The evidence continues to mount that only active management of Rim Country forests through thinning, logging and controlled burns can stave off disaster as the climate shifts.
One new study concludes that the “hands-off” approach that has dominated forest management in the past decades poses a much greater danger to the spotted owl than an active program of thinning, logging and burning.
Two other studies have demonstrated that the combination of dense stands of trees and warm winters can lead to catastrophic outbreaks of bark beetles, which have already wiped out hundreds of thousands of acres of forest throughout the West.
Taken together, the studies seem to support a large-scale shift to some version of the Four Forest Restoration Initiative, an effort to offer timber companies a guaranteed supply of small-diameter trees in hopes the sale of wood products will cover the cost of thinning millions of acres.
The first study, published in Forest Ecology and Management, concluded that uncontrolled crown fires racing through thick stands of unthinned timber pose a grave danger to the northern spotted owl, an old-growth forest dependent raptor long at the center of the timber wars.
The researchers from Oregon State University and Michigan State University concluded that after a century of suppressing fires and allowing unnaturally thick stands of timber to grow, the Forest Service has dramatically changed the impact of fire.
Instead of frequent, low-intensity fires that cleared out deadwood and saplings, millions of acres now face the threat of intense, soil-sterilizing fires that will consume the old-growth reserves set aside for the spotted owls.
Historically, ground fires burn through debris on the floor of old-growth forests, without climbing into the lower branches of the big trees. However, in a forest crowded with saplings, fire climbs into the tops of the big trees and spreads from treetop to treetop. As a result, fires start in the forests crowded with saplings then spread into the treetops of even old-growth patches set aside to protect endangered species like goshawks and spotted owls — which do best hunting under a closed forest canopy.
John Baily, with Oregon State University, observed that the Forest Service for “many years” has “avoided almost all management on many public lands.”
He said that the Forest Service has been “kicking the can down the road,” which makes eventual “stand replacing” fires inevitable. “Sooner or later a stand replacing fire will come that we can’t put out. Then the fires are enormous.”
The Wallow Fire in the White Mountains in 2011 consumed more than 500 square miles of forest, including many designated critical habitat areas for Mexican spotted owls. Only thinned buffer areas saved communities like Alpine.
The second set of recently published studies focused on the interaction between outbreaks of tree-killing bark beetles and climate shifts. The Southwest has lapsed back into one of the worst droughts on record in the past 1,000 years, with rainfall less than half of normal in Payson so far this year. Tonto Creek currently has just 17 percent of its normal flow, the Verde River about 60 percent of normal and the Salt River about 40 percent of normal.
Computer climate projections say that the current trend could make the drought conditions of the past decade the new normal in the Southwest. The great majority of climate scientists say that the buildup of carbon dioxide and other pollutants will result in a gradual global warming in the next century.
Some projections warn that such a trend could dramatically affect rainfall patterns in the Southwest, including shifting the summer monsoon storm patterns that provide about half of Payson’s annual rainfall.
The recent studies show that a decrease in rainfall and a rise in winter temperatures could result in repeated tree-killing epidemics of bark beetles.
Droughts — especially when interrupted by the occasional wet year — can produce population explosions among bark beetles, concluded researchers from the U.S. Forest Service’s Southwest Research Station in the journal Ecology.
Beetles bore into the trees during the dry years, when the dehydrated pines can’t produce enough pitch to expel them. The beetles leave their larvae behind. The grubs then hatch and begin eating the inner bark of the tree, which carries the nutrients up to the leaves. The dry years give the beetles a foothold and the wetter years provide the larvae with food.
The problem gets worse with mild winters, since bitterly cold conditions can kill the larvae waiting out the winter just beneath the bark.
The researchers concluded that climate predictions in the Southwest should provide ideal conditions to foster more bark beetle outbreaks in coming years.
A second bark beetle study came to similar conclusions.
This study examined a bark beetle outbreak in 2001-02, which killed most of the pines in 3,000 square miles of forest — an area six times the extent of the Wallow Fire.
The researchers from the University of Colorado at Boulder wanted to know whether the epidemic started in one area and spread — or started in several areas at once.
They concluded that scattered outbreaks of beetles spread out of control, eventually merging into a massive infestation. The outbreaks started in drought-stricken areas with sickly trees. However, those patches of forests eventually produced so many bark beetles that they overwhelmed even healthy stretches of forest nearby.
In addition, the researchers discovered that the outbreaks often started in thick clusters of trees growing into a burned out area. Those thickets of stunted trees not only had impaired defenses, but also offered the beetles an easy path to spread from tree to tree with their interlocking branches.
The study offers ominous portents for forest health in coming decades; give projections that call for ever-larger fires and a deepening drought in a landscape crowded with over-stressed trees.
The problem will likely affect much of North America. At the moment, British Columbia in Canada is suffering from a bark beetle epidemic that started in 1990 and now affects some 70,000 square miles of forested land.
“The current study suggests that under the continued warmer climate, the spread of the beetle in ponderosa pines is likely to grow until that food source is also depleted,” said CU-Boulder geography professor Thomas Veblen, one of the authors of the study funded by the National Science Foundation.