IMAGE: ALASKA WILDFIRE
Cary James  /  Homer Tribune file
Smoke billows from a wildfire burning northeast of Homer, Alaska, on April 29, 2005.
updated 4/19/2006 10:08:52 AM ET 2006-04-19T14:08:52

The internal time clock for Alaska's boreal forest calls for a good, healthy forest fire every 150 years or so.

The trouble is, fires in the forest that covers Alaska from below the Brooks Range to above the Panhandle have been coming fast and frequently. Climate warming has accelerated conditions ideal for conflagration, contributing to record fire seasons in America's largest state and starting a trend that forest managers fear has changed the forest into the next century.

"It's sculpting or shaping our forest to be something that we haven't seen," said Glenn Juday, professor of forest ecology at the University of Alaska Fairbanks.

Warmer summers are just part of the story. Unprecedented spring snow melt has added as much as month more to the firefighting season, allowing grass and other understory to dry sooner and spread flames as never before.

Drought at the end of the summer has extended fire season, sometimes until the snow flies in September.

The National Climatic Data Center reported 8.5 million forest acres burned in America in 2005. Alaska accounted for more than half, 4.4 million acres, the third-largest season in state history. The No. 1 season was 2004, when 6.6 million acres burned.

Alaska is 11 square miles short of the combined territory of Texas, California, Montana and South Dakota, and million-acre fire seasons are routine. Fighting them varies little from techniques in other Western states other than scale, said Lynn Wilcock, chief of fire and aviation for the state Division of Forestry.

The federal government owns 60 percent of Alaska, the state owns 25 percent and Alaska Native corporations and Native individuals own about 14 percent, with less than 1 percent owned by other private interests. But for wildfire suppression, the state is split in half, with the Yukon River as the rough boundary. The federal Bureau of Land Management oversees the northern half of the state. The state Division of Forestry fights fires in the south half. The U.S. Forest Service manages fires in the Chugach and Tongass national forests.

Deciding which fires to fight
For more than two decades, the agencies have had a plan that predetermines suppression levels, ranging from no response other than surveillance to full attack to save lives or buildings. When fire breaks out, firefighters can look at a map and tell whether it's likely to need suppression or monitoring.

Forests with little commercial value, and without structures or inhabitants, often are allowed to burn thousands of acres or more.

"Our area where we allow fires to burn is much broader that in the lower 48," Wilcock said.

It's good for the forest and often good for the wildlife, bringing an abundance of moose in following years.

Fire helps the predominant tree — black spruce — spread its seed and prepares the ground for those seeds to put down roots. The trees, rich in essential oils and resistant to moisture, are genetically predisposed to flaming.

Fifty-five percent of the boreal forest is black spruce, a short, slender conifer that can thrive in soil just 20 inches deep and withstand winter temperatures that routinely drop to minus 50 degrees. Another 20 percent of the forest is white spruce.

Black spruce, Wilcock said, will burn even if surrounded by standing water. The trees are "semi-serotinous," meaning some are sealed with pitch. When a fire moves through a stand of black spruce, the heat causes the cones to open. Cones not burned are made ready to spread seeds.

Black spruce has evolved to have waxy needles, preventing them from getting "wetted up" by rain, Juday said. The needles hold essential oils, volatile organic compounds that are highly flammable. Branches extend down to surface mosses and the trees act as ladders to lift flames on the ground to their tops, where fire can spread quickly from crown to crown.

Their proclivity for burning may be an adaptation to rid the forest floor of duff, thick organic matter that accumulates, Juday said. Spruce seeds don't do well on duff, Juday said. Such an insulating layer, protecting permafrost, also keeps soil cold and a fire allows warmth to penetrate for a time.

More and bigger fires
But summer warming has upset a balance in the forest death-and-regrowth cycle, Juday said. Eighty-five percent to 90 percent of the acreage is burned in fires started by lightning. Over history, for big fires to start, conditions just right for lightning without heavy rain had to find areas on the ground with extremely low moisture content, perhaps where winter snowpack was low.

With climate warming in Alaska, much more of the landscape experiences more days of extreme fire danger.

"You're getting more fires, bigger fires, more severe fires," Juday said. "When they burn, they burn hotter and more severely, and the interval between fires is getting shorter."

The northeast part of the state has been hit especially hard.

"In two years time, fires have burned one-fourth to one-third of all forest land," he said of the area. "It's really gone to a new set point in the whole system."

Warm weather in spring has extended the fire season.

A dangerous time for fires is the window between snow melt and "green up," when plants in the forest start sending up new shoots. Historically, grass from the previous year has not been much of a factor in spring forest fires because new growth appeared quickly. That's changed recently.

Dead grass exposed earlier
Snow in Alaska has been disappearing earlier but the soil has not warmed sufficiently to speed green up.

"Once the snow leaves, what you have in the understory is the dead grass from the previous year," Wilcock said. "All you need is two or three days of hot weather, and it can turn to tinder."

Fires broke out last year on the Kenai Peninsula south of Anchorage in late April, before all firefighting aircraft had arrived and more than a week before veteran crews were scheduled for refresher training.

Drought has extended Alaska's fire season in late summer.

Forest fires used to stop with a season-ending heavy rain in August. Alaska firefighting crews historically could be released to Western states, where the fire season starts and ends later.

The last two summers, 3 million acres have burned in August in Alaska, Wilcock said.

Two years ago, some forest fires didn't stop until snow fell in September. Some burned all winter, lodged deep in duff, itself more susceptible to burning because of drought.

Sharon Alden, meteorologist for the Alaska Interagency Coordination Center, forecasts above-normal fire potential on the Kenai Peninsula this year because of dry grasses and beetle-killed spruce. It's the same forecast for southwest Alaska because of low snowpack and warmer than normal predicted temperatures.

However, two years of El Nino and accompanying above-normal temperatures are expected to be replaced by a weak La Nina, which may mean more moisture in late summer.

"We have a better chance of seeing fire season end in a normal time frame as opposed to the last two extreme years when we had very, very dry Augusts," she said.

Copyright 2006 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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