In 1983-84, when precipitation was so heavy that whole mountainsides began to slip, a 1,000-acre landslide occurred in Twelve Mile Canyon, toward the south end of Manti-LaSal National Forest.

"It knocked down a whole bunch of spruce," weakening others, Cote said. At the time, forest officials had been preparing a timber sale of trees that were being attacked by beetles. Agency experts had prepared the environmental documentation and marked the site prior to the sale.

"The slide came along and took out the road," she said. "They had no way to get in there."

They decided to rebuild the road and resume their project, but that took some time.

Meanwhile, the bugs sensed all the downed and weakened trees, she said. "The bugs went into this damaged material, and their population just exploded."

The spreading beetles have killed all of the spruce from the southern end of the forest to Fairview Canyon about 50 miles away.

"It keeps moving north. It hasn't stopped," Cote said.

At the same time, the beetles have moved south onto the Fishlake National Forest. And Dixie National Forest has a beetle problem, too, apparently an entirely separate outbreak.

Aging forests

The age of the forests may be to blame. The last time a big die-off happened may have been about 300 or 400 years ago. Now, this generation of trees is vulnerable.

Contributing to the strength of this cycling effect is that Utah's Englemann spruce grow at high elevation.

According to the "Atlas of the Vascular Plants of Utah," the Englemann spruce grows between an elevation of about 7,900 feet and 10,000 feet. At that altitude, so much snow falls that the forest tends to be spared from fires.

In addition, Englemann spruce often grow in isolated stands, not in long continuous forests that are more vulnerable to unstoppable wildfires.

The upshot is that the spruce aren't continually renewed, like many other trees. They grow slowly until they reach the natural end of their lives.

"No tree lasts forever," Cote said. Spruce seem to be able to live more than 250 years in the Manti-LaSal National Forest.

When they are weak and old, stressors like the drought, now in its sixth year, or a beetle attack may suddenly wipe out thousands of acres of trees. It's nature's recycling system.

When Englemann spruce tree stands reach 180 or 200 years of age, generally "they get into a condition where the bugs go, 'Oh gee, supper!' " she said.

Death and life

Spraying to protect trees against beetles is difficult because the infestation is so dense.