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Martha Maletta, Hunterdon County Home Horticulturist
Drought last year plus the last few years - will take its toll on trees. Eventually, pruning will be needed. Proper pruning, that is.
Unfortunately, trees are still occasionally being topped, a practice that has for decades been deemed inappropriate, in most cases, and hazardous for trees by arboriculture professionals. Topping is the practice of removing a major portion of the tree canopy by severely lopping back major branches.
Why has this practice persisted in spite of the adverse consequences for both trees and safety? A survey, reported in the Journal of Arboriculture, of tree owners whose trees had been topped found that trees are topped because of incorrect beliefs about the effects of topping even among some professionals.
The most common reason cited by owners for topping trees was the tree being too big, most fearing for the home. Common misconceptions about the benefits of topping included: improves safety; improves vigor; prevents insect and disease; promotes root growth. In fact, the consequences of topping are just the opposite. A healthy tree that is topped is ultimately a weakened tree. A weak tree that is topped can only be that much worse off.
There are several ways topping is detrimental to trees. Removing the majority of the tree canopy removes the means of food production - the leaves. It also removes food reserves stored in the wood. Bark that is suddenly exposed to sun may be killed. The large wounds resulting from topping do not usually close, allowing entry of decay organisms and insects.
Vigorous dense growth of suckers (water sprouts) from just below the topping cuts may give the impression that the tree is being rejuvenated. But that growth, which uses up food reserves including those in the roots, will never develop into sound branches, even with careful follow up thinning and pruning. The trees root system suffers because of reduced food from the smaller canopy.
With rapid and vigorous sucker growth, the tree regains height and is more dense than before topping. Sucker growth tends to be susceptible to certain insects and diseases. Decaying branches and dense, weak sucker growth will ultimately make the tree vulnerable to wind and ice damage and increase the hazard potential. Trees species that do not tolerate severe pruning when mature - beech, birch, honey locust walnut, apple, pear, for example - decline rapidly. Lastly, but important, too, topping destroys the trees appearance.
What is the answer to a tree that is 'too large?' Preventing the situation in the first place by planting trees appropriate to the location is best, of course. But large trees can be reduced, if necessary, through proper thinning procedures, following the guidelines of the International Society of Arboriculture or the American National Standard Institute. It is clearly a job for professionals.
The test of a properly pruned tree: it should not be obvious that is had been pruned. Tree topping as an arboriculture practice has, fortunately, declined over the decades. Eliminating it almost entirely would be a good goal for the coming decade. More and better public education is the key, concludes the survey article.
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