Study: Beetle-killed pines burn 3 times faster than live trees

Posted: March 14, 2012

Source: Missoulian

Beetle kill trees burn faster than live treesA recently study should put to rest the notion that green lodgepole pine needles burn as fast as redones.

But more than that, Matt Jolly said, the study could help open firefighters’ eyes to the dangers lurking in mountain pine beetle-infested forests where the trees still look to be alive and doing well.

Jolly is a research ecologist with the U.S. Forest Service’s Rocky Mountain Research Station and co-author of a recent study that set out to document the flammability of lodgepole pine needles during different stages of pine-beetle attack.

The researchers collected foliage from lodgepole pine trees and tested changes in chemistry and flammability in an attempt to quantify how much heat was required for those needles to ignite and how fast they would burn.

Jolly said one focus of the study was to put an end to the debate over the flammability of green needles of a healthy tree and those that have turned red after a tree has died.

“In that case, we were quantifying things that we really should already know,” he said. “There were a lot of conflicting opinions out there that weren’t supported by fact. There were some who said green needles burned at the same rate as red needles. There were people latching onto that idea.”

That’s not the case, according to Jolly and his fellow researchers.

Their study showed that red needles ignite three times faster than green, living needles. Moisture levels in red needles were 10 times less than their healthy counterparts. And, Jolly said, there was also a change in chemistry that made the red needles burn faster.

But what was more interesting to this forest ecologist was the rapid rate that lodgepole pine trees change following a beetle attack.

“We found that the moisture content in the foliage started to decline quickly following a beetle attack,” he said. “While it can take quite some time for the tree to begin to show visible signs of the attack, it can be more flammable with no visible indicators.”

That piece of information could be very important for firefighters.

Before the study, there wasn’t much known about the physical and chemical changes that occur in lodgepole pine foliage when the trees die from a mountain pine beetle attack. There was also no documented evidence that showed how those changes affected the flammability of the tree’s foliage.

The researchers combined field sampling, laboratory analysis and bench-scale ignition experiments to gather data for their study.

The study will help provide information fire fighters can use to plug into fire behavior models that could help predict how fires will react as they burn through forests in early stages of mountain pine beetle attacks.

“It’s something that should help increase awareness and basically help firefighters know what to look for,” Jolly said. “They can see the pitch tubes and boring dust and assume those trees are dead and will be more flammable than green trees.”

This summer’s Saddle Complex fire in the Bitterroot and Salt Fire in Idaho challenged the traditional thinking that as trees die and lose their needles, those forests will be at less risk for large fires, Jolly said.

Both of those fires made large runs through stands of mostly dead and standing timber.

In the right conditions, Jolly said fire researchers are seeing fires burn through stands of gray trees too.

This study is a first step at looking at the more complex issue of how crown fires change as trees lose their needles, he said.

“There is still a tremendous amount of unknowns,” he said.

Co-authors in the study included Russ Parsons, Ann Hadlow, Greg Cohn, Sara. S. McAllister, John B. Popp, Robert Hubbard and Jose Negron. The study was published in the Elsevier Forest Ecology and Management Journal.