Forest Fires Linked in Many Ways to Climate Change


Forest Fires Linked in Many Ways to Climate Change

11 July 2012

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USA Heat Wave is Allowing Mountain Pine Beetles that Kill Trees to Proliferate in Higher Numbers than Usual

Heat waves. Dry lightning. Draught. Extreme windstorms. Overpopulation of tree-eating beetles. Wildfires.

What do all of these things have in common? They are the tangible effects of climate change, scientists say, rather timidly. Even the recent rash of wildfires across western states, which have fire crews and residents scrambling to identify causes, can list global warming as a ‘fuel.’

As of last month, the United States has seen over 40,000 hot weather records broken, roughly seven daily hot temperature records for every one cold. By this time last year, only 25,000 daily records had been broken. And 2011 was the ninth warmest year in the contiguous US.

“This is what global warming looks like at the regional or personal level,” says Jonathan Overpeck in a recent Time Science article. Overpeck is a professor of geosciences and atmospheric sciences at the University of Arizona. “The extra heat increases the odds of worse heat waves, droughts, storms and wildfire. This is certainly what I and many other climate scientists have been warning about.”

The heat is fueling the fire in another insidious way. It’s allowing mountain pine beetles to proliferate more than usual.

In many parts of the American West, and particularly in South Dakota’s Black Hills, pine forests are being ravaged by one of the worst infestations of mountain pine beetles in recorded history.

“If it’s not the largest, it’s got to be one of the largest [infestations],” says Craig Bobzien, Black Hills National Forest supervisor. The current infestation by the native beetles is in its fifteenth year. About a third of the forest, nearly 400,000 acres, have already been killed by the beetles. Bobzien assumes the blight will only continue to increase.

The match tip-sized beetles seek out healthy, wide diameter ponderosa pines. They tunnel through the moist bark, drying out and eventually killing the tree, and the next generation repeats the process the next year. The tree might remain upright for another year or two, its needles turning a rusty red before falling off.

Hiking through the Black Hills, you can see both the ravaged trees and forest crews’ attempts to hinder the infestation. Hand piles of slash sit by the road waiting to be burned. Thinned trees lie in piles to dry out. This gives healthy pines extra nutrients and moisture to pitch out the beetles. It also allows for more air circulation, an unfavorable condition for the beetles.

How did the beetle population reach such epidemic proportions? Conditions have been favorable to the beetle habitat, says Bobzien. A dense, wide diameter forest provided ample food and space. A warmer, longer spring made colonizing new trees in new areas easy. A study in Colorado found that a close cousin of the mountain pine beetle was actually producing two generations in a year instead of the usual one. Basically, the effects of climate change encouraged beetle population growth.

Which brings us back to the wildfires. Pine trees that are killed off by beetles are like ticking firebombs, just waiting for one strike of dry lightning in a drought stricken area. In the first few years after their deaths, the pines remain standing with dry needles attached. “It adds one layer of complexity to a complex fire environment,” says Bobzien. Fires can travel vertically as well as on the ground. A ‘crown fire’ high up in still-standing trees is hard to control and travels easily in hot, dry winds.

The pines’ real fire potential presents itself after the dead tree falls. The thick, dry stumps build up as “thousand hour fuel,” the type that burns hot and is difficult to contain. Fire crews usually burn off accumulated ground fuels in prescribed burns, but this year — thanks to the warmer weather, low moisture, and freak storms — fire season got an early start. Prescribed burns were out of the question as crews scrambled to gain control of wildfires that transitioned across the country as the season wore on.

“Fires become very large very quickly in places where conditions come together,” says Punky Moore, Acting Black Hills National Forest Public Affairs Officer. “We still have a long way to go through fire season.”

The areas affected by the current wildfires will recover quickly enough. New growth will push through, the beetles will eventually run out of healthy pines, humans will rebuild their scorched houses. The natural cycle will begin again. It’s the unnatural cycles and effects of human interference that we should be worried about.

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