Acer macrophyllum -dead?, causes?

[ArtB]

One of my favorite bigleaf maples is dying, none others in the yard affected, however, this one is in a lot more or D fir shade for the last ten years.
Suggested causes? Have driven dump truck and dozer past it for 25 years, possible cumulative root damage/compaction??

Center tree in the pix, top is dead, a few center branches still have leaves, but much smaller than previous years.

 

[ORclimber]

I've removed several big leaf maples in the past year that look similar to that. I asked the head of the OSU disease lab about them hoping for her to agree with my diagnosis of one. She said it could be any number of problems and was likely a combination. I took hollow section of maple into the local extension agent a few weeks ago. He got on the phone with "The (Fungus) Man" at the state dept. of forestry and it was the same story. Basically it could be about 25 things or a combination, and if they test it in a lab they may not even find the origional killer.