By Tim Clancy, for Let’s Talk Plants! July 2023.
Damper, Damper 10-4
Last time, we talked about trees and pruning a little bit and here is part II of that discussion.
Please let me know if you have any questions.
I can understand why people sometimes equate tree canopies to sails. We have all seen trees swing and sway in winds of all speeds and at times this may seem unsafe. While a sail and a tree canopy may have similar properties, they are indeed two different things.
In its simplest form, the job of a sail is to catch wind and use the resulting captured energy to propel a vessel through water (for instance.) This type of sail has worked for thousands of years and has aided mankind in countless ways. In the hands of a skilled sailor a sail is a magnificent invention.
The job of leaves on a tree (the sail) is to dampen the wind energy and transfer it to the branches, then to the trunk and finally, the energy is dissipated, into the ground. This is how trees are designed to work and this is how they work even if our trees and branches have some minor cracks and wounds.
When we prune some of the canopy, we are removing the baffling devices (leaves) and subjecting the remaining tree parts to higher winds and forces. Many times we can get away with it and the trees will survive. However, part of its survival strategy is to allocate resources into re-growing what was pruned off. This is because the tree grew the leaves to collect and convert sunlight into energy and was/is relying on them to serve that function as well as the mechanical function of dampening the wind.
Wikipedia has a nice article on Mass Dampers and that is essentially what the leaves in the crown of our trees do to remain standing in the face of high winds.
We are forecasted to have an El Niño winter and with it potentially heavy winds and rains over the next several months. Trees are designed to dampen the wind and, barring any other defects, do NOT need to be pruned in preparation for the winter storms.
Tree preparation for winter should include inspections looking for defects that may lead to limb or tree failure. This is also an opportunity to look for disease and pest issues. The fall is when we see the sulfur fungus mushrooms growing on the trunks of various species here in San Diego. It’s always a good idea to document your inspections and anything you see. I recommend a few photos as well. That way you have something to reference in the future.
Besides looking for defects, a focus should be on clearance. This can be clearance from stop signs, buildings, streets etc. The objective is to prune sufficient material so that no clearance issues will occur before the next cycle.
There are legitimate reasons to prune a tree but pruning to decrease the sail effect is not one of them.