Increased costs and problems taking beetle-killed trees from the forest make them less valuable for commercial uses the longer they stand, a report released Wednesday by the University of Montana found.

The study, authored by UM’s Bureau of Business and Economic Research and the U.S. Forest Service Rocky Mountain Research Station, examined the impacts that mountain pine beetles have on timber value and quality when compared to harvesting and processing.

“Over the past 15 years, the mountain pine beetle has caused considerable pine-tree mortality across Montana, affecting more than 9 million acres of forest,” said research associate Dan Loeffler. “The beetles have a negative impact on wood supply by reducing log quality and recoverable volume, as well as negatively impacting operability in the forest and at the sawmill.”

Loeffler said trees in the red or gray stage of a pine-beetle attack made up 25 percent of the state’s log supply from 2010 to 2014. That dropped to 5.8 percent in 2015.

For a typical lodgepole pine stand, Loeffler said, the volume suitable for lumber declined 15 percent between the green and red stages, and 50 percent between the red and gray stages.

Cracking in logs in the red stage of mortality had the highest negative impact on log value. Increased mill residue and log breakage during handling also impacted sawmill operations, Loeffler said.

“Because of the low moisture and sap content in standing dead wood, saws and chippers do not perform as well when working with green timber,” Loeffler said. “Logs from beetle-killed trees result in lower-grade lumber and the byproduct – wood chips from milling – also may be less desirable.”

The report, which included Nate Anderson from the Rocky Mountain Research Station, concluded that if a stand is found economically and environmentally suitable for salvage harvesting, there’s financial risk in delaying that harvest.