Mountain pine beetle, a small black to rusty-brown bark beetle that tunnels beneath the bark of pines, isn't a hitchhiker invading from a foreign land. Originally known as the Black Hills beetle, it is a native species that has always been part of the West’s forest ecosystems. And it has regularly caused epidemics — the first to be reported was in the late 1890s and nearly every decade since then.
Millions of acres in Colorado and Wyoming have been infested by MPB since 1996, killing almost all of the mature lodgepole pines in many regions. Infestations have crept into the western portions of a few Great Plains states, including the Nebraska Panhandle. Over the past 20 years, about 448,000 acres of the Black Hills region in South Dakota and Wyoming have been infested. High-resolution surveys from the air conducted in the Black Hills last fall indicated about 2,500 new acres were infested in 2016, down from 17,000 new acres in 2015. Experts tracking beetle populations say the current epidemic is coming to a close, and populations are returning to a more natural level. That's good news for ranchers and private woodland landowners.
However, woodland owners are encouraged to remain vigilant, as small pockets of beetles remain active and can attack remaining stands of thick pines. Landowners should report such occurrences to their local state forestry office.
Dave Thom, coordinator of 15 partners in the Black Hills Regional Mountain Pine Beetle Working Group, says it is critical to thin abundant pines emerging beneath the beetle-killed trees. "Since fire has always been a big part of the ecosystem, fires would historically keep the forest thinned out, with smaller patches and acreages of trees," Thom says. "This helped to keep MPB populations under control and keep wildfires at a lower intensity. Without natural fires over the past 125 years, woodlands have been thicker," he explains. "Forest density increased markedly over the last several decades, reaching a critical tipping point, where MPB in many areas could get a foothold and mass attack susceptible tree stands," Thom says.
"Thinning trees allows more airflow among the trees that disrupts the chemical signals, or pheromones, that beetles use to signal each other to attack certain trees," he notes. "Commercially harvesting trees is used to keep trees thinned out, but does not keep up with the prolifically growing smaller-sized pines that will host future beetle epidemics and the most severe wildfires."
There is an active market for green ponderosa pine. When the epidemic was at its height, "there was also a very strong market for 'blue-stained' ponderosa pines that were from beetle-killed trees and infected with a blue-staining fungi for tongue-groove boards for interior paneling," Thom says.
Open-grown pines with varied ages and sizes will be most resilient to future MPB and wildfire disturbances, Thom adds. "Also, landowners can try to diversify tree species," he says. "Depending on their property location, additional oak, aspen or spruce would be helpful."
Thom says that it is critical for woodlands owners to work together across broad landscapes to fight MPB. "Beetles don't recognize property boundaries, so in the Black Hills, managers coordinated treatments in priority areas to protect private and public lands alike," he says. "Such efforts will not end the widespread epidemic, which will run its course, but they will protect key places important to people until beetles decline."