Forestry experts say commercially thinned areas fared better in 5,524-acre 36 Pit Fire

Forestry experts say commercially thinned areas fared better in 5,524-acre 36 Pit Fire

29 May 2015

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USA — The bracken ferns already have come back strong, along with the wild irises and ground-hugging thimbleberries. But all around them are charred stumps and trees so badly scorched by last fall’s 36 Pit Fire that they are dying.

The fire, which broke out Sept. 13, 2014, at the old 36 Pit quarry, spread quickly through steep terrain on both sides of the Clackamas River, about eight miles southeast of Estacada. Before it stopped advancing, the fire burned 5,524 acres, drawing a total of 967 firefighters to the battle.

Several areas were safely evacuated. Only one firefighter was injured.

On Friday, the Oregon State University Extension Service, Northwest Fire Science Consortium and Oregon Forest Resources Institute led a tour of the burned area, discussing the unique set of circumstances that let the fire grow so rapidly, as well as lessons learned in the fire.

But first, said Mike Moore, fire management officer for the Mount Hood National Forest’s Clackamas and Zigzag ranger districts, firefighters don’t consider the 36 Pit fire officially “out.”

“It’s still not called out,” Moore said. “We were hoping for a heavy snow load this year, but we all know what happened.”

Moore said the U.S. Forest Service will make an aerial survey this summer, using infrared cameras at night to look for any lingering hidden hotspots.

The fire was started by a freak target-shooting accident at the 36 Pit quarry. Forest Service investigators determined that ricocheting bullets sparked the fire. Moore said in his 20 years on the job, recreational shooting has caused only three fires, the others by a signal flare and a tracer round.

Meanwhile, the conditions were extremely hot and dry when the 36 Pit fire broke out. Temperatures ranged from the high 80s to mid-90s, with relative humidity hovering around 34 percent. Moisture in the fuels was measured at 14 percent. And 30 mph winds were blowing steadily out of the east, with the Clackamas River canyon creating a Venturi effect that sped and directed the winds toward the fire.

By the end of the second day, the fire had exploded to 2,360 acres, then doubled over the next four days.

The fire burned in uneven patterns – almost a mosaic – that created side-by-side contrasts that depended largely on terrain and conditions in the woods. Flames shot up steep slopes unabated, but slowed to a crawl on flat areas. In some areas, the fire burned close to the ground, blackening the tree trunks, but didn’t get up into the trees’ crowns.

But one thing was clear: Stands that had been thinned by selective logging fared far better than areas that hadn’t been managed.

“Forest management definitely made a difference,” said Mike Haasken, forester for the Oregon Department of Forestry’s Molalla Unit. “Areas where there was commercial thinning, the fire slowed down.”

But the fire was an equal-opportunity destroyer. Almost 70 percent of the burned areas were in Forest Service stewardship. Almost 24 percent were managed by the U.S. Bureau of Land Management. Another 6 percent were in private ownership.

Salvage logging may be limited in burned-out areas. A BLM survey showed only 28 acres out of 1,315 acres suitable for salvage.

Todd Reinwald, soil resources officer for the Mount Hood National Forest, said the Forest Service immediately fixed the fire lines by restoring berms and reseeding the areas that had been laid bare. Next, hazard trees were removed to prevent accidents on Oregon 224 and other roads.

“And finally, we’ll be doing some aerial seeding on the slopes, spreading natural grasses,” Reinwald said. “The ‘green-up’ is pretty good already. And because less than 20 percent of the soil was subjected to a high-severity burn, the ‘seed bank’ in the soil wasn’t destroyed. That means there’s a good chance for the trees to come back on their own.”

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