I've been following the mountain pine beetle issue for years trying to winnow the hysteria and political posturing from the ecological insights. It seemed that the current plague of beetles was an entirely natural occurence made worse by decades of fire suppression and warming climate. (see Smokey Terror and Denim Pine). Realism makes a rare appearance.

Some environmentalists and scientists support the beetles. While they acknowledge the severity of the problems the beetles are causing, they argue that the insects, which kill only mature trees larger than five inches in diameter, are a natural phenomenon, like forest fires, and play a vital ecological role.

“It’s not the end of the forests, and they are not destroyed,” said Diana L. Six, a professor of forest entomology and pathology at the University of Montana here, who has studied the beetle for 16 years, as she walked in a beetle-infected forest near here recently .

“Lodge pole pine evolved to go out with a stand-replacing event, such as fire or beetles, then regenerate really quickly,” she said. “When they hit 80 or 90 years of age all of a sudden the beetles become a player — the trees are big enough for the beetles to attack. They reset the clock on the stand.”

Dr. Gregg DeNitto, a forest health specialist with the Forest Service here, said the beetles were not “an exotic like the emerald ash bore.”

“This is a native insect in a native host, and these are normal biological processes that have happened for millennia,” Dr. DeNitto said.

Nothing can or should be done to halt the spread of the beetle, experts say. After they kill the mature trees, the soil becomes more fertile as nitrogen levels increase, sometimes tripling. The growth rate of surviving trees increases when the infestation ends. After dead trees fall over or burn, grass grows and provides elk habitat, and slightly more diverse forests rise up.

Beetles help by breaking down fallen trees, as well. “They digest the wood and are valuable in terms of nutrient recycling,” said Dr. Ken Raffa, an entomologist at the University of Wisconsin who studies the beetles. “And they introduce micro-organisms that further break down the wood.”

All true, however as with fire we have made the natural phenomena worse with bad management.

Both Dr. DeNitto and Dr. Six allow that the current outbreak is not entirely natural. Human intervention in the form of fire suppression and large-scale clear cuts mean that many forests are simultaneously vulnerable.

Under natural conditions a forest is a patchwork of different-age trees, which means the beetles also create a patchwork of dead trees. “If they come up against a young patch, they’ll quit,” Dr. Six said. “If it’s old, they keep on going. But we’ve lost that mosaic, so they keep on going.”

The major human-caused element of the current outbreak, though, is a warmer climate, which has opened new territory to the beetles. And this has caused some experts to view the beetle infestations as unnaturally severe. “The absolute minimum temperatures are 6 to 10 degrees higher now,” said Dr. Steve Running, an ecologist at the University of Montana who is a member of the Internal Panel on Climate Change and is studying the effect of warming on Western ecosystems.

In the 1950s, minimum temperatures were 42 to 47 degrees below zero. The last decade, the minimum was 35 below, with fewer days at minimum. The rise in minimums is important, Dr. Running said, “because at the lower temperatures it only took a couple of nights for the larvae to freeze to death.” . . .

While more than 6 million acres in the United States have been affected by mountain pine beetles, the number is 34 million acres in British Columbia. “It’s a continental-scale phenomenon,” said Dan Tinker, a professor of forest and fire ecology at the University of Wyoming, referring to the total of the beetle kills. “We’re all taken aback right now.”

There is no forseeable end to the outbreak, Dr. Six said. “If it’s climate-driven,” she said, “we have to reverse climate change.”

That seems unlikely in the near term. Perhaps things will be different by the time the forest regenerates and matures again, and perhaps we will do better management next time.