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Trunk Protection
It has become increasingly apparent to us over the years, that where we once believed the bark of maples could hold up to the direct sun, that heavy sun exposure on the trunks of maples can do severe damage. The potential for sunburn and sunscald on the trunks of maples is greatly reduced in temperate climate but it is nearly a guarantee in the hottest of climate.
This type of damage usually happens on the lower part of the trunk near the ground where the bark is exposed to the most direct sun and reflected heat from surrounding structure, rocks, and walkways. When the damage begins the bark usually becomes discolored displaying and orange or darker hue than the bark with the least exposure. If continued exposure occurs this area can become blackened and desiccated. The scalding of the bark usually means death to the bark and underlying tissues that, once scalded, will begin to decay. On a rare occasion, when the plant is very strong, the outer bark can appear scalded but the inner cambium remains functional.
When the bark is damaged we create a at least two potential situation. The first problem, an invader like a borer of some sort will enter the tree and damage it from within. Usually the cambium will "remodel" around the scalded area if no other insult is present. When a borer gets into the trunk the damage is made more extensive by the insects activity and the entire trunk or branch can be girdled. The second problem, a pathogen like a topical pseudomonas or decay-causing fungus can enter the damaged desiccated area and potentially enter the tree. These pathogenic organisms can slow healing and further the damage done by the sun.
Bark damage is the plight of the thin-barked trees like Maples, Birches, and Cherries and it is important to try to protect them when we know the exposure will be high. This damage can happen in the heat of summer or in the winter. In winter sun can be reflected of snow or we can see some frost cracking. Often, sun on the bark of the trees in winter can "activate" the sap flow in a given area and then when the temperatures drop rapidly this area freezes. So, protection in all seasons is important. Lastly, young trees are most susceptible and as we gain age and caliper on the trunk the chance of damage can be lessened. Generally, only mature trees, where the bark has thickened sufficiently, are at a truly lessened risk.
Precautions
The precautions one takes are standard. Use a tree wrap or shield. Make sure it fits loosely as not to trap moisture and promote infection. Do not wrap over already open wounds, seal them first. You can use a couple coats of white latex paint to reflect the light and heat. This should probably be reapplied yearly as the tree grows or as it seems to wear off or show voids. You can also plant things around the trunk of trees that will shade the trunk like tall ornamental grasses. We have also heard of straw mats and other barriers being placed in front of or leaned up against trunks.
While these sorts of steps may look unsightly or stupid they protect the tree and give it the best chance to live a long and healthy life. If you do have a tree that has experienced damage on the trunk from the sun or otherwise take a look at this FAQ on treating bark wounds. Not every tree needs protection and not every locale or geographic area will be hot enough or have the intensity of sunlight to warrant these precautions. Consider you location and plant culture in deciding what steps you might need to take with your trees and e-mail us if you have questions.
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