Forest Health And Fire, A Dangerous Balance

Studies show fire managers caught between too much and too little

Studies have concluded that forest thinning and controlled burns can tame ordinary fire behavior, but are ineffective at slowing or stopping the mega fires that have become more common.

Studies have concluded that forest thinning and controlled burns can tame ordinary fire behavior, but are ineffective at slowing or stopping the mega fires that have become more common.



Roundup file photo

The task of saving the forest — and places like Payson — keeps getting more complicated.

A series of comprehensive studies suggest large-scale restoration logging can play a key role — but not without a dramatic change in the use of fire. However, without such a delicate balance between managing fire and fighting it — the southwest will likely lose most of its pine forests.

These conclusions emerge from some of the most recent studies on the impact of wildfires, logging, rising temperature and controlled burns on the forest.

The studies have sobering implications for Rim Country, where a dense, often-sickly forest poses an existential threat for forested communities. The U.S. Forest Service hopes to dramatically reduce tree densities across more than a million acres through the Four Forest Restoration Initiative (4FRI), which would rely on small-tree logging.

Wildfire wipes out pines

A massive study in California demonstrated that without big changes in forest management and restoration, northern Arizona could easily lose most of its current ponderosa pine forests after a big fire.

A study of 14 burned areas in 10 national forests found that in 40 percent of the areas almost no pine seedlings returned, even seven years after a high-intensity wildfire. The scientists were shocked to find not a single returning pine seedling in 43 of the 1,500 plots they monitored. Previously, the burned areas had been thickly forested, according to the study published in Ecosphere, a peer-reviewed scientific journal.

The researchers came up with a formula to predict where pines could not easily regenerate on their own after a high-intensity fire as a way to help the Forest Service decide where to make the effort to plant seedlings after a big burn.

The high severity fires apparently kill almost every tree, leaving behind no survivors as seed source. High intensity fires can also make it so the soil can’t absorb water normally, leading to erosion and loss of topsoil.

The researchers also concluded that brush comes back relatively quickly after a wildfire, shading out the pine seedlings. Fire and drought-resistant trees like ponderosa, sugar and Jeffrey pine can’t get started if they’re shaded by bushes.

As a result, the desirable, fire- and drought-resistant trees that could tolerate the increasing warmth and drought can’t come back at all in many areas after a high-intensity fire. Those trees are instead adapted to frequent, low-intensity fires — which create a patchy landscape with wide open spaces sprinkled with stands of large trees.

Thinning’s not enough

Severe, high-intensity fires go wild even in areas previously burned and thinned, according to an unsettling study by the Pacific Southwest Research Station published in the journal Forest Ecology and Management.

The study examined the behavior of the 2013 Rim Fire in Yosemite National Park, the largest wildfire in the recorded history of the Sierra Nevadas.

Land managers in the national park have used prescribed fires and low-intensity managed fires since the 1960s to try to maintain natural conditions in the park. The Forest Service has shifted to just such an approach in Rim Country, as evidenced by the large numbers of fires the Forest Service let burn in the spring and monsoon season this year.

This long use of managed fire in Yosemite gave researchers a chance to see how different areas responded to the high-intensity assault of the Rim Fire.

They found stark differences, depending on the behavior of the fire.

High-intensity fires can effectively create their own weather if the towering pillar of superheated air and smoke and flame rises to a certain height. When a “plume” forms, it sucks in air from all around — fanning the flames to a much greater intensity. Sometimes, this plume will then collapse. This blow-torches the fire outward in every direction.

The development of just such a plume was the fatal factor in the Dude Fire just below the Rim off the Control Road in 1990, when the collapse of a plume sent out 100-foot-long walls of flame that killed six firefighters in their fire shelters.

The researchers discovered that thinning and previous managed fires can tame normal fire behavior. However, once the plume conditions developed and a high-intensity fire resulted — the thinned and unthinned areas fared about the same. The ravenous fire blasted through without pausing in the thinned areas.

The finding raises ominous implications for Rim Country, where the Tonto National Forest has thinned buffer zones totaling some 50,000 acres on the edge of most communities, including Payson, Pine and Star Valley. The thinned buffer can slow or stop an ordinary fire, but probably not one of the mega fires becoming increasingly common as average temperatures rise and droughts lengthen.

The researchers concluded that the protection offered by a managed fire or a thinning project declines over time, largely disappearing after about 15 years. That’s mostly because brush grows into the thinned and burned area, providing enough fuel to carry a high-intensity fire — even without the thickets of trees.

The findings demonstrate the dangerous knife edge along which fire managers must run. They need to allow low-intensity burns to move through as much of the forest as possible when the weather cooperates. However, they must also quickly suppress blazes with a potential to grow into high severity fires, before they can start generating their own, disastrous patterns.


Use the comment form below to begin a discussion about this content.

Requires free registration

Posting comments requires a free account and verification.