The oldest trees are determined by growth rings, which can be seen if the tree is cut down, or in cores taken from the bark to the center of the tree. Accurate determination is only possible for trees that produce growth rings, generally those in seasonal climates. Trees in uniform non-seasonal tropical climates grow continuously and do not have distinct growth rings. It is also only possible for trees that are solid to the center. Many very old trees become hollow as the dead heartwood decays. For some of these species, age estimates have been made on the basis of extrapolating current growth rates, but the results are usually largely speculation. White (1998)[28] proposes a method of estimating the age of large and veteran trees in the United Kingdom through the correlation between a tree's stem diameter, growth character and age.
The verified oldest measured ages are:
Great Basin Bristlecone Pine (Methuselah) Pinus longaeva: 4,844 years[29]
Alerce Fitzroya cupressoides: 3,622 years[29]
Giant Sequoia Sequoiadendron giganteum: 3,266 years[29]
Sugi Cryptomeria japonica: 3,000 years[30]
Huon-pine Lagarostrobos franklinii: 2,500 years[29]
Other species suspected of reaching exceptional age include European Yew Taxus baccata (probably over 2,000 years[31][32]) and Western Redcedar Thuja plicata. The oldest known European Yew is the Llangernyw Yew in the Churchyard of Llangernyw village in North Wales, which is estimated to be between 4,000 and 5,000 years old.
