Go ahead — burn the forest.
But then don’t mess with it.
That’s the perhaps surprising conclusion that has emerged from a pair of studies on the impact of both controlled burns and wildfires on forest health and the severity of the next fire.
The twin studies of major fires in Oregon and California offer telling lessons for Rim Country, one of the most fire-menaced regions in the country and the epicenter of efforts to cope with overcrowded, tinderbox forests.
Forest managers and advocates in Rim Country have undertaken an ambitious program of controlled burns to create firebreaks on the outskirts of forest communities like Payson, Pine, Strawberry, Star Valley, Whispering Pines and Christopher Creek.
In addition, forest managers are working on a forest restoration plan to use a combination of controlled burns and timber harvests to dramatically reduce tree densities on millions of acres of land in Rim Country.
The two most recent studies on salvage logging and controlled burns hint at the complexities of that effort — and the perhaps unexpected unintended side effects of such dramatic shifts in forest management.
A study of controlled burns in California offers strong evidence to bolster efforts in Rim Country, where the Forest Service has burned tens of thousands of acres in the past three years, while letting many low-intensity wildfires burn themselves out whenever possible.
Turns out, controlled burns not only prevent later catastrophic wildfires, but result in a significant increase in the health of the forest and in the number and diversity of wildlife.
That conclusion emerged from a 20-year study that focused on 51 patches of mixed conifer forests in the Sierra Nevadas, conducted by Karen Webster, formerly with the Park Service and Charles Halpern, with the University of Washington in Seattle.
The study focused on the controlled burns scattered over a span of two decades on study plots — each of which was deliberately burned once or twice. The researchers carefully recorded the number of plants and animals in the experimental plots at regular intervals throughout the 20-year period to determine whether the regular, low-intensity burns had an impact on wildlife, according to the study published in the online journal Ecosphere.
The researchers found that the number of native plants doubled a decade after the first controlled burn in a given patch of forest. The number of plants actually tripled in the course of 20 years, compared to unburned comparison areas. The plots burned twice during the 20 years reaped the same benefits as the plots burned only once, indicating forest managers could use repeated burns to reduce debris on the forest floor without hurting plant and wildlife diversity.
The study suggests controlled burns do a lot more than reduce fire risks, the main reason forest managers in Rim Country have resorted to burns with increasing frequency.
The Forest Service spent a century stamping out natural wildfires, even as cattle grazing removed the thick swales of grass that used to carry periodic wildfires through the forest. As a result, tree densities have increased from 30 to 50 trees per acre to 500 to 1,200 trees per acre across millions of acres. A wildfire during the dry summer months can spawn a crown fire that threatens whole towns and effectively sterilize the soil — preventing recovery of the forest for decades.
The study of controlled burns demonstrates that such low-intensity fires can both reduce the risk of catastrophic wildfires and benefit plants and animals.
Decidedly less encouraging results emerged from a second study that looked at how to best hasten the recovery of the forest after such an uncontrolled, catastrophic, high-intensity wildfire. In this case, researchers studied the impact of the 500,000-acre, 2002 Biscuit Fire in Oregon. The Biscuit Fire forced 15,000 people to flee their homes, making it tragically similar to the 600,000-acre Rodeo-Chediski Fire, which forced the evacuation of Show Low.
The Oregon State University researchers compared the impact of the Biscuit Fire on areas that had burned in the 1987 Silver Fire. Forest managers had left some of the areas burned in 1987 to recover on their own. But in other areas, they contracted with timber companies to quickly cut down the dead and dying trees and replant the area with young pines.
Surprisingly, the areas left alone did much better than the areas subjected to salvage logging and replanting, according to the study published in the Proceedings of the National Academy of Sciences. Forest managers had previously assumed that removing dead trees and planting seedlings would speed the return of fire-resistant forests.
The Biscuit Fire’s severity increased by 16 percent to 61 percent in the areas that underwent salvage logging and replanting, after the researchers corrected for slopes, topography and a variety of other factors.
Researchers could not entirely account for the findings. They speculated that salvage logging might end up adding more debris to the forest floor than leaving the big snags standing. Moreover, the trees planted to provide cover for the denuded slopes might have been just the right size to make the next fire worse.
On the other hand, the natural regeneration of trees seemed to reduce the intensity of subsequent fires. That might reflect the more patchy natural regeneration of trees, with clumps of trees separated by open areas.
Researchers from Northern Arizona University who have studied Rim Country forests subject to a natural cycle of wildfires have concluded that the forests here were once far more patchy as well, which would prevent the spread of massive fires and provide much more diverse habitats for wildlife.
Taken together, the studies seem to validate the use of burns, but leave questions about trying to replace natural fires with salvage or restoration logging schemes.