Logging does not appear to prevent pine-beetle outbreaks, so policy makers should stop making such claims, according to a University of Montana researcher.
Diana Six, a University of Montana pine-beetle biologist, and two University of California-Berkeley policy experts published a review of the scientific evidence to date on whether forest manipulation is effective at preventing pine-beetle outbreaks. The answer is generally “No.”
Yet politicians and agency policy makers increasingly push logging projects supported by the claim that they will stop the spread of pine beetles.
Each year during the past decade, a handful of bills were introduced that often bypassed environmental laws in favor of beetle control. In 2013, that number rocketed to 13 including such bills as Rep. Doc Hastings', R-Wash., Restoring Healthy Forests for Healthy Communities Act.
Democratic Sen. Jon Tester's spokeswoman, Andrea Helling, said Tester's Forest Jobs and Recreation Act evolved out of concern over beetle outbreaks but does not argue that the mandated logging would control beetle populations.
“That said, dead trees in the urban interface are a significant fire hazard to forested communities and harvesting some of the dead trees would reduce some of the risk,” Helling wrote in an email.
Meanwhile, the U.S. Forest Service has a number of projects with the express intent of warding off beetle attacks, such as one in the Bass Creek area of the Bitterroot National Forest.
The paper, published Friday in the online journal “Forests,” doesn't oppose forest management – it argues for management guided by science and validated by long-term monitoring.
“We wrote this paper because we're seeing less of an interest for policy makers to include science in policy. We don't really have the time to write things like this, but someone has to do it,” Six said. “There's this big push to ‘do something,' and people take for granted that there's science behind these claims. Often, there is not.”
A recent survey out of Colorado indicates that the mountain pine beetle epidemic has slowed dramatically without the use of big logging projects. However, the spruce beetle outbreak is spreading.
Six scoured the scientific literature for any and all studies dealing with the control of pine beetles, from direct controls, such as traps, insecticides or wholesale salvage of infected trees, to indirect controls such as thinning that seek to improve the health of remaining trees to increase their odds of holding off beetle attacks.
Six pointed out that controls don't address the underlying conditions of a beetle outbreak: drought and ultimately climate change that causes trees to become stressed. By trying to correct short-term symptoms, controls can end up exacerbating the effects of long-term climate change.
“People tend to think that it's the forest's fault, that the trees are too thick,” Six said. “But in an outbreak situation, the trees are doing worse while the beetles are doing better because of the underlying conditions.”
It's hard to nail down the effectiveness of various controls, Six wrote, because forests are rarely monitored after controls are used, in spite of the fact that the U.S. and Canadian governments have spent millions to counter beetle outbreaks.
In one the few large studies that compared treated areas to untreated areas in Canada, results seem to show that clearing and beetle traps limited infestation only when beetle populations were small.
During an outbreak, controls made little difference as beetles swarmed and multiplied across large areas.
For that reason, studies showed that direct efforts to keep beetle populations down must cover a large area, continue long-term and go into effect at the beginning of infestation.
The problem is that researchers struggle to accurately assess beetle density, which is not surprising when dealing with a flying insect the size of a grain of rice that can lay many eggs.
So efforts to keep beetle populations low may come too late. By the time researchers are aware of the problem, populations have often already grown beyond the point of control.
Winter cold snaps used to provide a natural source of control. Scientists know that several days of minus-30 degree temperatures can keep beetle populations down. That doesn't happen often anymore.
Six said even extended cold is no guarantee – beetle populations bounce back after a few favorable seasons.
“Even when there's a cold snap, there will always be some that survive. That's what happened in the Big Hole a few years ago. Ninety percent were killed, but now they're back,” Six said.
Six wrote that scientists don't know how thinning improves tree health. Studies that record success in slowing beetle attack were often done right after thinning occurred and could have more to do with changes in local climate than tree health.
Studies of thinning operations that don't diminish beetle kills are often not published, Six wrote, leaving a gap in the information that scientists could use.
No long-term studies have looked at the effect of thinning during outbreaks.
The paper concludes that weakening environmental laws to combat beetle outbreaks is unjustified given the questionable efficacy, high financial cost of continual treatment, and the negative impacts such treatment can have on other aspects, such as wildlife or a forest's ability to adapt to future climate change.