Preventing Tree Girdling Injury
Our crews see many preventable problems in the landscape when we’re on customer’s properties. One that we occasionally see is girdling of a tree by the ropes used to support it after planting. This can cause disfiguring scars on the trunk, and in the most extreme situations, death of the tree by “strangulation”. When supports strangle the tree the decline can happen very slowly until the tree is finally dead. Here’s what you need to know so your tree doesn't turn into firewood.
A rope (or cable) and stake system is often used when installing trees that might be top-heavy. This prevents shifting or leaning due to wind forces or softening of the ground in heavy rain events. Ideally, the staking system should support the tree, but be loose enough to allow for some movement and “flex” of the trunk. This gentle movement, produced by wind, helps strengthen the trunk and promotes root growth. This helps the tree establish well in its new location. Excessive shifting of the root ball after planting can inhibit or tear new root growth, slowing the tree’s establishing in its location. Not all trees need to be staked however-the proportion of root ball to tree height with the density of the leaf cover factored in determines what trees need staking.
In most cases the staking system should be removed a year after planting. In the case of a very large tree, it may take two years for it to be well-rooted enough. To test if the stakes are ready to be removed, move the trunk back and forth, watching the area around the root ball. If you see any movement of the soil, the tree still needs the stakes. If they need to be left in place, inspect an d adjust the rope and ties to ensure that they are not too tight around the growing trunk.
If the rope (usually threaded through a piece of hose to cushion the trunk from abrasion) is not removed from the trunk, the consequences are usually severe, and vary depending on the type of tree. On some trees the trunk eventually grows so thick that the rope acts as a tourniquet on the vascular system of the plant, gradually crushing it in a slow-motion strangulation. This prevents the tree sap from freely flowing between the leaves and the roots, leading to decline and ultimately death. On other trees, the support ropes can cut into the trunk, leaving a constricted area that is weak and susceptible to breakage from wind or ice.
If your tree has already been damaged by tree supports it may survive depending on the extent of the damage. While the exact response to the injury depends on the species of tree and it's overall health, trees almost always survive if 1/2 or less of the circumference of the bark has been damaged. In this case, remove all supports that have become too tight and carefully cut away any loose or frayed bark with a sharp, sterilized knife. Do not cut into any callused growth that may already be forming to heal the damage. Do not paint the wound either-it might make you feel better, but trees have their own healing methods, and tree wound dressing or paint can interfere with those. Take particularly good care of the damaged tree for the next few seasons-give it deep watering when needed, and use a slow release or organic fertilizer. Pay special attention to the tree for insects or diseases that may prey on stressed trees, and treat accordingly.
There is a technique called "bridge grafting" (link opens Google search) that can save fully-girdled trees. It takes some experience to do, and the results can be unsightly for an ornamental tree..
Because of the way trees transport nutrients between leaves and roots, a fatally girdled tree may not succumb to it's injuries for quite a long time, leafing out and even blooming for a year or two after the damage. But eventually, the roots run out of nutrients and the tree dies.
To keep your new trees healthy, remember to check the support system a year after planting, whether you planted them of if they were installed professionally. This simple step can make the difference between enjoying your tree for years to come and ending up with a landscape headache.