Pine beetle infestation appears to be abating in sections of the state, but new concerns have emerged in forests across Northwest Montana, according to studies by the U.S. Forest Service and the Montana Department of Natural Resources and Conservation.
Aerial surveys of forestlands conducted last year showed signs of western spruce budworm and pine butterfly in parts of Northwest Montana and the southern Bitterroot Valley, according to the 2011 Montana Forest Insect and Disease Conditions report released this week.
The 2011 survey identified almost 1.2 million total acres defoliated by the western spruce budworm, compared to about 326,000 acres affected in 2010 and 2.6 million acres affected in 2009. Flathead, Lincoln and Sanders counties had the highest number of acres affected. Western spruce budworm attacks Douglas-fir, spruce, and true fir trees. The insect rarely kills trees but defoliation severely stresses the tree.
“Healthy, mature trees usually rebound once the outbreak subsides, as long as they have adequate moisture available to them and nutrients stored in their root systems,” Amy Gannon, DNRC entomologist, said in a statement.
Gannon also noted Douglas-fir tussock moth and pine butterfly are increasingly active in the western part of the state. Douglas-fir tussock moth overlaps with western spruce budworm on Douglas-fir, spruce and true firs and is most active in the northwest part of the state. Pine butterfly defoliates mature ponderosa pine and is at outbreak levels in the Bitterroot Valley.
The aerial surveys showed beetle-kill appears to be in decline in many of Montana’s forests.
“Conditions are improving. We are seeing a continued decline in mountain pine beetle activity in many areas across the state, indicating the epidemic may have reached its peak,” Gregg DeNitto, Forest Service pathologist and leader of the agency’s Forest Health Protection office in Missoula, said.
The 2011 survey recorded beetle-caused mortality on over 1 million acres, compared to 2 million in 2010, and 3.6 million in 2009.
The report presents county-by-county information gathered from aerial detection flights and ground surveys covering roughly 20.5 million forested acres across Montana, and includes lands of all ownerships, according to a news release from the DNRC.