01/02/2013 01:23 EST | Updated 03/03/2013 05:12 EST

Pine Beetles' Move Up Threatens Western Forests: Study

Scientists behind a new study say a warming world has not only made it easier for the mountain pine beetle to invade new and defenseless ecosystems, but also to better withstand winter weather that is milder and erupt in large outbreaks capable of killing entire stands of trees, no matter their composition.


With temperatures climbing from climate change, the mountain pine beetle is now moving to higher elevations on mountain slopes and is a "rising threat" to the whitebark pine, which is found mainly in the Rocky Mountains, coast range of B.C. and the northern U.S., says a new study.

The report was published Monday by the University of Wisconsin-Madison in the Proceedings of the National Academy of Sciences.

It's a significant finding in B.C. where a provincial report says the pine beetle epidemic has now killed an estimated 710 million cubic metres of commercially valuable pine timber — 53 per cent of all such pine in the province. The rate of damage has been slowing for several years, but is projected to grow to 58 per cent by 2017 (to 767 million cubic metres).

Both the provincial and federal governments have spent hundreds of millions of dollars on the mountain pine beetle epidemic. Beetle-killed pine forest is more vulnerable to forest fires, and it is possible that the drier wood from beetle-killed wood is responsible for the explosions at mills in Burns Lake and Prince George.

"Warming temperatures have allowed tree-killing beetles to thrive in areas that were historically too cold for them most years. The tree species at these high elevations never evolved strong defences," said Ken Raffa, a University of Wisconsin-Madison professor of entomology and a senior author of the new report.

A warming world has not only made it easier for the mountain pine beetle to invade new and defenceless ecosystems, the scientists say, but also to better withstand winter weather that is milder and erupt in large outbreaks capable of killing entire stands of trees, no matter their composition.

"A subject of much concern in the scientific community is the potential for cascading effects of whitebark pine loss on mountain ecosystems," says Phil Townsend, a Univeristy of Wisconsin-Madison professor of forest ecology and a senior author of the study.

The mountain pine beetle's historic host is the lodgepole pine, and it was widespread lower elevations until the pine beetle infestation began to spread in the late 1990s. The pine beetle, which is about the size of a grain of rice, played a key role in regulating the health of a forest by attacking old or weakened trees and fostering the development of a younger forest after the older trees died or were destroyed by fire.

However, recent years have been characterized by unusually hot and dry summers and mild winters, which have allowed insect populations to boom. This has led to an infestation of mountain pine beetle described by the scientists as "possibly the most significant insect blight ever seen in North America."

The B.C. government report says:

Over most of the Interior, extreme winter weather (colder than minus 35 Celsius for at least several days or even weeks) historically killed most of the pine beetle population, limiting the duration of, and damage from, periodic epidemics. Such a widespread weather event has not occurred in the B.C. Interior since the winter of 1995/96.

In the U.S., there have been a number of studies of pine beetle infestation of the whitebark pine.

In 2011, the Seattle Times cited a study in the mid-2000s that showed whitebark trees had declined by 41 per cent in the Western Cascades, while nearly 80 per cent of the trees in Mount Rainier National Park were infected.

The newspaper also quoted the U.S. Fish and Wildlife Service reporting in 2007 that beetles killed whitebark pine trees across half a million acres in the U.S. West — the most, at the time, since record-keeping began. Two years later, beetles killed trees on 800,000 acres.

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The lodgepole pine co-evolved with the bark beetle, and so it evolved chemical countermeasures, volatile compounds toxic to the beetle and other agents that disrupt the pine bark beetle's chemical communication system.

According to the Wisconsin study, despite that robust chemical defence system, the lodgepole pine is still the preferred menu item for the mountain pine beetle, suggesting that the beetle has not yet adjusted its host preference to whitebark pine. "Nevertheless, at elevations consisting of pure whitebark pine, the mountain pine beetle readily attacks it," says Townsend.

He adds the good news is that in mixed stands, the beetle's strongest attraction is to the lodgepole pine, suggesting that, at least in the short term, whitebark pine may persist in those environments.

However, the 2007 U.S. study quoted by the Seattle Times also warned that unlike the lodgepole, whitebark pines produce few seed cones and do so late in life, so they "aren't set up to survive massive slaughter."

The new study, conducted in the Greater Yellowstone Ecosystem, also showed that the insects that prey on or compete with the mountain pine beetle are staying in their preferred lodgepole pine habitat. That is a concern, says Townsend, because the tree-killing bark beetles "will encounter fewer of these enemies in fragile, high-elevation stands."

Whitebark pine trees are an important food source for wildlife, including black and grizzly bears, and birds such as the Clark's nutcracker which is essential to whitebark pine forest ecology because the bird's seed caches help regenerate the forests.

For a longer version of this story see Northwest Coast Energy News.