Isn't This Stuff Gonna Burn?
By Mark Cahur, Routt Zone Fire Management Officer,
Medicine Bow-Routt National Forests
As a fire management officer for the US Forest Service, I am constantly bombarded with a myriad of questions relating to the pine beetle epidemic. One recurring question is, "Isn't this stuff gonna burn?"
Fire behavior is dependent on countless complex environmental conditions. Fire needs the appropriate alignment of weather, fuels and topography. Weather is the most highly variable as temperature, humidity, wind speed and seasons are all in play. Available fuel is dependant on how the fuel is arranged, the amount, vegetation type and continuity. Topography considers slope, aspect and elevation. Add to that the uncertainty of where and when lightning will start a fire, and you have a volatile situation.
Although the conditions that will cause a fire in a beetle infested forest are complex and variable, the dying forest goes through predictable phases as it dies and becomes fuel. Understanding these phases–and the behavior of fire in each one–helps us prepare to combat fire, if and when it occurs.
Beetles are always present in the forest, typically at low levels. At times they progress to epidemic or even pandemic levels and the forest changes dramatically. Associated fire behavior also changes. In a healthy live forest, lodgepole stands can exhibit benign fire behavior, where fire is limited to the surface fuels consisting of dead needles and other natural debris on the forest floor. These fires can usually be easily suppressed. But with the right alignment of fuels, weather and topography these benign fires can become fires that make national news. This potential always exists, even in healthy forests.
Once the beetle infestation starts, things change rather quickly. The once live forest canopy is now a sea of dead needles at the tops of trees. This canopy layer no longer transports water to keep the needles green and thus the “red and dead” phase of the forest is upon us. During this phase the hair on the back of my neck stands on end. The dead, dry canopy is ripe for large, fast-moving fires. The semi-good news is that this red and dead phase lasts only about three years from beetle attack until the pine tree loses its needles. Once needle loss has occurred, the forest canopy fuels become too sparse to support large, fast-moving fires.
After the needles have dropped, surface fire will likely burn in the needles and branch litter that has been created from the dead and dying forest. This second phase may persist from year three outwards to ten to fifteen years. These fires should be considerably less intense than potential canopy fires of the red and dead phase and will likely be limited to shorter flame lengths and slower moving fires contained to the forest floor. These fires should be easier to manage. However, the hair on the back of my neck still stands on end. I see this phase as the most dangerous to fire fighters. These fires may be less intense and may be more easily suppressed, but the danger to fire fighters from falling dead trees, or "snags" will be immense. These snags are often referred to as "widow-makers."
Research indicates that by about fifteen years after initial beetle attack the lodgepole pine tree will be on the ground. In phase three all the beetle infested stands have fallen or blown over and the fuels accumulating on the ground will be so thick that you can't walk through it. These jack-strawed forests will look something like pick-up sticks, with the seedlings of the new forest poking up through the pick-up sticks. Fire in this phase will be very intense. It will not be as fast moving as the red and dead phase, but its resistance to fire suppression will be high. Digging fireline in these conditions is extremely slow for firefighters. The heat produced in this phase will affect soils and other ecological components and may be the worst of all three phases. The silver lining is that this will not occur for about fifteen or so years, leaving a margin of time to remove dead trees from the forest in areas of most concern, such as the wildland urban interface, watersheds and other high value areas.
Fire behavior and prediction it is not an exact science; it is part art, part science, part experience and part gut feeling. I cannot predict when, where or even if we will have a major fire, but by understanding the generalities of these three phases, we can all be better prepared to deal with fire if it occurs. 
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