We can't identify the exact fungal cause, but a number of fungi do not decay live wood (and bark is not living tissue, if the organism is only growing on the outer layer of bark). If you would like the tree's health assessed, we recommend that it be examined by a certified arborist or licensed tree expert. Arborists can't treat or cure every condition, but can help to narrow-down a diagnosis and look for sources of tree stress that might be able to be alleviated. If these patches do indicate fungal wood decay, the issue likely arose some time ago, as they tend to begin without any outward symptoms. Arborists need to be able to see the canopy fullness (while it's still full of leaves, before autumn leaf drop) to better evaluate a tree's vigor and health, so we'd suggest having it examined soon so the leaves don't start shedding en masse for autumn; otherwise, the evaluation might need to wait until late spring or so, but we defer to the recommendation of the arborist.

Miri