A tiny beetle and drier-than-normal seasons made hillsides of pine ripe for a blaze when lightning hit. Is it a sign of things to come?

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CORRAL BUTTE, Okanogan National Forest — This lookout offers a sobering vista of burned forests, stretching nearly 40 miles along the flanks and ridges of these northeast Washington mountains.

Here, the Tripod Complex fire fed on timber baked dry in the summer heat. In some places, the flames whipped up fierce winds that uprooted whole tree trunks.

Firefighting crews cleared lines as wide as highways, but the fire raged through large stands of trees that were already dead or dying, struck by beetles that had infested the forest. The trees exploded, unleashing fiery branches and bark that sailed for up to a mile.

“It blew right past,” said Mark Morris, a district ranger for the Okanogan National Forest. “The fire just got too intense.”

The Tripod Complex fire spread through more than 175,000 acres, an area roughly three times the size of Seattle, and still smolders amid September rains and snow. It was one of the largest wildfires in Washington in the past half-century, and has cost more than $82 million to fight.

It also may offer an unsettling glimpse of the future.

Researchers predict that climate change, wrought by greenhouse gases building up in the atmosphere, will bring milder winters and hotter summers, favoring larger fires in Western forests. At the same time, it also is expected to help the beetles that kill timber, making more prime fuel for fires.

Some areas of North American forests already have experienced big upswings in beetle infestations. Over the past two decades, there also has been an increase in big fires both in and out of beetle-infested forests, as well as an increase in the average length of the fire seasons, according to research published in Science Magazine this summer.

This year in the U.S., fires have burned in nearly 9 million acres of U.S. wildlands, the most since at least 1960, and the federal government firefighting bill has topped $1 billion.

Researchers caution that no one fire — or one single fire year — can be blamed on global warming. And, they note that fire seasons are greatly influenced by natural weather cycles of wetter and drier years, such as 1902, when more 1 million acres burned in northern Oregon.

But in the 21st century, the scientists say, climate change is expected to prime the land for more wildfire, and in some regions — such as the rainforests of Western Washington — perhaps shorten the intervals between fires.

“It’s kind of intuitive,” said Jeremy Littell, a University of Washington climate researcher. “When it’s warmer and drier, it’s more likely to burn.”

“A major concern”

Ranger Morris is a devoted hunter and horsepacker, whose backcountry trips take him through plenty of old burns, testimony to fire’s persistent role in reshaping forests.

But Morris would rather see smaller, patchy blazes that don’t threaten communities and create a mosaic of older and young forest stands. Ever since he arrived at the Tonasket District of the Okanogan National Forest seven years ago, he has feared a much larger-scale event.

The threat, in part, reflects decades of human effort to suppress fire, which has allowed a lot of fuel to build up in the forests. In the high country, it’s been heightened by mountain pine beetles that attack the skinny lodgepole pines, and another bark-beetle species that spreads through spruce.

“This was a huge forest-health issue, and a major concern for us,” said Morris.

Both beetles are small and black, less than inch long, but when enough of them bore into a tree to lay their eggs, they essentially girdle the trunk and cut off the flow of vital nutrients.

Both species are more likely to thrive in warmer years.

In milder winters, more of the insects are likely to survive under the bark. In hot, dry springs and summers, adults emerging from the bark appear able to synchronize larger, and more successful infestations in new areas of a forest. Add drought, and the trees are less able to produce pitch that bubbles out to eject the invaders.

In the Okanogan National Forest, a string of warmer years sent mountain pine beetle populations soaring, part of a larger increase in activity in Washington that in 2005 included more than 500,000 acres of lodgepole pine under attack from pine-bark beetles.

In Canada, milder weather set the stage for a gargantuan mountain pine beetle outbreak on some 20 million acres of British Columbia’s vast forests of lodgepole pine. In Alaska, a warming trend helped nurture a beetle attack that killed some 4 million spruce trees.

The warmer temperatures also appear to have altered some beetle life cycles, and expanded the insects’ range.

Spruce bark beetles, for example, typically take two years to complete their life cycle, from birth to adulthood, when they reproduce. As the climate has warmed, however, some have been able to complete that cycle in one year, according to Allan Carroll, a Canadian Forest Service researcher. As a result, there are more beetles to launch stronger attacks.

In recent years, warmer winters have allowed beetles to attack more northern reaches of British Columbia. They also have had greater success killing trees at higher altitudes. In the Okanogan National Forest, for example, the beetles now claim more white-barked pine, a long-lived species at treeline that produces food cones for bears.

There’s no easy control. The beetles are a natural part of the forest ecosystem. Under normal circumstances, they target aging trees at the end of their lifecycles, helping to thin the forests so more vigorous trees can grow.

But when the beetles reach epidemic levels, they may overwhelm the defenses of even the healthiest trees. Sprays are not a practical option since beetles are protected by bark. In British Columbia, they have salvage-logged large amounts of beetle-killed timber.

For Connie Mehmel, a U.S. Forest Service entomologist, the signs of a beetle attack are easy to spot. In a patch of forest outside the burn zone recently, she inspected a lodgepole pine covered with dozens of bubbles of pitch, the tree’s futile effort to expel the beetles.

“If you get massive attack like this, the tree’s defenses will be overwhelmed,” she said.

Conditions right

Even with lots of beetle-killed trees, it still takes the right conditions to set off a big fire in mid- to higher-elevation forests.

Over the past two decades, those areas, ranging from 5,300 to more than 8,000 feet, have had the largest increase in big western fires.

There is a strong association between those fires and the combination of an earlier spring snowmelt and warm summer weather, according to a team of researchers from Scripps Institution of Oceanography, the University of California, the University of Arizona and the U.S. Geological Survey, which published its findings in July in Science Magazine.

That scenario played out in at the Tripod fire, when very hot days in May rapidly melted a big snowpack, and persistent high summer temperatures pulled moisture from the wood.

Then on July 24, lightning ignited beetle-killed trees about six miles northeast of Winthrop. Smoke jumpers tried to quell the flames, but even by the time they hit the ground — a matter of minutes — the blaze had swollen from an acre to 20, forcing the firefighters to retreat, Morris said.

In the first week of September, the work force peaked at more than 2,300, including crews from New Zealand and Mexico. Through the summer, the crews succeeded in a key objective, protecting Winthrop, Twisp and Conconully. But through the course of the fire, at least a dozen lines did not hold and the fire moved east into the Loomis State Forest, and north almost to the Canadian border.

So for Morris, it has been a long fire season.

He has taken many drives through the burn zone, surveying the restoration work that will include easing soil erosion, protect trails from falling snags and replanting bulldozed fire lines.

In some areas, he notes the fire laid low and spared most of the big trees. There the forest will be quick to rebound.

In other areas, such as the charred-gray slopes around Corral Butte, the fire torched young seedlings that had sprouted since a fire in the 1990s. Pine and spruce forests should eventually return. But the process will take decades.

“There’s enough fire on the landscape, don’t you think?” he said.

Hal Bernton: 206-464-2581 or hbernton@seattletimes.com