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.

Live event to discuss wildfire wind tunnel studies

Above: The U.S. Forest Service tests burning pine straw in an IBHS wind tunnel earlier this year. Screen grab from IBHS video.

The Insurance Institute for Business and Home Safety (IBHS) will host a live wildfire-related event on Facebook Wednesday November 9 at 10:30 a.m. EST. They have not provided a ton of information about but it will “open up the curtain a bit on wildfire studies”. (Link to the IBHS Facebook Page.)

Dr. Steve Quaries will discuss the wildfire research that they have been doing in the huge wind tunnel. In 2011 using 105 huge fans and spark-generators, they launched embers at a structure to demonstrate what can happen when a wind-driven fire approaches a poorly prepared structure.

IBHS wind tunnel
The IBHS wind tunnel showing the 105 fans. IBHS photo.

The video below shows embers igniting flammable material on and around a structure in the IBHS wind tunnel.

Earlier this year the U.S. Forest Service used the facility to study the relationship between wildland fire rate of spread and wind speed used in the U.S. wildland fire behavior decision support systems. Previous experiments have been conducted in the Missoula Fire Sciences Laboratory wind tunnel that is more limited in size and wind speed than the IBHS wind tunnel.

This research is a collaborative effort with researchers at UNC Charlotte, University of Maryland, University of Texas Austin, and USDA Forest Service, and is funded by the Joint Fire Science Program.

Using soil moisture in grassland fire danger rating systems

“…Our research findings provide scientific justification for using soil moisture data from in situ monitoring networks in fire danger rating systems. Such soil moisture data are increasingly available and are not currently being used in the context of wildfire preparedness. ”

Above: The percent of maximum soil moisture available to plants in the top 16 inches in Oklahoma, September 11, 2016.

David M. Engle, along with other scientists at Oklahoma State University, are making a case that soil moisture should be used as one of the components in determining grassland fire danger ratings.

soil moisture station
Station that measures soil water at several depths and transmits the data. This image and the one above are courtesy of the researchers.

To assess the herbaceous fuel dynamics in grasslands, they conducted 3 studies:

1) A study that used a database of large wildfires in Oklahoma to examine the relationship of fire occurrence and fire size with soil moisture;

2) An intensive field-based study to quantify and subsequently model herbaceous fuel load and moisture content in grassland patches that differed in time since fire and, therefore, proportion of live and dead herbaceous fuel load, and;

3) Modeling the influence of herbaceous fuel dynamics and weather conditions on fire behavior in tallgrass prairie.

Their final report can be read HERE.

Goal-oriented decision-making

Goal-oriented training can change the balance between reflective and reflexive processes.

Emergency responders have all been there — they rush to get to an incident, very quickly size it up, and take action. But award-winning research looks at incident managers that include a third step, actually formulating a plan of action. It has been argued that the development of explicit plans enables shared situational awareness and goals to support a common operating picture.

An article written by Dr. Sabrina Cohen-Hatton and R.C. Honey, Goal-Oriented Training Affects Decision-Making Processes in Virtual and Simulated Fire and Rescue Environments, received the Best Paper of the Year Award from the Journal of Experimental Psychology: Applied in 2016.

The research evaluated 48 incident commanders from 11 Fire and Rescue Services in the United Kingdom who had just received one-hour of training on incident management. They were divided into two groups, one with standard training and the other that included information about decision-making:

For Group Decision, slides were included that highlighted the use decision controls, which involved using a rapid mental check list of questions at key decision points: Why am I doing this (i.e., what are my goals)? What do I expect to happen (i.e., what are the anticipated consequences)? and Are the benefits worth the risks? When participants given goal-oriented training watched the footage, and were asked what actions they would take next, they were directed to answer with reference to the decision controls.

After the brief training the firefighters participated in immersive virtual reality (VR) simulations of a house fire, a traffic collision, and a “skip fire that spreads to an adjoining shop”.

The results showed that goal-oriented training affects the decision-making process in experienced incident commanders across a variety of simulated environments
ranging from immersive VR through to live burns. There is evidence that the training can change the balance between reflective and reflexive processes which could have the potential to increase the effectiveness of communication between members of firefighting crews and to improve
safety.

Fire studies at Yosemite and Yellowstone National Parks

Above: A bison in Yellowstone National Park, May 25, 2014. Photo by Bill Gabbert.

Two recent and ongoing studies at the two big “Y” parks are yielding results about fire behavior and the effects of naturally occurring fire. The excerpts below are both from Phys.org.

The first is about allowing wildfires to burn at Yosemite National Park, rather than suppressing them:

An unprecedented 40-year experiment in a 40,000-acre valley of Yosemite National Park strongly supports the idea that managing fire, rather than suppressing it, makes wilderness areas more resilient to fire, with the added benefit of increased water availability and resistance to drought.

After a three-year, on-the-ground assessment of the park’s Illilouette Creek basin, University of California, Berkeley researchers concluded that a strategy dating to 1973 of managing wildfires with minimal suppression and almost no preemptive, so-called prescribed burns has created a landscape more resistant to catastrophic fire, with more diverse vegetation and forest structure and increased water storage, mostly in the form of meadows in areas cleared by fires.

“When fire is not suppressed, you get all these benefits: increased stream flow, increased downstream water availability, increased soil moisture, which improves habitat for the plants within the watershed. And it increases the drought resistance of the remaining trees and also increases the fire resilience because you have created these natural firebreaks,” said Gabrielle Boisramé, a graduate student in UC Berkeley’s Department of Civil and Environmental Engineering and first author of the study…

The next article covers a study into the fire behavior of this summer’s fires that spread through the footprints of the 1988 fires in Yellowstone National Park.

…”Largely up until this point, fire has not necessarily carried well through the ’88 fire scars,” Yellowstone fire ecologist Becky Smith said. “I mean, it definitely has before, but it usually takes very specific conditions, like high winds or a very specific fuel bed. But this year, we’re definitely seeing it burn much more readily in the ’88 fire scars.”

The park has called in a special federal team that studies fire behavior to find out why.

“We’re trying to use it as a good learning opportunity to try and really narrow our focus on how and when the ’88 fire scars will burn,” Smith said. The 1988 wildfires burned 36 percent of the park.

It’s the first time Yellowstone has used the special team’s services, she said.

The 13-member team is studying two fires burning in the 1988 fire scar. It has deployed special heat-resistant equipment with sensors, cameras and other instruments to measure things like temperature and wind where the fires are burning…