CU study: widespread spruce beetle outbreak in Colorado tied to drought

October 9, 2013

Oct. 10, 2013                                                                                    Sarah Hart

According to a new University of Colorado Boulder study drought high in the northern Colorado mountains is triggering a massive spruce beetle outbreak that has the potential to be equally or even more devastating in Colorado than the mountain pine beetle, says Sarah Hart, a CU-Boulder doctoral student in geography and lead author on the study.

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CU study: widespread spruce beetle outbreak in Colorado tied to drought

Oct. 10, 2013                                                                                    Sarah Hart

According to a new University of Colorado Boulder study drought high in the northern Colorado mountains is triggering a massive spruce beetle outbreak that has the potential to be equally or even more devastating in Colorado than the mountain pine beetle, says Sarah Hart, a CU-Boulder doctoral student in geography and lead author on the study.

CUT 1 “These warm and dry conditions are both really good for the beetle. It’s increasing beetle population and allowing them to survive winters. (:10) I think it’s reasonable to expect that a high proportion of Colorado’s forest – spruce fir forest – will be affected by the beetle in the next 10 years.” (:19)

The drought is tied to long-term changes in sea-surface temperatures from the Northern Atlantic Ocean called the Atlantic Multi-decadal Oscillation, or AMO, that changes sea-surface temperatures in the North Atlantic from cool to warm phases roughly every 60 years. This latest shift began in the late 1990s.

CUT 2 “The mechanism isn’t entirely well understood but we know that when we are in these periods of positive AMO, or when the sea surface temperatures are warm in the North Atlantic, that the Southwest and Midwest we tend to get periods of reduced precipitation and drought. (:14) And these periods last for anywhere from 20 to 40 years. We’re expecting we’ll continue to be in some period of drought that’s conducive for bark beetle outbreaks, including the spruce beetle.” (:25)

The new study is important because it shows that drought is a better predictor of spruce beetle outbreaks in northern Colorado than temperature alone, says Hart. Drought conditions appear to decrease tree defenses against the beetles.

CUT 3 “Drought is really important because the drought is stressing out the trees which means their ability to defend themselves by pitching out beetles is just not as high as it would be if there was more water available to them.” (:12)

Harts says the infestation is fairly widespread in Colorado and, much like the mountain pine beetle, people will be able to tell when spruce trees are being attacked.

CUT 4 “The trees needles start to fade from that green color to almost a yellow color and then the needles will start to turn entirely brown, similar to what you’re seeing with mountain pine beetle outbreak. (:10) And then the trees themselves are producing these pitch tubes – these little cones of sap where the tree is trying to get the beetles out inside of that bark.” (:18) 

Spruce beetles range from Alaska to Arizona and live in forests of Engelmann spruce and subalpine fir trees in Colorado.  The CU-Boulder study area included sites in the White River, Routt, Arapaho, Roosevelt and Grand Mesa national forests as well as Rocky Mountain National Park.

-CU-

 

 

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