I stumbled across the Sheffield Dendrochronology Laboratory (UK) where they have a continuous tree-ring database back to 5000BC or so.
Is this as far back as it’s possible to go with dendrochronology, or does anyone know of a more extensive database?
From Dendrochronology
Isn’t that back to before the world was even formed 
?
The bristlecone is awesome, but unfortunately they have sacrificed a couple of the very oldest- good ole’ WPN-114 they lovingly named one. Apparently a high speed swedish steel drill broke obtaining ring data, so rather than wait around for a replacement, they cut it down. It was roughly 4,900 years old! Several already dead specimens should indeed put the record back a couple thousand more as decomposition is slowed by altitude and dryness.
These aren’t stately trees like the redwoods or sequoias, so I suppose there isn’t going to be the same sort of outrage inherent to cutting down something that looks rather dead to begin with.
Apparently box huckleberry is extremely long lived as well, though I’m not sure if rings as such are obtainable. In one sense, Aspen groves are genetically the offspring of one plant… Crustose lichens in excess of x number of centimeters are quite old in some cases as well.