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STUDIA UBB CHEMIA, LXII, 2,Tom II, 2017 (p. 355-364)
(RECOMMENDED CITATION)
DOI:10.24193/subbchem.2017.2.28
RADIOCARBON DATING OF A VERY LARGE AFRICAN
BAOBAB FROM LIMPOPO, SOUTH AFRICA:
INVESTIGATION OF THE SAGOLE BIG TREE
ADRIAN PATRUTa,*, ROXANA T. PATRUTb,
ROBERT VAN PELTc, DANIEL A. LOWYd, EDIT FORIZSa,
JENÖ BODISa, DRAGOS MARGINEANUa,
KARL F. VON REDENe
ABSTRACT. The article reports the AMS (accelerator mass spectrometry)
radiocarbon dating results of Sagole Big tree, a giant African baobab from
Limpopo, South Africa. Several wood samples were collected from the walls
of its inner cavity and dated by radiocarbon. The age values along the cavity
samples increase with the distance into the wood. This anomaly shows that
the cavity is a false one. The oldest sample segment had a radiocarbon date
of 781 ± 29 BP, which corresponds to a calibrated age of 740 ± 15 yr. We
estimate that the oldest part of the Sagole baobab has an age of 800-900 yr.
We determined that the tree has a closed ring-shaped structure, which
consists of a large unit with six fused stems and of two additional leaning
stems.
Keywords: AMS radiocarbon dating, Adansonia digitata, tropical trees, ring-
shaped structure, age determination, false cavity.
a Babeş-Bolyai University, Faculty of Chemistry and Chemical Engineering, 11 Arany Janos,
RO-400028, Cluj-Napoca, Romania.
b Babeş-Bolyai University, Faculty of Biology and Geology, 44 Gheorghe Bilascu, RO-
400015, Cluj-Napoca, Romania.
c Institute for Redwood Ecology, Humboldt State University, Arcata, CA 95521, U.S.A.
d Nova University, 5000 Dawes Ave., Alexandria, VA 22311, U.S.A.
e NOSAMS Facility, Dept. of Geology & Geophysics, Woods Hole Oceanographic Institution,
Woods Hole, MA 02543, U.S.A.
* Corresponding author: apatrut@gmail.com
A. PATRUT, R.T. PATRUT, R. VAN PELT, D.A. LOWY, E. FORIZS, J. BODIS, D. MARGINEANU, K.F. VON REDEN
356
INTRODUCTION
In 2005, we started a long-term research in order to elucidate several
aspects related to the architecture, growth and age of the African baobab
(Adansonia digitata L.). The research is mainly based on our approach which
also allows to investigate and date standing and live baobab specimens. The
methodology consists of AMS radiocarbon dating of small wood samples
collected from inner cavities and/or deep incisions/entrances in the stems,
fractured stems and from the outer part of large baobabs [1-5].
Owing to the special ability of baobabs to produce stems periodically
during their life cycle, over time they develop architectures of increasing
complexity. That is why our research focused on superlative baobabs, i.e.,
very large and/or old specimens. According to radiocarbon dating results, all
large baobabs are multi-stemmed. We identified the open and closed ring-
shaped structures, which are the most important architectures that enable
African baobabs to reach old ages and large sizes [6, 7]. Old baobabs have
often large cavities, especially in the central area of their trunk/stems. In normal
cavities generated by wood removal, the pith/centre of the stem is located inside
the cavity. For wood samples extracted from normal cavities, age values
decrease continuously from the cavity walls toward the outer part of the stem.
Our research of large and old baobabs has identified a major anomaly in the age
sequence of cavity samples dated by radiocarbon. In these cases, ages of
samples collected from their inner cavities increase from the cavity walls up to a
certain distance into the wood, after which they decrease toward the outer part.
The only possible explanation for this finding is that such cavities are only natural
empty spaces between several fused stems disposed in a closed ring-shaped
structure, which were never filled with wood. We named them false cavities. The
first significant difference between false and normal cavities is the presence or
absence of the bark inside the cavity. Unlike normal cavities, which become
larger over time due to continuous decay, false cavities tend to become smaller
as a result of stem growth [7-10]. The oldest dated A. digitata individuals were
found to have ages up to 2500 years [11, 12].
Dated growth rings of several investigated African baobab specimens,
which may act as a proxy climate archive, were used for past climate
reconstruction in southern Africa [13, 14].
Here we present the investigation results of a giant baobab, i.e., the
Sagole Big tree from Limpopo Province, South Africa. The Sagole baobab is
included in the Big Tree Register. According to a very controversial formula
proposed by the Dendrological Society for calculating the tree size, it has a
size index of 426 and it has been officially declared the largest Champion
Tree of South Africa [15].
RADIOCARBON DATING OF A VERY LARGE AFRICAN BAOBAB FROM LIMPOPO, SOUTH AFRICA
357
RESULTS AND DISCUSSION
The Sagole Big tree and its area. The Sagole Big tree is located in
Zwigodini village at 54 km NNW of Tshipise, in Mutale Municipality, Vhembe
District, Limpopo Province, South Africa. The GPS coordinates are 22º30.002'
S, 030º37.995' E and the altitude is 359 m. Mean annual rainfall in the area is
354 mm.
Mapping results. The Sagole Big tree consists of a very large unit,
which is multi-stemmed and heavily buttressed; it also has two additional
leaning stems (Figure 1). It has a maximum height of 19.8 m, the circumference
at breast height (cbh; at 1.30 m above ground level) is 34.35 m and the basal
footprint of 60.6 m2, which corresponds to a formal diametre of 9.64 m.
Figure 1. General view of the Sagole Big tree taken from the west.
The overall wood volume is 414 m3, out of which 252 m3 below 5 m
and 162 m3 above 5 m. After the recent splits of Platland tree, which had a
total wood volume of 501 m2 [16], the Sagole Big tree becomes the largest
African baobab (Figure 2). The canopy has a total volume of 16,032 m3 and
a total surface of 134 m3, which corresponds to a mean crown diametre of
42.7 m.
A. PATRUT, R.T. PATRUT, R. VAN PELT, D.A. LOWY, E. FORIZS, J. BODIS, D. MARGINEANU, K.F. VON REDEN
358
Figure 2. Cross sectional areas of the trunk/stems of Sagole tree at different
heights (ground level, 1 m, 2 m, 3 m, 4 m and 5 m).
The Sagole Big tree has a closed ring-shaped structure with a false
cavity inside the large unit. The large unit consists of six fused main stems, out
of which four build the ring and two are outside the ring. By also considering
the two leaning stems, the Sagole baobab consists of eight stems.
The main part of the false cavity, which is covered by bark, has a
length of 2.20 m (NS) and a width of 2.70 m (WE); the maximum height is
7.41 m and the basal surface 4.8 m2. The cavity also has an appendix toward
the north, which is 1.10 m long, has a maximum width of 0.70 m and is not
accessible. The entrance into the cavity is possible from the south via a small
corridor with a length of 1.30 m, a width between 0.70 and 1.00 m and a
height of 3.90 m (Figure 3). Similarly to other false cavities, the cavity of
Sagole tree is only an empty space between the stems that build the ring.
This space which was never filled with wood becomes smaller over time, due
to stem growth. There is also a kind of extension toward the south between
the two leaning stems, like an uncovered aisle, with a length of 4.36 m and a
width of 1.07 m at its end.
RADIOCARBON DATING OF A VERY LARGE AFRICAN BAOBAB FROM LIMPOPO, SOUTH AFRICA
359
Figure 3. Cross-section of the Sagole tree (at 1 m above ground),
showing the position of the false cavity, the positions of the
five sampling points and the sampling directions.
Wood samples. Three wood samples (labelled 1-3) were collected from
the northern and western walls of the false cavity, at low heights between
0.33 and 0.40 m. The sample lengths were 0.56, 0.33 and 0.30 m. Other two
samples (labelled 11 and 12) were collected from the western and eastern
walls of the cavity, at greater heights of 1.36 and 1.30 m. These samples were
0.64 and 0.43 m long. A number of 13 small pieces/segments, each of the
length of 0.001 m (marked as a, b, c), were extracted from determined positions
of the five samples.
AMS results and calibrated ages. Radiocarbon dates of the 13 segments
are listed in Table 1. Radiocarbon dates and errors were rounded to the nearest
year. The radiocarbon dates are expressed in 14C yr BP (radiocarbon years
before present, i.e., before the reference year ad 1950). Calibrated (cal) ages,
expressed in calendar years, are also displayed in Table 1. The 1-σ probability
distribution was selected to derive calibrated age ranges. For five sample
segments, the 1-σ distribution is consistent with only one range of calendar years.
For the other eight sample segments, the 1-σ distribution is consistent with
two or three ranges of calendar years. For these eight segments, the confidence
interval of one range is considerably greater than that of the other(s); therefore, it
was selected as the cal AD range of the segment for the purpose of this
discussion. For obtaining single calendar age values of sample segments, we
A. PATRUT, R.T. PATRUT, R. VAN PELT, D.A. LOWY, E. FORIZS, J. BODIS, D. MARGINEANU, K.F. VON REDEN
360
derived a mean calendar age of each segment from the selected range
(marked in bold). Calendar ages of segments represent the difference between
AD 2017 and the mean value of the selected range, with the corresponding
error. Calendar ages and errors were rounded to the nearest 5 yr.
Table 1. AMS Radiocarbon dating results and calibrated calendar ages of
samples/segments collected from the Sagole baobab.
Sample
(Segment)
Depth1
[height2]
(10-2 m)
Radiocarbon date
[error]
(14C yr BP)
Cal AD range
1-σ
[confidence interval]
Sample age
[error]
(cal yr)
1a 20
[33]
195 [± 23] 1670-1696 [20.6%]
1725-1784 [38.2%]
1794-1808 [9.4%]
260 [± 30]
1b 46
[33]
390 [± 18] 1478-1509 [28.0%]
1580-1621 [40.2%]
415 [± 20]
1c 56
[33]
480 [± 25] 1436-1458 [68.2%] 570 [± 10]
2a 21
[33]
197 [± 26] 1668-1696 [19.2%]
1725-1786 [39.7%]
1793-1808 [9.4%]
260 [± 30]
2b 33
[33]
275 [± 21] 1640-1668 [68.2%] 365 [± 15]
3a 10
[40]
227 [± 18] 1667-1672 [6.2%]
1741-1796 [42.0%]
250 [± 25]
3b 20
[40]
335 [± 27] 1510-1576 [52.0%]
1622-1640 [16.2%]
475 [± 35]
3c 30
[40]
436 [± 21] 1452-1490 [68.2%] 545 [± 20]
11a 20
[136]
270 [± 19] 1644-1668 [68.2%] 360 [± 10]
11b 40
[136]
530 [± 25] 1419-1442 [68.2%] 590 [± 10]
11c 64
[136]
781 [± 29] 1234-1244 [12.2%]
1264-1291 [56.0%]
740 [± 15]
12a 25
[130]
212 [± 20] 1670-1688 [8.8%]
1734-1784 [53.8%]
1794-1800 [5.6%]
260 [± 25]
12b 43
[130]
333 [± 24] 1510-1551 [37.0%]
1558-1574 [12.4%]
1622-1642 [18.8%]
485 [± 20]
1 Depth in the wood from the sampling point.
2 Height above ground level.
RADIOCARBON DATING OF A VERY LARGE AFRICAN BAOBAB FROM LIMPOPO, SOUTH AFRICA
361
Dating results of samples (segments). We extracted and dated two or
three segments from each sample. For all five samples, the ages of segments
increase with the distance into the wood. Consequently, the oldest segments
were extracted from the sample ends. For the first three samples collected at
lower heights, labelled 1-3, the oldest dated segments, i.e., 1c and 3c, correspond
to distances of 0.56 m and 0.30 m into the wood. Their radiocarbon dates of
480 ± 20 and 436 ± 21 BP correspond to calibrated ages of 570 ± 10 and 545 ±
20 calendar yr. For samples 11 and 12 collected at greater heights, the oldest
segment 11c, which is also the deepest, was positioned at 0.64 m from the
sampling point. Its radiocarbon date of 781 ± 29 BP corresponds to a calibrated
age of 740 ± 15 calendar yr.
Architecture and age of the Sagole tree. For the five samples collected
from the cavity, the age values increase with the depth into the wood. This
anomaly is characteristic only to false cavities. We already mentioned that the
Sagole baobab has a closed ring-shaped structure with a false cavity inside
the ring.
The tree is composed of a large unit, which consists of six fused main
stems, and two leaning stems.
For baobabs that exhibit a closed ring-shaped structure, the oldest
stems are always around the false cavity. The oldest dated sample segment
11c has an age of 740 ± 15 yr. The segment originates from a distance of
0.64 m from the inner cavity walls. In this area, the depth of the cavity walls
was of 1.60 m. Taking into account our previous research on age sequences
along samples collected from stems that build the ring, we consider that
the position of segment 11c was close to the point of maximum age in the
corresponding direction. Therefore, we estimate that in the point of maximum
age, this stem has an age of 800-900 yr, i.e., 850 ± 50 yr. The age of the two
stems of the large unit which grow outside the ring, as well as the age of the
two leaning stems, that have not been dated, must be considerably lower
than the ring, probably up to 500-600 yr.
The age of 800-900 yr for the oldest part of Sagole tree determined via
radiocarbon dating, is considerably younger than the age values proposed by
other tree researchers. Such high values were suggested by considering the
girth of the baobab, which is exaggerated by the buttresses and especially by the
leaning stems, but also by the overall size which is due to the large number
of stems that build the tree. On the other hand, the age we determined for
the Sagole tree is comparable to the age of the large unit of the Platland tree,
which toppled and died recently [16]. Finally, we mention that the largest trees
are usually not the oldest. The largest specimens are those which had grown very
fast when they were young and continued their rapid growth [5].
A. PATRUT, R.T. PATRUT, R. VAN PELT, D.A. LOWY, E. FORIZS, J. BODIS, D. MARGINEANU, K.F. VON REDEN
362
CONCLUSIONS
The research discloses the main results of the radiocarbon investigation
of a giant African baobab, the Sagole Big tree, located in the Limpopo Province,
South Africa. The main aim of the research was to determine the architecture
and age of the baobab, as well as its accurate size. With a total wood volume
of 414 m3, the Sagole Big tree has just become the largest known African
baobab. Five wood samples were collected from the walls of its inner cavity.
The age values of segments extracted from these samples increase with the
distance into the wood. This anomaly is specific to false cavities. The oldest
sample segment had a radiocarbon date of 781 ± 29 BP, which corresponds
to a calibrated age of 740 ± 15 calendar yr. Based on dating results and
accurate measurements, we consider that the oldest part of the Sagole baobab
has an age of 800-900 yr. The tree exhibits a closed ring-shaped structure with a
false cavity inside. It consists of a large six-stemmed unit and of two additional
leaning stems.
EXPERIMENTAL SECTION
Measurements. The external measurements of the Sagole Big tree
and the measurements inside the inner cavity was performed by using a
Bosch DLE 70 Professional laser rangefinder (Robert Bosch GmbH, Stuttgart,
Germany) and graduated tapes. Cross-sections of the baobab at ground
level, 1, 2, 3, 4 and 5 m were mapped by setting up a frame around the tree with
a graduated tape. A compass and an Impulse 200 laser rangefinder (Laser
Technology, Inc., Centennial, CO, U.S.A.) were used to map the cross-sections.
Additional cross-sections on the largest section were mapped at 6.5 and 8 m.
All of the mostly round branch and stem sections above or around this had
their basal diameters estimated by using a Criterion 400 survey laser (Laser
Technology, Inc., Centennial, CO, U.S.A.). System lengths were either measured
directly or interpreted from detailed photos of the tree structure without leaves.
Parabolic or conic equations were used for these smaller systems based on how
robust and foliated each system was.
Sample collection. The wood samples were collected from the false
cavity walls in the time frame 2008-2011, by using Haglöf CH 600 (0.60 m long,
0.0054 m inner diametre) and Haglöf CH 800 (0.80 m, 0.0108 m) increment
borers. A number of tiny pieces/segments of the length of 0.001 m were extracted
from each wood sample. The segments were processed and investigated by
AMS radiocarbon dating.
RADIOCARBON DATING OF A VERY LARGE AFRICAN BAOBAB FROM LIMPOPO, SOUTH AFRICA
363
Sample preparation. AMS measurements. See our first article in this
issue [16].
Calibration. Radiocarbon dates were converted into calendar ages with
OxCal v4.2 for Windows [17], using the SHCal13 atmospheric set [18].
ACKNOWLEDGMENTS
Authors thank Diana H. Mayne and Sarah Venter for collecting samples,
for participating in field investigations of the baobab and for helpful discussions.
The research was funded by the Romanian Ministry of Scientific Research CNCS-
UEFISCDI under grant PN-II-ID-PCE-2013-76.
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