Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
AMS radiocarbon investigation of the African baobab: Searching for the oldest tree
Introduction
The African baobab (Adansonia digitata L.) is the angiosperm with the stoutest trunk. Based on the huge size of several specimens, certain tree experts stated that the baobab lives to a long age. The age of the oldest baobab specimens has remained however a controversial topic [1], [2], [3], [4], [5]. The baobab produces faint growth rings, considered by many researchers to be annual rings. Nevertheless, for large and old baobabs, a hypothetically accurate ring counting is not possible, as growth rings may no longer be observed in certain areas of the trunk and they are also missing in the area of large cavities [1], [5], [6]. Therefore, the solely accurate method for determining the age of African baobabs is considered to be radiocarbon dating. However, only a limited number of such investigations have been performed on different African baobab specimens for determining their age [7].
Several years ago, we started a long-term research for clarifying some controversial aspects concerning the African baobab, including its age limit, by using AMS radiocarbon dating. According to the published results, the oldest dated baobab sample originates from Grootboom, a large specimen which collapsed in Namibia, in 2004. The radiocarbon date of this sample was found to be 1254 ± 34 BP, which corresponds to a calibrated age of 1275 ± 50 years [4]. Traditionally, this research was limited to dating wood samples collected from the remains of dead specimens, which decay fast.
Recently, we extended considerably the possibility of aging baobabs via a new approach, which allows dating standing and live specimens, as well. This approach is based on AMS radiocarbon dating of very small wood samples collected from the inner cavities and/or from deep incisions in the trunk of large live baobabs [8], [9]. Hence, one can date accurately many large and very large live baobab specimens, some of them possibly older than Grootboom.
Here we report the AMS radiocarbon dating results of wood samples collected from the Glencoe baobab, a large and very old individual from South Africa.
Section snippets
The Glencoe baobab and its site
The Glencoe baobab is located on the Glencoe farm, 10 km from Hoedspruit in the Limpopo Province of South Africa. Its GPS coordinates are 24°22.430′S, 030°51.461′E and the altitude is 472 m. Mean annual rainfall and temperature in the area are 439 mm and 20.8 °C (Hoedspruit station). The tree lies outside its current area of natural distribution and is considered an exotic specimen by botanists.
The Glencoe baobab is an intriguing tree. Viewed from a distance, it looks like a small wood (Fig. 1).
AMS results and calibrated ages
Fraction modern values and radiocarbon dates of the seven samples are listed in Table 1. Radiocarbon dates and errors were rounded to the nearest year. For calibration we used the general IntCal09 data set [17], rather than the SHCal04 data set for the Southern Hemisphere [18]. This choice is justified by the fact that the SHCal04 curve does not yet contain information for lower southern latitudes and does not include results from Africa for the time frame corresponding to our sample ages. The
Conclusions
Several wood samples were collected from different positions of the Glencoe baobab, which suffered two splits in 2009. AMS radiocarbon dating results of these samples revealed that the Glencoe baobab consists of several stems of different ages. The oldest sample has a radiocarbon date of 1838 ± 21 BP, which corresponds to a calibrated age of 1835 ± 40 years. Thus, the Glencoe baobab becomes the oldest African baobab and also the oldest angiosperm with accurate dating results. According to the dating
Acknowledgements
We would like to thank Cecil and Yvonne Liversage, the owners of Glencoe farm, for granting permission for on-site investigation and also for sampling the Glencoe baobab. We also thank Gert Oosthuizen for permission to use photographs of the tree taken from a helicopter. The research was fully funded by the Romanian Authority CNCS-UEFISCDI under Grant PNII-IDEI 2354. AMS radiocarbon dating at the NOSAMS Facility is supported by the US National Science Foundation under Cooperative Agreement
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