Radiocarbon Dating of an Olive Tree Cross-Section: New Insights on Growth Patterns and Implications for Age Estimation of Olive Trees

Abstract

The age of living massive olive trees is often assumed to be between hundreds and even thousands of years. These estimations are usually based on the girth of the trunk and an extrapolation based on a theoretical annual growth rate. It is difficult to objectively verify these claims, as a monumental tree may not be cut down for analysis of its cross-section. In addition, the inner and oldest part of the trunk in olive trees usually rots, precluding the possibility of carting out radiocarbon analysis of material from the first years of life of the tree. In this work we present a cross-section of an olive tree, previously estimated to be hundreds of years old, which was cut down post-mortem in 2013. The cross-section was radiocarbon dated at numerous points following the natural growth pattern, which was made possible to observe by viewing the entire cross-section. Annual growth rate values were calculated and compared between different radii. The cross-section also revealed a nearly independent segment of growth, which would clearly offset any estimations based solely on girth calculations. Multiple piths were identified, indicating the beginning of branching within the trunk. Different radii were found to have comparable growth rates, resulting in similar estimates dating the piths to the 19th century. The estimated age of the piths represent a terminus ante quem for the age of the tree, as these are piths of separate branches. However, the tree is likely not many years older than the dated piths, and certainly not centuries older. The oldest radiocarbon-datable material in this cross-section was less than 200 years old, which is in agreement with most other radiocarbon dates of internal wood from living olive trees, rarely older than 300 years.

Radiocarbon analysis of modern olive wood raises doubts concerning a crucial piece of evidence in dating the Santorini eruption

“…We have shown here and previously 26 that the visual identification of growth rings in olive wood is unreliable. This is consistent with previous reports 1 , 33 , but here we use the tool of radiocarbon dating at high resolution, enabled by the “bomb peak” to demonstrate this.…”

“…As more than half the samples from the outermost ring dated to well before 2013, we decided to re-examine the trunk of another olive tree from a different location in northern Israel that was studied previously, Zippori 26 (Fig. 1 ).…”

“…In total, 20 samples (14 new samples compared to the previous study 26 ) were analyzed for radiocarbon dating from a cross-section of a whole olive tree cut down a few years after the tree had died, from the site of Zippori in northern Israel. As the tree had been dead for only a few years before felling in 2013, the wood nearest the bark would be expected to fall within a few years from this date.…”

“…This irregular cambial activity around the circumference of the tree is responsible for the characteristic non-circular cross section of olive trees 25 . Based on radiocarbon concentrations, we reported 26 that visually identified growth rings in olive trees are not necessarily annual, as there is a discrepancy between the number of rings identified and the number of years expected between them. We therefore try to avoid using ring number terminology, and refer to sampling points using arbitrary numbers for each cross-section.…”

“…Here we examine a cross-section from a living olive branch bearing green leaves, and we expand the investigation of the whole olive tree cross-section studied previously by us 26 . We first determine their chronological growth deposition using high resolution radiocarbon dating.…”