WILDFIRE DANGER:
Chaparral & Grasses / Trees & Forests

In August 2016, a wildland fire burned quickly through brush and grasses without igniting trees, including eucalyptus trees (top left).  So what vegetation brings fire to your door?

Chaparral and grasses pose the same - or greater -

wildfire risk as trees.  Here's why.

Confusion and misinformation about which wildland vegetation is safe or “safer" in a wildfire is rampant.  The public has been misled to believe that trees and forests constitute a wildfire threat, and thus need to "managed." "Management" is this context almost always means killing wild plants and trees, hence our use of quotations for these terms to alert readers to this common euphemistic distortion of meaning, and its intention to hide the reality of what "vegetation management" is.  All this is done to influence public attitudes and increase acceptance of a typically harmful practice that both increases wildfire danger and does environmental damage.

 

Modern fire science repeatedly demonstrates that forests — or any wild "vegetation" — aka, plants — over 100 feet from houses and structures — present little if any additional wildfire risk.  This website has extensive information about this research and Defensible Space guidelines that all of today's fire agencies recommend for home protection, over killing plants more than 100 feet from your house.  READ MORE about Defensible SpaceREAD MORE about fire risk & forests.

When mature trees are cut down, or forests are destroyed, the smaller plants that grow in their place are more fire-prone: ignitable and faster burning — and thus more of a wildfire risk.  In addition, forests act as wildfire-slowing windbreaks.  High winds are what have driven California's recent devastating wildfires making headlines in 2018 and 2019.  And what made the 1991 Oakland Hills fire so destructive and unstoppable.  It was only contained after winds dropped.

 

And cutting down mature trees and forests over 100 feet from structures is not only unnecessary, but can actually INCREASE fire danger because the smaller vegetation that grows in the place of felled trees are more easily ignited, and burn more rapidly.  These plants include broom, thistle, ivy, grasses, which then dry out in California's hot, dry summers and autumns, creating what fire agencies call "fine fuels."   If you think the volume, the amount of combustible material, of a grass fire is less than a forest, you're right.  But this is also why they burn so much faster, and that means the fire can reach your door before firefighters can.  Restated in reverse, because forests, compared to chaparral and grasses, burn more slowly because of their volume, density, and wind reduction, firefighters more time to contain them, set up fire breaks, etc.  READ: Protecting Our Communities from Wildfire

 

 

The average person has been conditioned in numerous ways, especially by under-informed media coverage, which often exaggerates and sensationalizes, to see a forest and think it's a wall of wood waiting to catch fire.  And of course forests can and do burn.  But the majority of WUI (Wildland Urban Interace) fires start in grasses and brush, including California's chaparral.  These can then ignite trees and forests and houses.  The "surface" fires, when driven by winds are the ones firefighters can't contain.

 

Ultimately, making your house Ignition Resistant is the most effective way to protect yourself from a wildfire. Put another way, "Don't cut down the forests, fireproof the houses."  There are multiple reasons for this advice.  Fire scientists do NOT consider living trees over 3" in diameter as fire risks.  Trees are not labeled "flammable" by fire scientists.  It's important to note, this is irrespective of tree species, and its country of origin.  This despite common, oversimplified media stories carelessly conflating living trees with "wood," which implicitly likens trees to firewood.  The massive difference in water content between living trees and dead trees makes the pronounced difference between what is and isn't flammable.

 

 

Flame lengths are an indication of the intensity of a wildfire.  Although grasses and brush are smaller plants than trees, they can burn with longer flame lengths than most trees, and thus can spread surface fires faster and farther.

 

 

 

 

Flame lengths are determined by measuring the distance between the flame tip and the midpoint of the flame depth at the base of the flame (generally the ground surface).

*In May of 2009, URS Corporation, a global engineering, design and construction company, wrote a letter to FEMA (Federal Emergency Management Agency) in response to a request to assess a multi-million dollar plan by UC Berkeley to cut down thousands of healthy trees in the Berkeley hills.  (The extensive and unnecessarily destructive plan was ultimately found NOT to offer the wildfire danger reduction it promised, and was successfully challenged in court by HCN.  READ MORE.)

 

 

 

All living trees, like all living humans beings, are, despite what your eyes tell you, primarily water.    You know this too, if you've ever put a "green" log atop an existing fire in a fireplace.  In stark contrast, dried grasses and shrubs, with little water content, much less mass and much finer diameters, ARE considered easily ignitable — and a high fire risk. 

 

Felling large numbers of trees increases local climate warming by reducing the substantial shading effects, cooling effects, moisture-collecting effects, and moisture-retention effects of tree canopies.  And by increasing local warming and reducing moisture, wildfire risk increases.   READ WILDFIRE RISKS AND FORESTS.

 

Those promoting deforestation in the guise of "vegetation management" or "fuels reduction" have other agendas beside wildfire mitigation because no fire agencies advocate cutting down forests as a wildfire defense.  Forests are not the enemy of humanity, and never have been.  Quite the contrary in our era of anthropocentric global warming. 

 

Two Bay Area wildfires have their own pages on this website because they are so instructive about wildfire behavior, and what vegetation constitutes fire danger and why: 1) The 1991 Berkeley-Oakland Hills Fire, and; 2) recent wildfires on Angel Island, in the San Francisco Bay, before and after eucalyptus deforestation.  (CLICK ON their name to learn more.)

“Chaparral is one of the most hazardous wildland fuel types in California due to the woody, persistent nature of the plants. A chaparral dominated landscape in the post treatment project [cutting down Monterey Pine, acacia and eucalyptus trees] area would create a fire hazard profile with its own suite of risks and concerns for fire protection, including flame lengths that far exceed those of other possible vegetation types.”  -  URS Corporation, May 2009*

Flame Lengths

 

A measure of wildfire intensity.

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