List of oldest trees

This is a list of the oldest-known trees. Definitions of longevity vary between clonal trees, ones where parts of the tree continue to live after the death of the first trunk or trunks, and non-clonal trees. Tree ages are derived from a variety of sources, including documented "tree-ring" (dendrochronological) count core samples, radiocarbon dating, girth-to-age formulas, and estimates from growth rates. For these reasons, there are three lists of "oldest trees" here, using different criteria.

The three tables of trees are listed by age and species. The first table includes trees for which a minimum age has been directly determined, either through counting or cross-referencing tree rings or through radiocarbon dating. Many of these trees may be even older than their listed ages, but the oldest wood in the tree has rotted away. For some old trees, so much of the center is missing that their age cannot be directly determined. Instead, estimates are made based on the tree's size and presumed growth rate. The second table includes trees with these estimated ages. The last table lists clonal colonies in which no individual tree trunks may be remarkably old but in which the organism as a whole is thought to be very old.

The record-holders for individual, non-clonal trees are the Great Basin bristlecone pine trees from California and Nevada, in the United States. Through tree-ring cross-referencing, they have been shown to be almost five millennia old.

A clonal colony can survive for much longer than an individual tree. A colony of 48,000 quaking aspen trees (nicknamed Pando), covering 106 acres (43 ha) in the Fishlake National Forest of Utah, is considered one of the oldest and largest organisms in the world. Recent estimates set the colony's age at about 16,000 to 80,000 years, although tree ring samples date individual stems at rarely more than 130 years. A colony of Huon pine trees covering 2.5 acres (1.0 ha) on Mount Read (Tasmania) is estimated to be around 10,000 years old, as determined by DNA samples taken from pollen collected from the sediment of a nearby lake. Individual trees in this group date to no more than 4,000 years old, as determined by tree ring samples.