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TREES, PLEASE! Boats Have Mainsails, Trees Not So Much (Part l of ll)

By Tim Clancy, for Let’s Talk Plants! May 2023.

Boats have mainsails, trees not so much. . . WiX stock photo.

Boats Have Mainsails, Trees Not So Much (Part l of ll)

I am always looking for trees and plants that are out of the ordinary in some way. By out of the ordinary I am referring to a tree that has a disease, or one that has been extensively manipulated (read heavily pruned) to the point that it will have a negative effect on the tree. You get the idea. Such is the case of a large diameter Eucalyptus on a well-travelled residential street in Encinitas. Whilst driving by at 25 m.p.h. one day on that way back from the local Vons I noticed what I thought was a Sulphur fungus conk growing at the base of the tree.

Large diameter Eucalyptus in full canopy in September 2022, and is growing on a well-travelled residential street in Encinitas. Photo credit: Tim Clancy.

I stopped and confirmed the presence of the conk and therefore the ultimate fate of the tree. Sulphur fungus is very good at its job and will ultimately kill the tree. I have seen the disease on several species of tree over the years but by far the most prevalent host I have seen is Eucalyptus. It is worth noting that the conk is the “flower” of the pathogen and represents a kind of life cycle completion meaning that while the fungus may be our first clue that a tree has sulphur fungus the disease is already very advanced inside the host and the conk is a clue as to how far advanced the fungus is in the process.

The tree is a big one. With a diameter approaching 42” and a height of around 70’ it could do some damage if indeed it fell. It’s located in a front yard between two recent vintage homes and big enough that if it falls away from the homes it could at least touch a home across the street.

Expert eucalyptus tree mutilation 11/22. Photo credit: Tim Clancy.

Returning from a shopping trip last fall I noticed that the tree had been all but denuded. Eucalyptus tree mutilation is nothing new to me and this tree had been previously assaulted. As always, I was curious as to why the tree was subjected to the treatment and lo and behold there was the homeowner out in his yard.

I stopped and introduced myself and briefly explained my reason for stopping. I wanted to know why he had the tree so severely pruned. Was he advised by the tree company? Did he have some other information that would help me understand the reasoning behind the work.

It turns out the homeowner was concerned that the tree was in danger of falling because the tree’s canopy was so full that wind would act on it like a sail and topple the tree into his and/or his neighbor’s home. This is a common misconception when it comes to trees and wind. It is very easy for me to understand why people think this way. After all big tree canopies are somewhat reminiscent of a sail and could conceivably "catch” the wind and the forces could be strong enough to take a tree down.

Trees of course have other strategies. After all, it is a massive investment of resources to grow and photosynthesize and grow some more both above and below ground. Then of course there is the time element. Meaning, it takes a (relatively) long time to become a big tree, why would the design encourage failure? Well, it doesn’t.

Part ll of this article will appear in the July 2023 issue of Let’s Talk Plants!, and will explain how trees deal with wind.


Tim Clancy & Associates LLC

P.O. Box 1180 – Cardiff-by-the-Sea, CA 92007

International Society of Arboriculture Certified Arborist No. WE-0806A

International Society of Arboriculture - Tree Risk Assessment Qualified


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