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People, Grass, and Fire

posted Apr 23, 2015, 4:14 PM by Joe Christy   [ updated Apr 23, 2015, 4:28 PM ]
No, this isn’t another story about 420, but we will get back to that.
It seems that every few months I’ve written about the most dangerous element in California wildfires – people. The sad fact is that people start over 90% of wildfires, and that over 90% of those are started within 10 feet of a road.
Last week, I read an interesting research brief exploring just why that that is. The explanation is grass! Dry grass is just about the easiest fuel to ignite and it’s often found along the side of the road. Our 2008 Trabing Fire is an example close to home.
On our mountain, chaparral is a seral, or transitional, community. In other words, after you first secure your defensible space, what grows back next on the margins is chaparral, an archetypal fire evolved community, and one of the most dangerous vegetation types have near a structure. The only thing more dangerous than chaparral, though, is grass. Grass dries out quickly, once dry carries fire extremely well, and when alight produces flame lengths proportionally much longer than other fuels. In particular, it can readily ignite the chaparral, which eagerly burns since fire is necessary for its health and survival. Chaparral burns extremely hot and throws off many embers.
Later, while studying ecological gradients in Big Sur, I discovered that between the grasslands and scrub & chaparral there is often a natural bare zone separating them, perhaps due to the inhibition of grass growth by the aromatics exuded by the scrub and chaparral. The grasslands of Big Sur are almost entirely composed of non-native grasses; the native grasses would be bunch grasses growing in clumps separated by bare soil. Nature knows to keep grasses and scrub well apart.
What can you do? Keep the grass within 30’ of your home lower than 4”, and lower than 12” between 30 and 100 feet out. Be careful working with metal tools since they can readily produce the spark in the hot zone just above ground level on a sunny day.  Consider planting bunch grasses instead of lawn grass or the dreadfully invasive “Santa Cruz Mountain Erosion Mix” around your home.
Which is why on the damp morning of April 20, UCSC had a phalanx of mowers out on Porter meadow, preparing for the 420 crowds.