Fireproofing The Forests

(4 of 6)

The frequent-fire regime that prevailed in the ponderosa pine forests of Arizona and New Mexico, for example, kept fuels low over widespread areas. In the ponderosa pine forests of Colorado's Front Range, however, big burns were spaced farther apart, allowing flammable material to accumulate. These fires rolled through every few decades or so and occasionally burned extremely hot. Their legacy, says Merrill Kaufmann, a senior scientist with the U.S. Forest Service's Rocky Mountain Research Station, was a mosaic of forested areas that alternated with clearings ranging from 5 acres to 100 acres in size.

It was this scale of patchiness in the landscape that once minimized the danger of horrific conflagrations like the infamous Hayman fire of 2002. In a single day, it is sobering to recall, the Hayman fire flared across some 60,000 acres in Denver's watershed, torching the crowns of trees and cooking the soil. Among the casualties were most of the 300-to-600-year-old ponderosa pines on a 7,500-acre site that Kaufmann has closely studied. It was a beautiful site, he says, ungrazed and unlogged. The only problem was that fuel loads were off-scale because a good fire had not moved through in more than 120 years.

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