A massive spruce beetle outbreak that’s been decimating coniferous forests in the northern Colorado mountains has been caused mainly by drought, according to a new study.
The study, published this week in the journal Ecology by University of Colorado scientists, found that drought is a better predictor of beetle outbreaks in the West than temperature. The drought is tied to long-term changes in sea surface temperature from the Northern Atlantic Ocean — a pattern known as the Atlantic Multi-decadal Oscillation (AMO), which warms sea surface temperatures about every 60 years. The most current AMO began in the late 1990s, so the University of Colorado’s finding is troubling: since sea surface temperatures are expected to continue to rise for the next several years, drought could continue to persist in the West, a scenario which means the spruce beetles will continue to thrive.
The researchers found that dry conditions weakened trees’ defenses against spruce beetles. The beetles kill trees by burrowing into a tree’s soft inner bark and feeding and laying eggs there, impeding the tree’s growth and eventually killing it.