There are promising results from 2015's battle in the two decades of warfare between Black Hills National Forest and the mountain pine beetle.
The latest surveys of the national forest and surrounding land show that the beetle epidemic has slowed overall, largely as a result of cutting down and sanitizing trees.
Some 16,000 to 17,000 acres of forest in the area were still infested by the mountain-pine beetle last year, about the same size as in 2014, but the population of young beetles has decreased, suggesting a downward trend, Black Hills National Forest Supervisor Craig Bobzien said on Thursday.
“Our thinning the forests in those at-risk areas is resulting in the thin forests remaining green and healthy,” Bobzien said on the day the U.S. Forest Service released the results of high-resolution aerial photography and on-the-ground surveys conducted last August and September.
But the studies also deliver bad news: The on-the-ground survey registered population increases in some areas. Places that were at high risk of beetle expansion, according to the survey, were in the west central part of the Black Hills near the South Dakota-Wyoming border, the northwest corner of the Hills and southeast of Custer.
Since 1996, the mountain pine beetle has infested some 447,000 acres of forests in the Black Hills forest region, with the problem area expanding each year. The epidemic reached a peak in 2013 when 34,000 acres of forest were infested by the wood-burrowing insects.
Forestry officials find that forest thinning, or cutting down trees to be processed into forest products, is the most effective way to get rid of the beetles. “You remove the beetles from the forest, they are destroyed, and the tree is dying anyway so you get a wood product out of it,” Greg Josten, a forester with the South Dakota Department of Agriculture, said.
Thinning forest areas also creates an environment that is less habitable for the beetles, since they flourish in dense forests.
Another option — if the infested trees cannot be brought to a sawmill, or for private owners of small plots in forest — is non-commercial sanitation, better known as cutting-and-chunking.
That involves cutting a tree into 2-foot lengths and leaving the chunks onsite without piling them, which results in their drying out. That will kill up to 80 percent of the beetles that have infested the tree, preventing them from breeding or moving to other trees, Josten said.
But that has to be done between October 1 and March 1, the period when the treatment will be most effective in killing the beetles, he said.
It’s important that people work with their neighbors when cutting-and-chunking a larger forest area, said Dave Thom, coordinator of the Black Hills Regional Mountain Pine Beetle Working Group, which is made up of 14 public and private agencies.
“You treat your trees but your neighbor doesn’t treat their trees, it will just fly from one place to another,” he said.
Every year about 210,000 acres of forest are treated, including areas that have not yet been infested, as part of efforts to prevent the spread of the beetle epidemic. The treatments cost $18.2 million annually from federal, state, county and private funding.
Bobzien, the Black Hills National Forest supervisor, said that this 20-year pine-beetle epidemic has been one of the longest-running of its kind this century – past the period when it had been expected to end.
“It’s trending in a positive direction towards an end,” Bobzien said, “but there’s no guarantee when that end would occur.”
Get local news delivered to your inbox!
Subscribe to our Daily Headlines newsletter.