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Written by Jeff Shimonski, BT Contributor   
September 2017

Improper pruning will kill your trees, not save them

SPix_YourGarden_9-17o now we’re entering the active period of another hurricane season. What have you done to protect your property?

Were you talked into “lifting” your trees to allow the wind to blow through the branches in a storm? Or did you cut off all the branches over your property line of the tree that’s growing in your neighbor’s yard?

The accompanying photo shows a mahogany tree that has been “over-lifted” to death -- well, it’s not quite dead yet, but one strong wind and the entire tree will end up in the tree guy’s wood chipper.

This mahogany has also been “topped” at least three times. Topping is a practice whereby a tree’s branches are cut, usually without regard to their size or location in the tree’s canopy. Topping is used to reduce the size of a tree and is sometimes called “hat-racking.” The tree’s owner may feel the risk of storm damage has been reduced, but if the pruning hasn’t reduced the branches to another viable branch that can take over apical dominance and continue to grow, those pruned branches will start to decay.

The new branches that begin to grow on or near the end of a topped branch usually come out in a cluster. This looks healthy at first, especially as the mass of foliage begins to grow. But since the initial pruning cut was large, it created an infection court that allows pathogens to enter the cut wood. This is where the decay begins to spread downward into the branch. Cuts over three or four inches in diameter rarely heal.

So as the new branches grow, the interior of the cut branch continues to decay. As often happens, once the new branches grow too heavy, they break off. Even though they are attached to the vascular system of the original branch, the vascular system itself is on the periphery of the branch or trunk; thus, the branches are not strongly attached because they’re attached to only one side of the now-decaying branch.

Also you can see that this mahogany was lifted, i.e., all the small lateral branches in the canopy’s interior were removed. This was likely done to allow the wind to blow through the canopy. Or maybe it was lifted to make it look good.

Aside from all the decay from the topping cuts that rendered these mahogany branches weak, the branches are vertical. They’re weaker than lateral branches. Lateral branches have to deal with the forces of gravity more so than vertical branches. Lateral branches grow reaction wood, which is a stronger type of wood that supports branch attachments and keeps them from breaking as the branches grow heavier or move in the wind.

These vertical branches also have poor taper. There’s little change in size from the bottom to the top. They should be thicker at the bottom. Without proper taper, these are just skinny branches waiting to be broken off in a storm.

One way poor taper is created is when all the interior branches have been removed. There are no attached lateral branches to provide assimilates, or food, to the section of the branch, and it will also have more difficulty isolating the decay that was first initiated by the topping cuts.

Topping a tree also removes its food-making ability. No foliage, no food. You can put thousands of dollars of fertilizer beneath the tree, but it all first needs to be processed by the foliage, the food-making machinery of the tree. If the tree is already under stress -- if, for example, there’s decay in the tree due to topping or developers butchered the root system or some public works crews banged the crap out of the trees they were operating near -- the stress issues will multiply rapidly.

Unfortunately, tree issues related to stress and poor working practices can take years to become obvious to the average property owner. So the tree owners think they’re getting a good deal. All this foliage has been removed, and there’ll be less wind resistance, so there will be less damage in a storm.

Watch trees move in the wind. Trees with a full canopy will have all the branches move together as a single unit. When the canopy moves back into position, it doesn’t just snap back; the smaller branches and leaves turn in the opposite direction to lessen the movement of the entire canopy. Trees evolved this mechanism to deal with wind events. When the lateral branches are all removed, the vertical branches begin to break.

When some guy wants to prune your trees to mitigate wind damage, ask him about tree biomechanics.

 

Jeff Shimonski is an ISA-certified arborist municipal specialist, retired director of horticulture at Parrot Jungle and Jungle Island, and principal of Tropical Designs of Florida. Contact him at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

 

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