No, we’re not talking about your grandmother’s undergarments. Girdling, or ring-barking, refers to the removal of a complete ring of bark from a stem, branch, or trunk that generally kills whatever was growing past that point.
Sometimes girdling happens on purpose and sometimes it’s an accident. Accidental girdling frequently occurs when tree supports are used incorrectly. They may be allowed to rub against the bark enough to create a ring, or supports may be left on for too long and then removed, ripping off the bark that has started growing over the support. Beavers and rabbits are notorious pests aboveground and voles do the same work underground. Girdling can also be caused by grazers forced to eat bark during a harsh winter, or by birds or insects that have bored so many holes around an area that it is girdled. There are some insect pests who girdle tiny twigs or flower parts. Girdling is one reason why you see young saplings with protective plastic around the trunk. (Sunburn and protection against herbicides are other reasons.) Vines, such as English ivy and Wisteria, a tree’s own roots, and your weedwacker can cause girdling, too.
How does girdling kill a tree?
To understand how girdling can kill a tree, we first have to understand how trees grow. Trees grow by adding new layers (sapwood) on top of old layers (heartwood), underneath protective bark. It is the inner layer of bark, called the cambium, where this growth of sapwood occurs. Looking from the outside in, bark has several layers that serve different functions:
If you recall, trees, like other vascular plants, have structures that help move water and nutrients. Interrupting that action can result in wilting and death. Surprisingly, the center of an entire tree can be rotted out and the tree can continue growing, as long as the vascular bundle is intact! A quick review of those important parts:
Girdling removes the phloem. This interrupts the flow of sugars created in the leaves through photosynthesis. Since water and minerals are still being brought up though the xylem, death is not immediate, but it is nearly inevitable. In some cases, trees and shrubs are able to put out new branches below the girdled area, but pests and diseases will find easy access through the dying upper parts. It is possible to repair a girdled tree, if you want to try.
How to repair girdling damage
A tree that has been girdled can be saved by replacing the phloem path with healthy twigs. The twigs act as bridges and their healthy phloem tissue will provide a path for the tree to use until it is able to grow a new cambium layer. Follow these steps to repair girdling damage:
Done correctly, these repairs will provide a path for critical sugars. In time, the tree will grow new layers that will cover your handiwork - but you’ll know it’s there and that you saved a life! In some cases, an entirely new tree is planted right next to a girdled tree, to act as root stock to the damaged tree. Partially girdled trees can be aided by covering the damaged area with damp moss and wrapping it with waterproof adhesive tape to keep the moss in place and moist.
Girdling on purpose
Girdling on purpose is called cincturing, or scaffold girdling. It is an agricultural method used to force fruit-bearing plants to produce bigger, sweeter fruit. Think about it. You have a mature fruit tree. The roots are pulling water and minerals up from the ground through the xylem. Leaves are producing sugars which are distributed through the phloem. You girdle the trunk just below a major branch, or scaffold, blocking the path of sugars headed elsewhere. The only place for these sugars to go is in the fruit on the branches above the cut. The fruit gets more sugar, grows bigger, tastes sweeter. Viola! This method is commonly used on a surprising number of trees and vines:
Care must be taken when using this method that only the layers above the cambium layer are removed. Done correctly, the tree will heal itself within a few weeks. (Part of me can’t help think how cruel we can be, as a species. Other methods for improving or increasing yield include beating on a tree, hammering nails into the trunk, or pruning the roots. From the trees’ point of view, it all sounds brutal.)
On purpose or by accident, girdling is a severe tree injury that should receive immediate attention if possible.
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