Dead trees equal big fires? New study says no

Dead trees equal big fires? New study says no

26 September 2010

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USA —  The red swaths of forest killed by mountain pine beetles might not be the fire menace many have assumed they are, a recent study has found.

Researches from the University of Wisconsin and Yellowstone National Park have surveyed pine forests in and around the park, comparing stands that have been hit with the burrowing bug to those that have not.

Using computer programs that model wildfire behavior, they found that dying and dead stands of trees might be less susceptible to major fires than stands that are lush and green, since there is less fuel to burn. Also, fewer needles on trees make it harder for fires to become crown fires.

“Our results do no support the assumption that there’s an increased fire risk after the beetle outbreak,” said Wisconsin researcher Martin Simrad, “and it possibly could decrease it under certain conditions.”

“When we looked at the fuel data, it was really obvious that … there was much more fuel in the undisturbed stands,” he said. “It was clear that even in the red stage and the gray stage, the amounts of fuels just plummeted.”

The outbreak of mountain pine beetle has affected an estimated 4.5 million acres of national forest in Montana alone.

As the forests have turned red and gray, many have argued that that the dead forests are prone to catastrophic forest fires.

Simrad said that’s a reasonable assumption, but said it was just that, an assumption, and that very little research has been conducted on the subject.

“If you want to build a campfire, you don’t use green needles, you use red needles,” he said. “But it seems when we are talking forest-wide fires, it’s a completely different scale.”

Yellowstone National Park vegetation management specialist Roy Renkin said in a story published by NASA that beetle-killed forests have long been assumed tinderboxes, but that in his 32 years at Yellowstone, “observations never quite met with the expectation.”

The assumption that beetle-killed trees are more susceptible to forest fire has gotten a lot of play from Sen. Jon Tester, D-Mont., as he touts his Forest Jobs and Recreation Act.

“The bill emphasizes the harvest of ready-to-bun beetle-killed trees near Montana communities,” Tester’s office said as it unveiled the bill, which would mandate 10,000 acres of logging annually for 10 years.

A Tester spokesman said the office was aware of the study, but said the findings did not challenge Tester’s bigger contention that Montana’s forests are susceptible to fire.

“Wildfire still is and will continue to be a significant challenge facing our national forests unless we address it,” Aaron Murphy said in a statement. “Jon’s bill addresses this challenge through a carefully balanced plan put forward by a lot of Montanans to restore our forests and watersheds while creating new wilderness and recreation areas, and jobs in Montana.”

Simrad emphasized that the study didn’t suggest beetle-killed forests do not burn. Rather, in dry conditions, they are just as likely to burn as green forests are. But under “intermediate” fire conditions, models did show them less combustible.

To further their understanding of beetles and fire, Simrad and his fellow researchers plan to use satellite imaging to compare where, in recently history, forests have been infested with beetles and where forest fires have occurred.

The research took place across Yellowstone and Bridger-Teton National Forest. The study will be published in the journal “Ecological Monographs.”

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