We have an older large oak tree (I think Live Oak). Almost immediately just above ground level, the tree branches into four main trunks, each reaching around fifty feet high. One main branch has been loosing chucks of bark. It otherwise appears health (leafy green shoots, etc.) Any ideas about why the bark is coming off?

Look for clues:

Where the bark has come off, what does it look like? Can you tell if it is only outer bark, or does the lost bark expose wood beneath it?

Is there any sign of fungal growth, discoloration, sap leakage, insect frass, etc.?

Has there been any activity near the tree that could have mechanically damaged the bark? (or could another branch have fallen, striking the tree bark?)

Is there any sign that an animal could have clawed or bitten the bark?