The bark beetles that turn pine trees reddish-brown and may kill them have advanced briskly in Montana and another forest pest, the spruce budworm, surged as well, a new report says.
Montana land with trees attacked by mountain pine beetles totaled about 820,400 acres last year, the highest since 1984 and an increase of 55 percent from 2004, according to Montana Forest Insect and Disease Conditions and Program Highlights. Spruce budworms had attacked trees on about 208,500 acres, up 64 percent from the year before, said the report released by the state natural resources agency and the U.S. Forest Service.
Drought, mild winters, hot summers and overall forest health get some of the blame for the bug infestations. Insect-killed trees, in turn, sometimes end up as fuel in major wildfires.
Findings in the report are based on air and ground surveys of government and private land in Montana.
Aerial work last summer accounted for most of the 2005 surveying and covered about 29.7 million acres, 7 million more than in 2004. The results show an increase in pest prevalence largely because the insects have spread, not merely because the survey acreage expanded, said Amy Kearney, pest management specialist for the Montana Department of Natural Resources and Conservation.
Budworm infestations and beetle attacks on lodgepole and other species of pine are problems elsewhere in the West. Of particular concern in Montana is an increase in beetle damage to whitebark pines, which are a source of food for grizzly bears, Kearney said Thursday.
Long-term drought in Montana has helped make trees vulnerable to beetle infestations, the report said. In addition, mild weather in recent years has helped beetles survive at higher elevations.
Other factors favoring beetles include dense forests in which trees are weakened - and less able to withstand pests - as they compete for the resources that nourish them, Kearney said.
"Anything people can do to help increase the vigor of their trees will help them be more resilient to bark beetles," she said. Thinning stands of trees is one option, she said, adding that wildfire suppression over the years has contributed to forest density.
Spruce budworms are a leading cause of tree defoliation in Montana, according to the report, which says budworms are particularly strong in the Helena, Bozeman and Philipsburg areas. In Montana the budworms attack Douglas fir trees, hemlocks and other conifer species.
"The numbers of these insects began to increase several years ago and they are now at an outbreak stage in many areas," said Gregg DeNitto, who works in forest health for the Forest Service's regional office in Missoula. "Our records indicate that this is a natural cycle that is influenced mainly by weather conditions."
Spruce budworm ordinarily does not kill trees, but does reduce growth and kill their tops, DeNitto said. The more defoliation over a span of years, the greater the chance the tree will die.
Researchers say that if Montana recovers from drought, then there may be a related decrease in insect activity.
There are chemicals for responding to some kinds of tree insects but efficacy varies and timing is critical, Kearney said. Science-based management of forests is the best response, she said.
"It's a lot easier to manage for insects and diseases before they get into your forest," she said.Associated Press via The Missoulian
