I had begun to wonder if Sam was unhealthy or diseased in some way. I suspected a canker problem when I noticed a dead spot in the bark near the bottom of the trunk. I could feel a soft spot running a considerable distance up the trunk. I really figured it was diseased and would have to go, which wouldn't be so bad cuz the rasberries seem to be spreading in that direction. Here's a picture:

Sam Cherry Tree

I decided to get a sharp knife and explore the problem area. I carved out all the dead bark, exposing quite a wound in the tree. It was moist underneath with some cotton-like fungus. The fungus didn't appear to be within the wood and was easily pulled away. What I found was actually quite encouraging. The wound has a healthy lip of healing tissue closing in from each side of it. I may have damaged this a bit but I feel exposing the wound to air and light has done a world of good. I now think Sam's lack of vigor was due to being about 40% girdled. Though it seems well on the road to recovery. Here's a closeup of my surgery:

Closeup of Surgery

With any luck, a full recovery is possible. I'm keeping my fingers crossed. On a separate note, I switched to summer pruning last year and early indications are for a bumper crop of pluots, asian plums, euro plums, and peaches, where I've gotten practically none before. After some concrete results are in later in the season I'll post a full summary, but for the time being, I'm sold on summer pruning, particularly on the stone fruits.