Wouldn’t a tree without rings still reasonably capture the atmospheric C13:C12 ratio as it grows? Or is the carbon motility within the trunk too high, or the ratio differences too small, to sample a bit near the core and use the ratio there as an age indicator?
Could be (I have no idea), but it sounds like that would be possible to investigate only by complicated laboratory tests. Not a visible change that makes it easy to calculate age by just sawing up a cross section and counting visible rings.
