Clearing up misinformation about the Los Angeles fires

Don't blame the chaparral or coastal sage scrub

As I type these words, blustery winds scatter leaves from swaying tree branches. A dry, scratchy feeling at the back of my throat lets me know that Southern California is experiencing a full-on Santa Ana condition. Temperatures are warm, and sparks fly when I touch a doorknob. Although Los Angeles is burning, San Diego, where I live, has been spared from the conflagrations that are ripping through L.A.

Whenever there are fires in Southern California, misinformation spreads as fast as the flames. From my more than 15 years’ experience studying these fires, and as a horticulturist specializing in Southern California plant communities, I thought I would try to clear up some of the misinformation surrounding these fires.

Is climate change to blame for the wildfires?

Answer: Probably, at least somewhat.

Large conflagrations have swept through what is now Los Angeles and San Diego for millennia. They result from the annual cycle of at least six months of summertime drought coupled with hot and very dry Santa Ana winds blowing in from the deserts to the east. These winds can reach 60, 70, sometimes 100 miles per hour, with humidity dropping to the single digits.¹

Seasonal wildfire conditions have thus existed for a long, long time in Southern California, but historically there were few sources of ignition; thus, through the ages, major fires were infrequent. To the detriment of Southern California residents and the environment, our electrical lines, barbeques, and sparks from our machinery now readily ignite the local landscape. These are the largest reasons why Southern California fires are so frequent.

The science indicates that global warming is making the western United States hotter and drier. Further examining the effects of global warming on wildfire, researchers found that the increasing heat and longer dry spells increase the mortality of the shrubs and trees in chaparral. These dead and dying plants exacerbate fire conditions.

So fires have increased because of human-caused ignition, and more recently, fires in California have become worse due to climate change. Current trends seem to confirm these observations: the eight largest wildfires in California have occurred in the last seven years. Our largest fire to date, the August Complex Fire of 2020, consumed more than a million acres, an area equal to the state of Rhode Island.

Normally by this time of year, coastal Southern California would have received at least half of its wintertime/springtime rains, which vary a lot within the Los Angeles area. However, Los Angeles has received less than one-third of an inch of rain this year, bone-dry conditions that are not totally out of the ordinary but still unusual for Southern California. Climate change may be playing a part in this latest anomaly.

Didn’t the very wet winter last year create a lot of growth in the shrublands of Los Angeles, making the current fires worse?

Answer: No, not really.

Very wet years are thought to create a lot of growth, which becomes ready fuel for fires during our dry years. This seems to make sense, but it is not proved out by my observations and what others know about chaparral and coastal sage.

Coastal sage scrub and chaparral are both slow-growing plant communities. And once they reach maturity at a certain height—waist- to chest-high for coastal sage scrub and perhaps seven to eight feet for coastal chaparral—they essentially stop growing. No amount of rain will make the sages grow much taller or fill out much more. The same can be said of the ceanothus and manzanita of the chaparral. Heavy rains do not influence growth any more than normal rainfall. It is the same for invasive grasses and forbs. They only grow so big, then they die.

Donald Trump said the fires could have been prevented by cleaning the forest floors. And prescribed burns are also advised as a remedy for fire safety. Would these have worked?

Answer: No.

A scientific study compared fire incidence in San Diego County after 1950, when modern fire suppression was adopted, to fires before 1950. The study found no significant difference in the fires before and after. In their paper the researchers said, “Under these conditions [Santa Ana winds], fires readily burn through all age classes of fuels and thus, rotational burning programs that attempt to modify vast stretches of chaparral landscape through age class modification are not likely to be effective in stopping these catastrophic fires.”² Research of my own on this matter can be found below in The misconceptions of San Diego wildfires.

Wouldn’t prescribed burns help control these fires when there aren’t Santa Ana winds?

Answer: No

Prescribed burns work well in western forests but not in chaparral or coastal sage. Western forests have a naturally occurring regime of ground fires that recur every seven to twelve years. These fires burn fallen branches and other flammable material on forest floors. If these flammable materials build up, as they do when there is fire suppression, they can ignite and quickly get out of control, consuming the forests in raging, dangerous crown fires. For western forests, prescribed burns can help avoid crown fires and can be a good thing.

Prescribed burns cannot serve the same function for chaparral and coastal sage. Firstly, chaparral has a fire regime of 20 to 60 years, and sometimes longer. Some old growth chaparral has not burned in well over that time period. Coastal sage scrub may have a fire regime even longer than chaparral.

Also, the rationale of prescribed burns to avoid crown fires does not apply to chaparral and coastal sage. When fire does come to these plant communities, entire plants are consumed, not just the leaf litter and the crown.

I’ve written a lot about chaparral, coastal sage, and California wildfires. If you’re curious, please check out:

1. Halsey, Richard A. ‘Fire, Chaparral, and Survival in Southern California” Sunbelt Publications 2008 pp 48,49.

2. Keeley, Jon E., Fotheringham, C.J., Morais, Marko “Reexamining Fire Suppression Impacts on Brushland Fire Regimes” Science 284, June 11 (1999): 1829-1832