Answer: It sounds like your young trees suffered some extremes of weather. Unfortunately, once the bark is gone, the tree has been weakened and probably won't recover.
Young trees that have been growing in nurseries have bark like baby's skin, tender and in need of protection until they become adjusted to the elements. Sunscald usually occurs on the southern side of a tree's trunk, and can happen in summer and winter. The sun actually dries out and burns the bark, which splits and falls off. On sunny winter days, the quick plunge from warm sun into a cold night can cause the bark to split open.
You can avoid these problems by painting young tree trunks with whitewash or white interior latex paint, or wrapping them with tree wrap paper (available at most garden centers). Keep trunks protected for at least two years. Check to make sure the paper stays loose as the tree grows.
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