Why topping hurts treesQuestion: We have several very large maple trees in our front yard. A neighbor told us he knew someone who could "top" them for us. Is it OK to have this done?

Answer: Topping is perhaps the most harmful tree pruning practice known. Yet, despite more than 25 years of literature and seminars explaining the harmful effects, topping remains a common practice. The most common reason given for topping is to reduce the size of a tree. Often homeowners feel that their trees have become too large for their property. People fear that tall trees may pose a hazard. Topping, however, is not a viable method of height reduction and certainly does not reduce the hazard. In fact, topping will make a tree more hazardous in the long term.

Topping often removes 50 to 100 percent of the leaf-bearing crown of a tree. Since the leaves are the food factories of a tree, this can temporarily starve a tree. The severity of the pruning triggers a sort of survival mechanism. The tree activates latent buds forcing the rapid growth of multiple shoots below each cut. Unlike normal branches that develop in a socket of overlapping wood tissues, these new shoots are anchored only in the outermost layers of the parent branches.

The new shoots grow very quickly, as much as 20 feet in one year in some tree species. Unfortunately, the shoots are very prone to breaking, especially during windy conditions. The irony is that while the goal was to reduce the tree's height to make it safer, it has been made more hazardous than before.

The cost of topping a tree is not limited to what the perpetrator is paid. If the tree survives, it will require pruning again within a few years. It will either need to be reduced again or storm damage will have to be cleaned up. If the tree dies, it will have to be removed.

Question: Are there any alternatives to "topping" a tree?

Answer: There are times when a tree must be reduced in height or spread. Providing clearance for utility lines is an example. There are recommended techniques for doing this. If practical, branches should be removed back to the point of origin. If a branch must be shortened, it should be cut back to a lateral that is large enough to assume the terminal role. A rule of thumb for this is to cut back to a lateral that is at least one-third the diameter of the limb being removed.

This method of branch reduction helps to preserve the natural form of the tree. However, if large cuts are involved, the tree may not be able to close over and compartmentalize the wounds. Sometimes the best solution is to remove the tree and replace it with a species that is more appropriate for the site.

Question: We are really confused. One neighbor tells us we should paint a wound dressing on pruning cuts, another neighbor told us its not recommended. Who is correct?

Answer: Research conducted in the past several years indicates that wound dressings do not prevent decay and that they are of limited value for wound closure. In fact, applying a dressing to exposed wood (caused by breakage or a pruning cut) only seals in disease microorganisms and creates a perfect habitat for advancing decay.

When a tree is wounded, the injured tissue is not repaired and does not heal. Trees don't heal; they seal. They have a unique defense system called compartmentalization that sets up a protective boundary between injured and healthy tissues. This area is highly protective and physically and biochemically resists the spread of infecting organisms. The most important thing you can do to enhance this natural process is to prune wisely and carefully and keep your trees vigorous and healthy.

Question: We were recently told that if we prune certain trees now, they will bleed to death! Is this true?

Answer: Bleeding of pruning wounds can be heavy on certain trees, such as birch, dogwood, maples and elm if done just before growth begins in the spring. Bleeding doesn't harm the tree, but if it's heavy and persistent, it may injure the bark below the cut and result in slow callusing of the lower wound. Unless we have very mild February temperatures, bleeding from tree pruning wounds should be minimal if done now, even on birches and maples.

EDITOR"S NOTE: For answers to local gardening questions, contact Master Gardener Rachel Gana at 642-8723 or e-mail at baiter1@pacifier.com

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