The problems of prescribed fire


There has been a growing chorus of political leaders and often firefighting agency personnel who suggest that greater use of prescribed fire could preclude the establishment of large blazes or at least slow advances. Advocates also assert it could reduce overall smoke and improve forest health. 

The rationale for prescribed burning is justified by the assumption that past burning by tribal people precluded large blazes and maintained healthy forest ecosystems. 

I will not go into details here about why tribal burning was unlikely to affect large landscapes nor substantially reduce fires under extreme fire weather conditions but suffice to say the influence of pre-Anglo ignitions was primarily localized and did not preclude large blazes. Under low to moderate fire weather, prescribed burning can influence fire intensity and spread. Particularly if the burn is recent, it can slow or even stop a fire but not under extreme fire weather. 

The first problem is that prescribed burns typically involve a few hundred acres at best. 

Part of the reason for this is the limited financial and personnel resources to implement prescribed fires, but it is also due to the small window when a prescribed fire is possible.

However, the goal of prescribed burning is often to prevent large blazes, but this ignores the correlation between climate and large fires. Low severity fires do not emulate, nor are responsible for large blazes which are primarily climate/weather-driven events. Prescribed burning (or thinning) does not change the weather. 

However, the vast majority of all fires are ignited and burn under less than extreme fire conditions, and research has demonstrated that nearly all of these fires burn a small area (usually less than a few acres) and even if left alone will self-extinguish. For example, in a study in Yellowstone where 235 fires were permitted to burn without suppression between 1972 and 1987, 222 burned less than 5 acres, while a few grew larger. And all 235 blazes went out with any suppression efforts. 

Did Yellowstone suddenly gain far more fuel in 1988 than in 1987? What accounted for the massive 1988 fires that swept through more than 1.5 million acres of Yellowstone and surrounding national forests? The only significant difference was that in 1988 Yellowstone experienced the most severe drought in its entire recorded history. The drought combined with low humidity and with winds of 50 mph drove the fire through the forests. 

This is a key point. Under extreme fire weather conditions, fuel reductions (prescribed burning and thinning) are typically ineffective in slowing or stopping the spread of blazes. 

In nearly all the instances where suppression efforts were deemed successful due to prescribed burns (and/or thinning), a closer examination typically shows that the weather changed. It rained. The wind died down. In other words, the fire is no longer burning under “extreme fire weather.” 

Even if one can demonstrate that the only explanation for halting fire progress was due to a prescribed burn, there are numerous other examples where fuel reductions have failed. The Labor Day blazes that charred hundreds of thousands of acres on the Western slope of the Oregon Cascades burned through fuel reductions created by prescribed burns, clear cuts and previous wildfires. Yet none of these fuel reductions slowed the fires. What drove these fires, as with nearly all large blazes, was drought, high temperatures, low humidity and, most importantly, wind. 

A second problem with prescribed fires is the very low probability that a fire will encounter a treated area in the time when it might be effective. Time is important since once a site is burned, the plant communities usually respond with increased new growth. Within a short time, usually five to 10 years in many ecosystems, there is often more fuel on the site than prior to treatment. 

In order to maintain effectiveness, you must continuously reburn — forever. Frequent burning can’t be done on a landscape scale, though focused burning near communities might be feasible. 

The dominant perspective that frequent fires kept fuels low, and hence precluded large stand-killing blazes is questioned by some researchers. 

The advocates of prescribed burning typically pose the question as “good fire” (low severity/frequent) and “bad fire” (high intensity/infrequent). For most ecosystems, the “natural” fire regime includes a significant amount of mixed to high severity blazes where the majority of trees and other vegetation is killed. 

However, the high-frequency low severity model is typically associated with low elevation dry pines like ponderosa pine. Nearly all other major plant communities experienced much longer fire rotations, typically in the multiple decades to hundreds of years, which means they aren’t adapted to frequent fires of any kind. 

Since most prescribed burning is done at lower elevations, it often chars non-forest ecosystems such as chaparral, Great Basin sagebrush, or pinyon-juniper woodlands which historically burned infrequently, with several decades or even centuries between fires. 

Furthermore, most prescribed burning occurs in the spring or late fall, while natural fires generally occur in the summer months. Timing of fire influences ecosystems.

This gets to the better alternative. You can “treat” far more acreage with managed wildfire and achieve fuel reductions, forest health benefits, than any prescribed burning program. Within any large fire, there is a mosaic of fire severity. Indeed, in most large fires, the percentage of acres burned are at low severity but with mixed and high severity as part of the total. 

Managed wildfire combined with the reduction of the flammability of the home ignition zone around houses, is the best way to deal with the rising number of wildfires and home loss. 

In the end, we must also reduce greenhouse gas emissions that are contributing to climate warming and exacerbating wildfire occurrence.

George Wuerthner is an ecologist who has spent decades researching fires. He has published two books on wildfire including “Wildfire: A Century of Failed Forest Policy.”

Tags Climate change fire management forest fires prescribed burning thinning wildfires Yellowstone

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