Radiocarbon ages of 6 ancient holm oaks growing in Montecristo Island, Italy

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.本研究公开了采自意大利托斯卡纳大区蒙特克里斯托岛的6株大型古老圣栎（Quercus ilex L.）的放射性碳定年数据，相关成果发表于2023年《生态学（Ecology）》期刊的论文《重现蒙特克里斯托的珍宝：该岛圣栎展现超长寿命》中。了解树木的潜在最大寿命，是解析生态系统功能与动态的关键性状。然而，老龄树木的树干常出现腐朽与中空现象；此外，地中海生境中的假年轮与缺失年轮，进一步加剧了树木年轮研究的复杂性。放射性碳定年法（Radiocarbon Dating）是解决上述问题的可行方案。研究人员从每株树干的内部最低位置采集腐朽木样本，采样点尽可能贴近推测的根颈（root collar）与髓心（pith）。所有采集的木碎片均表现出中等程度的年轮弯曲，但研究人员无法可靠估算髓心偏移量（pith-offset，即最内侧年轮增量样本与髓心之间缺失的年轮数量）。然而，由于存在髓心偏移，且采样点距根颈的垂直距离可达1米，放射性碳定年结果可能低估了树木实际年龄数十年。本研究采用加速器质谱仪（AMS，Accelerator Mass Spectrometry），于意大利莱切市萨伦托大学的应用物理、定年与诊断中心（CEDAD）完成放射性碳定年实验。研究人员通过校正后的放射性碳年龄与公元2022年的差值，计算每株树木的树龄。经计算，采样树木的树龄范围为：最幼龄个体为444±90（概率92.3%）个日历年，最老龄个体为761±42（概率91.7%）个日历年。