I've got a big black oak that is not looking well in my front yard. This tree is about 3-3.5 feet across, and sits about 10 feet from the Chesapeake Bay (Maryland). I was going to take some of the dead limbs out of it, but if its done for, I'd rather just take out the whole tree. Basically, its upper canopy seems to be dying. Any ideas why? Is this tree salvageable?