Trees need their bark to protect the inner vascular tissues that move water and nutrients throughout the plant. If they lose too much bark, particularly if the loss completely circumnavigates the trunk, then the tree will die because it can no longer transport those needed nutrients. This deadly condition is called girdling. The following can help you prevent that from happening.
Animal damage
Deer, rodents, and other animals often chew bark or scratch at it to sharpen claws, which can lead to girdling. Installing a wire mesh tree cage around the trunk solves the problem. The cage should be tall enough so deer can't reach. It must also be a few inches wider than the trunk so it won't restrict the tree as the trunk grows. There are also plastic cages available commercially. Check the cage annually, and replace it if the trunk becomes too large.
A too-high mulch layer can also lead to animal damage. Rodents often nest in mulch in the winter. When mulch is stacked against the trunk of a tree, the rodents may be drawn to chew on the bark to extract nutrients from the inner layers. They can do this easily below the mulch, without exposing themselves to the elements or to predators. Pulling back mulch so it doesn't rest directly against the trunk solves this issue.
Mechanical damage
This type of damage is caused by humans, or at least their tools. For example, lawnmowers repeating bumping a tree trunk can cause this damage. String trimmers are even worse, since the whipping trimmer line strips away large swathes of bark on some tree species. A cage can prevent mechanical damage, but a better option is to mulch over the area surrounding the trunk so there's no need to use lawn tools so closely. A border of landscaping bricks around the mulched area provides even more protection.
Pruning damage from tools and hardware can also cause girdling. Don't screw anything into the trunk, especially heavy items. When pruning the tree, also be careful not to pull a branch and tear the bark on the trunk. Cutting with sharp pruners and saws are key. Make the cut through the branch above the raised collar at it's base. This ensures that you don't inadvertently cut into the trunk's bark.
For more help, contact a tree removal service for professional maintenance. Sometimes minor bark damage can be treated before girdling can occur.
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