Spruce Beetles Don't Increase Severity Of Colorado Forest Fires, Researchers Say

Spruce beetles have often been blamed for increasing the severity of raging wildfires throughout Colorado. While the bugs invade Engelmann spruce and subalpine fir forests and scar the trees they feed on, this destruction is not linked to the occurrence of forest fires plaguing the state, a new study revealed.

Within the past decade, spruce beetles have chewed through roughly half a million acres of forests in Colorado. In 2014 alone the beetles reportedly infested more than 87,000 new acres of trees planted throughout the state, according to a news release. This caused many to believe that restoring forests was only adding fuel to the fire.

Researchers from the University of Colorado Boulder (CU-Boulder) closely examined several large wildfires that have occurred in the state over the past decade to see if they correlated with spruce beetle infestations and found that increasing amounts of spruce beetle damage did not directly increase the amount of forest fires, according to their study. (Scroll to read more...)

"Our study is unique because we were actually out in the forest peeling bark off of the burned trees, looking for evidence of the beetle," Robert Andrus, a graduate researcher in the Department of Geography at CU-Boulder and lead author of the new study, said in a statement. "We were interested in the ecological effects of the interaction between these two disturbances and determining whether more trees were killed by fire in areas of higher beetle infestation."

Adult spruce beetles (Dendroctonus rufipennis) are dark brown to black in color, with some reddish brown to black coloration on their wing covers. Generally, beetle infestations occur between May and July, but this can vary based on local factors such as climate. Past outbreaks have occurred in various spruce forests ranging from Alaska to Arizona. Since the insects ultimately kill the trees they infest, scientists previously believed that the trees would readily burn in the wake of a forest fire. 

The recent study, published in the journal Ecological Applications, is the first to use direct field measurements rather than satellite or aerial imagery to record tree loss. For their study, researchers analyzed five recent subalpine fire zones in the San Juan Mountains of southwestern Colorado. Using field measurements allowed them to see first-hand that there was no correlation between beetle infestation and severe fire damage. This suggests that other factors such as topography or weather conditions have a larger impact on the Engelmann spruce and subalpine fir forests in the area, researchers noted in the release.

This study will help Colorado land managers better allocate resources for fire suppression and regulating spruce beetle populations.   

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