Researchers find tree-bark thickness is affected by fire occurrence

The researchers found that the bark thickness of closely related species is linked to whether the species lived in a fire-prone or non-fire-prone region, which provided further evidence that bark thickness is an evolutionary adaptation to fire.

Above: firefighters mop up hot spots near a residence on the Eiler Fire in northern California, August 6, 2014. Photo by Bill Gabbert.

Researchers have determined that the thickness of bark on a tree can be affected by the frequency of fires within the region. Findings released in a paper today suggest that bark thickness could help predict which forests and savannas will survive a warmer climate in which wildfires are expected to increase in frequency.

Trees in regions where fire is common, such as savannas and the forests of western North America, tend to have thicker bark, while trees in tropical rainforests have thinner bark, researchers at Princeton University and collaborating institutions reported Jan. 11 in the journal Ecology Letters. Bark protects the inside of the trunk from overheating and is one of a handful of adaptations that trees use to survive fire.

“We found large-scale evidence that bark thickness is a fire-tolerance trait, and we showed this is the case not just in a particular biome such as a savanna, but across different types of forests, across regions and across continents,” said first author Adam Pellegrini, a NOAA Climate and Global Change Postdoctoral Fellow at Stanford University who led the study while a graduate student in Princeton’s Department of Ecology and Evolutionary Biology.

The research suggests that the link between bark thickness and fire resistance should be included in global climate models, Pellegrini said. “Trees from regions that burn frequently could still become vulnerable if the risk of fire increases,” he said. “The open question is whether the bark is thick enough to help trees survive.”

Pellegrini and his colleagues looked at 572 tree species in regions across the globe. They compared bark thickness from trees in areas that experience frequent wildfires — and where rain falls only seasonally — to trees in regions where fires are rare, such as tropical rainforests. They found that in areas where fires are frequent, most trees, no matter the species, have thicker bark than closely related tree species growing in low-fire areas.

The study suggests that tropical rainforests — which are mostly composed of thin-barked trees — may have a more difficult time recovering from fire, whereas savannas and seasonal forests with thickly barked trees should be able to better withstand fire. A savanna was defined as land with continuous grass cover that is 20 to 80 percent trees, while a forest was defined as having complete tree coverage and little to no grass.

Periodic fires are necessary for the health of some types of savannas and forests. Fires burn off excess plant matter such as dead wood and grass — as well as competing fire-sensitive species — and rejuvenate the soil so that the dominant, fire-resistant plant species can flourish. However, fires also can be detrimental to the environment by releasing stored carbon back into the atmosphere, and causing the decades-long loss of a valuable carbon-storage system.

North Pole Fire
North Pole Fire, west of Custer, South Dakota March 10, 2015. Photo by Bill Gabbert.

The researchers also addressed the question of where thick-barked trees come from: Did they evolve to have thick bark in response to living in a fire-prone region, or do thick-barked trees come from plant families with species that all tended to develop thick bark irrespective of fire activity? Continue reading “Researchers find tree-bark thickness is affected by fire occurrence”

Study links firefighter accidents to sleep problems

fire Whiskeytown National Recreation Area
An incident base at Whiskeytown National Recreation Area in California, 2009. Photo by Carol Jandrall.

A study of almost 7,000 firefighters from municipal fire departments found that 37 percent screened positive for common sleep disorders, including obstructive sleep apnea, insomnia, restless leg syndrome, and shift work disorder.

The researchers found that compared with sound sleepers, those with a sleep disorder were about twice as likely to have a motor vehicle crash, to nod off while driving, and to have cardiovascular disease or diabetes. They were more than three times as likely to suffer from depression and anxiety.

The study, published in the Journal of Clinical Sleep Medicine, said that nationwide 61 percent of firefighter on-duty fatalities are caused by heart attacks or motor vehicle crashes.

National Interagency Fire Center data that we reported for 1990 through 2014 shows that 45 percent of the wildland fire fatalities were from vehicle accidents or medical issues.

Wildland firefighter fatalities 1990-2014
Wildland firefighter fatalities, 1990-2014. Data from NIFC, compiled by Wildfire Today.

Most, 97 percent, of the 7,000 firefighters in the study worked extended shifts of at least 24 hours. Wildland firefighters work 8-hour shifts —  except when they don’t. While on fires their shift schedules and sleep routines are often disrupted. The 8-hour shift can be extended to 12 to 16 hours, and their usual sleeping times may be changed and sometimes shortened; not unlike the jet lag of traveling to a different time zone. The first shift on a fire may be longer than 16 hours and a crew used to working during the day can be placed on a night shift.

The municipal firefighters in the study work very different schedules from their brothers and sisters in wildland fire, so a direct comparison of sleep disorders and accidents is probably not valid, but this issue should be watched closely. Crew supervisors and incident management teams should, at least, see that firefighters have an opportunity to get an adequate amount of quality sleep.

The same journal that published this study has another interesting one titled, “The Association between Sleep Disturbances and Depression among Firefighters: Emotion Dysregulation as an Explanatory Factor”.

Australians expect to put wildfire modeling in the hands of firefighters

Above:  the Aurora national bushfire prediction, detection, simulation and early warning system.

Researchers in Australia are designing a wildfire modeling system that firefighters can access on a portable device in the field even if they are not connected to the internet. The Australis Wildfire Simulator is intended to be part of Aurora, a national fire prediction, detection, simulation and early warning system that simulates bushfires in real time and rapidly communicates the spread predictions via the web, email and the National Telephone Early Warning System (NTEWS).

Researchers at The University of Western Australia are developing the new touchscreen device that can be mounted in a fire truck to help firefighters predict where and when a bushfire will spread.

The researchers are modifying bushfire simulation software Australis into a high-end tablet to provide accurate predictions of fire behaviour more rapidly than current methods.

UWA Professor George Milne
UWA Professor George Milne.

Professor George Milne from UWA’s School of Computer Science and Software Engineering said the technology could protect lives, homes, crops and livestock in Western Australia’s bushfire prone areas.

“Having the Australis fire prediction technology in the cab of a fire truck or a farmer’s ute will enable first-responders to get the best information necessary to create appropriate firefighting and evacuation strategies,” Professor Milne said.

“This can happen in the very early stages of a bushfire, when time-critical responses are required.”

Professor Milne said the touchscreen device would complement the Aurora system used by the Department of Fire and Emergency Services (DFES) which currently runs the simulator from one central location for all fires in WA.

“On a day where there are several bushfires across the state, it may take too long to predict each individual fire’s progress using a single system in the central headquarters,” Professor Milne said.

“The advantage to local brigades with access to this technology is that it will give them location-specific information about which communities are at risk and which need to be evacuated.”

The Australis system analyses data including geographical topography, vegetation types, WA bushfire prone hotspots, time since last burn, rate of spread, fuel accumulation and forecasted weather.

Australis
Screen capture from the Australis fire modeling system.

In a matter of minutes, and without internet connectivity, it can accurately predict where the fire could be from 30 minutes to 24 hours into the future.

Professor Milne said WA is unique in the world; it has bushfires burning every day of the year, from the north during the winter dry to the south in summer.

“This technology could significantly minimise the impact of bushfires, the loss of lives and homes, by predicting the direction, intensity and rate of bushfire spread in real time,” he said.

Funding is still required to get the technology off the ground and made available to local bushfire brigades.

Along with DFES, Department of Parks and Wildlife and Landgate, the University of Western Australia has an application for Royalty for Regions funding under consideration by the WA State Government.

Victoria’s advanced systems for engine crew protection

Above: Country Fire Authority test of engine burnover protection systems. Screen shot from CFA video.

The Aussies are far ahead of wildland firefighting agencies in the United States when it comes to the protection of personnel during fire engine burnovers and rollovers. Since 1977 Victoria’s Country Fire Authority (CFA) has been creating, evolving, and improving systems to increase the odds of firefighters on an engine surviving if their position is overrun by fire. These efforts were intensified after two engine burnovers in 1983 and 1998 killed a total of 17 firefighters.

During the last 39 years the vehicles have been hardened in various ways. Examples include internal radiant heat curtains and nozzles positioned around the exterior of the truck that spray water as the fire approaches.

We did a quick search on Wildfire Today for “engine burnover” and were surprised at the number of results. Take a moment and at least look at the titles and brief excerpts. These, of course, are just articles on our website. We make no claim that all engine burnovers are included since we started this website in 2008.

On November 21 the CFA posted a video (below) about their crew protection systems. It covers the history of their efforts and several minutes of video recorded during a test when a fire was ignited that burned over three of their engines to evaluate the effectiveness of the designs. The maximum temperature recorded was 728°C (1,342°F)

Below is a screen shot from the CFA video.

engine burnover protection system
Country Fire Authority test of engine burnover protection systems. Screen shot from the CFA video.

What if — in 2006 the five U.S. Forest Service firefighters that were entrapped and killed on the Esperanza Fire, instead of working on an engine similar to the USFS engine farther down this page, had been assigned to one built to CFA standards. Would they have taken refuge in the engine, pulled down the thermal protection shields and turned on the truck protection water spray instead of attempting to survive the fire outside the engine?

One feature of the CFA engines we noticed was a heavy-duty internal roll bar.

Internal roll bar Country Fire Authority engine
Internal roll bar in a Country Fire Authority engine.

We have written before about the need for U.S. wildland firefighting agencies to improve the survivability of engine crews during rollovers. These accidents involving large fire trucks, especially water tenders, are common.

In our opinion it is disgraceful that the outfits employing thousands of firefighters on engines have not taken this step to provide a safer working environment for their personnel.

The photo below is from one of the 34 articles on Wildfire Today tagged “rollover”.

Engine 492 crash Wyoming
On August 8, 2013 Engine 492 from the Medicine Bow-Routt National Forest and Thunder Basin National Grasslands was involved in a rollover accident on Wyoming State Highway 450 southwest of Newcastle, Wyoming. Three firefighters were injured, one seriously.

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

Research: Wildfires in Sierra Nevada driven by past land use

Changes in human uses of the land have had a large impact on fire activity in California’s Sierra Nevada since 1600, according to research by a University of Arizona researcher and her colleagues.

Above: Indian Canyon Fire near Edgemont, SD, 2016. Photo by Bill Gabbert.

By Mari N. Jensen, University of Arizona College of Science

Forest fire activity in California’s Sierra Nevada since 1600 has been influenced more by how humans used the land than by climate, according to new research led by University of Arizona and Penn State scientists.

For the years 1600 to 2015, the team found four periods, each lasting at least 55 years, where the frequency and extent of forest fires clearly differed from the time period before or after.

However, the shifts from one fire regime to another did not correspond to changes in temperature or moisture or other climate patterns until temperatures started rising in the 1980s.

“We were expecting to find climatic drivers,” said lead co-author Valerie Trouet, a UA associate professor of dendrochronology. “We didn’t find them.”

Instead, the team found the fire regimes corresponded to different types of human occupation and use of the land: the pre-settlement period to the Spanish colonial period; the colonial period to the California Gold Rush; the Gold Rush to the Smokey Bear/fire suppression period; and the Smokey Bear/fire suppression era to present.

“The fire regime shifts we see are linked to the land-use changes that took place at the same time,” Trouet said.

“We knew about the Smokey Bear effect — there had been a dramatic shift in the fire regime all over the Western U.S. with fire suppression. We didn’t know about these other earlier regimes,” she said. “It turns out humans — through land-use change — have been influencing and modulating fire for much longer than we anticipated.”

Continue reading “Research: Wildfires in Sierra Nevada driven by past land use”

Understanding fire scars on trees

How does a tree damaged by a wildfire heal the wound?

Above: Annual rings of a Douglas-fir tree injured by two fires. The rings growing before the injury in 2003 were filled with resin to create a boundary from infection at the injury site. Wood grew over the dead cambium, enclosing the injury. Then the tree was injured in 2007 and woundwood again enclosed the injury. Note that the bark apparently remained intact both times. Photo: U.S. Forest Service.

From the U.S. Forest Service

When trees are injured they develop physical and chemical boundaries around the injury wound to resist infection. Trees also grow new wood to close over the injured place. Injuries caused by fires result in fire scars and we use the patterns of scarring among many trees to understand when and how often fires burn.  This research helps to understand the biological process of fire scar formation and use it to improve fire history analysis.

Fire history information is used to interpret the ecological role of fire and other disturbance events in ecosystems and is required in environmental assessments. Fire scars in different tree species don’t all look the same, which can lead to confusion about whether irregular growth in wood is a scar. This research examined the process fire scar formation and the anatomy of fire scars in conifer and hardwood trees.

In three species of trees that survived wildfires near Missoula, Montana (western larch, Douglas-fir, and ponderosa pine) we found that injuries happened even when bark was not charred. This was also true of oak trees we examined that burned in a prescribed fire in Ohio hardwood forests. It would be impossible to know that the tree had a scar by just looking at it. Where a tree’s bark was rough, both hardwoods and conifers sometimes had several small injuries next to crevices in bark where heat could get to living cells more easily. Hardwood trees produce chemicals to resist infection, mostly phenols. Conifer trees produce resin (terpenes) as a physical and chemical barrier to block infection.

larch fire scar
Disk taken from a western larch injured in a wildfire in 2003, showing the development of a fire scar in following years around the edges of the killed cambium as wood grows over and around the dead cambium. Photo: Ken Dudzik.

Key Findings

  • The stems of western larch, Douglas-fir, and ponderosa pine trees can be injured from fire even when the bark isn’t visibly charred. Heat alone causes the injuries, especially where bark is thinner.
  • Western larch, ponderosa pine, and Douglas-fir ordinarily make resin in cells called resin ducts. After an injury western larch and ponderosa pine produce many extra (traumatic) resin duct cells, and in turn these ducts produce and transport a lot of resin. Traumatic resin seems to be a better disinfectant than the usual resin. In larch traumatic resin ducts are especially large and effective at transportation. Douglas-fir trees don’t produce traumatic resin ducts, so after an injury they produce relatively less resin, and less effectively transport it. They tend to die more easily than larch or ponderosa after a fire.
  • In years following a fire, wood grows around the edges of the injury. The density of wood cells is higher at the edge of the injury and when they grow, the tree ring at that point is unusually wide. If the injury is small, within a few years it can close over and be invisible from the outside. Sometimes injuries are never visible from the outside.
  • Knowledge about why these differences occur in a particular species can help us understand how scars are formed, why some trees survive or die after injury, and determine whether irregularities in wood anatomy are likely to be a fire scar.
tree fire scar
Kevin Smith (Northern Research Station) and Elaine Kennedy Sutherland (Rocky Mountain Research Station) examine a fire-caused injury up the length of a tree from the Lolo National Forest, Montana.