Dendrochronology is the scientific method of dating trees based on their rings. David Stahle, a professor a the University of Arkansas first visited the Black River area in the 1980s with friend. They estimated the cypress trees were around 1,800 years old. One of Professor Stahle’s graduate students wanted to study the cypress trees in Black River in 2011. Professor Stahle, the graduate student, and a guide from the Nature Conservancy revisited and did a more in-depth analysis of the cypress trees. They discovered one of the trees to be 26 centuries old.
https://allthatsinteresting.com/fifth-oldest-tree