Experts: Fire doesn’t always follow beetle kills

Experts: Fire doesn’t always follow beetle kills

02 October 2010

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USA —  The millions of acres of beetle-killed forests in the Rocky Mountain West are their own worst public relations nightmare, as witnessed by their picture-postcard ugliness.

They’re red, dead and dry.

They could erupt in wildfires under the right conditions, said Dan Tinker, an associate professor of botany at the University of Wyoming.

On the other hand, the millions of acres of green, healthy forests could do likewise, Tinker said.

“It’s a risk either way,” said Tinker, a specialist in forest and fire ecology.

A beetle-killed forest is not necessarily at a greater risk for fire than a healthy, green one, he said.

Two recent fires illustrate the absence of that correlation, Tinker said.

The Illinois Creek fire in the Medicine Bow National Forest in early September burned 112 acres, and many of the dead lodgepole pines had been killed by the mountain pine bark beetle, he said.

The Fourmile fire in Colorado west of Boulder at the same time covered nearly 7,000 acres and destroyed about 170 homes, but the tiny bugs can’t be blamed for that, Tinker said. “Very, very little if any of that was caused by the bark beetle.”

To underscore his point, no major fires have occurred in the millions of acres of dead lodgepole pines around Grand Lake, Colo., he said.

And when fires happen, they don’t burn uniformly or kill everything in their paths, Tinker said. “Rarely is there a 100 percent mortality of trees.”

None of this minimizes the severity of this epidemic, Tinker said.

Mountain pine bark beetles occur naturally in the Rocky Mountain West and maintain forest health in normal conditions.

Epidemics have occurred in the past, Tinker said.

But the one starting about a decade ago is different, he said, because of the threefold combination of severe drought that weakened the trees, lack of cold winters that often kill beetle larvae, and the numbers of trees about a century old — beetles prefer old trees at least 5 inches in diameter — and their location.

In addition to these three factors, the federal government’s policy of suppressing wildfires as much as possible may have contributed to the epidemic and the fire risk, wrote UW science major and law school graduate David Willms in the current issue of the Wyoming Law Review.

“Years of strategic fire suppression have exacerbated the volatile situation on the ground,” wrote Willms, who earned degrees in wildlife and fisheries biology and management, and environment and natural resources.

The policy has hindered naturally-occurring wildfires from clearing forests, making trees more susceptible to beetle attacks, and leaving more fuel for fires, he wrote.

“Today, forests contain nearly twice as much biomass as they contained under historic natural conditions,” Willms wrote. “In turn, the beetle epidemic may increase the risk of a large-scale fire that could sterilize the soil and lead to the delayed regeneration of our forests, increases in erosion, and pollution of our water sources. Alternatively, if fires do not burn the beetle-killed areas, then ghost forests could become a predominant feature for dozens of years.”

While the century mark corresponds with the fire-suppression policy, Tinker said he doesn’t believe a connection exists with the current epidemic.

He’s studied the aftermath of the fires in Yellowstone National Park in 1988 that burned 1 million acres, and said the park has no fire-suppression policies, other than for inhabited areas, because it is managed to be an untouched ecosystem.

Climate change may be affecting the spread of the beetles, too, but Tinker said whether people have contributed to that change is another question.

Green and red

Instead, weather — temperature, humidity, wind, lightning, precipitation and other factors — leads the causes of fires, he said.

People can’t do anything about the weather, or the terrain affected by a fire.

But they can do something about the fuel, to a point.

The fuel can be either living or dead trees, either of which offer their own flammable kind of support.

“Green needles are not any less flammable than red,” Tinker said.

As anyone who has had a live or fresh-cut Christmas tree knows, caution must be exercised because of the potential for fire.

Green needles have a variety of volatile chemicals that can burn very hot and offer an excellent fuel for “crown fires” — when the flames jump from treetop to treetop, Tinker said.

In the case of beetle-killed trees, some of those chemicals are lost, a U.S. Forest Service fire specialist said.

However, the moisture content also is lost in these needles and the rest of the tree, which creates its own kind of fire danger, said Paul Langowski, the Forest Service’s branch chief for fuels and fire ecology in the Rocky Mountain region.

The only moisture they have is pulled from the air, and that can fluctuate within an hour, Langowski said.

So a recent beetle-killed forest poses a somewhat greater hazard than a live forest, Langowski said. “In general, the red and dead stage is a little bit more flammable than green trees.”

That changes after a few years, he said.

The needles and small branches fall, leaving standing dead trees called snags apart from each other and unlikely to spread fire, Langowski said. “As needles and branches fall off, the crown fire danger decreases.”

However, those snags of lodgepole pines with their shallow root systems will eventually fall in 10 to 20 years at a rate estimated at 100,000 a day for those killed a decade ago.

As they do, they will cover the forest floor and cause access problems for firefighters.

The moisture level of the tree is about 65 percent after beetles attack, even though the needles remain green that summer, he said. “They’re dead, but they don’t know it yet.”

On dry, hot and windy days, the dead trees’ moisture content can fall to the single digits, which is similar to the kiln-dried 2-by-4s available at a home improvement store, Langowski said.

“Then it’s a very high fuel content fire hazard,” he said. “It’s very difficult to fight.”

All of which puts the U.S. Forest Service in some awkward positions.

“The relationship between bark beetle mortality and fire is extremely varied,” Langowski said. “On top of that is the intensity of the mortality across the landscape.”

The Forest Service can’t clear-cut the Rocky Mountains, so it sets firefighting priorities for inhabited areas, infrastructure and places that offer the fewest hazards to firefighters, he said.

Tinker complimented the Forest Service for its handling of fires in beetle-killed areas, especially with threats to power lines, roads and inhabited areas.

“I think they’re doing a great job,” Tinker said. “If they get rid of it now, they won’t have a problem in 10 years.”

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