You're right that it's a fungus - that appears to be stromata of Hypoxylon (recently reclassified as Biscogniauxia). This is an opportunistic fungus that is basically an indicator of a tree (or portion of the tree) that is dead or dying. The fungus is commonly present as a harmless resident in the inner bark of healthy trees, but will move into the sapwood once the stem is severely stressed or declining for some other reason. The spore-producing structures will grow and cause the bark to slough off in patches.

If that's happening on the main stem, I would regard it as a sign that the tree is on its way out. Because it acts as a decay fungus, Hypoxylon can also cause the stem to become structurally unstable fairly quickly.

Here is a link that might be useful: USFS - Hypoxylon canker of oaks

Thanks for the info. I have a local tree service that I trust; just made the call to have them come out and assess it. Hopefully it can be saved, but we'll just put another one in its place if not. Lord knows we have enough acorns.

it looks to me.. like the wound started with an ax ....

insure the the local tree SERVICE l.. is an ISA certified tree surgeon ...

not every dude with a chainsaw is such

does this tree overhang the house.. or any other investment????

ken

Here is a link that might be useful: link