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Why Fire Suppression Has Little Influence on Forest Fires

A common assertion, oft repeated by the timber industry, the Forest Service, and far too many conservation groups (such as, The Nature Conservancy) is that a century of fire suppression has contributed to the large wildfires we are seeing around the West.

The logic goes like this. Due to effective fire suppression, fuels have accumulated in most forest types and hence we are experiencing larger fires. The solution, therefore, is to reduce the fuels—usually proponents of the fire suppression paradigm want to accomplish this by logging.

The main problem with this logic is that most plant communities in the forests of the West are not characterized by frequent fires under natural conditions, thus fire suppression, even if it were effective, would not have altered the natural fire patterns.

These include forests of lodgepole pine, spruce, various fir species, and even shrub ecosystems dominated by sagebrush and chaparral. The natural fire rotation of these plant communities is often on the scale of hundreds of years.

FIRE ARE NOT CLOCKS

Fires are not like clocks. I’ve heard some suggest that if the natural fire rotation was 200 years for some forest types, than half of the landscape should have burned in the previous hundred years. But fires are more like floods on rivers. When you have the right conditions for a major 100-year flood, you get the high water. But you don’t get a percentage of that high water in the years leading up to the 100 year event. Fires are similar.

Large fires only occur when there are weather/climate conditions that facilitate fire ignition and their spread. These special conditions include drought, high temperatures, low humidity and high winds. Assuming you have the other conditions, high winds are the major driver of large fires. These conditions do not occur very often in most ecosystems.

ONE HUNDRED YEARS OF FIRE SUPPRESSION QUESTIONED

Even the assertion that fire suppression was effective for 100 years can be questioned. Fire-fighting ability has radically changed over the past century. Early fire-fighting ability was extremely limited. To suggest that widely scattered Forest Service rangers riding mules across miles of wilderness and working with nothing more than shovels and axes were “effective” at significantly reducing fires begs credibility.

In these early years, livestock grazing, by eliminating the fine fuels (grasses) in the understory of some plant communities, likely had a greater influence on fires than fire-fighting and suppression by humans.

It was not until after WW II when air support became common in the 1950s and 1960s with the advent of smoke jumpers, air tankers and helicopters that fire fighters could easily reach ignitions. Add to that air access, the greatly expanding road access due to a logging boom on public lands that occurred throughout the 1960s, 1970s, 1980s, and 1990s, and one could perhaps suggest that fire suppression may have been effective in some locations.

However, at the same time that massive fire-fighting capabilities were implemented, the climate was less conducive for fire ignition and spread. From the 1940s to the end of the 1980s, most of the West was cooler and moister than in earlier decades and since that time. The climatic conditions may have contributed to the notion that fire suppression was actually effective.

HOW EFFECTIVE IS FIRE SUPPRESSION?

I remember attending a conference where a Forest Supervisor remarked that his agency was “darn good at putting out fires when it rained, but not so good when it was hot and dry”. What he was admitting is that fire suppression is largely effective when the weather conditions make it easy to put out a fire.

Another interpretation is that most fires would self-extinguish whether they were attacked by firefighters or not. Indeed, there is evidence to suggest that even in the absence of fire suppression, the majority of fires would simply burn out without affecting much of the landscape.

For instance, an experiment in Yellowstone appears to bear this out. Between 1972 and 1987, some 235 fires were permitted to burn without any fire suppression. Most of them went out after scorching less than 100 acres. And all of these fires self-extinguished.

MAJORITY OF FIRES ARE SMALL

The vast majority of all wildfires burn very little acreage. We may be effective at squelching the small fires—the fires that are most likely to self-extinguish anyway. But thus far, we are not very successful (fortunately) at affecting the larger fires. And these fires account for the vast majority of all acreage burned.

Between 1980-2003 there were 56,350 fires on federal lands in the Rockies which burned 3.6 ha (9 million plus acres).

Some 55,228 blazes out of 56,350 fires burned only 4% of the entire area.

Even more telling 0.1% (50) of the fires were responsible for half of the acres burned.

It is the occasional large fires that pose the threat to homes and communities but they are rare and unpredictable.

FIRE STUDY BIASES

Another factor that is part of this debate is the accuracy of the “fire scar” studies which are the primary means of establishing fire history. Researchers find trees that have been burned, but not killed, by fires. Trees that survive fires often have scars that can, in theory, be read like tree rings, establishing the frequency of fires on that particular tree.

One of the problems with this method is sampling bias. Most fire scars are found by walking through the forest looking for scarred trees. However, this method is not random. And one can’t assume that the trees with scars represent the fire history of the surrounding landscape, any more than a survey of people in a bar represents an accurate reflection of the overall alcohol use in a community.

A second common problem is the use of “composite” fire scars, whereby all the trees with any fire scar in a particular year are counted as a fire year. The problem with this method, according to critics, is that composite fire histories consider all fires as equal. However, we know that most fires are not large, and tend to self-extinguish without burning more than a few acres, so counting every fire scar as a fire “year” may tilt the sample toward shorter fire intervals.

More recent fire scar history studies have attempted to get around this problem by only including fire years where more than a certain number or percentage of trees were burned in that year. This helps to reduce the bias, but does not necessarily overcome the problem completely.

FIRE DEMOGRAPHICS AN ISSUE

Even if fire scars accurately portrayed the historic fire regime for a particular site, it’s important to consider the ecological influence of fires. One large blaze will burn far more acreage than hundreds of small blazes.

Consider a 1,000 acre study plot where over a 100 years, 100 fires were recorded. This would lead one to conclude that the fire frequency was one fire per year. But if each fire burned an acre or less, even a 100 blazes would only char a 100 acres or a tenth of the 1000 acre study area. At this rate, it would take a 1000 years to burn an equal amount of the entire study area.

Since large blazes are, by their definition, infrequent, counting only the larger fires that have burned across a significant proportion of the landscape may be more accurate characterization of the fire history. Often in fire history studies there are certain decades with many fires (often small) and many decades without any fires in between.

For instance, you could have 10 fires in a 100 years or a fire every 10 years on average. But those fires may be temporally irregular. We know that fires tend to occur in “fire decades” so you could have 5 fires in the first decade, and five fires in the last decade but a fire free period of 80 years in between.  Thus even forests characterized by “frequent fire, low intensity” may still have long periods without any fires at all.  As a result even these forest types may not have been that influenced by fire suppression—even assuming that it is effective.

WHAT ABOUT LOW ELEVATION PINE FORESTS?

Some argue that fire suppression must have reduced blazes in low elevation ponderosa pine forests since this particular forest type is commonly assumed to have been influenced by frequent, low intensity fires. In all likelihood it is possible that fire suppression has had an effect upon these forests, especially at the lowest driest locations. However, even this assertion has some nuance to it.

For example, a number of recent studies have documented that high severity fires historically occurred even in the ponderosa pine zone. Some studies in Colorado’s Front Range suggest that 80% of the pines were burned in stand-replacement high-severity fires. Another study of ponderosa pine along the Payette River in Idaho found evidence for periodic large stand replacement fires there as well. A third study of dry forests in British Columbia found similar results. So the idea that even ponderosa pine forests are somehow outside of their “historic” condition because we see an occasional mixed to high-severity fire in these ecosystems may be inaccurate.

FIRE DEFICIT SUGGESTED

The hand wringing over the occurrence of large blazes around the West ignores the fact that historically we always had large fires. There are many plants and animals that have evolutionary adaptations and requirements for periodic large blazes. These evolutionary adaptations would not have occurred if large fires were historically absence.

Some ecologists are suggesting that we have a fire deficit due to the decades of moist, cool weather. The acreage burned annually in recent years while seemingly large compared to the 1940-1980s period, is still quite a bit less than what burned earlier in the last century, as well as much less than has been established for earlier dry, drought conditions such as occurred during the Medieval Warm Period between 800-1300 AD. This was the same time period when Greenland was mild enough for colonization by Vikings, and Anasazi Indian cliff dwellers successfully colonized the Four Corners region.

Given that wildfire is a major contributor to snags and woody debris in the ecosystem, we really need to have more large fires, not less. Even if fire suppression were really having an influence, it would be problematic to control such fires. We need large fires for a healthy forest ecosystem.

More articles by:

George Wuerthner has published 36 books including Wildfire: A Century of Failed Forest Policy. He serves on the board of the Western Watersheds Project.

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