Primer on Causes of Catastrophic Fires in California and Fire Ecology

Fire is natural. Wildfires occur naturally in almost all terrestrial ecosystems and plant communities, even if the fire is extremely rare in some areas.

In California and the arid western states, fire is extremely common. The issues we face now with catastrophic fires are complex. To understand the causes, we need to first understand the basics of fire ecology. Let’s just talk about California.

California has what is called a “Mediterranean climate” – long, hot dry summers and short moist, cool winters. For most of the history of California as we know it, the forests, scrub, chaparral and grassland communities that make up most of the state would have burned within their own fire “regime.”

What is a “fire regime?” In general, it has two variables: fire frequency and fire intensity. Fire frequency is how often it is normal for a given ecosystem to burn – every 50 years, every 150 years, every 500 years, or whatever. Fire intensity has to do with the temperature of the fire, and will be related to the amount of fuel present, as well as other factors such as wind speed and direction, moisture levels (related to recent drought or rain), etc. Related to fire intensity is how quickly a fire moves through an area. The less fuel, lower the temperatures and the faster it might move. However, remember that higher fuel loads, especially if they are really dry, could also cause the fire to move very fast and burn very hot.

It is also important to know that that plants (and animals) in these communities have evolved adaptations to fire over time. For instance, many conifers in frequent-fire communities have “closed cones” which require hot temperatures to burst them open and spread their seeds into the post-fire cleared forest. Other plants have fruit or seeds that fall off each year but simply lay dormant in the ground until fire passes over, and either heat or other soil chemistry changes that only come after fire trigger the seeds to sprout. So, you see, even though we think of fire as destructive, it is also regenerative. It is a natural part of the cycle of fire-adapted area

Next thing to know: most of the plant communities/ecosytems in California, from the swaths of forests in the coastal and inland mountain ranges to the extensive arrays of scrub, chaparral and grassland communities across those same mountains are all adapted to fairly frequent fire frequency, on the order of 75-150 year cycles. Given this, fire historically would have moved through these areas quickly because there is a not of accumulated dead material and the last fire came through not too long ago. Mostly you would have mature dying plants but not a lot of dead/downed plant material.

Does this make sense? So, think about it. That would also lead to low fire intensity. Because the fire would move quickly and not have a lot of accumulated fuel, the temperatures would be lower. Right? You with me?

Then think of what happened over the past century or two. The first thing is, a whole lot more people of European descent came west and started “settling” the west and California. Those people started to suppress fires because they didn’t understand that the fire was needed. So for a long time fires in these forests and scrub communities were put out before they could complete their natural cycle. Wildfire was not seen as natural and even in remote areas with little to no human population, forest managers put fires out. (Probably also from the point of view of trees as crops and needing to protect economic interests.)

As a result, fuel started to accumulate from plant material that died in place. Then when fires came again (because remember they are natural and they will come again), there was more material to burn.

So, what happened? The fires burned hotter and they were more intense. That led to a real disruption for the adaptations of the plants involved (for instance, fires might burn so hot that they killed seeds in closed cones and in the dormant soil seed banks instead of stimulating them to grow). And of course, hotter, more intense fires were harder to control or put out. They got way out of control pretty easily and burned fast and hot. Which freaked everyone out and made them suppress the fires even more.

Imagine this happening for a century or so. Finally the understanding of fire regime and fire as natural came into play for ecologists starting and made its way into management understanding and methodology starting in maybe the 1980’s and 90’s.

But by then, it was too late because so much fire had been suppressed that there was an INTENSE accumulation of “unnatural” fuel everywhere in California and across the western U.S.

Add to this, the fact that human population has exploded and there’s been a massive influx of people to California, and thus human communities have expanded more and more into fire-prone ecosystems and plant communities across the state. Because, remember, the entire freaking state is fire-prone and is adapted to frequent fire intervals.

And, bam, we have had a mess to deal with for a long time.

Now, yes, one management tool is to do “controlled” (a.k.a., “management”) burns in an attempt to burn up accumulated fuels. It’s a great idea in theory. But, seriously. Can you imagine how difficult that is to do well, to control, and to implement across large areas? Just pull up Google maps, turn on satellite and peruse the state of California. Look at the massive amount of area we are talking about, most of it incredibly remote with steep, inaccessible terrain.

Also, it is super hard to do controlled burns near any kind of human development. Do you think that the residents are very keen on it when black smoke billows out of a hillside on the edge of their subdivision, and fire trucks are parked on the road there? What kind of conditions do you think are needed for it to be safe to conduct such a fire? How many things can go horribly wrong? What is the narrow margin of it possibly going right?

And now, finally, let’s add in a few climatic factors.

Number 1. California is fire adapted to frequent fires because it is a VERY DRY PLACE and has been for a long time. Remember, Mediterranean climate. Remember, “long, hot, dry summers.” Got it? Good.

Number 2. In addition to a long summer, California is also prone to prolonged droughts. I don’t remember the details, but things like lake bed sediment analysis and tree ring analysis of super old trees in the Sierra Nevada have shown evidence of really long droughts many times over the past few thousand years (I should really Google this right now for more facts here, but I’m not going to. You can if you want and let me know what you find out).

Number 3. Global climate change. I’m not really ready to dive into the modeling or projections or studies or any of that, and I’ve been out of the field for too long to be up to date on any of the details. But I know there’s a ton of data out there. Clearly the catastrophic fires are related to the increased severe weather of all kinds. The specifics of how it’s playing out in CA and what kind of evidence we have for it is beyond the scope of what I feel up to here. 

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