Dogwood trees in full sun like this one are under constant stress. They usually lose bark because of freezing and thawing action in winter when exposed to full sun and also hitting with mowers and weed trimmers when young. Both of these increase borer damage into the trunk leading to further bark loss. There is really not much to do for a tree in this condition. Killing grass and weeds for several feet around the tree and mulching about 2-3 inches deep is helpful. Spraying with permethrin in May each year (lower trunk only) to prevent further borer damage may help. Water when under drought stress is always a good idea in the heat of the summer. Do not fertilze very much (3 pound 10-10-10 each May is enough).