BOISE — The number of acres charred by wildfires across the West this year is almost double the 10-year average, but this summer's forest fires have not been as big nor as devastating as those in past years.
Fire behavior experts say the apparent contradiction is due to the unusual moisture patterns in the region earlier this year, which favored big grass fires on the open range. Timber in the mountains got more moisture than usual well into the summer, keeping forest fires small.
And fate has played a role.
"It's sort of like Swiss cheese. All the holes have not lined up at the same time," said Tom Wordell, a wildland fire analyst for the U.S. Forest Service and leader of the multiagency group of scientists and meteorologists that predicts fire danger around the nation.
"To get a big fire, you need high temperatures, low relative humidity, dry fuels and winds all aligned on the same day," Wordell said. "We haven't seen that much this year, yet our overall acreage burned is much higher than in the past."
According to the National Interagency Fire Center, more than 7.3 million acres — more than 11,000 square miles — have burned in the United States since May. About half of that was in Alaska, where large fires often are not fought aggressively if they pose no threat to people or structures.
The national total is more than a million acres ahead of the record fire season of 2000 and is nearly double the 4 million acres that burned on average through late August over the past decade.
But with the 2005 wildfire season two-thirds over, the high acreage figures belie the consensus of public land managers that this has been a relatively tame fire year. The number of fires is down — about 44,000 compared to the 10-year average of 62,000 — and the number of firefighters summoned to help suppress the blazes has been lower than in recent years.
Analysts say the primary reason for the higher-than-average fire acreage this year is huge range fires that burned in the Southwest and Great Basin, where a wet winter allowed fine grasses and vegetation to flourish. Those "flashy" fuels then dried and cured early in the dry spring, inviting the spread of range fires as summer approached.
"Earlier this season, when we knew we had large fine-fuel loading, one of the sage old firefighters said to me, 'Man, the fires are going to be in the deserts this year and not the mountains.' And that's been the case," said Brad Smith, a Texas Forest Service fire behavior analyst who represents state foresters on the national fire prediction panel.
By the end of August in the Great Basin — which includes western Utah, southern Idaho and much of Nevada — the number of acres burned this season was 250 percent of normal. That was an improvement from the end of July, when the amount of land burned in the Great Basin was five times the normal amount.
Many of the range fires in the Great Basin and Southwest have been epic in size and speed. The Clover fire in late July in southwestern Idaho at one point was burning 500 acres an hour. It eventually blackened an area 35 miles wide and 10 miles across.
Despite their size, though, the range fires have frequently burned in areas far from civilization and have caused relatively little structural damage.
"I'm always cautious to downplay range fires because if it's your ranch building or grazing allotment that got burned up, it's pretty important," said Wordell, head of the National Predictive Services Group at the Interagency Fire Center in Boise. "But timber fires require a lot more people, equipment, time and money to put out, and so far even when we've had lightning ignition, we didn't get the large fire initiation."
The primary reason for this year's lack of huge timber fires — the 100,000-plus acre blazes that make national headlines — is the moisture retained by trees and foliage in the higher elevations of the Cascades, the Sierra Nevada and the Northern Rockies, captured during an unusually long, wet spring.
"We're just not seeing significant spread through the alpine zones" because of the moist fuels, said Jack Cohen, a research physical scientist for the U.S. Forest Service's fire sciences laboratory in Missoula, Mont. "The fire is abating as it burns in these areas."
While the slow spread of fires in alpine conifer forests has helped firefighters, it's been a disappointment to those who advocate wildland fire as a natural rejuvenator of the woods.
"You're just not getting much use out of wildland fire if the fires don't get very big," said Greg Aplet, a forest ecologist with The Wilderness Society in Denver. "Rocky Mountain National Park had a wildland fire that kept burning in the park, and every day they reported its status and were very proud of it. But it was basically just a pile of duff smoldering at the bottom of a tree for a week."
Between the moist timber in the high mountains and the fine dry grasses on the desert range lies the greatest potential for catastrophic blazes in the remainder of this season, fire analysts say.
Mid-elevation woodlands with a heavy buildup of dry, dead material on the forest floor mixed with open areas that have heavy grass and shrubs are yielding higher than average "energy release components" — a measure of the available energy that would be released in the flaming front of a fire.
"In the area that runs from northern California through central and eastern Oregon on into central Idaho, we are seeing energy release components that are setting records," Wordell said.
Eastern Washington's School fire, the season's worst wildfire thus far in terms of property loss, was in that mid-elevation zone where prairie, woodlands and agriculture fields are interspersed. It broke out Aug. 5 and burned nearly 50,000 acres and 109 houses before it was extinguished some two weeks later.
"With the School fire, you had so many structure ignite because they generally had continuous grasses right up to them," said Cohen, a fire physicist who studies how wildfires burn houses. "It wasn't that you had this big humongous fire. It was that at significant times during the fire, the intensity was high but the rates of spread were extremely high. And that's just very difficult to contain."