Do California’s beetle-killed trees constitute an emergency?

Western Pine BeetleSome of the forests in California are experiencing a natural phenomenon that other areas in the Rocky Mountains, the Pacific Northwest, and British Columbia have been dealing with for years. Pine beetles, in this case Western Pine Beetles (WPB), are attacking and killing millions of trees. These things run in cycles and in this case the extended severe drought in the state has stressed the trees making it more difficult for them to fend off insects.

Politicians, residents, and even some individuals in fire organizations look at the hillsides with numerous dead or dying trees and intuitively think — dead vegetation — increased wildfire hazard.

Here are examples from the California Department of Forestry and Fire Protection (CAL FIRE):

From a 2015 news release:

These dead and dying trees create an environment more readily susceptible to dangerous and destructive wildfires.

In a video on YouTube the narrator says when referring to a beetle-attacked stand of trees:

…an increase in extremely flammable vegetation which could lead to larger, more intense and damaging wildfires.

SFGate quoted spokesperson Daniel Berlant:

“No level of rain is going to bring the dead trees back,” Berlant said. “We’re talking trees that are decades old that are now dead. Those larger trees are going to burn a lot hotter and a lot faster. We’re talking huge trees in mass quantity surrounding homes.”

A phone call to Mr. Berlant was not returned.

Those warnings are not 100 percent accurate. In increasing numbers, scientists are determining that generally, insect damage reduces burn severity. In one of the more recent studies, researchers from the University of Vermont and Oregon State University investigated 81 Pacific Northwest fires that burned in areas affected by infestations of two prevalent bark beetle and defoliator species, mountain pine beetle (Dendroctonus ponderosae) and western spruce budworm (Choristoneura freemani). The fires spanned the years 1987 to 2011.

Pine trees killed by bark beetles
Pine trees killed by bark beetles. Photo by Ethan Miller.

Few of the 81 fires occurred in forests while the needles were still on the trees in the red highly flammable stage of the outbreak shortly after the trees were killed by mountain pine beetles, so more research is needed about this phase. Aside from the one to two year red stage, the burn severity decreased for more than 20 years following a MPB attack. 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. This data was derived from fire behavior and data on actual fires, not laboratory experiments.

We contacted one of the researchers that conducted the study in the Pacific Northwest, Garrett Meigs, a Postdoctoral Research Associate at the University of Vermont, and asked him if their conclusions about reduced fire severity following a Mountain Pine Beetle attack in the Northwest could be compared to California’s situation — a drought combined with a Western Pine Beetle attack:

I am aware of the impressive amount of tree mortality in California but have not seen it with my own eyes. As such, I am hesitant to comment on the current conditions in California forests, which are beyond the scope of our recent studies in Oregon and Washington. My understanding is that most of the dying/dead trees are ponderosa pines, which have been affected by intensive drought and the western bark beetle (whereas in the PNW, we studied lodgepole pines affected by mountain pine beetle and mixed-conifers affected by western spruce budworm).

Another thing that is a bit different in California is that many of these forests are generally closer to large human populations, so there are more human values/resources at risk…and these forests at the wildland-urban interface have elevated fuel/fire hazard with or without dead trees (whether caused by insects or drought).

Regarding your specific questions, I would expect that fire behavior and effects would be similar in forests with similar amounts of dead trees, whether the tree mortality was caused by bark beetles or drought (or some combination).

This does not mean that residents near insect-damaged forests can ignore the dead trees. There is legitimate cause to be concerned about fires during the one or two year red needle stage after a pine beetle attack when fire intensity may be temporarily increased, although more research studying actual fires is needed in this area. And there is danger from falling snags (dead trees) 5 to 20 years after an attack. Snags are dangerous for firefighters and any structures, hikers, traffic on roads, and any improvements that could be damaged by the falling trees.

In a fire prone environment, residents should remove any dead vegetation within 100 feet of structures. If there are numerous trees near homes, thinning them so that the crowns are at least 10 feet apart will not only reduce the intensity of an approaching wildfire, but will make more water and nutrients available to the remaining trees, giving the them a better chance of fighting off an insect attack.

More research confirms insect damage reduces wildfire severity

pine beetle damageAdditional research about the effects of insect outbreaks on fires confirms that generally, insect damage reduces burn severity.

Researchers from the University of Vermont and Oregon State University studied 81 Pacific Northwest fires that burned in areas affected by infestations of two prevalent bark beetle and defoliator species, mountain pine beetle (Dendroctonus ponderosae) and western spruce budworm (Choristoneura freemani). The fires spanned the years 1987 to 2011.

Insect fire severity

Few of the 81 fires occurred in forests while the needles were still on the trees in the red highly flammable stage of the outbreak shortly after the trees were killed by mountain pine beetles. The researchers recommend more studies in this area.

Aside from the transient red stage the burn severity decreased for more than 20 years following a MPB attack. Forests affected by western spruce budworm (WSB) exhibited a sharp decrease in fire severity immediately after an attack. This decrease is likely due to the fact that the WSB defoliates the tree, removing fuel from the canopy. The MPB kills the tree from the inside, leaving the dying needles on the tree until they fall off in one to two years. 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. But in the WSB-affected forests, the fire intensity slowly increased after 20 years to a neutral condition, then continued to increase in the 5 to 10 subsequent years. The researchers elaborated on that effect:

The relatively rapid increase of the budworm-fire coefficient with time indicates that the thinning effect on fuel profiles is less persistent for the defoliator (WSB) than for the bark beetle (MPB). In addition to relatively lower per-unit-area tree mortality impacts, WSB affects host forests that are more productive than those affected by MPB in the study region , leading to more rapid accumulation of live overstory and understory vegetation. Thus, as time elapses following WSB outbreaks, fuel density and connectivity likely increase in multiple strata, including dead surface fuels and total live biomass, the latter of which is associated with higher burn severity.

The research was conducted by Garrett W. Meigs, Harold S. J. Zald, John L. Campbell, William S. Keeton, and Robert E. Kennedy. The paper is titled, Do insect outbreaks reduce the severity of subsequent forest fires?


Our analysis

There is legitimate cause to be concerned about fires during the one or two year red needle stage after an insect attack, although I think more research studying actual fires is needed in this area. And there is danger from falling snags 5 to 20 years after an attack. Snags are dangerous for firefighters and any structures, hikers, traffic on roads, and any improvements that could be damaged by the falling trees. But as numerous researchers have found, after the needles are on the ground fire behavior, intensity, and severity decrease.

We first wrote about a post-attack decrease in burn intensity in a 2010 article titled Firefighters should calm down about beetle-killed forests.

Rather than panicking and rushing out to cut every tree affected by insects, preventive measures to keep forests healthy could be more effective, such as prescribed fire and thinning.

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 http://dx.doi.org/10.1890/ES15-00037.1.

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.

More science indicates pine beetle outbreaks do not lead to catastrophic fire

mountain pine beetle
Mountain pine beetle

Scientists continue to develop evidence showing that pine beetle outbreaks do not lead to catastrophic wildfires. This should not be a shocking development to those who have been keeping abreast of the studies on the subject, including one that Wildfire Today first covered in 2010 (Firefighters should calm down about beetle-killed forests).

In a soon to be published paper, University of Colorado Boulder researcher Sarah Hart determined, “The bottom line is that forests infested by the mountain pine beetle are not more likely to burn at a regional scale. We found that alterations in the forest infested by the mountain pine beetle are not as important in fires as overriding drivers like climate and topography.”

The CU-Boulder study authors looked at the three peak years of Western wildfires since 2002, using maps produced by federal land management agencies. The researchers superimposed maps of areas burned in the West in 2006, 2007 and 2012 on maps of areas identified as infested by mountain pine beetles.

Western U.S. forests killed by the mountain pine beetle epidemic are no more at risk to burn than healthy Western forests, she found. Results that fly in the face of both public perception and policy.

The area of forests burned during those three years combined were responsible for 46 percent of the total area burned in the West from 2002 to 2013.

Co-authors on the new study include CU-Boulder Research Scientist Tania Schoennagel of the Institute of Arctic and Alpine Research, CU-Boulder geography Professor Thomas Veblen and CU-Boulder doctoral student Teresa Chapman.

Sarah Hart CU Boulder
Sarah Hart

The impetus for the study was in part the severe and extensive native bark beetle outbreaks in response to warming temperatures and drought over the past 15 years that have caused dramatic tree mortality from Alaska to the American Southwest, said Hart. Mountain pine beetles killed more than 24,700 square miles of forest across the Western U.S. in that time period, an area nearly as large as Lake Superior.

“The question was still out there about whether bark beetle outbreaks really have affected subsequent fires,” Hart said. “We wanted to take a broad-scale, top-down approach and look at all of the fires across the Western U.S. and see the emergent effects of bark beetle kill on fires.”

Previous studies examining the effect of bark beetles on wildfire activity have been much smaller in scale, assessing the impact of the insects on one or only a few fires, said Hart. This is the first study to look at trends from multiple years across the entire Western U.S. While several of the small studies indicated bark beetle activity was not a significant factor, some computer modeling studies conclude the opposite.

The CU-Boulder team used ground, airplane and satellite data from the U.S. Forest Service and the U.S. Geological Survey to produce maps of both beetle infestation and the extent of wildfire burns across the West.

The two factors that appear to play the most important roles in larger Western forest fires include climate change — temperatures in the West have risen by about 2 degrees Fahrenheit since 1970 as a result of increasing greenhouse gases — and a prolonged Western drought, which has been ongoing since 2002.

“What we are seeing in this study is that at broad scales, fire does not necessarily follow mountain pine beetles,” said Schoennagel. “It’s well known, however, that fire does follow drought.”

The 2014 Farm Bill allocated $200 million to reduce the risk of insect outbreak, disease and subsequent wildfire across roughly 70,000 square miles of National Forest land in the West, said Hart. “We believe the government needs to be smart about how these funds are spent based on what the science is telling us,” she said. “If the money is spent on increasing the safety of firefighters, for example, or protecting homes at risk of burning from forest fires, we think that makes sense.”

Firefighting in forests that have been killed by mountain pine beetles will continue to be a big challenge, said Schoennagel. But thinning such forests in an attempt to mitigate the chance of burning is probably not an effective strategy.

“I think what is really powerful about our study is its broad scale,” said Hart. “It is pretty conclusive that we are not seeing an increase in areas burned even as we see an increase in the mountain pine beetle outbreaks,” she said.

“These results refute the assumption that increased bark beetle activity has increased area burned,” wrote the researchers in PNAS. “Therefore, policy discussions should focus on societal adaptation to the effect of the underlying drivers: warmer temperatures and increased drought.”

The entire paper can be downloaded (1MB).
Reports about other pine beetle studies, and general articles on the insects, are tagged beetles.

Researchers: insects and drought more of a threat to forests than wildfires

custer engine highland fire
Custer FD’s Engine 6 at the Highland Fire west of Custer, SD, July 1, 2012. Photo by Bill Gabbert.

New research shows that the most significant current threat to western dry forests is from insect outbreaks and droughts, not wildfires; and historically abundant small trees offer the greatest hope for forest survival and recovery after these events. Dry forests are low-elevation western forests with tall pines. The study used government records of insect and wildfire damage to compare current threats to dry forests and used records from land surveys conducted in the late-1800s to understand how dry forests persisted for thousands of years in spite of insect outbreaks, droughts, and fires. These forests persisted, this study suggests, by having both young and old trees that together provided bet-hedging.

Data on recent threats to dry forests used government maps of insect outbreaks and wildfires from 1999-2012 across 64 million acres of western dry forests or 80% of the total dry-forest area. “When comparing the rates of insect outbreaks and wildfire over the past fourteen years, we were surprised to discover insect outbreaks impacted 5 to 7 times the area that wildfire did.” said Dr. Mark Williams, a co-author of the study and recent PhD graduate of the University of Wyoming’s Program in Ecology. “In contrast, restoration efforts to increase resilience of dry forests to changing climate focus primarily on threats from wildfire. Our work suggests that impacts from insect pests should be considered with greater weight when formulating restoration prescriptions.”

To understand how forests were resilient to multiple disturbances in the past, the researchers utilized historical data which included 45,171 tree sizes measured along 13,900 section-lines traversed by land surveyors in about 4.2 million acres of dry forests in Arizona, California, Colorado, and Oregon in the late-1800s.

“The late-1800s land surveys provide us with a spatially extensive and detailed view of how these dry forests persisted through unpredictable episodes of insect outbreaks, droughts, and wildfires” said Dr. William Baker, a co-author of the study and Professor Emeritus in the Program in Ecology and Department of Geography at the University of Wyoming. “What we see from the surveys is that dry forests historically had many large trees, that often survived wildfires, but even more small trees that were less prone to be killed during insect outbreaks and droughts. The combination of abundant youth and older trees provided bet-hedging insurance that allowed these forests to survive and recover regardless of whether an insect outbreak, drought, or wildfire occurred. These unpredictable events may increase with global warming.”

The study’s findings suggest current programs that remove most small trees to lower the intensity of wildfires in dry forests and restore large trees lost to logging, may reduce forest resilience to the larger threats from insect outbreaks and droughts. “Using historical forests as a guide, our study suggests we may want to modify our restoration and management programs so they do not put all our eggs in one basket, but instead hedge our bets by keeping both large trees and abundant small ones” said Dr. Baker.

Key findings:

  • Over the last fourteen years, insect outbreaks have impacted 5 to 7 times more dry forests than have wildfires.
  • Historically, dry forests had large trees, but were numerically dominated by small trees, 52-92% of total trees.
  • The variable structure of past forests provided bet-hedging insurance against multiple disturbances and continued persistence. Removing most small trees for modern restoration treatments may reduce the resilience of these forests.

The study was published Open Access online in the international scientific journal, Frontiers in Ecology and Evolution and is freely available to download on their website.

Wednesday morning one-liners

Engine rollover, Warm Springs, Oregon
Engine rollover, Warm Springs, Oregon, July 18, 2014.

*The Wildland Fire Lessons Learned Center has published a report on a BIA engine that rolled over near Warm Springs, Oregon, July 18, 2014. Two people were injured, one seriously. The LLC says more than 50 fire vehicles have rolled over in the last 10 years.

*A Colorado artist has created a work consisting of rectilinear pillars suspended from the ceiling, each measuring nine feet tall, meant to convey the idea of a wildfire.

*A man spotted running from the 50-acre Foothill Fire in Ventura, California was arrested on suspicion of setting the blaze.

*Fire officials in Washington state suspect an arsonist is responsible for igniting 23 fires in less than two weeks. Most of them have been vegetation fires.

*A firefighting vehicle in Australia has been outfitted with drop-down steel wheels so that it can follow a steam-powered train, putting out wildfires started by the steam engine.

*In other news from Australia, a Senator gave a speech, titled, Thank you For Smoking, praising nicotine fiends for their $8 billion a year contribution to the economy. He said he did the math: Last year smokers cost the health care system $320 million and another $150 million in bushfire control.

*Researchers have found that “recent (2001–2010) beetle outbreak severity was unrelated to most field measures of subsequent fire severity, which was instead driven primarily by extreme burning conditions (weather) and topography.” Unfortunately, to read the article, researched and published by government employees, it will cost you $10 for two days of access. If the researchers, Brian J. Harvey, Daniel C. Donato, and Monica G. Turner, are going to hide the results of their taxpayer-funded research behind a pay wall, what’s the point in hiring researchers? Support Open Access.

*Firefighters are on alert in the Philippines for wildfires that may start from an eruption of the Mayon volcano.

*Firefighters are on lessened alert in the Black Hills after the area received two to five inches of rain over the last few days.

*California has burned through its wildfire-fighting budget — $209 million — just as it faces what is historically the worst of the fire season.