Why Thinning Forests is Poor Wildfire Strategy

Much of the current political discussion about forest thinning and many of the efforts being implemented or proposed for federal forest lands are aimed at reducing large severe wildfires. It seems intuitively obvious to most people that reducing fuels will eliminate or minimize large fires that burn across large swaths of the West and occasionally threaten homes and communities.

But it is also intuitively obvious that the sun rises in the East and sets in the West, and thus must circle the Earth—yet we know that what seems intuitively obvious about the sun’s relationship to the Earth is false. Similarly while fuel reductions may appear to be a panacea for halting large fires, in reality they are not.

To evaluate thinning for fuel reduction effectiveness we need some context. First there is the issue of how fires burn and don’t burn. Fires only ignite and spread when the weather/climatic conditions are appropriate to sustain a blaze. You can have all the fuel in the world, and not get a fire if the fuel is too moist or otherwise unable to sustain a flame. That is why there are few large fires in the old growth coastal forests of the Pacific Northwest even though there is tons of fuel per acre.

Because fires only burn when weather/climatic conditions are “ripe” for a fire, most ignitions go out whether we do anything or not. For instance, between 1972 and 1987 Yellowstone National Park decided to experimentally allow all natural fires to burn without suppression. There were 237 blazes during that period, and the vast majority burned only a few to a hundred acres, and no more. Even more telling, all self-extinguished without any intervention.

Yet under normal fire policy on public lands, such fires would have been “put out” by fire fighters who would have claimed credit for extinguishing the flames. The vast majority of all wildfires are in this category—in that they would go out on their own with or without suppression and they will only char a small amount of forest.

On the other hand, there are a few blazes that are ignited under severe fire weather conditions of low humidity, high temperatures, drought and wind. Under these extreme conditions, fires are difficult to impossible to extinguish. They may burn hundreds of thousands of acres before they go out—usually on their own whether we do anything or not. These are the fires that everyone knows, such as the Yellowstone fires of 1988, the 2002 Hayman fire in Colorado, the Biscuit Fire of Oregon in 2002, the 2007 Murphy Fire in Idaho, the Rim Fire near Yosemite in 2013, and other well-known blazes that have charred millions of acres of the West in recent years.

There is a consistent theme to these fires. They all burned under extreme fire weather conditions—and often burned through thinned forests, clearcuts, overgrazed rangelands and previously burned acreage. In other words, fuel reductions did not appear to appreciably change the course of these blazes.

When you look at statistics it is these few well known fires that burn the vast majority of all acreage in the West. One study concluded that more than 96% of all acreage burned was the result of 2% of the blazes and, even more telling, half of all acreage burned was the result of less than 0.1% of all blazes. In other words, it is a few very rare, and very large, fires that burn the bulk of all forest acreage and, it should be noted, these do the bulk of all ecological work and provide most of the benefits associated with fire.

So it is these few fire that most fire-fighting policy and related thinning efforts are designed to halt or control. Yet it is never asked whether thinning can actually effectively halt such blazes.

There are good reasons to believe that thinning cannot and will not effectively halt such blazes.

First, most thinning projects are not done properly. A properly performed fuels reduction project would include not only mechanical removal of smaller trees and reduction of canopy density, but also broadcast prescribed burning to reduce ground fuels. In fact, mechanical thinning alone often INCREASES fire spread by putting more fine fuels on the ground.

Additionally, thinning in some instances can INCREASE fire spread by exposing the forest floor’s fuels to greater sun drying and greater penetration by wind through the open forest stands. What is surprising to learn is that often the most dense forest stands (i.e. those with the most fuels) do not burn well because they retain moisture the longest, and wind is impeded from pushing flames through such dense forests.

Second, thinning by removing competition between trees and brush often increases rapid regrowth of vegetation. Therefore, any thinning/fuels reduction program must have follow-up maintenance in the form of recurring prescribed burns and/or thinning to be effective. Yet most thinning projects do not even get the first prescribed burning, much less follow up burns.

There are several reasons for this. The first is that many thinning projects, although consistently money-losing affairs, do recoup some funds by the sale of wood to timber companies. But once a site has been logged, it is decades before it can be logged again. So there is no financial incentive for follow-up maintenance work.

Also, prescribed burning is risky, and the opportunity for agencies to set fires is limited to short windows of time. Many forest managers are loath to okay a prescribed burn unless conditions are ideal for containment. No one wants to be the person who signed off on a prescribed burn and then had it get away and burn homes to the ground. However, when conditions are good for controlling a blaze, they are usually not good for fire spread.

In the last analysis, the politics of forest thinning promotes more logging. The timber industry has successfully sold the idea that fuel reductions work and it has great influence with politicians who buy into to its assurance that logging reduces large fires.

Due to rapid regrowth of vegetation released from competition from other trees and shrubs, the effectiveness of fuel reduction projects—even those done properly—is lost relatively quickly.

Since one cannot predict where and when fire will occur, the vast majority of fuel reduction projects are a waste of time and money because the probability that a fire will start or move into a thinned forest in any given time period that matters is exceedingly small.

Worse, all thinning projects have unintended ecological consequences. Nearly all require roads for forest access. Roads are a major cause of the spread of weeds. Roads also increase access for hunters, trappers, and poachers, reducing security for wildlife. Roads also are the major source of sediment flow into waterways, thus negatively impacting fish. Removal of biomass off-site also has impacts on forest ecosystems, eliminating nutrients and reducing wildlife habitat.

So even where fuel reductions are done and maintained properly, and happen to be in the path of a major fire, one must ask if the negative impacts associated with these thinning projects don’t outweigh the benefits—especially, since they all lose money.

And here’s the clincher. Even if thinning/fuel reductions did stop fires under moderate fire weather conditions, it would likely not matter because most of such fires self-extinguish anyway.

The fires that thinning is designed to halt are the very few large severe wildfires that are driven by drought, high temperatures, low humidity and, most importantly, wind. The fires that make the news stories across the country and are responsible for burning the vast majority of all acres in the West are exactly the fires thinning—even when done properly—cannot halt. The reason? Wind!

Wind blows burning embers several miles ahead of a fire front, easily hopping over thinned forest patches. Wind also increases the intensity of the blaze as anyone who has blown on a smoldering fire and seen it flare up can attest. All large fires around the West burn under high wind conditions and in those situations, fire fighters and their techniques are ineffective. Indeed, under high winds, fires will jump highways, rivers, and lakes where there is no fuel. They will race across grass stubble on over-grazed rangelands. Fuels do not limit fires under such weather/climate conditions.

Even if it were possible to reduce large fires by thinning, one must ask whether it would be advisable to do so. It turns out that the severely burnt forests that result from large conflagrations are among the most biologically important habitats. The snag forests that result from severe stand replacement blazes have the second highest biodiversity of any forest habitat in the West. The dead trees that result are a long term biological legacy critical to forest ecosystem health.

So is there any place for forest thinning/fuel reductions? There is. But it should be limited to the areas immediately surrounding homes and communities. Since one can’t predict where a fire will start and burn, thinning forest willy-nilly is a waste of effort. Not only are most thinning projects done improperly, most are done for the wrong reasons and lose taxpayer money to boot.

No one wants houses and towns to burn up. Focusing thinning on the immediate area around structures is cost effective. It is also easier to maintain fuel reductions near homes because access is easy, and even though there are negatives with any logging operation, by focusing those impacts to the area immediately around homes and towns—places already impacted by human use—we minimize those negative ecological impacts.

Thinning trees/shrubs near homes, combined with a reduction in home flammability by installation of metal roofs, removal of flammable materials adjacent to homes, and other measures can virtually guarantee a home will survive even a severe high intensity forest fire.

Thinning forests for fuels reductions, unless strategically done, is a waste of taxpayer funds, and has significant ecological impacts. It is unwise forest policy.

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