Dating the Noah trees to improve age estimates in centennial and millennial olive trees

The olive tree is an iconic component of Mediterranean agricultural landscapes. Many monumental olive trees are regarded as millennial individuals, but their ages cannot be estimated through tree ring dating. Alternatively, ¹⁴C-dating of pith wood sample provides age estimates for these old trees. However, published age estimates indicate that most ages of old olive trees range between 200 and 700 years. Nevertheless, some rare individuals may be millennial or even older. Here we report the oldest dated olive tree, sampled in the so-called Noah olive grove in Bshaaleh (northern Lebanon), and having an age of 1161 ± 131 years according to ¹⁴C dating. By measuring tree diameter, ring counting, and ¹⁴C wood dating in old olive trees in Mediterranean countries an equation was obtained to estimate the ¹⁴C-estimated age of old olive trees: age = 37.56 + 1.835 diameter. We conclude that most monumental olive trees are centennial but not millennial, with very old trees probably restricted to harsh sites where trees show slow growth rates.