By Tim Clancy.
Sometimes it almost seems as if trees have a mind of their own. This is especially true when it comes to pruning and altering a tree’s canopy by removing branches and foliage. Someone decides, for some reason, to prune and cut back a tree. The tree, of course, has no idea what we were thinking and responds by trying to return to its previous state.
I had the pleasure of assisting a colleague in the preparation of an updated report on heritage trees in the city of Carlsbad,CA. For the report, we used both contemporary and historical photographs. One photo we used was taken in 1916. It depicts a sugar gum (Eucalyptus cladocalyx) on the left of the train tracks on what is now Carlsbad Village Drive (formerly Elm Ave.) Look at the old photo above. Note particularly the size and form of the canopy. It is difficult to say precisely when the tree was planted, but judging by its size in the picture, I would say at least 30 years prior to 1916, if not more.
Fast forward to 2001. The picture above shows the tree, on the left again, as it looked then. We can see that the canopy has been heavily pruned and reduced to a mere shadow of its former glory. The pruning operation left spindly branches and severely compromised the tree’s ability to provide for itself. Look closely and you can see that the basic shape shown in the 1916 picture is still evident. The trunk has grown considerably, but it is clearly the same tree. Why the tree was pruned has been lost to history. If you ask me, the purpose was to enrich some tree company. The tree was topped in a surprise attack and its dignity clearly damaged. Yet it remained in place and grew, determined to return to its former self.
How do we know this? Look at the tree in the picture above, taken in 2019. As you can see, the tree has “recovered.” It has replaced the foliage and branches needlessly removed on 2001 with new branches and foliage. It has the same form as it had in 1916. It is essentially the same tree!
What is going on? Well, the canopy and the roots worked together. The roots depend on the canopy to provide energy. The canopy depends on roots for water and nutrients. A tree has two choices to make in the case of heavy pruning. Either it can allow some of the roots to perish and in the process recover at a smaller size than before, or it can regrow the canopy to its previous size and then continue to increase in size.
In this case, the tree took the second path. The tree used its “food” to reconstruct the canopy. Root growth slowed until the former canopy was regrown. When roots are cut, the opposite is true. Food is preferentially sent to the roots until the previous root volume has been replaced. Then the canopy grows again. Of course, this does not always work out; sometimes we end up with a smaller tree because the tree cannot replace the roots or canopy due to a lack of stored energy.
Either way when I look at these pictures I ask myself: why prune the tree if it is only going to end up right back where it started?
Tim Clancy is an International Society of Arboriculture Certified Arborist #WE-0806A. Tim welcomes comments and questions and can be reached at email@example.com