Fireproofing the Forests

WILLIAM CAMPBELL FOR TIME
In Arizona, a weary fire fighter walks away from a blaze he just set

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To many forest ecologists, manipulating fuel loads whether by thinning, prescribed burning or a combination of the two constitutes the best strategy we have for ensuring that the ponderosa pine forests of the present survive into the future. And the good news, says Mark Finney, a researcher with the U.S. Forest Service's Fire Sciences Laboratory in Missoula, Mont., is that it's probably not going to be necessary to thin or prescribe-burn every acre of forest at risk. According to mathematical models that Finney has developed, reducing fuels in a strategic pattern across a more manageable 20% of the landscape may well be sufficient.

To date, most fuels-reduction measures have had fairly narrow goals, such as protecting valuable stands of trees. The logical next step, as Finney sees it, is to implement these measures across hundreds of thousands of acres. It is already clear, he notes, that prescribed burns have the power to modulate the behavior of big fires. One branch of the Hayman fire, for example, stopped at the edge of an area where a large prescribed burn had been conducted the year before, and the Rodeo-Chediski fire, for its part, was forced to detour around prescribed burns on forest lands managed by the White Mountain Apache tribe.

In many ways, prescribed burns are preferable to mechanical thinning, which is labor intensive and therefore time-consuming and costly. But prescribed burns are not risk free, especially in areas that have been deprived of fire for long periods of time. Three years ago, for example, a prescribed fire at the Bandelier National Monument in New Mexico went off the reservation, igniting the blaze that swept into Los Alamos. Lost in the finger pointing that followed was the fact that the fire would probably not have proved so dangerous had fuel loads in the adjacent forest been lower. And this is precisely why thinning can be useful. As Arizona State University environmental historian Stephen Pyne sees it, thinning is just a tool for "re-creating a habitat for fire."

Do No Harm
Not all forests are good candidates for thinning. Among the prime examples are the lodgepole pine forests that occupy higher elevations across the mountain West. Lodgepole pines, which are thin-barked, flourish only in areas where sufficient moisture and cool temperatures keep fires at bay for long periods of time. There they grow quite densely together so densely, in fact, that numerous trees are shaded out by more vigorous competitors. These dead and dying trees, intermingled with low-limbed spruce and fir, add a vertical dimension to the fuels structure that one day will carry fire into the canopy as happened across a third of Yellowstone National Park in 1988.

Yet attempting to thin lodgepole pine forests to prevent such blowups would be ludicrous, say scientists, for these seemingly catastrophic blazes serve important ecological functions. Among other things, lodgepole pine saplings do not flourish beneath the shade of mature trees and thus are dependent on fires to clear sun-filled openings. Moreover, many lodgepole pines package their seeds in resin-sealed cones that can be opened only by intense heat. "What you have to keep asking yourself is what range of fire frequency and severity a particular forest has experienced," says Tania Schoennagel, a University of Colorado researcher who studies postfire recovery. "Using forestry practices to mimic these fires is O.K., but if you mimic fires outside that forest's experience, then I think you're doing the forest harm."

Thinning also seems of dubious merit in many mixed-severity fire regimes, except as a protective measure around the perimeter of communities. Consider, for example, the Biscuit fire that hopped and skipped across 500,000 acres in southern Oregon's Siskiyou National Forest last year. Slightly more than 15% of this rugged, geologically complex region was so seriously burned that virtually all the trees died. Around 65%, however, experienced fires of light and moderate severity, while some 20% escaped unscathed. Seed from areas where vegetation survived is already drifting into areas where vegetation was lost, and many important species knobcone pine trees, flowering kalmiopsis bushes and carnivorous cobra lilies are taking root in the ashes. "This is not a catastrophe," says World Wildlife Fund ecologist Dominick DellaSala, "but a process that drives biodiversity."

Even in forests where frequent, low-severity fires are the rule, the possibility that thinning may have unintended consequences merits careful consideration. Among other things, thinning can open forests to drying winds, making branches and needles even more flammable. It can expose pristine areas to vehicle and foot traffic that compacts soil and facilitates the spread of exotic grasses and weeds. And then there are all the other considerations, ranging from the aesthetic (what a forest should look like after it's thinned) to the practical (what to do with all the small-diameter trees a massive thinning program would generate).