Issue: June 1, 1996

Don't top trees

You have said it is not good to top trees. However, I still see tree care companies topping trees. If it is bad for trees, why do they still top trees?

It is impossible to explain someone else's motives, but I have spoken to a few of them and can relay what they say even though I sometimes disagree.

Some say they top trees because their client wants them to top their trees. The client has a tree which has become too large and wants a smaller tree. It is easier and more profitable to do what the client wants rather than argue or try to educate them that topping is incorrect. There are some tree care professionals who will refuse to top the trees and suggest that you hire someone else. The problem with this argument is that the tree which is too large was the wrong tree for that location in the first place. I feel the correct solution to the problem is to "underplant" with another tree which will be appropriately sized for the site. As the new tree develops, the old tree can be removed. By underplanting and leaving the old tree for a while, the benefits of the trees is not lost.

Some people top trees in the mistaken belief that topping "rejuvenates" the tree. If the tree was healthy at the time of the topping, it responds with vigorous growth attempting to repair the loss of a major portion of its leaf-bearing structure. This growth occurs at the expense of the root system and uses the stored nutrients which are necessary for surviving difficult years (which are common in New Mexico). The growth following topping is weakly attached to the old branches and subject to breakage in wind and snow as the branches get larger. Those branches developed following topping can become hazards in the years following topping. And finally, if the tree was healthy when it was topped, it is no longer healthy following topping.

It is unfortunate that trees are so capable of surviving our damage. They just aren't able to repair the damage, just survive it. They can never become as strong or healthy again as they would have been.

Topping allows diseases and insects to bypass the trees' natural protective mechanisms and invade the wood of the trunk and major branches. Rotting of these areas follow, further depleting the stored food reserves in the tree and reducing structural strength. Besides the branches being weakly attached, this rot weakens the branches, trunk, and root system. The tree becomes much more likely to fall over in a storm, damaging homes, cars, and people. If you take a branch from a tree which was topped several years ago and split the branch from the point of topping downward, you can easily see the disease in that branch. It appears as darkened wood stained by the fungi and oxidation of compounds in the wood that were not intended to be exposed to that much oxygen.

There are other reasons, some better than others. The worst reason is people top trees because they can. A chain saw, a ladder, and a lot of luck (that they don't hurt themselves) is all it takes to top a tree. It is cheap (not inexpensive), quick, and doesn't require any knowledge of proper pruning techniques. Proper pruning requires knowledge and skill.

If you or your tree care professional would like to learn more about proper tree pruning and tree care, you are invited to attend the annual "Think Trees Conference" which will be held in Albuquerque in January. National, regional, and local tree care experts will be present to teach proper tree care techniques. This conference is spnsored by the Cooperative Extension Service, the International Society of Arborists, the City of Albuquerque, New Mexico State Forestry, New Mexico Association of Nurserymen, and private tree care professionals and homeowners to improve the care of trees in New Mexico because we value our trees. For more information about the Think Trees Conference and registration fees and forms, contact your local New Mexico County Extension Office.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!