The good news: Returning fire to the forest can work wonders for the ecology.
The bad news: The Forest Service will have a hard time making the transition back to a healthy, fire-dominated ecosystem while towns like Payson, Show Low, Pine and Springerville remain unprotected by Firewise programs and a wildland-urban interface building code.
California has demonstrated the terrible danger faced in an era of megafires, with giant fires in the past six months that have consumed hundreds of homes and killed scores of people. To underscore the lesson, a series of mudflows off recently burned areas have killed even more people and buried homes in recent weeks.
But California researchers have also demonstrated how a return to periodic, large-scale wildfires can solve many of the problems created by a century of fire suppression. The studies underscore the need for a combination of forest thinning and managed fires that lie at the heart of the Four Forest Restoration Initiative in Arizona, the largest restoration project in U.S. history.
One study reported the encouraging results of what amounted to a 40-year, 40,000-acre experiment in an isolated valley in Yosemite National Park.
Back in 1973, the National Park Service decided to end its century-long effort to quickly snuff out every single wildfire in the park. Instead, park managers decided to mostly let fires burn in the Illilouette Creek basin, isolated from the rest of the park and the rest of the forest by sheer, granite walls.
Back in 1910, The U.S. Forest Service adopted a comprehensive, expensive fire suppression effort after a fire called the “Big Burn” in Montana and Idaho charred a million acres and killed dozens of firefighters. The fire suppression effort dramatically reduced fires throughout the West, but also resulted in a huge increase in tree densities across millions of acres.
Now, a group of researchers from the University of California, Berkeley has completed an in-depth study of the return of natural fires to the Illilouette Valley, with encouraging results for forest restoration efforts elsewhere.
The researchers spent three years measuring stream runoff, tree densities, forest health and other factors, according to the report in the peer-reviewed journal Ecosystems.
Compared to nearby areas, the valley had fewer trees and huge clearings and meadow areas. This resulted in a significant increase in stream runoff and improved health in the remaining trees. The cleared areas also acted as firebreaks, preventing a single fire from covering the whole valley.
Even in drought years, the valley had more soil moisture and stream runoff into the Upper Merced River than adjacent areas where the fire suppression policies continued.
“We know that forests are deep-rooted and that they have a large leaf area, which means they are both thirsty and able to get water resources,” said co-author Sally Thompson, according to a UC Berkeley release describing the results. “So if fire removes 20 percent of that demand from the landscape, that frees up some of the water to do different things, from recharging groundwater resources to supporting different kinds of vegetation and it could start to move into the surface water supplies as stream flow.”
The results bode well for the major effort by Payson, the U.S. Forest Service and the Salt River Project to thin and return managed fire to the 60,000-acre watershed of the C.C. Cragin Reservoir. The Bear Fire last year burned a 7,000-acre chunk of the watershed, which helped stop the subsequent, high-intensity Highline Fire. Forest managers hope the effort to thin and burn the watershed will not only prevent the kind of high-intensity fire that caused devastating mudflows in California, but will also increase runoff into the reservoir.
Another study found suppressing fires causes a huge increase in the amount of downed and dead wood on the ground. The study focused on experimental forest plots in the Sierra Nevada and was published in the peer-reviewed journal Forest Ecology and Management.
The study focused on three experimental forest plots monitored continuously since 1929 in the Stanislaus National Forest, according to the researchers from the Forest Service’s Pacific Southwest Research Station.
The researchers wanted to document the changes in the course of a century of active fire suppression. The three plots had not burned since 1889, but had been logged to varying degrees.
They used old records to document the downed trees and logs in 1929, then to chart the changes.
Back in 1929, the forest floor was relatively free of tangles of downed wood and logs and had a modest number of standing dead snags. However, the snags were generally much larger — and so were the downed, decaying logs. That stemmed from the preponderance of big, old-growth trees. Those huge decaying logs provided shelter and habitat for a wide variety of insects and wildlife.
By 2015, the number of downed logs had increased threefold. The downed trees were generally much smaller and despite their soaring numbers actually offered fewer benefits for wildlife.
The forest floor littered with the remains of smaller-diameter trees actually provided a much more dangerous base for fires — even ground fires that didn’t climb up into trees.
That agrees with the findings of University of Arizona forester Wally Covington, who discovered that a century of fire suppression had left the forest floor so piled with pine needles and debris that even a prescribed fire remaining on the ground could burn so hot it killed the roots of the remaining big trees.
The Forest Service researchers concluded a combination of forest thinning and prescribed fires can eventually restore natural deadwood conditions to the forest floor. Ultimately, restoring forest health will require getting rid of the overgrowth of small trees and returning to a forest dominated by big, old-growth trees.
Those studies support the Forest Service’s effort to let more low-intensity fires burn and thin huge stretches of overstocked forest to prevent the megafires that have done billions of dollars in damage to California forests and communities this year.
However, in the short run, the return of managed fires also poses an increased danger for communities like Show Low and Payson.
Forested communities need thinned buffer zones, Firewise clearing within community boarders and WUI building codes that prevent embers from an approaching fire from setting roofs and porches on fire within the community.
The devastation caused by the Yarnell Fire, including the death of 19 firefighters, underscored that point in Arizona.