Here we present radiocarbon dates of 6 large and ancient holm oak (Quercus ilex L.) trees collected in Montecristo Island (Tuscany, Italy), reported in the paper “Rediscovering Montecristo’s treasure: the island’s holm oaks reveal exceptional longevity” published in Ecology in 2023. The knowledge of the potential maximum lifespans of trees is a key trait for understanding ecosystem functioning and dynamics. However, old trees present often rotten and hollow trunks; moreover, in Mediterranean environment, false and missing rings can further complicate tree-ring studies. Radiocarbon dating is an interesting solution to overcome these problems. Rotten wood samples were collected from the inner and lowest part of each trunk as close as possible to the hypothesized root “collar” and pith. All the sampled wood fragments showed a moderate tree-ring curvature, but we were not able to calculate a reliable estimate of pith-offset (i.e. of the number of missing rings between the innermost annual increment samples and the pith). However, because of the pith offset and the vertical sampling distance from the collar (up to 1 m), radiocarbon dates may have underestimated tree age by a few decades. Radiocarbon dating was carried out by AMS (Accelerator Mass Spectrometry) at CEDAD, the “Centre of Applied Physics, Dating and Diagnostics”, University of Salento, Lecce, Italy. The difference between the calibrated radiocarbon ages and the year 2022 CE was used to calculate the age of each tree. The calculated age range is between 444±90 (probability 92.3%) calendar years for the youngest sampled tree and 761±42 (probability 91.7%) calendar years for the oldest one.

The uploaded file reports for each sampled tree the type of dated material, the alphanumeric ID codes assigned by the Dendrologylab and CEDAD institute, the age determined by radiocarbon dating and referred to the year 2022, the diameter at breast height and the elevation above sea level.