The new study is important because it shows that drought is a better predictor of spruce beetle outbreaks in northern Colorado than temperature alone, said lead study author Sarah Hart, a CU-Boulder doctoral student in geography. Drought conditions appear to decrease host tree defenses against spruce beetles, which attack the inner layers of bark, feeding and breeding in the phloem, a soft inner bark tissue, which impedes tree growth and eventually kills vast swaths of forest.
Spruce beetles, like their close relatives, mountain pine beetles, are attacking large areas of coniferous forests across the West. While the mountain pine beetle outbreak in the Southern Rocky Mountains is the best known and appears to be the worst in the historical record, the lesser known spruce beetle infestation has the potential to be equally or even more devastating in Colorado, said Hart, lead author on the new study.
“It was interesting that drought was a better predictor for spruce beetle outbreaks than temperature,” said Hart of the geography department. “The study suggests that spruce beetle outbreaks occur when warm and dry conditions cause stress in the host trees.”
...The new study also puts to rest false claims that fire suppression in the West is the trigger for spruce beetle outbreaks, said Veblen.
...The strongest climate correlation to spruce beetle outbreaks was above average annual values for the Atlantic Multi-decadal Oscillation, or AMO, a long-term phenomenon that changes sea-surface temperatures in the North Atlantic. Believed to shift from cool to warm phases roughly every 60 years, positive AMO conditions are linked to warmer and drier conditions over much of North America, including the West....
Wolf Creek Pass ski area in Colorado, shot by Doc Searls, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license
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