It turns out that drought is the most critical factor behind a spruce beetle outbreak, which in 2012 infested more than 300,0000 new acres of Colorado forests.
“We were surprised that we could actually pull out the difference between drought and temperature here,” said Sarah Hart, the lead author on the study. “We found that drought was really more important than just temperature alone."
To draw their conclusions, researchers compiled 300 years of data in Northwest Colorado derived from tree rings and Forest Service records. In addition to 2012, history has documented spruce beetle outbreaks in the 1850s, 1880s and 1940s.
The spruce beetle is a cousin to the mountain pine beetle—both of which have infested hundreds of thousands of acres of Colorado forests. In 2012, the amount of new acreage affected by the spruce beetle surpassed that of the mountain pine beetle by a factor of 10.