ASPEN — Since finding West End trees infested with the very same mountain pine beetle that is devastating forests all across Colorado, city of Aspen officials are taking steps to prevent further spread.

“This would be without a doubt the largest number of pine beetle strikes we’ve seen,” said Stephen Ellsperman, the city’s parks and open space director.

The beetles, though native to the area, are for unknown reasons traveling in swarms and boring into lodgepole and Scotch pine all across the state, Ellsperman said. The beetles lay eggs, cutting off the flow of water and nutrient and eventually killing the tree before finding a new host.

Chris Forman, Aspen’s city forester who manages some 8,500 trees in the city limits, is plotting the infested trees on a GIS map in the hope of preventing further spread of the beetles in 2008.

Out of the 5,168 “street trees” on city of Aspen right of ways, Forman said 164 trees are either lodgepole or Scotch pine and susceptible to the beetle. And of the 2,463 trees in city parks, 79 pines are vulnerable, Forman said.

The survey does not account for trees in homeowners’ backyards, Forman said.

“It’s not going to sweep through and completely wipe us out in town,” Forman said. “But I’m not going to kid myself and say we aren’t going to lose any trees. We will.”

Aspen’s diverse forest population of Douglas fir, aspen, cottonwood and pinyon pines protect the area from the kind of wholesale forest loss that is happening near Grand and in Summit counties, Forman said.

Preventative sprays are effective, but there is no treatment once the beetle takes hold of a host tree, Forman said.