Peeling bark can be from environmental issues. Cold temperatures can cause some damage to the leaves and trunks.
The natural aging of the tree can also account for changes in the bark. The young wood starts out as a light tan to gray color and with age cracks to revel reddish colors.
African Sumac is quite drought tolerant and will actually do better with less water.
Inspect the plant carefully to determine if you see any insects or other signs of fungus.