What is the symbosis between a shelf fungus and hickory tree?

The type of symbiOSis is commensalism. The shelf fungus obtains a place to live, water that is absorbed by the Hickory tree bark, and nutrients from the decaying surface bark. The Hickory tree is neither harmed nor helped from the relationship. However, scientists do admit that in relationships that appear to be commensalism, there may really be a benefit to the plant that is being used. We just don't know enough about the plant and/or the various relationships to be able to determine that it is really mutualism, where both plants benefit.