You haven't told us where you are in the USA. Could this be frost or wind damage? I doubt very much if it's voles -as you say, it's a big tree. I can't tell what the tree is from your photos, I'm afraid, but it appears to be an evergreen - is it?

It's difficult to see from the photograph, but this looks as if it might be some kind of Viburnum, Ben. If it is, then mine did exactly the same a couple of years ago, and a Goy member suggested it was outgrowing its space and to cut it back hard. I did, and it has had a resurrection and now looks beautifully healthy. Does it ever flower at all?

Sorry, we are in Zone 9, Sunset Zone 21 (Pasadena CA area).

Thanks so much for the comments. The tree has never flowered but is evergreen. I agree that it could have been outgrowing the space, but I did recently cut it back a bit, mostly for shape. Could this happen due to disease? Or perhaps fungal infection from my shears?

Even if I can't figure it out, should I cut back all the dead stuff now? Or wait and see what happens?

Thanks SO much! :)

I'd cut it back to healthy growth and give it a feed, I think.