[addaon]

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?

[CRConrad]

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.