beetle killed frequent fire (FF) forests may be little affected over current conditions. Other than a brief increase during the “red phase” when most dead needles are still on recently killed trees, the reduction in canopy fuels is counterbalanced by an increase in surface fuels (figure 2). However, these are no grounds for complacency because current conditions in the majority of mixed-conifer and yellow pine forests in California already consist of unnaturally high surface fuel loads and corresponding elevated fire hazards (figure 2; Lydersen et al. 2014, Stephens et al. 2015).

The more troubling projection is how extensive loading of large-sized woody fuels in future decades may contribute to dangerous mass fires beyond the predictive capacity of current fire models. These fires can generate their own wind and weather conditions and create extensive spotting, making fire behavior and its impact on structures and public safety difficult to manage and predict. In addition, such intense fires could prevent forests from becoming re-established. Lacking the legacy of live trees that historic FF would have left (Stephens et al. 2008), large unburned areas of dead trees may also produce unusual forest succession patterns. These patterns will likely favor shade-tolerant and hardwood tree regeneration, limited shrub growth, and accumulating large woody fuels that would likely kill regenerating forests when wildfire inevitably occurs. The scale of contiguous tree mortality entrenches the homogeneity produced by fire suppression, reducing the fine-scale heterogeneity of forest conditions that contributes to resilience and biodiversity. Management could enhance adaptation to climate-change-induced stress if it focused more of its resources on creating spatially and temporally variable patterns in green FF forests that are better aligned with local moisture availability and fire patterns (North et al. 2009).

Many of our FF forests have failed to receive the very management that could increase resilience to disturbances exacerbated by climate change, such as the application of prescribed fire and mechanical restoration treatments (Stephens et al. 2016). Recent tree mortality raises serious questions about our willingness to address the underlying causes. If our society doesn’t like the outcomes from recent fires and extensive drought-induced tree mortality in FF forests, then we collectively need to move beyond the status quo. Working to increase the pace and scale of beneficial fire and mechanical treatments rather than focusing on continued fire suppression would be an important step forward.

More evidence of the “fireproofing effect” of insect outbreaks in a forest

Additional research finds evidence of a “fireproofing” effect on host trees from defoliation due to western spruce budworm outbreaks.

Above: Grand fir in Oregon defoliated by western spruce budworms. William M. Ciesla.

There is no dispute that severe outbreaks of western spruce budworm (WSB) and mountain pine beetle (MPB) in a forest have huge visual impacts. Many land managers have worried about more, larger wildfires and politicians have used it as an excuse for more logging.

But the commonly held belief that the effects will lead to higher intensity, more rapidly spreading wildfires has been disproven many times in the last eight years by scientists.

We first wrote about this issue in 2010 (Firefighters should calm down about beetle-killed forests) when some early research started to bring the facts to light.

The WSB and MPB attack trees very differently. The WSB defoliates the tree, consuming the needles and removing fuel from the canopy relatively quickly. The MPB kills the tree from the inside, leaving the dying “red” needles on the tree until they fall off in one to two years. The possibility of crown fires may increase during that red needle period, but it makes sense that fewer fine fuels in the canopy would reduce the fire intensity and make it less prone to transition from a ground fire to a crown fire. Both types of attacks eventually produce more course fuel on the forest floor as the branches break off and  the trees eventually fall over.

Research conducted by Daniel G. Gavin, Aquila Flower, Greg M. Cohn, Russell A. Parsons, and Emily K. Heyerdahl found evidence of a “fire proofing effect” for outbreaks of WSB. It does not address the MPB.

Below is an excerpt from their work:


“Extrapolating Results: Reduced Tree Mortality

“Taken together, the tree-ring and modeling studies suggest a lack of synergism between WSB outbreaks and wildland fires. However, a different kind of synergism may exist: Defoliation might dampen the severity of a subsequent wildfire. To explore this possibility, we used existing empirical equations that show the probability of mortality due to defoliation (fig. 3A) and the probability of mortality due to crown scorch (fig. 3B), combined with the simulated results of canopy consumption at different levels of defoliation (fig. 3C), to extrapolate the summed probability of mortality under a range of surface fire intensities and defoliation levels (fig. 3D). The results suggested a distinct “fireproofing” effect of defoliation: The increased risk of mortality by WSB is more than compensated for by reduced foliage consumption during moderate surface fire intensities. For example, trees with 50-percent defoliation have a distinctly lower probability of mortality when surface fires are less than about 74 kilowatts per square foot (800 kW/m2 ).

“However, we considered only the partial effect of defoliation on fire occurrence; we did not take into account other effects of WSB outbreaks, such as mortality of small trees. Of course, field observations are required to test our prediction. Remotely sensed burn severity maps, in combination with prior surveys of insect effects, could address this issue. One such study of the 2003 B&B Complex Fire in Oregon showed that prior defoliation had a marginal effect on reducing fire severity that was not statistically significant (Crickmore 2011). However, an analysis by Meigs and others (2016) of all post-WSB fires in Washington and Oregon from 1987 to 2011 showed that there is a statistically significant reduction in fire severity that persists for up to 20 years following an outbreak. Thus, the effect of defoliation on crown fire behavior modeled by Cohn and others (2014) appears to be confirmed by the analysis of burn severity data by Meigs and others (2016).

“Fireproofing Effect?

“It may seem reasonable to assume that extensive defoliation, causing sustained low levels of tree mortality in mature trees, should have a measurable effect on wildfire occurrence. However, fire is a highly variable disturbance in itself, and it is highly sensitive to specific climate and winds during the fire event. The scale of fuel changes wrought by WSB may be too small to affect subsequent fire probability in ecosystems where fire is limited by fuel moisture and ignition sources rather than fuel availability. Our data show that these two disturbance types do not share similar histories, despite a common link to drought events.

“Nevertheless, we hypothesize a “fireproofing” effect on host trees from defoliation due to WSB outbreaks. Although such an effect has been detected statistically from recent fire events (Preisler and others 2010; Meigs and others 2016), the inferred processes at play remain to be studied in detail at the site scale.”


UPDATE January 5, 2018: These researchers are not the only ones with similar findings on this subject. If you would like to read more, scroll through the articles on Wildfire Today tagged “beetles”.

Ponderosa pines are not adapted to high-severity fire

And this type of fire is increasingly common in the Southwest

Regenerating Ponderosa Pine
Regenerating ponderosa pine in a high-severity burn patch, 13 years after the 2000 Pumpkin Fire. (From the Fact Sheet)

The increasing size and severity of wildfires in the Western United States may have long term effects on species composition. A Fact Sheet published this month by Northern Arizona University and the U.S. Forest Service looks at ponderosa pine regeneration in patches of high-severity areas of the 2000 Pumpkin and the 2002 Rodeo-Chediski wildfires in the Southwest. Below are excerpts from the document written by Suzanne Owen, PhD student, School of Forestry, Northern Arizona University:


Introduction

Over the past three decades, wildfires in southwestern U.S. ponderosa pine (Pinus ponderosa) forests have increased in size and severity, leaving large, contiguous patches of tree mortality. Ponderosa pines evolved under fire regimes dominated by low- to moderate-severity wildfires. They are poorly adapted to regenerate in large patches of high-severity fire because they are not a sprouting species and do not have serotinous cones or long-lived soil seedbanks. Consequently, the lack of seed-producing trees in high-severity burn patches may prevent or significantly delay ponderosa pine regeneration. Previous studies have documented low ponderosa pine regeneration densities in large high-severity burn patches, but less is known about the spatial patterns of ponderosa pine regeneration and interactions with sprouting species near residual live forest edges or the interiors of high-severity burn patches.

[…]

Results

  • Ponderosa pines were re-establishing in all of our study plots, however regeneration densities were lower farther from forest edges.
  • Ponderosa pines seedlings were found in areas more than 980 feet from potential parent trees on all interior study plots.
  • Regenerating ponderosa pines displayed patterns of small-scale spatial aggregation in all plots, except one edge and one interior plot on the Pumpkin Fire, which displayed random distributions.
  • Dense resprouting trees dominated tree regeneration on the Rodeo-Chediski Fire, but did not influence the spatial location or height of regenerating ponderosa pine.
  • Regenerating ponderosa pine height was positively correlated with neighboring ponderosa pine densities and height.

Implications

  • Tree regeneration densities and species composition in high-severity burn patches are highly variable in different geographic locations.
  • Regeneration patterns suggest both short- and long-distance dispersal may play important roles in ponderosa pine regeneration in high-severity burn patches.
  • Ponderosa pine regeneration could be more strongly influenced by intraspecific facilitation than interspecific competition from dense sprouting species.
  • Future forest spatial patterns and composition are still unclear, but at this stage of development, these heterogeneous patches, characterized by drought-tolerant sprouting species or low pine densities, could be more resilient to climate change and severe wildfires than the overly dense ponderosa pine forests that were present before the wildfires.
  • Managers may want to use a “wait and see” approach before replanting in some areas to monitor natural regeneration over time.