Healthy forest ecosystems need dead wood to provide important habitat for birds and mammals, but there can be too much of a good thing when dead wood fuels severe wildfires. A scientist with the U.S. Forest Service’s Pacific Southwest Research Station (PSW) compared historic and recent data from a forest in California’s central Sierra Nevada region to determine how logging and fire exclusion have changed the amounts and sizes of dead wood over time. Results were recently published in Forest Ecology and Management.
PSW Research Ecologist Eric Knapp and a field crew visited three research plots initially established in 1929 in old-growth, mixed conifer stands on the Stanislaus National Forest. The stands had not burned since 1889 and were logged with a variety of methods later in 1929, shortly after the first survey of the plots. In this study, Knapp and a research crew first used digitized maps to locate and re-measure all live and dead trees in the plots. They later used old plot maps to reconstruct the number and size of downed logs in the 1929 plots and also surveyed logs in the present-day plots.
The research crew compared their present-day data with those from 1929 and documented a more than nine-fold increase in the density of standing dead trees (snags) coupled with a decrease in the average diameter of the snags. Additionally, they observed nearly three times as many logs on the ground (coarse woody debris), but found a substantial decrease in the size of these logs. The majority of downed logs in the present-day re-measurement were highly decayed.
“Because larger-sized dead wood is preferred by many wildlife species, the current condition of more, smaller, and more decayed woody pieces may have a lower ratio of habitat value relative to potential fire hazard,” says Knapp. Long-term dead wood changes in these forests pose a challenge for forest managers who must balance concerns for wildlife habitat with reducing the chance for damaging wildfires.
But dead trees, like live trees, can be managed. “To restore dead wood to conditions more like those found historically will require growing larger trees and reducing the addition of dead wood from small and intermediate-sized trees,” says Knapp. “Forest thinning, through mechanical means and/or fire has been shown to slow the mortality rate of the remaining trees. In addition, using prescribed fire and low-intensity wildfire, which preferentially consume smaller and more decayed wood, would shift the balance to larger and less decayed pieces of dead wood, and help reduce fuels that contribute to uncharacteristically severe wildfires.”
A safety zone constructed on a wildfire in 2014. Is this like a tactic used in the Vietnam war? “We had to destroy the village in order to save it.” (Screen grab from the video below.)
The calculation of the size of a safety zone is somewhat complex for a firefighter in the heat of battle, and these various guidelines can only be used if the firefighter on the ground is carrying the latest written directions about how to do the math. While it is laudable that researchers are working to improve the safety zone guidelines, changing them every two to four months is too confusing.
In the video (webinar) below the new revision is discussed in detail in the one hour and 15 minute presentation, including questions. (A three-minute executive summary version would be very much appreciated.) This new November, 2014 version of the “Preliminary Proposed Safety Zone Rule” appears at 44:00. The fact that it is called both preliminary and proposed leads us to believe there will be still more changes in the near future.
Below is the description of the December 2, 2014 webinar, presented by Mr. Butler.
Current safety zone guidelines for wildland firefighters are based on the assumption of flat ground, no wind, and radiative heating only. Recent measurements in grass, shrub and crown fires indicate that convective heating can be significant especially when wind or slope are present. Measurements and computer modeling supports this finding and suggests that convective energy transport should be considered when assessing safety zone effectiveness any time wind or slope is present. The results of the research are presented along with recommendations for modifications to current safety zone guides.
Even though I hated taking statistics classes in college, I am now an interested consumer of compilations and analysis of data that help to explain our world. One of the best statisticians at doing that is Nate Silver, who runs the FiveThirtyEight web site. Mr. Silver became a public figure after using very successful and innovative techniques to analyze the performance of baseball players and to predict the outcome of elections. For several years he wrote for the New York Times, but now he is associated with of ESPN.
One of Mr. Silver’s latest projects was to study weather patterns, resulting in the article, Which City Has The Most Unpredictable Weather? The title is a little misleading and seems to imply that in those “unpredictable” cities, the professional weather forecasters are more frequently wrong in their forecasts than in other more “predictable” cities. What he actually studied was the degree to which the daily weather in those cites deviated from the average for that day. He should have named the article, Which City Has The Most Variable Weather?
But we’re nitpicking. And in spite of the semantics issue, Mr. Silver came up with some data that could be of interest to wildland firefighters.
In the “predictable” areas, the weather one day is more likely to be similar to that of the previous day, and is not too far off from the average. That is not the case in the “unpredictable” cities.
Variable weather is the bane of wildland firefighters. They don’t like to be surprised by sudden changes in humidity, wind speed, or wind direction.
Generally, Mr. Silver found that weather east of the Rocky Mountains was more variable than in areas west of the mountain range. Rapid City has the crown for the most variable weather.
In May we recorded the video above and told you about the Simtable which projects 3-D wildfire simulations onto a sand table which can be molded to resemble the topography in a specific area. Fire modeling algorithms simulate the spread of fire through the vegetation and across the topography while also taking weather and fuel conditions into account. You can simulate a fire at your choice of location, or you can view the spread of historic fires. The system can also be used to simulate and train for evacuations, floods, and hazardous material incidents — at a starting price of $25,000.
A researcher at San Diego State University is developing the next generation of the Simtable which he hopes to put into the hands of wildland firefighters out on the ground.
10News reports:
“Any firefighter with a smartphone or tablet could download it and have the mapping system,” said [Justin Freiler of SDSU’s Visualization Center].
They are not there yet, as a mobile app is still in development, but the hope is to make the system available to firefighters in the near future.
(Note from Bill: A Fire Behavior Assessment Team (FBAT) has been studying the King Fire east of Placerville, California. Rae Brooks, an Information Officer at the fire, sent us this article describing what a FBAT does.)
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These scientists set up equipment in front of a fire to collect fire behavior data
by Rae Brooks
FORESTHILL, Calif. — Fire scientists call them “plots.” Dotted ahead of the leading edge of the King Fire, they were deliberately placed in the anticipated path of the flaming front. Each plot contained a video camera, wind-speed gauge and other monitoring devices.
If the flames came, a data logger buried a foot underground would collect information that would allow the scientists to better understand the science of wildfire, gauge the effectiveness of fuel treatments, and contribute to firefighter safety.
So while thousands of firefighters were building line, clearing brush from roads and bulldozing contingency lines to suppress the King Fire, the scientists patiently waited for flames to sweep over their plots, if control efforts failed.
“We want our plots to burn,” said Carol Ewell, co-lead of the FBAT, or Fire Behavior Assessment Team, at the King Fire. “Firefighters put the fire out. It’s a difficult balance.”
A plot BEFORE the fire passed through. Photo by FBAT team at the King Fire.The same plot AFTER the fire passed through. Photo by FBAT team at the King Fire.
Mark Courson, a division-qualified firefighter and an operations section trainee, served as operations lead for the FBAT at the King Fire. His job was to keep the team safe and advise on site selection.
“Usually I’m thinking of putting the fire out,” said Courson. “Now I’m bucking the system, thinking where suppression might not hold it.”
The team, a U.S. Forest Service module, draws members from around the country to work 14-day assignments on wildfires. Since 2006, the FBAT has recorded data at 16 wildfires, including last year’s Rim Fire, the third largest in California history. Generally, emerging fires with potential for growth suit the FBAT better.
At the King Fire, just three of 10 sites selected burned over. The team averages 50 percent, but sometimes gets lucky and finds all its plots burned.
“It’s a big gamble,” said Ewell. “Our success rate is quite variable, and I’m not sure that’s a hurdle that we can fix.”
The King Fire was particularly difficult to read after it made a speedy 15-mile run northward beginning late in the afternoon of Sept. 17, Ewell said. Rain has since quelled the fire, which is now 89 percent contained.
Despite the inherent difficulties, free-burning wildfires provide conditions that cannot be replicated in laboratory, experimental or prescribed fires. For instance, no prescribed fire would ever be set during California’s current historic drought. The team has recorded active crown-fire runs, fire whirls, spot-fire ignitions, and merger of spot fires with the main flame front.
The team’s prime mission at the King Fire is to study the effectiveness of fuel treatments. Team members set up plots in treated and nearby untreated areas to provide comparisons.
Because they are working ahead of the flaming front, they follow standard firefighting safety protocols, carefully considering whether they can get safely into and out of selected sites. “Unburned fuel between you and the fire,” is one of the 18 Firefighting Watch Out Situations, and, by necessity, their equipment must be placed in unburned fuel ahead of the fire.
“There is risk involved,” said team member Matt Dickinson, an ecologist at the Delaware, Ohio, location of the Forest Services’s Northern Research Station. “One way we mitigate is to set up plots early in the day before the peak burning period. We pull out quite often when we’re not feeling comfortable.”
It takes about an hour for nine FBAT members to install their gear and inventory the vegetation at each site. If firefighters are trying to build line and the team is trying to set up a plot, the firefighters, of course, have priority, said Ewell. “In comparison, we’re just a geek squad,” she said, although most FBAT members are experienced firefighters.
Some of the team’s equipment. Photo by Mike McMillan.
At each plot, the team sets up temperature sensors, heat flux sensors, anemometers to measure wind speed, and video cameras encased in heat-resistant steel boxes. The cameras start when trigger wires are burned over. Each camera captures about 80 minutes of footage.
The flames often melt the anemometer’s plastic cups, so wind speeds might only be collected before flames arrive. At each site, team members also bury a data logger in a military surplus ammunition box. Other members collect information about the vegetation, down to counting sticks on the ground.
At the King Fire, the team also recorded fuel moisture data to help fire behavior analysts working on the fire.
In the future, Ewell would like to equip the team with more heat-flux sensors, Go-Pro video cameras with new triggers, and anemometers that can better withstand heat. The team relies on grant money and project funding from the Forest Service to continue its work.
When sites burn over, team members return, when it is safe, to collect their equipment and the data. They also record how the vegetation has fared. Plots that don’t burn are permanently marked with rebar, so they can provide fuels information for other uses.
The team spends evenings entering data and crunching numbers, and tries to complete a summary report before demobilizing from a fire.
Seeing a wildfire burn during severe drought has been an eye-opener, said Dickinson. Most of his experience has been with prescribed fires. He found the tremendous consumption of fuels and the severe damage to trees hard to witness.
William Borovicka, who normally works at the Vinton Furnace State Experimental Forest in McArthur, Ohio, was a first-time FBAT member at the King Fire. Back home, he studies how oak and hickory forests, if left undisturbed, convert to beech and maple woods. His work in Ohio, he feels, plays into management techniques to stabilize the oaks and hickories.
Using FBAT findings to gain a deeper understanding of fire behavior might similarly help forest managers someday with decision-making, Borovicka said.
“Maybe more prescribed fires, or different harvesting techniques,” he said. “Whatever it takes to prevent this kind of blow-up.”
PSW Research Ecologist Eric Knapp and a field crew visited three research plots initially established in 1929 in old-growth, mixed conifer stands on the Stanislaus National Forest. The stands had not burned since 1889 and were logged with a variety of methods later in 1929, shortly after the first survey of the plots. In this study, Knapp and a research crew first used digitized maps to locate and re-measure all live and dead trees in the plots. They later used old plot maps to reconstruct the number and size of downed logs in the 1929 plots and also surveyed logs in the present-day plots.
