Study: fires in beetle-killed spruce less predictable

Posted: Sunday, June 27, 2010

Firefighters should take extra precautions when battling blazes in spruce bark beetle-infested areas, according to the Caribou Hill fire model.

Clarion File Photo
Clarion File Photo
A firefighter from the Denali Hot Shots crew is dwarfed by flames in June 2007 as he uses a fuse to ignite grass near a structure that his Fairbanks-based crew was fighting to protect from the Caribou Hills fire near Ninilchik. A recent study looks at fire behavior in the various fuel types found in that fire.

Spruce Bark Beetle Mitigation Program Forestry and Fire Specialist Wade Wahrenbrock said that beetle-killed areas burn hotter and are less predictable than standard "green" forest fires. Firefighters need to plan well-defined evacuation routes, said Wahrenbrock, who authored the study, and closely follow weather and wind patterns. The level of humidity plays an important role, according to the fire specialist, because dry air leads to drier fuels.

"Let's say you clean your sink out at night and leave the sponge out," he said. "The next day it's quite dry."

Fires in beetle-attacked areas spread faster because of the blue joint grass, which typically fills infected forest floors, he said.

The grass, called calamagrostis canadensis, creates a thick mat and cools the soil to enable its growth, according to the fire specialist. He described the grass as a flashy fuel.

The combination of trees and grass is particularly hazardous because the blue-joint will burn quickly, whereas the infested spruce will stay aflame longer, he said, which allows the fire to smolder and meander through the forest.

"Dead spruce and grass has the capability of creating a fast rate of spread," he said.

The grass grows to around three to four feet tall, which also limits mobility, according to Wahrenbrock.

"You can't see where you're putting your feet," he said.

Wahrenbrock said that dropping flame retardants from helicopters is less effective as well. Beetle-bitten trees fall on top of one another, he said, which adds various levels of fuel for the chemicals to penetrate. Air deployed fire retardents add moisture to burning areas, he said, which acts as an "instant mud."

The forests are drier in part because the beetles eat away the fleshy tissue between the bark and the wood, which prevents water and nutrients from circulating through the tree.

"It's just like when you take a chainsaw and do a circle around it," the fire specialist said.

The added drieness can make trees reach an ignition temperature much quicker.

The research also allowed Wahrenbrock to study different types of trees and help develop what fire specialists call a custom fuel model for the Kenai Peninsula.

Division of Forestry Area Forester Hans Rinke said that the Caribou Hill study will help predict potential growth rates and the total size of the fires. The model will be particularly useful when dealing with fires in the central and southern regions of the Peninsula, said Rinke.

Tony Cella can be reached at

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