For the last few weeks, I’ve worked under the direction of Arlington County staff to shape several hawthorn trees that suffered topping by the utility company; these mature trees were unfortunately planted years ago under the transmission lines along the W&OD trail in Bon Air Park. What I’ve seen has shown me how important it is to not only plant the right tree in the right place (i.e. small trees near overhead lines) but the horrible things that follow when a tree is incorrectly pruned through topping.
I learned during TreeSteward training that as a tree grows it sends its energy to the apical meristem tissue where the dominant leader is located. Those cells are special, and on the dominant leader there are lots of them! They are just like stem cells: youthful, undifferentiated – they can become any kind of cell. I’ll spare you the waxing poetic about the miracle of growth.
So obviously what happens when you chop off a leader? It’s a cellular train wreck. The tree’s still sucking dissolved nutrients; the xylem and phloem are still coursing through the bole. You haven’t killed the tree. What you’ve done is created a flat surface without anywhere for the energy to go, so it just goes to the flat surface and starts sprouting on the sides, like a garden hose you plug with your finger, like a palm tree or a fistful of limp spaghetti. It’s not the shape it is supposed to be.What happens next year? The sprouts continue to grow, but much faster than the branches, and note that the connection between the sprouts and the flat surface created from topping the tree is much less strong simply because it covers less than the full flat surface. When we talk about strength, we have to think of the physics behind bearing the weight of branches and leaves. Sprouts are one big energy suck – they take much more than they contribute. To restore nutrition balance to the older parts, they need to be removed.
Then it comes to the art behind how to correct for topping. Well, you can start by trying to train the tree laterally, so you might leave some sagging sprouts to hope they continue their horizontal growth. You can HOPE for one of the sprouts to take on a leader role but that can NEVER perfectly happen. You are stuck with an “anti-form” object. Tree topping is the best illustration of the saying “Haste Makes Waste” that I know.
Tree Stewards can educate against topping, but our best bet is to RALLY for pruning to save trees. There really is no excuse for power companies to allow the topping of trees. The height of trees can be lowered; it just takes careful technique, and a little more patience.
In summary, topping is an awful thing to do to a tree. The economic cost of maintenance is higher than it was before. It exposes the most vulnerable part of the tree to rain, diseases and pests. Sudden sunburn and heat will crack the branches and invite differential die off. The pathological effects mentioned here, and more, increase the potential danger from wind damage. Finally, a topped tree will not win a beauty contest! For more, visit: