Spruce beetles still on the march in Colorado

Global warming taking a toll on forests worldwide

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Aerial surveys help track the health of Colorado forests. @bberwyn photo.

By Bob Berwyn

Spruce beetles continued to expand in Colorado in 2016, at least in part due to global warming and drought, as well as the density of old-growth spruce forests.

In all, spruce beetles were active across 350,000 acres of higher-elevation stands of Engelmann spruce statewide, including about 136,000 acres of new activity, causing widespread tree mortality, according to the results of the latest aerial surveys conducted by the U.S. Forest Service and the Colorado State Forest Service. Since 1996, spruce beetle outbreaks have caused tree mortality on more than 1.7 million acres in Colorado.

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Spruce beetle activity in Colorado in 2016.

The survey also showed that Douglas-fir beetle populations also continued to expand across the West Slope, affecting about 19,000 acres. Douglas fir-killing beetles have been most active in scattered pockets in Eagle, Garfield and Pitkin counties, along with most of the Gunnison Basin.

Going back to the early 2000s, various insect outbreaks have affected about 5.1 million acres of Colorado forests on scale outside the known range of natural variability. According to many forest scientists, the changes are part of a global forest health crisis due to human-caused global warming.

The survey also showed that western spruce budworm, Douglas-fir tussock moth and fungal leaf diseases of aspen trees declined across Colorado in 2016.Mountain pine beetle activity, which affected nearly 3.4 million cumulative acres statewide over the past two decades, remained at a low background level.

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