About Lightning Strikes and Live trees

by Placerville Newswire / Jul 01, 2019 / comments

[Cris Alarcon]

A study I read about wildfires in the Sonora forest used "Lightning Scar Dendrology"

Many times lightning hits Live trees and seldom do they ever burn. The under-story catches on fire and that may cause a fire, but not the tree (live trees). This was a study of a dry forest without any significant fire suppression efforts.

This is why our own fire safety depends on clearing the under-story and trimming trees to several feet off the forest floor. Trees get lightning hits all the time and stopping that from lighting dense underbrush is essential to us.

I reviewed a dissertation (unpublished) many years ago about fires started by lightning strikes in forest with No fire suppression in forests in dry climates (Sonora/Sinaloan in Mexico) and how fires spread.

The basic finding is that letting fires started by lightening strikes burn, is a natural process that burns up under-story and seldom grows over 5 acres before burning itself out. This is in a large dry forest in Mexico with no fire suppression efforts ever made.

The study was based on the scars left on trees (that still lived and continued to grow). This is the "Lightning Strike Dendrology." What happens is lightning strikes start fire and burn the brush regularly but the live trees do just fire with maybe a haircut to low-lying branches. [In the study of the Sonoran forest it had burned off underbrush by these small fires every 5-15 years]

In our area the local native Miwok's would burn local patches of land here and the trees would live and the brush would burn then new (pioneer) species would replenish and the cycle continued. This seldom ever resulted in large fires or firestorms (like Crown Fire). 

The under-story is needed to get the tree fires hot enough to create its own intense wind currents thereby turning a bad fire into a kind of fire that is highly destructive and not natural. These extreme fires are so hot they sterilize the land and new growth is inhibited and sever erosion is common.

Why are these Firestorms becoming more common in U.S. "Managed" forests?

The main reason is that we stop small fires right away and the under-story grows to unnatural loads. The USFS stopped that about 15 years ago when the natural ecology of forests and their fires was better understood. Today the modern USFS policy is to let it burn and only suppress fires to save "Assets" meaning man-made stuff like buildings and infrastructure, and certainly Human life.

Today on a State level we have yet to find the best mix of Burn/Suppress. In part due to the density of "Assets" in California. And then a lack of $ or willingness of State Legislators to seriously fund the cutting out of the under-story in forest with dense Assets.

This is compounded by our State's anti-logging stance. Proper logging replicates the natural burn/grow cycle of nature. Including the burning, in-place, of much vegetation that therein dissolves into the ground as it would in the natural period burn cycle.

This better understanding of the natural burn/grow cycle is also the basis of what we often call making a Fire Safe zone around our property and buildings. (removal of the vegetative matter from above the duff [rotting matter] to about 8 feet up. This removes a "ladder" fuel and breaks one of the steps fire uses to turn an initial little fire (like fires started by lightening strikes) into fast growing destructive fires.

This is going to be an Extreme Fire danger year caused by excessive brush & grass growth from the wet winter. Make sure your property is Fire Safe. If you are not sure contact your local fire department to ask for assistance in finding a local Fire Safe Council for valuable and detailed information on becoming Fire Safe.