Due to surface fuel accumulation, Fourmile Canyon Fire burned more intensely in some treated zones
By Bob Berwyn
SUMMIT COUNTY —A report on the 2010 Fourmile Canyon Fire will probably raise more questions than it answers for firefighters and land managers, concluding that, in some cases, the ferocious fire near Boulder may have burned more intensely in treated areas than in adjacent untreated stands.
That may have been due to the relatively high concentration of surface fuels remaining after treatments, as well as the higher wind speeds that can occur in open forests compared to those with denser canopies, Forest Service researchers concluded in the report published last month.
Up until the horrific fire storms of this summer, the Fourmile Canyon blaze was the most destructive wildfire in Colorado history measured by the number of homes lost (162), and a recently finalized U.S. Forest Service report on the Fourmile Canyon fire is eerily prescient.
The final report, done by the Forest Service’s Fort Collins-based Rocky Mountain Research Station, was issued right around the time firefighters were mopping up from this year’s even more destructive High Park and Waldo Canyon fires, which together destroyed more than 600 homes.
Foreshadowing this year’s disasters, it warned that fires in the wildland-urban interface are likely to become more frequent and more destructive, and concluded that the Fourmile Canyon Fire even burned more intensively in some areas that had previously been treated to try and mitigate the fire danger.
The report also concluded that beetle-killed trees had “little to no effect on the fuels within the area burned by the Fourmile Canyon Fire, the fire’s behavior, or the final fire size,” explaining that crown fires are “driven by abundant and continuous surface fuels rather than beetle-killed trees.”
The report also included a section describing extensive sociological research, including surveys with residents of the Fourmile Canyon area, as well as other at-risk neighborhoods.
Perhaps not surprisingly, the researchers found that the “it won’t happen to me” sentiment runs strong among people who choose to live in the wildland-urban interface. From the report:
“A critical finding was that despite their relatively high familiarity with wildfire, most respondents did not believe that characteristics of their structure and the immediate surroundings of the structure were significant factors influencing the likelihood of a wildfire damaging their property within the next 5 years.”
Only one in five residents said they believed that the condition of the trees and brush on their property and the type of house they live in contribute significantly to the chance of a wildfire damaging their property.
That feedback is somewhat discouraging to fire-safety experts, who have long emphasized that the best way for people to protect their homes is to use fireproof materials and to create a buffer zone by clearing and trimming vegetation immediately around homes.
Nearly all the residents surveyed said they had some some mitigation, with only 4 percent responding that they hadn’t taken any action.
The researchers said they weren’t able to reach any conclusions about how the effectiveness of neighborhood-level wildfire mitigation efforts. In the seven years leading up to the Fourmile Canyon Fire, about 600 acres in the area were treated, but piles of slash left behind, lack of ongoing maintenance of the treatment areas and incomplete treatments made it challenging for investigators to reach any conclusions.
In the end, the report found no evidence that fuel treatments changed the progression of the Fourmile Canyon Fire, and that the treated areas were “probably of limited value to suppression efforts on September 6.” Large quantities of surface fuels in the treatment area also rendered them ineffective in changing fire behavior.
Satellite photos taken after the fire clearly showed that the fire burned just as intensely inside treatment areas as it did in adjacent untreated stands. In some cased, the fire appears to burned more intensely in treated areas, the investigators said, explaining that additional surface fuels, as well as higher wind speeds, may have been factors. From the report:
“One clear example of this comes from near Gold Hill where the piles of slash were scattered in the understory of a thinned stand but where the intended slash burning had not yet been completed. This situation reinforces the notions that fuel treatment performance metrics should be described and treatments need to be executed as planned to be effective.”
As was seen again this summer at the High Park Fire and the Waldo Canyon Fire, the rate of the fire’s spread simply overwhelmed fire-fighting resources, leaving hundreds of homes exposed to potential ignition within just a few hours. The investigators concluded those findings suggest that simply having more engines available is not the solution to the wildland-urban interface fire problem. When those fires are burning intensely, it’s just not possible to protect all the homes in the danger zone.
Instead, the report once again calls for a change of approach — instead of increasing expensive fire protection capabilities that have proven to strategically fail during extreme wildfire burning conditions, efforts should be focused on reducing home ignition potential within the immediate vicinity of homes, the investigators concluded.