It has been nearly two weeks since a tongue of lightning touched down in the foothills of the Colorado Rockies, sparking the biggest wildfire in Larimer County history and the most destructive -- with almost 200 buildings damaged to date -- in the state's memory.
The High Park fire comes as a kind of second death for this stretch of the Arapaho-Roosevelt National Forest, where mountain pine beetles have held at epidemic levels for almost half a decade. Vast stretches of rust-red canopy, dry and primed for fire, are a testament to an infestation that has affected some 70 percent of the trees in the region.
Thanks to the beetles, there has been no shortage of ready fuel and the fire has spread quickly, whipped by sporadic winds from the southeast.
Since the blaze was set on June 9, fire crews have been working ceaselessly, and have reined in the fire at its eastern and northern edges. But converging forces are working against them.
Hot, dry conditions have fanned the flames, while beetle kill and a long-standing policy of fire suppression have left forests thick with dry, available fuel. In the rugged, forested mountains to the west, the fire has continued to advance, claiming 59,500 acres as of Tuesday evening.
Without rain, forest managers say, the blaze could continue throughout the summer.
Agents of change
When pine beetles take over a forest, fire is typically not far behind, said Cal Wettstein, incident commander with the Rocky Mountain division of the Beetle Incident Management Organization.
"When trees die, they go through a natural process of drying" -- leaving them vulnerable to fire -- "and eventually falling," he said. "When beetles get into a forest, they essentially shortcut that first stage."
Mountain pine beetles attack en masse, coordinating by pheromone signal to converge in the hundreds on a single pine tree. They carry in their mouths a potent blue stain fungus -- a kind of natural, viral weapon -- which, once it has infected a tree, pulls moisture from the wood, weakening it.
The tree's only defense against the intruding beetles is to fight back with secretions of sap, further draining it of moisture.
If beetles attack in great enough numbers, the tree is eventually sapped of life, and dies of dehydration.
A forest in the grip of a pine beetle epidemic resembles the aftershock of a severe drought -- reddish-brown canopies of tinder-dry needles, waiting only for the touch of a spark to set them ablaze.
Those trees burn hotter -- and the fire spreads faster -- than they would in a forest untouched by beetle blight, said Rocco Snart, a fire behavior analyst trainee who has been working on the ground with crews battling the High Park fire.
"In the Arapaho-Roosevelt forest, you've got pine trees in just about every stage of beetle kill," he said. "You've got the greenish yellow of last year's killed trees, the red-needled trees that were killed before, and in a few places you'll see what we call the 'ghost forests'" -- trees killed long ago that have since lost their needles.
While the yellowing needles can ignite with enough temperature, it's the reddish-brown canopy you most have to worry about, he said. Those dry, brittle needles can ignite with explosive force, hurling embers up into the air to be carried by the wind to set other fires.
"It's the difference between gasoline and a pile of grass," he said. "Those flammable compounds can induce more fire behavior in the crowns, they're more flashy and they have more energy."
An old story, often retold
Fire is as much a part of Western forest ecology as the trees themselves, clearing old growth and allowing new seeds to take root and grow. So intricately linked are the forces of destruction and rebirth that the pine cones of some trees release their seeds only under extreme heat.