Tree Girdling

Cathy Kavassalis – Halton Master Gardener

Girdling, also called ring-barking is the loss of a strip of bark from around a branch or trunk of a woody plant. The width and depth of the strip, the age of the plant, the time of year, the presence of disease and other environmental factors, determines if a tree can recover from such an injury. Significant loss of bark can leave a plant open to desiccation and infection. If vascular tissue is also lost, the plant may starve. While plants have some capacity to recover from minor injuries, serious girdling injuries can kill.

Girdling can happen through neglect as in photo on left, above (shutr.bz/2TMSD0S) AND with Rabbit damage -Photo: http://bit.ly/2wBqh1N

The bark of a tree, is made up of many layers. The outer layer is a tissue called phellem or cork. The cells are dead but they form a protective barrier for the plant. Just inside the cork layer, is a single layer of cells called the cork cambium or phellogen. (This is a layer of undifferentiated cells, called meristemic cells, which produce the cork on the outside and in some species a layer of phelloderm on the inside). If only the outer bark is lost, woody plants can typically recover with a bit of extra attention to watering.

However, just inside the outer layer is secondary phloem tissue. This is a very important part of a plant’s vascular system. The phloem is composed of various specialized cells that circulate nutrients like sugars and starch as well as other important compounds like hormones. If disrupted the plant can no longer move these important materials to where they are needed.

Read: Preventing Girdling

If the vascular cambium or some of it has been undamaged, the plant may recover some function. Like cork cambium, vascular cambium is a single layer of meristemic cells that can differentiate to form more specialized tissue. This layer is important, not only because it produces secondary phloem, but also because it produces xylem. Secondary xylem tissue is produced just inside the vascular cambium. This tissue has a distinct construction that allows water and minerals to move through it from the roots all the way up the trunk and to the leaves. The xylem tissue is referred to as sapwood. (As sapwood ages and the xylem gets clogged with gums and resins it no longer transports water, it can become distinctly coloured, and is often referred to as heartwood.

Read: Why some trees are ‘girdled ‘on purpose’! (page 14)

The heartwood provides structural support for trees, but the tissue is dead and no longer functions). Tree rings reflect the seasonal variation in the development of xylem tissue.

Deer and or squirrels and rabbits often remove strips of bark over the winter. If this is just a small portion of the bark, woody plants can completely recover. However, if the plant is ring-barked with 100% disruption of phloem tissue, water can move up to new growth, but as leaves become photosynthetically active, they will not be able to move sugars and starches back down to support growing roots. The trunk or branch above the ring will swell as compounds accumulate. Tissue from the vascular cambium and cork cambium below and above the cut will begin to differentiate forming callus tissue followed by woundwood. If the width of the ring is narrow, a young actively growing tree may be able to seal over an injury, and reconnect phloem. But if the ring is wide or the tree is old, the injury may not be bridged by woundwood.

In such cases, artificial bridges can be created using grafts from thin branches. This is a tricky operation, but can be tried if the alternative is loss of the tree. See links below.

A seriously injured tree or shrub may try to send up suckers or alternative shoots from below the point of damage. Removing the damaged trunk or branch can encourage the growth of an alternative leader and may reduce the risk of infection if done carefully.