I came across this tree yesterday in the Bull of the Woods Wilderness.  I'm guessing that the damage was done by a bear, but I don't know for sure.  Whoever did it worked really hard at it, as you can tell by the large pile of shredded wood and bark at the base.   Can anyone explain what happened here?

That looks like the work of a porcupine.  They're notorious for chewing up road signposts throughout the Willamette National Forest, so I wouldn't rule out porcupines being in the Bull of the Woods Wilderness as well.

A woodchuck would chuck all the wood that a woodchuck would if a woodchuck could chuck wood.
(Ducking and running...)

I second the porcupine verdict... I've seen lots of that. If you look closely, there should be a distinctive pattern/texture like this:

Do porcupines climb tree trunks to do that?

I enlarged the photo a bit to get a better look at the pattern/texture of the damage.  Looks like this:

Doesn't look too much like the porcupine damage in jley's photo.  Surprisingly (at least to me), I have been told that this is most likely the work of a pileated woodpecker.  I had no idea that a bird could cause this type of damage.  A biologist friend of mine told me that she had observed these birds at work on her wooded property near Eugene and that this is exactly the kind of thing that they do.  They are large birds, comparable in size to a crow.  They will pull away strips of wood and toss them aside, resulting in the shredded look that is seen here and the pile of wood chips at the base of the tree as seen in the original photo.  This tree is in poor health, if not already dead, and probably was home to carpenter ants or other insects which the woodpecker was after.  From what I've read, this is the typical situation where a pileated woodpecker would go to work.  I wish I could have been there to see it while it was going on.  From what I've heard, they can put on quite a show when they really get going.

Pileated woodpeckers rarely punch holes in healthy trees. They are after insects, and bugs are much more common in decaying but not necessarily dead trees. Pileateds can punch very large holes deep into the tree. I'd vote for the porcupine! Last summer one went after a maple tree down on the Clackamas below our house. The critter was never seen but the damage is obvious. He is after the inner layer under the bark so sizable strips of bark get removed in the process.

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--Bryon

http://clackamas-outlook.blogspot.com/