In much of the west, forests exist in three states: burned, recovering from being burned, and waiting to be burned.  Until recently, the time between burns in northern Arizona was two to ten years.  But as logging became both feasible as well as profitable, fire suppression became an article of faith in the management of national forests.  Only in the last few years has that policy been reversed, with the recognition that naturally occurring fires are a necessary and important part of maintaining forest health.  The difficult question necessarily arises, however, of how to make the transition safely back to a state of nature.

The Warm Fire on the Kaibab plateau provides an interesting example of how this transition is being addressed in practice.

On June 8 of this year, a lightning strike ignited a fire in the interior of Kaibab National Forest, near Warm Springs Canyon (hence the name, the "Warm Fire").  Consistent with the new policy of the National Forest Service, it was decided to manage rather than extinguish the blaze, and to therefore classify it as a "wildland fire use fire, managed for resource benefits" (this and other details are taken from a National Forest Service report available at the National Forest visitor centers).  What this means principally is that conditions were deemed appropriate to allow a naturally occurring fire to clear out the "fuel load" (i.e., dead logs, branches, needles and so on) that had accumulated through the decades during which the preceding fire suppression policy was in force.

As you doubtless know, the issue with too much fuel is that when a fire does start, it is likely to become so intense that it will kill all trees, leaving a denuded landscape ripe for severe soil erosion from the annual monsoonal rains, as well as to invasion by non-local weed species.  Historically, fires would sweep any particular acre of land frequently enough that fires of such intensity would develop only in unusual conditions.  This is especially true in mature, naturally occurring ponderosa pine parkland, where trees are widely spaced, and the fires clear out the accumulated detritus with little damage to existing trees of any size.

Such a fire is today called a desirable “low intensity fire.”  After a low intensity fire, there is little visual damage to mature trees, although there may be some charring of their bark.  Seedlings and smaller are destroyed, as is much of the forest litter. 

 

In a medium intensity fire, visual damage extends higher into tall trees, and some may die as a result.  But overall, the forest survives, with the added benefit that holes are opened in the forest canopy that allow new trees to sprout and grow, thus varying the ages of trees, and also allowing other transitional species, such as aspens, to take hold.  The result is a more diverse forest with better wildlife habitat, a recycling of nutrients in the soil, and a lowered risk of a more catastrophic result the next time around.

 

In the case of this summer’s fire on the Kaibab, all went well for two and a half weeks, with a low intensity burn predominating.  Then, a strong wind pushed the fire several miles to the north, although still within the boundaries established for the fire to continue to burn without intervention.  The wind shifted direction again, however, and the fire now pressed towards the southern boundary that had been established in the management plan.  As a result, the Forest Service decided on June 24 to bring in a team to suppress the burn.

 

By the evening of June 25, the fire team had arrived, but was not yet deployed.  That night, a strong wind turned what had been a reasonably well-behaved burn into a roaring conflagration, destroying more than half of the total acreage of the entire fire in a single night.  Most of that destruction was neither low intensity nor medium intensity, but high intensity — destroying everything, according to the post-burn analysis performed by the Forest Service.

 

The next day, humidity levels rose, and scattered showers moved in, as did the fire crews.  Peak season access to the north rim of the Grand Canyon was sealed off from June 26 to July 3, however, as dense smoke and flames crossed the access road.  Those that make their living around and on the Kaibab during a few short periods of public access were not pleased.  By the fourth of July, the fire was contained.

 

When the smoke had (literally) cleared, 58,658 acres had been burned.  19,558 of those acres had burned during the two and a half weeks during which the fire was in its “wildland fire use” managed status.  The remaining 39,010 were destroyed during the suppression phase.  17,280 acres were identified as having been subject to high intensity fire.

 

With the fire largely out, the Forest Service went into recovery mode, watching for flare-ups, but also aerially seeding the burn areas with sterile rye seed, in an effort to stabilize the thin soils of the burn area until natural regeneration of native species could occur.  Also, one expects, spin control set in, and the name “Warm Fire” was assigned to a fire that was one-third high intensity.

 

What does a forest look like following an event like this?  I’ll write about that tomorrow. 

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