CU professor sheds light on pine beetle epidemic
The dichotomy in the photograph projected across the wall is stark.
From a vantage point in the Williams Fork Mountains, the Gore Range’s skyline cuts a rugged shark-tooth profile across a clear mountain sky.
The eye is drawn to the sharp relief of the range’s peaks, but as the gaze drops below tree line, the picture becomes eminently more troubling.
Where a lush blanket of greenery once nestled up against the alpine tundra, a rusty, scabrous pall spreads across the range’s sub alpine forests.
“That’s not a bad picture,” says Jeff Mitton, Ph.D. “It’s a picture of a sorry subject.”
Litton is a professor in the University of Colorado Boulder’s Department of Ecology and Evolutionary Biology.
“I don’t have to tell you that the brown there is not bad photography,” Mitton says. “That’s beetle kill.”
Mitton came to Adolf’s Event Center & Tavern on Thursday evening, Aug. 13, to speak about the Mountain Pine Beetle epidemic as part of a reception held by CU Boulder.
Mitton has been interested in bark beetles, the genus of insects that includes the Mountain Pine Beetle, since 1976 when he began studying a similar beetle epidemic in Ponderosa Pines.
He’s written a book on bark beetles in North America and is a leading authority on the subject.
During his presentation, Mitton discussed some of his findings from studying the epidemic that has plagued the West since the mid ’90s and what they mean for future outbreaks.
In the last 25 years, the beetle has climbed 2,000 feet above its previous range in Colorado, Mitton said. In that time, it’s also traveled 400 miles farther north into Canada than ever before.
From any location in the Fraser Valley, one can gaze up into the hills and see a patchwork of green and brown.
The fact that some trees seem to be resistant to pine beetles is key to understanding the epidemic, Mitton said.
When examining a cross section of a lodgepole or limber pine, a spattering of dark pockmarks is visible among the tree’s dark brown growth rings.
These marks are resin canals, and they’re the tree’s only defense against pine beetle attacks, Mitton said.
Two researchers working outside Flagstaff, Ariz., in 2010 observed that beetles were passing over trees with a greater density of resin canals, Mitton said. Using that data, the researchers could designate trees resistant or susceptible with 80 percent accuracy.
This epidemic is also especially memorable because of its intensity, which was about 10 times worse than the next comparable outbreak, Mitton said.
“I don’t really have to tell you folks that, but in places 80 to 90 percent of the trees were gone, and nobody saw this coming,” Mitton said. “We didn’t anticipate it at all.”
So what factors contributed to the scale and intensity of the epidemic?
Temperature at the root of epidemic
Ask anyone about the cause of pine beetle epidemic, and most will tell you it’s a result of rising temperatures.
They may also tell you that, more specifically, recent mountain winters haven’t been cold enough or long enough to naturally pare down the beetle population.
Though a widely held belief, it’s incorrect, Mitton said.
Rather, early springs have allowed the beetles to emerge six to eight weeks early, Mitton said. As a result, they now produce two generations each summer.
“Two generations instead of one means that there’s an exponential increase in the number of beetles in the forest,” Mitton said. “That means there’s an exponential increase in the number of trees being attacked.”
This correlation between rising temperatures and severe beetle epidemics is being seen in other species, too.
On a recent trip across Wolf Creek Pass, Mitton said he encountered a similar scene to that in the Gore Range photograph.
This time, however, it was the Spruce Beetle, which now produces annual rather than biennial generations.
Southern Pine Beetles are also expanding their range in the South.
“Three species of bark beetles all doing similar things – it’s all related to temperature,” Mitton said.
Longer summers also weaken trees, Mitton said, making it easier for the beetle to kill them.
“I really think it’s summer temperatures that are hurting them more than winter cold,” Mitton said.
Resin canals hold secret to prevention
Bark beetle epidemics are cyclical, and are almost always sparked by drought.
The current epidemic is waning, but an endemic population of pine beetles will remain in Colorado’s forest for decades, taking weakened trees when they can, waiting for the next drought, Mitton said.
Epidemics in lodgepole forests typically occur every 60 years, Mitton said, but can be much more irregular.
It’s unclear how climate change could affect the cycle of bark beetle epidemics in the future, Mitton said.
As a result of this epidemic, researchers and foresters are armed with more knowledge to fight future epidemics than ever before.
Using what they know about resin canals and resistance, foresters can cut forests to eliminate susceptible trees, Mitton said. It’s a sort of unnatural selection called resistance thinning.
“We can actually improve our forests in such a way that they are more resistant to beetles,” Mitton said.
In forests already decimated, Aspens will fill in the stands killed off by beetles, returning the forest to a more natural state, Mitton said.
“Yes, it’s awful that the trees died,” Mitton said, “but hey, that’s not so bad.”
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