‘Topping’ is sometimes referred to as “heading”, “tipping,” “hat-racking,” or “rounding over”. Topping is when you cut tree branches down to stubs or cut lateral branches to reduce the size (usually the height) of a tree. Many homeowners believe that by topping their tree, they’re reducing risks to the tree, home, and yard, but the ISA warns that topping trees will increase risk in the long term.
The shoots that turn into the branches that grow out of the topping wounds are only weakly attached to the tree, and because they grow so quickly, they are very prone to breaking, especially in windy and icy conditions. Homeowners who think that they can reduce the risk of limb failure by topping a tree only do more harm and create a higher risk by topping.
Topping trees typically consists of removing half to all of a tree’s leaf-bearing crown (top of the tree). But, since leaves create food for the tree, removing the leaf-bearing crown can temporarily starve the tree and set in motion survival mechanisms that ultimately leave your tree looking ugly and unhealthy and can kill your tree. When a tree is starved, it forces rapid growth of limbs below the cut so that it can produce as many leaves as possible as soon as possible. If the tree doesn’t have enough energy to do this, it will be seriously weakened and may die. Also, topping trees leaves large, open wounds, which makes the tree more vulnerable to disease and insect infestations, which can also kill the tree.
Trees aren’t equipped to heal topping wounds, but it is able to heal proper pruning cuts. When the tree can’t heal the wounds from topping, exposed wood begins to decay, and because topping leaves multiple large, open wounds, the tree cannot defend itself from decaying completely. Tree branches and trunks are also ill equipped to absorb all of the sun’s light, which is why they produce so many leaves. Leaves create food for the tree and protect the trunk and branches from high levels of light and heat by absorbing sunlight. When a tree is topped its protection is lost and it becomes vulnerable to sunburn which leads to cankers, bark splitting, and even death of branches.
Topped trees don’t look good. Topping destroys the natural form of the tree and makes it appear to be disfigured, mutated, and sickly. Moreover, a tree can never heal from being topped. Topping trees can greatly decrease your property’s value and can increase the risk of limb failure and storm damage to the tree and the property.
There are alternatives to topping trees, such as cutting small branches back to their point of origin, pruning large limbs back to a lateral branch, or sometimes completely removing the tree and planting a more appropriate species. Talk to your local certified arborist about alternative options to topping your tree.
For more information, check out this page from the International Society for Arboriculture.