Many years ago I collected a yamadori (collected from the wild, SW of Rapid City, SD in the badlands) Black Hills Spruce, to become a bonsai, growing in a natural bowl in a rock that over time became filled with duff. When I lifted it, there was only a single long root growing out of the duff and into a rock crevice, which assumed was it's water supply line. It had a secondary trunk that was dead, but too long for the composition, so I cut it off. I was curious about it's age but couldn't see any rings. For the fun of it, I cut the end off with a band saw polished the cut with cerium oxide and then jeweler's rouge. We mounted a sewing needle on a clamping device as a reference point, then used it as a pointer to count the rings as we moved a 500x microscope table to count the rings. The trunk where I cut it was 1.727" thick (used a micrometer) and we counted about 390 rings. Each time we counted, it was always within a few rings either side of 390. That would put the living part of the tree at somewhere near 500 years old, because it was noticeably thicker. The tree must have been living on an unbelievably meager supply of nutrients and water. Unfortunately, I had 7 of my best trees stolen about 6 years ago, and that was one of the trees taken. I still mourn losing those trees as though they were pets. They almost were.
Al