New aerial maps show Montana's forests still suffer from mountain pine beetle infestations, but the scourge might be lessening.
The 2010 survey of 23 million acres shows about 2.1 million acres have the bright red trees indicating a current beetle attack. That's down from the 3.6 million acres observed in 2009, according to U.S. Forest Service pathologist Gregg DeNitto. But the change may not be all good news.
"There could be several factors involved," DeNitto said Monday. "In many areas, they're running out of susceptible trees. But to a lesser extent, the cool damp spring and summer of last year really slowed down expression of symptoms and the fading of crowns."
In other words, some of last year's beetle-infested trees might still have green needles instead of the characteristic red-and-dead of a recently killed lodgepole or ponderosa pine. DeNitto added that the 2010 survey wasn't able to map all the areas covered by the 2009 effort.
Any acre with red trees is considered infested, whether it's a small grove or an entire hillside. But the mapping project does not count long-dead trees that have lost their needles - often called gray ghosts. So each year's study shows the current area infested, but does not add up to a cumulative total of acres damaged over time.
"You can't take multiple years of data and add them together," DeNitto said. "It's different from forest fires, with unique acres burned in each year. It may take four to six years for beetles to finish off a whole acre."
Mountain pine beetles are smaller than a grain of rice. But they burrow under the bark of pine trees and lay thousands of eggs. The subsequent larvae eat the soft cambium layer of the tree, essentially destroying its circulatory system.
If all the infected acres were plotted on a map of Montana, the beetle epidemic would have touched about 5.6 million acres in the past decade. The outbreak appears to have faded in areas around Helena and Butte, where it is running out of trees. But it's growing around Lewistown and the Flathead Valley.
"It's continuing to move east out of the Big Belts into Little Belts, Snowys, Judiths and Moccasins (mountain ranges)," said Montana State Forester Bob Harrington. "We're seeing entire stands of ponderosa pine hit, and smaller trees we wouldn't have thought susceptible."
But foresters are also seeing some resilience in pine groves where thinning has occurred before beetles reach the area. And it appears 2009's October cold snap slowed beetle progression in some areas, although the effect seems very limited.
The 2010 winter's sub-zero periods probably weren't enough to do any serious beetle damage, because the insects had already hardened up their cold defenses.
"The survey results remind us that, particularly with mountain pine beetle, we have millions of affected acres in various phases of the outbreak: red-needled trees, standing dead trees, and dead down trees," said Rob Ethridge, forestry assistance bureau chief for the DNRC. "There will continue to be implications for wildfires, public safety, the forest industry and forest health. We may be on the backside of the mountain pine beetle outbreak, but Montana will continue to feel its effects for many decades into the future."
Reporter Rob Chaney can be reached at 523-5382 or at email@example.com.