Scientists Sorting Out Beetle-Fire Relationship

Inside university laboratories and government research facilities across the country, scientists are playing with dozens of variables – mixing and matching and rearranging – to gain a better understanding of what makes wildfire go.

They’re busy building computer models as firefighters toil on steep mountainsides to put out more than a dozen new blazes in what has already become a vicious summer of destruction.

Colorado is having its worst fire season in a decade, while New Mexico is recovering from two record fires – one that charred more than 465 square miles and another that destroyed more than 240 homes.

The experts all agree: The dry conditions and strong winds are driving this year’s super fires.

So what happens when researchers add to their formulas the devastation caused during the last 15 years by an epidemic of hungry bark beetles? The tiny insects have turned more than 40 million acres of the nation’s forests into an unsightly patchwork of red and gray death.

“We’ve always had bark beetle infestations, but we’ve never had anything that’s been so widespread and spread so quickly,” said Tom Tidwell, chief of the U.S. Forest Service. “The only place it’s really starting to slow down is just where we’re starting to run out of trees.”

From Colorado’s resort towns of Vail and Aspen to mountain communities in Wyoming, Idaho and Montana, local leaders are worried about fires burning hotter and faster due to the beetle kill.

Some of this year’s fires have already burned through areas affected by the native insects, but fire behavior analysts and researchers say the result isn’t always a hotter, more severe fire. Sometimes it is.

With the ingredients of topography, fuels and weather always changing, the beetle effect comes partly down to timing. Then there’s the species of beetle (there are 15 in the West), the type of trees being attacked and the intensity and rate of tree mortality.

“It just isn’t anything that’s straight forward,” Tidwell said.

Peter Fule, a forestry professor at Northern Arizona University, ticked off a list of factors. “This is one of the big problems with trying to assess fuel hazards and how dangerous the potential really is for fire,” he said.

In some circles, the thought is that fire danger is highest when beetle-killed trees still have their red needles. These fine fuels add to the probability of crown fires, which are the most difficult to suppress.

A study released last year by U.S. Forest Service ecologist Matt Jolly showed that the needles of beetle-killed trees contain 10 times less moisture and a different chemical makeup than healthy trees. That means the red needles can ignite three times faster and burn more intensely than healthy trees.

Yet, another study done by ecologists at the University of Wisconsin found that a beetle-damaged stand of trees will probably not burn any more intensely than a green stand under intermediate weather conditions. Their modeling showed insects and fire are linked, but that one doesn’t cause the other.

The standing gray skeletons that are left a few years after a beetle infestation are less of a problem. But once they fall, they add to the fuels on the forest floor, again becoming a concern for land managers and firefighters.

Some researchers say the fallen trees actually decompose faster, lessening the length of time the debris can influence fire behavior.

Annual aerial surveys done by the U.S. Forest Service show the number of new acres being attacked by beetles has actually decreased overall from a peak of 8.8 million in 2009 to 3.8 million last year. However, there are pockets in some parts of the West where beetle infestations continue to accelerate.

The federal government is spending about $100 million a year as part of its five-year strategy for tackling the beetle kill. It includes reducing the danger of falling trees along roadways, trails and in campgrounds as well as thinning and insect control projects, particularly in watersheds and areas that are becoming more populated. Part of the plan also includes trying to make forests more diverse in terms of tree species and ages to avoid the mass die-offs such as those happening in lodgepole pine and spruce forests in the Rockies and Canada.

The goal is to treat more than 2.5 million acres over five years. However, that’s only a fraction of the landscape that has been devastated by beetles in just the last few years.

Like fire, the beetles are feeding on the inability of trees to overcome the stress of a worsening drought and intense competition for resources that results from decades of fire suppression.

“These are native beetles,” said Robert Mangold, the U.S. Forest Service’s director of forest health protection. “We are not trying to log our way out of this. We are not trying to eradicate these beetles. We are living with them, but when they exceed the normal level of activity, we try to mitigate.”

Mangold said a changing climate has resulted in mild winters, which have failed to keep beetle populations in check in the north. There are also signs the insects are moving up in elevation and attacking Whitebark and other pine species that usually don’t have to contend with the pests.

Researchers at Colorado State University, Los Alamos National Laboratory and the Rocky Mountain Research Station are working on new models that will help managers deal with fire and beetles.

“What our research has been showing is that the beetles can have an influence but they really only influence that fire behavior under certain conditions,” said Chad Hoffman, an assistant professor of fire science at CSU. “Those conditions can be present at one place and not at another place, or one hour the beetle kill might not really make a difference and then an hour later it could make a big difference.”

A decade ago there was little research on the beetle-fire relationship. Now, there are papers being published on everything from the severity of fire in beetle-kill areas to fire behavior and the probability of fires breaking out.

“It’s an exciting time,” Hoffman said. “The models that are being developed are allowing us to ask very different questions than we were able to ask a few years ago.”