Veblen said a 1980s outbreak of the pine beetle in Colorado's Grand County ended when extremely low minimum temperatures were reached in the winters of 1983 and 1984, killing the beetle larvae.
But during the current outbreak, minimum temperatures during all seasons have been persistently high since 1996, well above the levels of extreme cold shown to kill beetle larvae in laboratory experiments.
"This implies that under continued warming trends, future outbreaks will not be terminated until they exhaust their food supply--the pine tree hosts," said Veblen.
Chapman said there has been a massive and unprecedented beetle epidemic in British Columbia, which also began in the early 1990s and now has affected nearly 70,000 square miles.
"It is hard to tell if this current beetle epidemic in the Southern Rockies is unprecedented," she said. "While warm periods in the 16th century may have triggered a large beetle epidemic, any evidence would have been wiped out by the massive fires in the latter 19th century."
The rate of spread of the mountain pine beetle in lodgepole pine forests has declined in the southern Rocky Mountains during the past two years because of a depletion of host pine population.
But surveys indicate that the rate of beetle spread in ponderosa pine forests on the Front Range has increased sharply over the past three years.
The current study suggests that under a continued warmer climate, the spread of the beetle in ponderosa pines is likely to grow until that food source also is depleted.
"Our results emphasize the importance of considering different patterns in the population dynamics of mountain pine beetles for different host species, even under similar regional-scale weather variations," said
|Contact: Cheryl Dybas|
National Science Foundation