Researchers find insect-killed forests pose no additional likelihood of wildfire

flames wildfire

Photo by Bill Gabbert

As mountain pine beetles and other insects chew their way through Western forests, forest fires might not seem far behind. Lands covered by dead trees appear ready to burst into flame.

However, an analysis of wildfire extent in Oregon and Washington over the past 30 years shows very little difference in the likelihood of fires in forests with and without insect damage. Indeed, other factors – drought, storms, and fuel accumulation from years of fire suppression – may be more important than insects in determining if fire is more or less likely from year to year.

Scientists reached this conclusion by mapping the locations of insect outbreaks and wildfires throughout Oregon and Washington beginning in 1970. Researchers discovered that the chances of fire in forests with extensive swaths of dead timber are neither higher nor lower than in forests without damage from mountain pine beetles.

The same comparison done on forests damaged by another insect – western spruce budworm – yields a different result. The chances of wildfire actually appear to be slightly lower where the budworm has defoliated and killed trees in the past. While the mechanics of such an association are unconfirmed, it’s possible that budworm outbreaks could reduce the risk of wildfire by consuming needles in the forest canopy.

“Our analysis suggests that wildfire likelihood does not increase following most insect outbreaks,” said Garrett Meigs, lead author of a paper published this week in the open-access journal Ecosphere. Meigs is a former Ph.D. student in the Oregon State University College of Forestry and now a post-doctoral researcher at the University of Vermont.

Across more than 49 million forested acres in both states, insects and fires typically affect less than 2 percent of the land in a given year. More forestland is usually disturbed by insects than by fire.

“Most forests have plenty of fuel already,” Meigs said. “Green trees burn, not always as readily as dead ones, but they burn. The effects of insects are trumped by other factors such as drought, wind and fire management.” For example, the 2002 Biscuit Fire, the region’s largest at nearly 500,000 acres, occurred in an area with little tree damage from insects.

“Even if mountain pine beetle outbreaks do alter fuels in a way that increases flammability, the windows of opportunity are too small – and fire is too rare – for those effects to manifest at landscape and regional scales.”

“In the case of the budworm, our findings suggest that there may be a natural thinning effect of insect-caused defoliation and mortality, and it is possible that insects are doing some ‘fuel reduction’ work that managers may not need to replicate,” said Meigs. That possibility needs more research, he added.

These results are consistent with other studies that have investigated the likelihood of fire across the West. For example, a 2015 study published in the Proceedings of the National Academy of Sciences by University of Colorado scientists found that despite extensive outbreaks of mountain pine beetles in the Rockies and the Cascades, fires in recent years were no more likely to occur in beetle-killed forests than in forests not affected by the insects.

Public perception may reflect our experience with starting campfires, said John Bailey, Oregon State professor of forestry and co-author of the Ecosphere paper.

“We choose dead and dry wood for kindling, not green branches,” Bailey pointed out. “A dead branch with lots of red needles is ideal. At the scale of a forest, however, the burning process is different. Wildland fire during severe weather conditions burns less discriminately across mountainsides.”

For managers of forestlands, these results suggest that emphasis needs to be put on fuel reduction, forests near communities and on preserving ecosystem services such as biodiversity and water quality. “Forests will continue to burn whether or not there was prior insect activity,” Meigs and his co-authors write, “and known drivers like fuel accumulation and vegetation stress likely will play a more important role in a warmer, potentially drier future.”

The Ecosphere paper is available at

In addition to Bailey, Meigs’ co-authors included John L. Campbell, Harold S. J. Zald, David C. Shaw and Robert E. Kennedy, all of Oregon State. Funding support was provided by the NASA Earth and Space Science Fellowship Program and the USDA Forest Service.

Articles on Wildfire Today tagged Beetles.


Radiation heat transfer once believed to dominate over convection heat transfer in wildfire spread — study reveals that’s not the case

MSO Fire Lab flame research

Researchers at the Forest Service’s Missoula Fire Sciences Laboratory study how a wildfire spreads, May 21, 2014. Photo by Bill Gabbert.

A new study about the physics of how a wildfire spreads has been completed by government employees, and thankfully it is freely available to taxpayers. A success for Open Access to the products of government-funded research!

The phrase “spreads like wildfire” is well-known but until recent discoveries through experiments conducted by scientists from the Missoula Fire Sciences Laboratory, University of Maryland and the University of Kentucky, it wasn’t well-known how wildfires actually spread. Specifically, it was unclear how radiation and convection heat transfer processes, which both occur in wildfires, are organized to produce wildfire spread. Now, evidence presented in a new study, Role of buoyant flame dynamics in wildfire spread, reveals how flame dynamics that produce and transport convective heat effectively governs the spread of wildfire.

Previous studies focused mainly on radiant heat so little was known about the respective roles of convection and radiation on fire spread and most often the assumption was made that radiant heat was the governing factor. But scientists recently found that the net rates of heat transferred by radiation are insufficient because the fine fuel particles that constitute wildland vegetation cool efficiently by convection until contacted by flame.

As stated in the study, “if radiation itself is insufficient to account for fire spread…convection must provide the explanation.” So a team of scientists, led by Mark Finney of the USDA Forest Service Rocky Mountain Research Station, began looking at flame dynamics.

Utilizing specialized burn chambers and wind tunnels at the Missoula Fire Sciences Lab and the University of Maryland, scientists were able to assimilate and measure flame dynamics. They found this process can correctly scale up to those found in large-scale wildfires. They also conducted outdoor experiments and prescribed fires at Camp Swift, TX. The experiments led to the discovery of previously unrecognized flame behaviors and how those behaviors cause wildfires to spread. They also discovered that flame vorticity (circulations) and instabilities due to the buoyancy of flame gasses, cause wildfires to spread by forcing flames downward into the fuel bed and bursting forward ahead of the fire into fresh fuel (grass, brush, etc.).

“This study opens the door into the little known world of flame dynamics and gets us closer to understanding the complexities of radiative and convective heat and how they affect wildfire spread,” said Finney. The information obtained through this research is significant with the potential to:

  • Improve firefighter safety by providing better training to recognize and anticipate wildfire behavior
  • Simplify the physical principles of wildfire spread that can lead to the development of improved prediction models, and,
  • Improve the ability to mitigate fuel hazards by accurately modeling and describing fuel contribution to wildfires

The team of ten scientists who contributed to this study comes from the USDA Forest Service Rocky Mountain Research Station’s Missoula Fire Sciences Lab – lead scientist Mark Finney, Ph.D., the University of Maryland’s Department of Fire Protection Engineering – lead scientist Michael Gollner, Ph.D., and the University of Kentucky’s Department of Mechanical Engineering – lead scientist Kozo Saito, Ph.D.

Six brief videos supporting the research are available, but you have to download them onto your device in order to view them.

The study is available as a free .pdf download at WildfireToday/Documents.


Researchers determine that fire seasons are becoming longer

Fire Season Length

We keep hearing that wildfire seasons are becoming longer. One way to verify this for a particular location is by analyzing times of the year that fires occur and the acres burned by date. But researchers have provided more information for the longer fire season discussion by studying weather across planet Earth. They used the data for a 34-year period, from 1979 to 2013, to calculate the U.S. Burning Index, the Canadian Fire Weather Index, and the Australian (or McArthur) Forest Fire Danger Index. They normalized the daily fire danger indices to a common scale and resampled to a common resolution.

What the researchers found was that fire seasons have lengthened across 29.6 million km2 (25.3%) of the Earth’s vegetated surface, resulting in an 18.7% increase in global mean fire season length. They also show a doubling (108.1% increase) of global burnable area affected by long fire seasons.

There were no significant trends in mean annual total precipitation or total precipitation affected area but they did observe a significant increase in mean annual rain-free days, where the mean number of dry days increased by 1.31 days per decade and the global area affected by anomalously dry years significantly increased by 1.6% per decade.

Global Mean Rain-free Days


Scientists study how, why butterflies survive fires

adult Frosted Alfin Butterfly

An adult frosted alfin butterfly

GAINESVILLE, Fla. — Deciding how often and when to use prescribed fire can be tricky, especially when managing for rare butterflies, University of Florida scientists say.

That realization stems from a UF Institute of Food and Agricultural study in which researchers experimented with pupae — insects in their immature form between larvae and adults — of butterflies known to frequent fire-prone habitats of Florida.

Prescribed burns and wildfires can damage animals and plants in their paths. But they can also promote species and create habitat, maintaining the ecological balance of the forest and the region’s most frequent natural disturbance over the long term. Immature butterflies may die immediately following controlled burns, but populations can recover over time, with the amount of time depending on the species.

Scientists are concerned that butterflies with small, isolated populations may be in severe peril if their habitats are burned too frequently and in large blocks at a time, which can mean that butterfly refugia – unburned areas that provide refuge — are limited.

In the UF/IFAS study, scientists wanted to know how and why some butterflies survive wildfires and prescribed burns, particularly where the insect feeds and lays eggs on fire-adapted plants.

Prescribed fire, butterfly research

Prescribed fire for butterfly research

To date, most studies on the impact of fires on insects have been done in the Midwest, said Jaret Daniels, a UF/IFAS associate professor in entomology, who supervised the study as part of a dissertation by former UF doctoral student Matt Thom.

“We are increasingly faced with developing appropriate strategies to help conserve a growing list of rare organisms, including many insects,” Daniels said. “Understanding how prescribed fire and other land- management techniques impact these populations is critical to ensure their long-term survival.”

Thom also worked on the study with Leda Kobziar, a UF/IFAS associate professor in forest resources and conservation. The study appeared online May 27 in the journal PLOS ONE.

“Although we have a fairly robust understanding of how fire affects plant communities, the relationships between fire and insects is a greater mystery,” Kobziar said. “How is it that some organisms sensitive to fire also depend on specific plants that require fire to persist in a given environment? This research helps provide answers to this question, while revealing how much more we need to know to conserve the full spectrum of species through science-based fire management.”

To find out how and why some butterfly species survive fires, UF/IFAS scientists tested pupae in two North Florida forests that are typically managed with prescribed burns. Thom and his colleagues studied atala hairstreak and frosted elfin, two butterfly species that frequent fire-prone habitats.

Researchers collected data on burial depth of the frosted elfin at the Ralph E. Simmons Memorial State Forest in Nassau County. They conducted burn experiments with the atala hairstreak at the UF/IFAS Ordway Swisher Biological Station in Putnam County. They also put the pupae in laboratory baths at the UF Gainesville campus.

The atala hairstreak butterflies develop into pupae within or at the base of its host plant, while the frosted elfin sometimes goes down into the soil to pupate, Thom said.

In the experiment, scientists placed atala pupae at the soil surface and at different depths. The pupae died at the soil surface and in very shallow depths below ground, Thom said. However, when buried at 1.1 inch or more below ground, butterflies survived 75 percent to 100 percent of the time, as the temperature and the amount of heat they were exposed to decreased, Thom said. Scientists saw a similar pattern in their lab experiments.

“Butterfly pupae that bury themselves deep enough in the soil can protect themselves from fire,” said Thom.

But there are important caveats.

For example, if a non-adult atala lives in an area that’s burned, it will probably die, said Thom, now a post-doctoral scientist with the Agricultural Research Service of the U.S. Department of Agriculture. The situation also isn’t very promising for the frosted elfin. But there’s hope.

“The patchiness of fires increases where fires occur more frequently, because there’s less leaf litter.  “Less material burning translates to decreased heating of the soil,” Thom said.  “A more patchy fire probably means pupae on the ground have a better chance for survival, and there are more refugia for escaping adults.”


Photos credit: Matt Thom, Agricultural Research Service of the U.S. Department of Agriculture and former UF/IFAS doctoral student.


Historic fire frequency, 1650 to 1850

map historic wildfire frequency

The map (click on it to see a larger version) represents the estimated wildfire frequency for the period 1650-1850, according to research by Daniel Dey, Richard Guyette, and Michael Stambaugh.

Their description of the project:

Knowledge of historic fire frequency is important in guiding restoration of fire dependent ecosystems, but it is often missing or cannot be determined locally due to lack of fire-scar tree records. A Northern Research Station scientist and collaborators have developed a new model called PC2FM that predicts historic fire frequency for the continental United States. The model uses mean maximum temperature, precipitation, their interaction, and estimated reactant concentrations to estimate mean fire intervals. Having science-based estimates of historic fire frequencies for specific project areas is a major advancement in ecosystem restoration. Another important use of the model is in assessing potential changes in climate (temperature and moisture) on the likelihood of wildland fires. The PC2FM model can be used to map large-scale historic fire frequency and assess climate impact on landscape-scale fire regimes.

UPDATE June 5, 2015:

One of the comments from a reader what that they would like to have a poster-sized print of the image. If you go to Fine Art America you can order prints starting at $17, ranging in size from 8″ x 6″ up to 60″ x 44″. Frames are optional for an extra charge. The map can also be printed on cell phone cases, greeting cards, duvet covers, and throw pillows.


Colorado to use new system to predict wildland fire behavior

Janice Coen Gov. John Hickenlooper sign bill

Gov. John Hickenlooper traveled to an Arvada fire station to sign the bill that will implement a wildfire prediction system. Dr. Janice Coen, one of the developers of the system, is on the left. Photo provided by COHOUSEDEMS.

The Governor of Colorado signed a bill Wednesday that authorizes the state to spend $1.2 million over the next two years on a “revolutionary” wildfire prediction system that uses weather data, groundbreaking computer modeling, and high resolution satellite imagery to predict the spread of fires up to 18 hours in advance.

Below is an excerpt from an article at the (Colorado Springs) Gazette:

…”This bill will predict the intensity and the direction of fires 12 to 18 hours ahead of time. That is really important so we know where to direct our planes, the aircraft we had a bill for last year, and our firefighters,” said Rep. Tracy Kraft-Tharp, D-Arvada, who introduced the bill. “This is really revolutionary.”

Under the new law, the Division of Fire Prevention and Control will contract with a nonprofit Colorado-based research organization with expertise in atmospheric science to predict wildfire behavior. The National Center for Atmospheric Research, a federally funded program headquartered in Boulder, is the only state agency that meets that criteria. NCAR has used modeling to accurately recreate the behavior of historic fires, including the Yarnell Hill fire that killed 19 Arizona firefighters in 2013.

She said the new technology could be in place by next spring and will work with the state’s new aerial fire fleet, a multimillion-dollar investment into wildfire detecting and fighting aircraft lawmakers made in 2013…

Janice Coen at the National Center for Atmospheric Research is one of the scientists working on this program. We have written about her work previously:

Thanks and a tip of the hat go out to Barbara.