Thanks to Derek for submitting. From the Missoulian here.
Last summer, a wall of flame roared through a three-mile stretch of tinder-dry, bug-killed lodgepole pine forest and forced a large group of firefighters to retreat to a safety zone.
An official said later the flames moved through the trees like fire does through grass.
In the upper West Fork of the Bitterroot, another fire blew through 17,000 acres in a day. Much of that area also was covered by lodgepole pine killed by mountain pine beetle.
That unusual fire behavior now has some fire ecologists questioning conventional research that suggests that wildfires won’t burn as fiercely through forests filled with bug-killed trees.
“We definitely saw some unusual and pretty amazing runs under fire conditions that we would normally consider to be moderate,” said Matt Jolly, a research ecologist with the Rocky Mountain Research Station’s Fire Sciences Laboratory in Missoula.
Earlier research based on modeling suggested that stands of dead and dying trees were not as prone to flare into fast-moving crown fires. And if the fire did manage to make it into the crowns, the research said it was unlikely to stay there long.
Firefighters and researchers saw something quite different happen this summer.
“These fires were quite a bit more active than what the conventional research suggests,” Jolly said. “The problem is most of the conventional research used simulation models. If you don’t have good observations, then you have to assume the models are correct.”
Before this year, the past three summers were marked by very wet Augusts, which is typically the peak of the wildfire season in western Montana.
“We’ve been dodging the bullet, if you will, over the last three seasons,” Jolly said.
Canadians have been reporting similar fires in their own forests filled with beetle-killed trees for a number of years.
The fires this summer burned in conditions that weren’t considered extreme over an understory that was often still green. At times, the solid walls of flame reached from the ground to far above the canopy.
In some cases, the fire was burning through a forest of mostly dead trees that had already shed most of their needles.
Jolly said trees attacked by mountain pine beetles start a downward spiral that makes them more susceptible to fire early on. Once the trees die, their needles turn red before falling off. The red needles are extremely flammable.
Once the needles fall off, the forest has a gray appearance. This summer, Jolly said the fires blew through those standing gray stands.
“A lot of people have proposed that once the needles fall off, there’s little opportunity for a crown fire,” he said. “In these gray stands, you essentially have a vertical dead fuel with extremely low fuel moistures that once ignited, can create a flaming front.”
Fire researchers also noted the fires were quick to form a column that created its own weather, which further enhanced burning conditions.
For these fires to occur, Jolly said fuel conditions, weather and topography have to be aligned just right.
In many cases, the fire conditions were not considered extreme.
“These fires burned under less than extreme conditions in the same way that a healthy stand would burn under extreme conditions,” Jolly said.
The dead stands are made up of vertical fuels that respond quickly to changes in the weather and humidity levels.
“That’s why it happens very quickly,” he said.
With hundreds of thousands of acres of bug-killed stands scattered across the West, Jolly said there is a “very real possibility” of seeing more fires like this past summer’s.
“It’s totally dependent on weather,” he said. “As soon as we have a dry year like we saw in 2000 or 2003, which came with a very prolonged period of drying, it will be very interesting to see what happens.”
Bitterroot West Fork District Ranger Dave Campbell said research like Jolly’s will be important to those who fight and attempt to manage the blazes.
“This was a good opportunity for us to partner with the fire lab, which has some of the best fire scientists around,” he said. “Hopefully, we will be able to make the models for the future.”
Read more: http://missoulian.com/news/local/article_33e5c862-f930-11e0-9771-001cc4c03286.html#ixzz1bEYungr1