Did You Know? Lake Mud Can Tell Us The History Of Spruce Beetle Outbreaks In The Wasatch Plateau

May 1, 2019

In the 1990s, Utah experienced its first recorded severe spruce beetle outbreak. Over 122,000 acres were infested and over 3 million spruce trees were killed. 

However, it may be possible that other severe spruce beetle outbreaks in the Wasatch Plateau have occurred before the outbreak in the 90s – and we just haven’t seen any of them in the 170 years since the pioneers arrived.

“Most of us haven’t experienced or witnessed a severe bark beetle outbreak, but if we look into the distant past we might see evidence of these outbreaks having occurred before, it’s just not over the span of a human lifetime,” said Jesse Morris, a paleo-ecologist who studies the history of plant communities in the Wasatch Plateau.

Morris and his team took a pontoon boat to Emerald Lake and Blue Lake in the Manti-La-Sal National Forest and took core samples of lake mud. After washing the mud to reveal pollen, they were able to reconstruct 10,000 years of plant history in the Wasatch Plateau.

“Throughout that entire period, Engelmann Spruce had been parked up there – through significant changes in climate over the past 10,000 years, through changes in fire regimes, spruce had just been hanging out there,” Morris said. “In fact, at the very bottom of the core that was dated to about 13,000 years [ago], there was a perfectly intact female spruce cone, and so spruce was right there when the glaciers receded and has hung out right there up until modern times.”

Morris saw that when the pioneers arrived and began logging in the 19th century, spruce trees were decimated, decreasing by 85%. Although they grew back, the new spruce trees were the same age and size making them extremely susceptible for a bark beetle outbreak as soon as the trees were mature.

“Between the spruce beetle outbreak in the 1990s and the harvesting during the 19th century, those appeared to be the most significant declines in spruce over the past 10,000 years,” Morris said.

Morris’s research concluded that the spruce beetle outbreak in the 90s was unprecedented and probably due to logging by pioneer settlement.