Thinning ponderosa pines in the Black Hills is helping to slow an epidemic of mountain pine beetles, Forest Service officials say.

"We know thinning is a good way to keep our forests green and healthy," Black Hills National Forest Supervisor Craig Bobzien said.

Logging, non-commercial thinning and prescribed burns in dense stands of ponderosas give individual trees better access to water and nutrients, Forest Service natural resources officer Dave Thom said.

Larger, healthier trees are better able to reject bug attacks.

"Like humans, if they're malnourished, dehydrated and crowded they're more subject to illness," Thom said.

Recent Forest Service aerial photographs show patches of reddish-brown trees killed by beetles in dense stands of timber, next to logged and thinned timber where there are no red "bug trees."

Thom said thinning programs were focusing on areas around Custer, Hill City, Keystone and Deerfield Reservoir.

Other large pine beetle outbreaks are in Custer State Park, upper Spring Creek near the Medicine Mountain Boy Scout Camp and in the Norbeck Wildlife Preserve, including the Black Elk Wilderness Area and Harney Peak.

The Forest Service also is thinning in the Norbeck Wildlife Preserve, which includes state and federal land, but thinning is prohibited by law in the Black Elk Wilderness.

About 700,000 acres of the 1,000,000 acres of ponderosa pine in the Black Hills are at "high" risk for major beetle infestations or catastrophic wildfires, according to a recent Forest Service report.

"We're thinning more than 50,000 acres a year," Thom said.

Bobzien said he had requested authority for even more thinning, but he added that the current thinning level is close to what's possible given the current staff.

Contact Bill Harlan at 394-8424 or at bill.harlan@rapidcityjournal.com