Question
I have a very large (over 30 feet tall) Japanese Maple the bark is drying out and falling off. Some of the branches are loosing leaves and appear to look dead.  Also there are small (largest is about the size of a nickle) green circles that look like mold.  I love my tree and don't want it to die, can you help me?

Answer
What you describe does not sound good.  Anytime the bark falls off of the trunk, the tree is in peril.  The green circles are lichens and pose no threat to the tree.  Dont worry about them.  Check the branches to see if they are dead by scratching with a pocketknife.  If there is green tissue underneath the bark the branch is still alive and new leaves may come out. If the tissue is brown underneath the bark, the branch is dead and needs to be cut off.  Check the mulch layer around the base of the tree and make sure it is not too deep.  Pull the mulch back and see if the trunk has dark rotten areas on it.  If so, leave the mulch pulled back from the base.  Maples trees are notorious for doing what you describe.  I have a small one that is doing the same thing.  I would make sure the tree is watered during dry periods and fertilize with a tree fertilizer.  This is about all that can be done.  I wish you good luck.  Thanks.