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Wildfire Science: Patterns and Suppression

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Most of the wildfires in Southern California are contained, but there are still things to consider after the smoke clears. USGS Research Ecologist Jon Keeley talks about wildfire patterns and the notion of suppression in the chapparal regions in Southern California.




Public Domain.


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Dave Hebert

Hello there, and welcome to the USGS CoreCast, episode 17, November 2007. I'm Dave Hebert.

The wildfires in Southern California have been largely contained, but the burning itself presents just one of many challenges and concerns related to wildfires.

USGS science addresses many of these issues, before, during, and after fires, and over the next few weeks, we'll be bringing you a variety of topics related to wildfire and the concerns that remain after the smoke clears, so to speak.

Today, we're going to talk about wildfire patterns in Southern California and clear up some of the notions of fire suppression and prevention.

To shed a little more light on these topics, USGS Research Ecologist Jon Keeley is joining us on the phone. Jon, thank you very much for being with us.

Jon Keeley

It's a pleasure to be here, David.


Jon, I want to start off by asking you, what do we know about chaparral or shrubland fires historically? How often do such fires naturally burn?


Well, we don't have clear numbers on precise frequency because we don't have the very detailed fire or scar records that forested ecosystems have. What we can say about fires is that when we look at these large, almost catastrophic fires that we're currently seeing on our landscape . . . we do know that that these are not anomalies restricted to the modern era and that we have had fires like this historically in the past.

The record shows that certainly in the latter part of the 1800s, when we had newspaper reports and various comments in books . . . we know that really large fires, not unlike the scale that we saw last week in San Diego, have occurred.

In fact, one of the biggest fires on record-at least as best we can piece together based on newspaper reports-occurred during Santa Ana wind conditions in the last week of September 1889 in Southern California, where people described essentially much of the Santa Ana mountain range on fire.

They remarked about how spectacular the displays were at night looking eastward towards the mountain range, and 60 miles away, newspaper reports from the town of Riverside reported looking westward, seeing the very same phenomena.

So what we know is that these large fires have been present on this landscape. What we don't know what is if the frequency of such fires has increased or decreased over the 20th century. I do think we can make some inferences, though, about how the frequency of fires has changed.

We know that almost all of the fires, at least in the coastal regions of California, are started by people, and we know that the numbers of those fires have increased through the 20th century as more and more people have moved into the region.

And so it appears that we now have many more fires on our landscape than we ever did historically. However, in terms of really large Santa Ana wind-driven fires, we may actually be seeing more of those now than we might have seen historically.

Because historically, very large fires would have been dependent upon late summer lightning storms that ignited fires that burned and smoldered around on the landscape for a few weeks until the weather changed. And this Santa Ana wind condition picked up and drove that fire probably over large portions of the landscape. And it was probably these sorts of scenarios that accounted for most of the area burned during the historical times.

Today, these large Santa Ana wind-driven fires seem to be more and more frequent because people are igniting more and more of these fires during this Santa Ana wind events.


Is a lot of fuel buildup causing these fires?


Well, the notion that fire suppression, which has excluded fires and caused fuels to accumulate . . . is a widely applicable theory to a lot of parts of the West. But in general, it really only applies to the forested ecosystem, and it really does not apply to Southern California landscapes.

And the primary reason is that fires that have begun in many forested ecosystems are largely ignited by lightning. And they occur, under conditions-weather conditions-that are not conducive to real rapid spread. Plus, they tend to burn surface fuels in the understory of the forest.

All of those conditions have led to the ability of fire suppression forces to put those fires out. And so what we see real clearly from the records is that in many forested ecosystems, fire suppression policy can be equated with fire exclusion during much of the 20th century. And the outcome of that is that we have seen accumulation of excessive fuels in these forests, which are now leading to bigger fires that have very different fire behavior.

In chaparral shrublands, it's a totally different story, and that model is simply not applicable to our Southern California ecosystems. And the primary reason is our fires don't burn in the understory. They burn through the canopy of the shrublands and produce very intense crown fires. And as a result, they're extremely difficult to put out.

And if you look if the fire records of the 20th century, you see that despite a policy of fire suppression, fire fighters simply have not been able to exclude fires from those landscapes. And recent U.S. Forest Service maps, which have tried to map the departure of contemporary fire regimes from historical regimes, show uniformly throughout Southern California that the bulk of the landscape in the 20th century has had more fire than historically it ever had.

And as a consequence, they haven't accumulated unnecessary or unnatural levels of fuel. And so it seems very unlikely that fuels and excessive fuel loads can be used to explain these phenomena.


Can you briefly define fire suppression and fire exclusion for us?


Fire suppression is a policy that dictates fires are attacked, and we attempt to extinguish them as rapidly as possible. Fire exclusion is the result of that policy on some landscapes, and it means fires have been simply eliminated.


So if fire suppression is not an option, what can be done to prevent such devastating fires?


Well, I think we can stop thinking from . . . about the perspective of stopping these fires. The bottom line is these large Santa Ana wind-driven fires are natural phenomena, and there's no reason to believe we could ever stop those fires on these landscapes.

What we need to do is change our thinking along the lines of other types of hazards. For example earthquakes: Earthquake specialists never talk about stopping earthquakes. They recognize they're inevitable, and they plan the human infrastructure all round of those events in order to minimize the vulnerability of communities to these hazards.

And I think this is the approach we need to take with fires. We need to realize were not going to be able to alter their outcomes, but rather, we need to think about altering the way we live on these landscapes, and infrastructure changes.

And one of the big things I think we need to move away from is this notion that if we spend a lot of money before the fires manipulating fuels-for example, with fuel breaks and prescription burns-were going to effect great changes in the outcomes of these fires. And I think that's probably demonstrated no more clearly than last week's fires in San Diego County, where we had hundreds of thousands of acres burned.

And what was interesting is that out of those fires, we know that when we look at the patterns of burning, that about 60,000 acres or more of those fires re-burned through areas that had burned in 2003. In other words, they burned very young fuels.

Or, to look at it a different way, if 4 years ago, fire managers had spent a lot of money doing prescription burning and they had managed somehow . . . which is not possible, but say, miraculously, they managed to do 60,000 acres of prescription burning, the patterns of fires last week suggests that would have been completely ineffective at stopping these big fires.

So the big thing we need to do is rethink our allocation of resources, perhaps away from things like trying to manipulate the fuels across the landscape and think more in terms of trying to alter the way people live.


So what we're looking at here is, even if you took human beings out of the equation, these fires would still occur naturally, correct?


Very much so, but what is important to keep in mind is that when were talking about fire, it's not sufficient to talk about whether it's a fire-prone landscape or not. It's important to keep in mind what type of fire regime is present on that landscape. And if we took people out of the picture, we have a very different fire regime. We'd probably not see fires in most years, and then probably once or twice a century, we would see these big, catastrophic fires.

Today we see lots and lots of very small fires. In fact, well over 90 percent of all the fires that occur in California are very small fires, like less than an acre in size or less than 10 acres in size. It's only a few percent that become really large.


What research is the USGS doing on the best fire management practices on this chaparral landscape?


Well, the number-one thing that we're working on at the present time is were trying to evaluate what is the strategically most useful application of fuel treatments. Because both State and Federal agencies are involved in fuel treatments, which primarily consist of fuel breaks, where the native shrublands are completely removed. But they also include prescription burning, where it's done on a rotational basis so the shrublands come back after some period of time.

At the present time, we know relatively little about how effective those treatments are in general or strategically what the best placement of such treatments would be. So we're now doing research to pull together a database of past fuel treatments on all the forests of Southern California, as well as lands protected by Cal Fire, the State fire agency.

And then using a GIS platform . . . look at the distribution of those treatments relative to past fire activity and a number of other parameters and try and make recommendations as to what would be the strategically most useful means of applying such treatments.


Jon, thank you very much for joining us. We really appreciate your time.


OK. Well, it's been a pleasure.


Well, that's it for this episode of CoreCast. For more information on wildfires, make sure you check out

Also remember to visit the CoreCast site at for this and other episodes-we've got a lot of good stuff on there, including a bit on the science of wildfires, which is episode 14.

As always, CoreCast is a product of the U.S. Geological Survey, Department of the Interior. Until next time, thanks for listening. I'm Dave Hebert, and you take it easy.

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Musical credit:

"Old Hen Cackle" by Coleman & Harper


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