Tree topping is usually done to improve a view or to stop trees growing into power lines. But the main concerns are not aesthetics, but tree health, public safety and costs to the homeowner.
“Topping is perhaps the most harmful tree-pruning practice known,” writes Kevin Zobrist of WSU Extension. “… topping is so effective at killing trees that it is a common method for artificially creating snags.”
Despite these warnings, tree topping remains common in the Pacific Northwest. Why is this and what alternatives do we have?
Reasons not to top
Proper pruning improves the growth habit, health and beauty of a tree. Indiscriminate cutting, or topping, of tree branches to stubs or lateral branches that are not large enough to assume the terminal role does none of these things.
When topped, deciduous trees grow sprouts, and conifers grow competing leaders, both of which may get tall enough to impede the view or tangle in power lines.
Cass Turnbull of Plant Amnesty says a topped deciduous tree will return to near its original size in a few years. However, the weak new growth may break off in high winds, causing damage to surrounding property. To prevent damage, topped trees often need expensive maintenance to keep new growth in check.
Topped trees are likely to become diseased for three main reasons:
-First, exposed cuts at the tops of trees are highly susceptible to rot. As the rot spreads, branches become an unstable hazard.
-Second, trees that lose their upper canopy may experience sunburn, which leads to cankers, bark splitting and the death of some limbs.
-Third, trees draw nutrients from their upper branches. If too many are removed too often, trees become stressed and susceptible to insect infestations and to root rot.
By topping a tree, you may be condemning it to a long, lingering death.
Topped trees also can never regain their original graceful forms, and disfigured trees may adversely impact property values. The International Society of Arboriculture estimates that healthy, well-maintained trees can increase a property’s value by 10 percent to 20 percent, while topped trees are considered an “impending expense.”
Alternatives to topping
Crown reduction can reduce the height of trees with a rounded shape. The upper branches are cut back to laterals at least one-third the diameter of the limbs being removed and large enough to outgrow lateral branches directly below. “Topping — Tree Care or Tree Abuse” (see References) explains this procedure and includes a sketch of how to do it.
Crown reduction does not work for trees with a pyramidal shape, such as conifers. For these trees, consider skirting, thinning and windowing reduction methods.
Skirting, or limbing up, cuts off all the branches from the ground up to the desired level. Lower branches contribute less energy to tree growth than upper branches, so the tree can survive the removal of numerous branches without ill effects. For an aesthetically pleasing shape, don’t limb up higher than half the visible height of the tree. If the limbed-up tree looks top heavy, thin out some of the remaining upper branches.
Thinning, or interlimbing, removes branches to allow partial views through the tree. This may also allow more sunlight into your yard.
Windowing removes all the branches from a specific area of the trunk to frame a view with branches above and below.
Skirting, thinning and windowing methods work because trees grow from the top, so the areas you clear will always be at the same height. These techniques are illustrated in “Managing Vegetation on Coastal Slopes” (see References).
There are times when it is better just to replace the offending tree. If you find yourself in this situation, WSU Extension Bulletin EB2036 “Small Trees for the Home Landscape” gives suggestions for trees that will not outgrow their welcome.
A word of caution
Unless you are experienced, leave large-tree pruning to professionals. Local arborists certified by the International Society of Arboriculture can be found by visiting www.treesaregood.com. Avoid tree-pruning services that insist tree topping is your only option.
They may just be guaranteeing themselves work in the future.
Jane Billinghurst is a Washington State University/Skagit County Master Gardener. Questions may be submitted to the WSU Extension office, 11768 Westar Lane, Suite A, Burlington, WA 98233. 360-428-4270 or http://skagit.wsu.edu/MG.