Whew! I finally worked through the initial stage of this particular portion of a larger work. The “tree rings to bark” represents a conifer cut down a year ago in the very early stage of decay. The wood rounds have been exposed to weather and checking/crack lines have formed over the surface. The bark has started to pull off the main trunk. Bark actually has properties that keep it from decomposing quickly in comparison to the rest of the tree structure.
The rings vary, sometimes becoming more squished together, probably due to something that confined the tree more (the house, shade, who knows!). I only cut 41 years of growth, but it was more like a 50 years old tree. Some of the early years were too difficult to cut.
Now it will need an application of acrylic washes, mounting to mulberry paper, and eventually a frame with back-lighting. Many more opportunities to flub things up!