Just a few years after simultaneous bark beetle outbreaks decimated trees in the Rocky Mountains, scientists have found that large portions of these high-elevation forests are already showing signs of recovery, according to a new study of 14,000 trees published in the journal Ecology.

From 2005 to 2017, a severe outbreak of spruce bark beetles killed more than 90 percent of the Engelmann spruce trees across 800,000 acres in the southern Rocky Mountains. During the same period, an outbreak of western balsam bark beetles decimated subalpine fir across 116,000 of those acres.

The new research, conducted by scientists at the University of Colorado, Boulder, examined trees in 105 affected stands in the San Juan Mountains, a high-elevation range in the Rockies in southwestern Colorado. Scientists recorded surviving species and the number of dead trees. “Even though we had multiple bark beetle outbreaks, we found that 86 percent of the stands of trees that we surveyed are currently on a trajectory for recovery,” Robert Andrus, an ecologist at the University of Colorado, Boulder and lead author of the new study, said in a statement.

Andrus and his colleagues also found that pre-infestation biodiversity was a key indicator of a forest’s ability to recover from the beetle outbreaks. “This is actually a bright point, at least for the next several decades,” Andrus said.

One thing that could slow recovery are ungulates like elk and deer, the researchers said. Beetles tend to infest mature trees more than juveniles one, since they offer more nutrients and shelter. But scientists found that elk and deer had eaten half of the tops of the remaining juveniles in the study plots, which could stunt the trees’ growth.

“It’s important that we perform these sorts of studies, because we need different management responses depending on the forest type and the kind of disturbance,” said ecologist Thomas Veblen, a coauthor of the research.