Douglas fir beetles and mountain pine beetles — these insects attack evergreen trees, burrowing in, eating away, eventually leaving the tree a red-needled husk of itself.
The U.S. Forest Service has been working to limit this damage near populated places like campgrounds, summer cabins and the Ketchum-Sun Valley area. They used pheromone-infused plastic flakes, hung from trees in pouches and aerially distributed, on Bald Mountain last June. So far, those efforts seem to be working.
“The flakes did successfully reduce the Doug fir tree mortality when the right dosage was applied,” said Kurt Nelson, district ranger at the Forest Service’s Ketchum ranger district. “It’s something we recognize can’t be done in a broad scale across all the forest that may be affected, but in certain high-value areas or important visual areas it could have some application.”
The Forest Service anticipates that the pheromones will need to be reapplied annually for between one and four more years in those areas, unless the beetle populations fall off naturally.
“Overall in this area, (the mountain pine beetles have) been outbreaking since around 2000, going on 11 years,” said Laura Lazarus, a forest entomologist with the Forest Service’s Forest Health Protection office in Boise. The mountain pine outbreaks typically subside in an average of 12 years.
Lazarus acknowledged that the visual impact of the beetle kill — the hillsides full of dead, red-needled trees — looks bad to the untrained eye. However, because the beetles only target trees of a certain size, there are plenty remaining to repopulate the forest over time.
“It’s very shocking right now, but it’ll be fine in the long-term,” she said. “Really, we’re just left with younger stands of trees. Generally, those trees will grow more vigorously. I don’t always see it as a bad thing.”
However, Lazarus, Nelson and their colleagues are paying close attention to where the beetles are active, in part to know where dead needles and fallen trees are adding to the fuel load for a potential wildfire.
“It does change our fire regimes in terms of how often and how large a fire could occur if the right conditions occur,” Nelson said. “It’s all connected and we need to recognize there are some things we may not be able to control but we can manage in terms of what we might anticipate.”
The mountain pine beetles have also been moving into higher altitudes than they have since the 1930s, Lazarus said. In some places, their lifecycles are sped up as well, so they’re completing it in a single year rather than in two years elsewhere.
This could be linked to warming temperatures, Nelson said, and could have a longer-term impact on the ecosystem because the affected white pines that grow at those higher altitudes take longer to grow and make seed cones than their lower-altitude counterparts.
In coming years, forest users can expect to continue seeing evidence of beetle kill, though less in areas of heavy public use where pheromone treatments have been applied.