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Age determination of large live trees with inner cavities:
radiocarbon dating of Platland tree, a giant African
baobab
Patrut, Karl Reden, Pelt, Diana Mayne, Daniel Lowy, Margineanu
To cite this version:
Patrut, Karl Reden, Pelt, Diana Mayne, Daniel Lowy, et al.. Age determination of large live
trees with inner cavities: radiocarbon dating of Platland tree, a giant African baobab. Annals
of Forest Science, Springer Verlag (Germany), 2011, 68 (5), pp.993-1003. <10.1007/s13595-
011-0107-x>.<hal-00930675>
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ORIGINAL PAPER
Age determination of large live trees with inner cavities:
radiocarbon dating of Platland tree, a giant African baobab
Adrian Patrut &Karl F. von Reden &Robert Van Pelt &
Diana H. Mayne &Daniel A. Lowy &Dragos Margineanu
Received: 9 October 2010 / Accepted: 23 January 2011 / Published online: 1 July 2011
#INRA and Springer Science+Business Media B.V. 2011
Abstract
&Introduction For large trees without a continuous
sequence of growth rings in their trunk, such as the African
baobab (Adansonia digitata L.), the only accurate method
for age determination is radiocarbon dating. As of today,
this method was limited to dating samples collected from
the remains of dead specimens.
&Methods Our research extends significantly the dating of
such trees to large live specimens with inner cavities. The
new approach is based on collecting samples from the
cavities and their subsequent radiocarbon dating.
&Results The giant two-stemmed Platland tree, also known
as Sunland baobab, was investigated by using this new
approach. AMS radiocarbon dates of the oldest sample
segments originating from the two inner cavities indicate
that the large stem I (364.5 m
3
) is 750±75 years old, while
the much smaller stem II (136.7 m
3
) has 1,060±75 years.
Results also show that stem I is still growing very fast,
while the older stem II slowed down consistently its growth
over the past 250 years. The complete mapping of Platland
tree determined an overall wood volume of 501.2 m
3
.
&Conclusions Dating results demonstrate that the size–age
relation cannot be used for estimating accurately the age of
African baobabs.
Keywords Adansonia digitata .Radiocarbon dating .Age
determination .Growth rate .Accelerator mass spectrometry
1 Introduction
For trees which exhibit annual or seasonal growth rings,
ring counting, possibly refined by cross-dating, represents
the most accurate and reproducible method for age and
growth rate determination. Ring counting is typically
performed on the remaining stumps of dead trees. Never-
theless, there are several cases in which this procedure
cannot be utilized. Relevant examples are trees with growth
rings that are not strictly annual or seasonal, with no well-
defined rings or without a continuous sequence of rings, as
a consequence of their hollow parts. In such cases, ring
counting is replaced by alternative direct (radiocarbon
dating) or indirect dating methods (relation size/diameter-
age, projections of short-term growth data, projections
based on mortality rates, etc.) (Worbes 2002; Patrut et al.
2010a). The most investigated species of this type is the
African baobab (Adansonia digitata L.), the angiosperm
with the stoutest trunk. For large and old baobabs, a
Handling Editor: Erwin Dreyer
A. Patrut (*):D. Margineanu
Department of Chemistry, Babes-Bolyai University,
Arany Janos 11,
400028 Cluj-Napoca, Romania
e-mail: apatrut@gmail.com
K. F. von Reden
NOSAMS Facility, Department of Geology & Geophysics,
Woods Hole Oceanographic Institution,
Woods Hole, MA 02543, USA
R. Van Pelt
College of Forest Resources, Box 352100,
University of Washington,
Seattle, WA 98195, USA
D. H. Mayne
Baobab Trust,
Parklands 2121,
Johannesburg, South Africa
D. A. Lowy
FlexEl, LLC,
College Park, MD 20742, USA
Annals of Forest Science (2011) 68:993–1003
DOI 10.1007/s13595-011-0107-x
hypothetically accurate ring counting is not possible, as
growth rings may no longer be observed in certain areas
ofthetrunkandtheyarealsomissingintheareaoflarge
cavities.
As indirect methods often provide questionable results,
radiocarbon investigation represents the only alternative
method for the accurate dating of such trees. Given its
higher costs, so far, radiocarbon dating was not used on the
large scale. Several noteworthy investigations were per-
formed, however, on different tropical species, for deter-
mining the age of trees and/or growth rates, for accurately
dating the observed growth rings, for checking and
correcting ring counting, or for providing climate informa-
tion (Martinez-Ramos and Alvarez-Buylla 1998; Worbes
and Junk 1999; Poussart et al. 2006). Traditionally, for large
trees, such as the African baobab, this research was
limited to dating wood samples collected from the
remains of dead specimens, which decay very fast (Swart
1963;Patrutetal.2007). Work reported here extends
considerably the possibility of aging African baobabs, by
introducing a methodology which allows, to date standing
and live specimens. This new approach is based on
radiocarbon dating of very small wood samples collected
from the inner cavities of live baobabs. The first live
specimen investigated by this methodology was the huge
two-stemmedPlatlandtree.
Dating results for segments extracted from samples
originating from the two cavities of Platland tree, which
correspond to a depth of over 20 cm in the wood, are
presented and discussed. As these segments consist of
the original old wood, dating results made it possible to
determine the age of the two stems of Platland tree,
which was the main goal of our research. We also present
for the first time results of the complete mapping of a
large African baobab. The age difference of the two
stems is discussed in the framework of the questionable
size–age relation.
2 Materials and methods
2.1 Dating live African baobabs
The main characteristics of the new approach for age
determination of large live trees via dating samples
collected from their inner cavities, applied to the case of
the African baobab, can be summarized as follows:
1. Collection of samples from inner cavities through
cavity walls and subsequent radiocarbon dating of
these samples define the new methodology.
2. The extant wood collected with an increment borer
from cavities, at depth values exceeding 20 cm, is the
original old wood which corresponds to the respective
positions. Such a depth is needed for excluding
successive regrowth layers triggered by cavity fires
and also by a somewhat limited ability of the baobab of
repairing its wounds, i.e., for closing its cavity. A 60-
cm increment borer is more than sufficient for reaching
the original old wood and preventing collection of any
regrowth layer.
3. The age of an investigated baobab is calculated by
extrapolating age values of the oldest radiocarbon-dated
samples to the symmetry/geometric center of the trunk
at that height. Extrapolation is done by using growth
rate values of the trunk, calculated from different
sample ages, as well by considering growth rate values
reported in the literature.
4. The symmetry center at a certain height above ground
level can be accurately determined from a cross-section
of the trunk at this height.
5. In order to evaluate more accurately both the age and
the growth rate dynamics, one collects additional
(younger) samples from the exterior (through the bark);
these samples are also radiocarbon dated.
6. Usually, the pith of a tree, including the African
baobab, is not perfectly centered. However, with the
exception of certain individuals with a highly
irregular trunk, it is reasonable to assume that in
single-stemmed baobabs, the pith is relatively close
to the symmetry center of the trunk. If one assigns
the symmetry center to the pith and one considers the
fast growth rate of young baobabs, an additional
error of ±50 years for the final age value would
cover for all these assumptions.
7. In the case of baobabs with a multi-stemmed trunk,
the current symmetry center of a stem cannot be
assigned to its pith. One should consider that, after
fusion, the growth of stems continued only in
directions where there was room for accommodating
their growth. Thus, one must calculate the symmetry
center of a stem prior to fusion, which can be
reasonably approximated by the pith. The moment of
fusion must be estimated from the age of samples
collected from the fusion area.
2.2 The study area
The Platland tree (Fig. 1) is located on the Sunland Nursery
of the Platland farm, 10 km from Modjadjiskloof (formerly
Duiwelskloof) and 25 km from Tzaneen in the Limpopo
Province, South Africa. Its GPS coordinates are 23°37.255′
S, 030°11.884′E, and the altitude is 719 m. Mean annual
rainfall in the area is 492 mm (Mooketsi station; 1925–
2009).
994 A. Patrut et al.
2.3 Measurements
The common external measurements of the Platland tree and the
measurements inside the two inner cavities were performed by
using a Bosch DLE 70 Professional laser rangefinder (Robert
Bosch GmbH, Stuttgart, Germany) and graduated tapes.
Cross-sections of the Platland tree at ground level, 1, 2, 2.5,
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
Fig. 1 (top) The very impressive Platland tree, which is also called
Sunland baobab. General view taken from the east; (bottom) The
image taken from the north shows the two-stemmed trunk of Platland
tree, with the larger and taller stem I to the left, while stem II is on the
right. The fusion area of the stems can also be observed
Age determination of large live trees 995
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.
2.4 Sample collection
Seven wood samples (numbered 1 to 7) were collected from
different positions of the walls of the two cavities of Platland
tree, according to the previously described methodology. Due
to the irregular profile of the cavities' walls, the inner samples
originate from heights of 0.40–1.70 m above cavity level. A
number of three additional samples (numbered 11 to 13)
were collected from the exterior of the two stems through the
bark. The sampling was performed at heights of 1.20–2.75 m
above ground level. All samples were obtained by using a
Haglöf CO600 increment borer (60 cm long, 0.43 cm inner
diameter) (Haglöf Sweden AB, Langsele, Sweden).
The projections of sampling points on a cross-section of
the trunk with the cavities included are shown in Fig. 2.
One should mention that all seven samples collected from
the two large cavities, as well the three samples collected
from the exterior, were shorter than 60 cm, having lengths
between 22 and 51 cm. These values indicate the existence
of additional hollow parts between the open cavities and the
exterior of the stems. Segments with a length of 0.5 cm
were extracted from determined positions of the original ten
samples. The segments were processed and investigated by
accelerator mass spectrometry (AMS) radiocarbon dating.
2.5 Sample/segment preparation
The standard acid–base–acid pretreatment method (Olsson
1986) was used to remove soluble and mobile organic
components. The resulting cellulose samples were combusted
to CO
2
by using the closed tube combustion method (Sofer
1980). Then, CO
2
was reduced to graphite on iron catalyst,
under hydrogen atmosphere (Vogel et al. 1984). Eventually,
the resulting graphite samples were analyzed by AMS.
2.6 AMS measurements
Radiocarbon measurements were carried out at the National
Ocean Sciences AMS Facility of the Woods Hole Ocean-
ographic Institution with the Pelletron ® Tandem 500 kV
AMS system (Roberts et al. 2010) and the Tandetron 3MV
AMS system (von Reden et al. 1994). The surface of the
graphite samples was sputtered with cesium ions, and the
secondary negative ions were extracted and accelerated in
the AMS system.
12
C and
13
C ions were measured in
Faraday cups, where a ratio of their currents was recorded.
Simultaneously,
14
C ions were recorded in a particle
detector, so that instantaneous ratios of
14
Cto
12
C were
also recorded. These raw signals were compared to ratios
obtained with a known standard material (Oxalic Acid I,
NIST-SRM-4990) and converted to a fraction modern
value, which was corrected for isotopic fractionation with
the normalized δ
13
C value of −25
0
/
00
. Fraction modern
values were ultimately converted to a radiocarbon date.
2.7 Calibration
Fraction modern values were calibrated and converted into
calendar ages with the OxCal v4.1 for Windows (Bronk
Ramsey 2009), by using the IntCal09 atmospheric data set
(Reimer et al. 2009).
3 Results
3.1 Mapping results
The trunk of Platland tree, which consists of two stems (I
and II), has a total circumference at breast height (cbh;
1.30 m above ground level) of 34.11 m and a footprint of
67.9 m
2
, which corresponds to a functional diameter of
9.30 m at ground level. It is to mention that the huge trunk
is covered by a very thin silver colored bark, which is less
than 1 mm thick. The canopy dimensions are of 37.7 m (in
direction NS) and 32.4 m (in direction WE).
The larger stem I has a height of 18.9 m, a cbh value of
24.20 m, a footprint of 43.9 m
2
, and a cross-sectional area
Fig. 2 Cross-section of the two-stemmed Platland tree (at 1 m above
ground), showing the two connected cavities (displayed at cavity
level), the positions of the ten sampling points and the sampling
directions. Because the samples were collected at various heights,
several sampling points are not located right on the contour of the
cavity or of stems, which are figured at a well-defined height
996 A. Patrut et al.
at bh of 42.7 m
2
. The formal diameter at bh calculated from
the cbh value in circular approximation is 7.70 m, while the
much more accurate functional dbh derived from the cross-
sectional area at bh is of 7.37 m. The smaller stem II has the
height of 15.8 m, a cbh value of 18.34 m, a footprint of
24.0 m
2
, and the cross-sectional area at bh of 23.3 m
2
.In
this case, the formal dbh is 5.84 m, while the functional dbh
becomes 5.45 m.
The two stems are connected by a fused section, which
covers a shared cbh of 4.10 m and has a maximum height of
2.20 m. The trunk comprises two interleading cavities on either
side of the fused section, connected by a small opening/
doorway. The very large cavity inside stem I has a maximum
length of 4.60 m, a width of 4.81 m, and a height of 4.88 m. The
irregular cavity inside stem II has a maximum length of 1.67 m,
amaximumwidthof2.50m,andaheightof2.47m;italsohas
an elevated extension towards the north, with a length of
2.24 m. The basal surface of cavity inside stem I is 15.9 m
2
,
while the cavity inside stem II has the surface of 2.8 m
2
.
There is also an elevated cavity located inside stem I, at the
height of 5.80 m. This cavity with two entrances, which is
visited and used by birds as a night shelter, has the maximum
dimensions of ca. 2×2 ×1.5 m.
For hollow baobabs, the large cavities are located at ground
level or, more seldom, at a certain height above ground.
However, for the Platland tree, the level of cavities is at 0.78 m
below the current ground level, suggesting that the inside level
corresponds to the original ground level. The increase of the
ground level over the past centuries is very probably the result
of mud and sediment left behind by several flood episodes of a
creek located in the close proximity of the tree. One can state
that today, the trunk/base of the Platland tree is buried in the
soil up to the height of 0.78 m. After 1990, the new owners of
the Platland farm opened a pub in the very large cavity inside
stem I. Consequently, the tree has become heavily promoted
as the Sunland “pub”baobab.
Formally, one can consider the Platland tree composed of
two sections: Platland I (stem I and the corresponding
branches) and Platland II (stem II and the corresponding
branches). The total wood volume of the Platland tree
above the present ground level was found to be 448.2 m
3
,
i.e., 273.1 m
3
below 5 m and 175.1 m
3
over 5 m. This total
volume of 448.2 m
3
above ground level consists of the
volume of Platland I, which is 330.2 m
3
, and the volume of
Platland II, which measures 118.0 m
3
. Nevertheless, the
overall wood volume of stems and branches should be
calculated above the cavities level, which is the initial
ground level. Thus, the overall wood volume of the
Platland tree becomes 501.2 m
3
, out of which 364.5 m
3
for stem I and 136.7 m
3
for stem II.
Cross-sections of the Platland tree at different heights are
displayed in Fig. 3. The measured and calculated charac-
teristic parameters of the Platland tree are summarized in
Table 1.
3.2 AMS results and calibrated ages
Fraction modern values and radiocarbon dates of the oldest
segment of each of the 10 samples collected from the
cavities and from the exterior, which were labeled by the
sample code/number followed by the additional index x, are
listed in Tables 2and 3. Radiocarbon dates and errors were
rounded to the nearest year.
For calibration, we used the general IntCal09 data set
(Reimer et al. 2009), rather than the SHCal04 data set for
the Southern Hemisphere (McCormack et al. 2004). Our
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 offset between
calibrated ages obtained when using the two calibration
data sets is of several decades.
Calibrated (cal) ages are also displayed in Tables 2and 3.
The 1-σprobability distribution was chosen to derive
calibrated age ranges. For three segments (1x,3x,7x), the
1-σdistribution is consistent with only one range of
calendar years (marked in italics), while for the other seven
segments (2x,4x,5x,6x,11x,12x,13x), the 1-σdistribution
corresponds to several ranges of calendar years. For these
segments, the confidence interval of one range (marked in
italics) is much greater than of the others; therefore, it was
selected as the cal AD range of the segment for the purpose
of this discussion.
Fig. 3 Cross-sectional areas of the trunk/stems of Platland tree at
different heights (ground level, 1 m, 2 m, 2.5 m, and 5 m)
Age determination of large live trees 997
For obtaining single calendar age values of segments, we
derived a mean calendar age of each segment from the 1-σ
range with the highest probability. Calendar ages of segments
represent the difference between AD 2010 and the mean value
of the selected 1-σrange, with the corresponding error.
Calendar ages and errors were rounded to the nearest 5 years.
Table 2 AMS radiocarbon dating results and calibrated calendar ages of the oldest segments of samples collected from the cavities
Segment code
[stem]
Depth
a
[height
b
]
(10
−2
m)
Fraction modern
[error]
Radiocarbon date
[error]
(
14
C years BP)
Cal AD range(s)
1-σ
[confidence interval]
Segment age
[error]
(calendar years)
1x[I] 23 [148] 0.9401 [±0.0034] 496 [±27] 1415–1438 [68.2 %] 585 [±10]
2x[I] 21 [145] 0.9316 [±0.0036] 569 [±29] 1320–1350 [39.8 %] 675 [±15]
1391–1412 [28.4%]
3x[I] 25 [90] 0.9501 [±0.0034] 411 [±27] 1441–1485 [68.2%] 545 [±20]
4x[I] 48 [50] 0.9601 [±0.0022] 327 [±18] 1515–1529 [10.4%] 440 [±20]
1542–1599 [44.8%]
1618–1634 [13.0%]
5x[II] 45 [102] 0.9597 [±0.0033] 330 [±27] 1495–1529 [18.2%] 440 [±30]
1541–1602 [38.2%]
1616–1634 [11.8%]
6x[II] 21 [170] 0.8930 [±0.0029] 909 [±23] 1045–1095 [39.6%] 940 [±25]
1120–1142 [16.0%]
1147–1164 [12.6%]
7x[II] 23 [40] 0.9003 [±0.0030] 845 [±24] 1168–1221 [68.2%] 815 [±25]
a
Depth in the wood of the oldest dated segment (from the cavity wall)
b
Height above cavity level (which is 0.78 m below ground level)
Parameter (unit) Platland tree Platland I Platland II
Height (m) 18.9 18.9 15.8
Circumference at bh (m) 34.11 24.20 18.34
Formal diameter at bh (m) 10.86 7.70 5.84
Footprint (m
2
) 67.9 43.9 24.0
Basal functional diameter (m) 9.30 7.48 5.43
Cross-sectional area at 1 m (m
2
) 66.8 43.2 23.6
Cross-sectional area at bh (m) 66.0 42.7 23.3
Functional diameter at bh (m) 9.17 7.37 5.45
Cross-sectional area at 2 m (m
2
) 63.2 40.4 22.9
Cross-sectional area at 2.5 m (m
2
) 57.3 36.2 21.1
Cross-sectional area at 5 m (m
2
) 39.7 29.7 10.0
Wood volume below 5 m (m
3
) 273.1 186.8 86.3
Wood volume over 5 m (m
3
) 175.1 143.4 31.7
Total wood volume above ground level (m
3
) 448.2 330.2 118.0
Overall wood volume above cavities level (m
3
) 501.2 364.5 136.7
Cavity/cavities area (m
2
) 18.7 15.9 2.8
Table 1 Measured and calculated
main parameters of the
Platland tree
998 A. Patrut et al.
3.3 Dating results of samples collected from the cavities
The segments of samples collected from the cavities of Platland
tree, which correspond to a depth in the wood up to 15–20 cm,
consisted exclusively of new growth layers triggered by
successive fires. The dating results revealed six major fire
events that affected the cavities of the Platland tree, which were
dated around AD 1550, 1650, 1780, 1900, 1955, and 1990 (as
established by using the general IntCal04 or IntCal09
calibration); however, this investigation did not enable to
determine the age of the two stems (Patrut et al. 2010a).
Here, we present dating results of the oldest segment of
each of the seven cavity samples, labeled by an additional
index x. For a given sample, the oldest segment corresponds
to depths in the wood from 21 to 48 cm. The AMS results
and calibrated ages are listed in Table 2. The results are in
good agreement with the original positions of the respective
segments/samples in the two stems, showing that these
segments consist of the original old wood. The sequence of
segment ages demonstrates that the trunk of Platland tree
comprises two stems which fused partially some time ago.
The radiocarbon date of the oldest segment 2xoriginat-
ing from the cavity inside stem I was of 569± 29 BP (before
present, i.e., before AD 1950), which corresponds to a
calibrated age of 675±15 years. However, the oldest dated
segment 6xoriginates from the cavity inside stem II; its
radiocarbon date was of 909±23 BP, corresponding to a
calibrated age of 940±25 years.
The radiocarbon dates of the deepest segments collected
from the two cavities toward the fusion/common area, i.e.,
4xand 5x, were 327±18 and 330±27 BP, respectively. These
values correspond to calibrated ages of 440 ±20 and 440±
30 years. The practically identical values indicate that the
two stems of Platland tree fused partially at least 440 years
ago. Consequently, one can consider that the stems of
Platland tree fused ca. 450 years ago, around AD 1560.
3.4 Dating results of samples collected from the exterior
The dating results and calibrated ages of the deepest and
oldest segments of the three samples collected from the
exterior of stems are shown in Table 3. The two deepest
segments (45 and 51 cm) originating from stem I, i.e., 11x
and 12x, at different heights above ground (1.34 and
2.75 m), were radiocarbon dated to 49±27 and 122±25 BP.
The corresponding calibrated ages are 120± 25 and 150±
25 years.
The deepest segment 13x(20 cm) originating from stem
II, at a height of 1.20 m above ground, had a radiocarbon
date of 170±22 BP, with a corresponding calibrated age of
250±25 years.
3.5 Growth rates of the stems
Calibrated ages and positions of segments 11xand 12x,
which originate from samples collected from the exterior of
stem I, were used to derive the mean radial increase. Thus,
stem I had grown by 3.75×10
−3
m year
−1
over the past ca.
120 years to the height of 1.34 m, and by 3.40×
10
−3
m year
−1
over the past ca. 150 years to the height of
Table 3 AMS radiocarbon dating results and calibrated calendar ages of the oldest segments of samples collected from the exterior
Segment code
[stem]
Depth
a
[height
b
]
(10
−2
m)
Fraction modern
[error]
Radiocarbon date
[error]
(
14
C years BP)
Cal AD range(s)
1-σ
[confidence interval]
Segment age
[error]
(calendar years)
11x[I] 45 [134] 0.9939 [±0.0034] 49 [±27] 1706–1720 [12.1 %] 120 [±25]
1819–1833 [10.4%]
1862–1915 [45.7%]
12x[I] 51 [275] 0.9849 [±0.0031] 122 [±25] 1685–1707 [12.1%] 150 [±25]
1719–1732 [7.1%]
1808–1826 [9.2%]
1833–1885 [31.5%]
1913–1928 [8.2%]
13x[II] 20 [120] 0.9791 [±0.0028] 170 [±22] 1669–1682 [11.6%] 250 [±25]
1736–1781 [40.1%]
1799–1805 [5.5%]
1931–1945 [11.0%]
a
Depth in the wood of the oldest dated segment (from the bark)
b
Height above ground level
Age determination of large live trees 999
2.75 m. Such high values indicate that the very large stem I
is still growing very fast.
However, as reported elsewhere (Patrut et al. 2010b), the
mean radial increase expresses only an apparent growth rate
of trunk/stems. Trees grow in three dimensions and their size
is accurately expressed by the wood volume of the trunk/
stems, which is in proportion to the cross-sectional areas at
different heights. Consequently, the area increase and volume
increase are much better estimates of the growth rate than the
radial increase. If one considers in this respect the dating
results and positions of all six samples/segments collected
from the cavity and the exterior of stem I, one can state that
stem I accelerated its growth over the past ca. 150 years.
This result corresponds to our previous research on African
baobabs (Patrut et al. 2010b), as well to other research done
on giant tree species (Sillett et al.2010).
The calibrated age and position of segment 13x, which
originates from the sample collected from the exterior of
stem II, shows that this stem had grown by only 0.80 ×
10
−3
m year
−1
over the past ca. 250 years to the height of
1.20 m. This low value demonstrates that the smaller and
older stem II slowed down its growth considerably and that
it could be close to the final stage of the African baobab's
life cycle, when trees almost stop growing.
3.6 Ages of the stems
The oldest segments 2xand 6xfrom the cavities inside stem
I and stem II consist of the original old wood, which
corresponds to the respective positions in the stems. The
extrapolation of their calibrated ages to the presumptive
center/pith of each stem enabled us for determining the ages
of the two stems of Platland tree.
The segments 2xand 6xoriginate from heights of 1.45
and 1.70 m above cavity level, corresponding to values of
0.67 and 0.92 m above ground. For extrapolation, we used
field measurements, as well a cross-section of the two
stems at 1 m, which is close to the segment heights
(see Fig. 4).
The cross-sections at ground level and at 1 m show that
both stems of the Platland tree have relatively symmetrical
transversal sections, with quasi-ellipsoidal shapes. In this
case, for determining the presumptive center/pith of each
stem, i.e., the symmetry center, it is sufficient using the axes
which touch the center of the fusion section.
Age of stem I In the cross-section of stem I, we displayed
the minor axis of the ellipse, from an external point Y to the
fusion point O, which is the conjugate diameter from SE to
NW. Its length is YO=7.40 m. The present center of stem I
can be approximated with the midpoint of the axis YO,
denoted as C
I
. In this case, the two minor semi-axes/minor
radii are YC
I
=C
I
O=3.70 m.
It is mandatory, however, to determine the presumptive
position of the original center/pith of stem I, labeled C
I(o)
,
which can be approximated by the midpoint of the conjugate
diameter at the fusion moment, that occurred ca. 450 years
ago. After fusion, stem I had no more room for growing in
direction NW. Therefore, the original center C
I(o)
is shifted
toward NW relative to the present center C
I
. Therefore, we
calculated the linear increase in radius of stem I over the past
450 years, in direction SE. The age of segment 11xindicates
that stem I had grown toward SE by 0.45 m over the past ca.
120 years. In a very conservative estimate, if we consider
that this relatively large mean radial increase was constant
over the past 450 years, the radial increase toward SE over
this period was of ca. 1.70 m. In this case, the corresponding
axis/diameterofstemIwasof7.40−1.70= 5.70 m at the
fusion time, with the two semi-axis/radii, including C
I(o)
−O,
of 2.85 m. Thus, the distance between the present center C
I
and the original center C
I(o)
becomes C
I
−C
I(o)
=0.85 m.
The point 2x, which represents the intercept with the YO
axis of the virtual annual ring corresponding to the
position of segment 2x, is located at 3.75 m from the
external point Y and at 0.80 m from the original center
C
I(o)
,i.e.,Y−2x=3.75 m and 2x−C
I(o)
=0.80 m.
In order to determine the age of stem I, one should
add to the age of the oldest segment 2x(675± 25 years)
the time needed by stem I for growing from 0 to a radius
of 0.80 m. The growth rate of African baobabs, especially
during their early life stage, is very different. However, if
we consider that the stem I of Platland tree had grown fast
and it is still fast growing, then, based on its current
dimensions, sample ages and also our previous research
(Patrutetal.2010b), one can estimate that the time needed
tostemIforreachingaradiusof0.80mwasofca.
75 years. All these approximations sum to a maximum
Fig. 4 Cross-section of the two stems (at 1 m above ground) showing
the accurate positions of the oldest dated segments from each cavity
(2x,6x), along with the present center (C
I
,C
II
) and the original center
(C
I(o)
,C
II(o)
) of each stem
1000 A. Patrut et al.
error of ±75 years for the final age of stem I, including the
age error of segment 2x. Hence, the calculated final age of
stem I is 750±75 years. One can state that it started
growing around AD 1260.
Age of stem II In this case, we showed in the cross-section
of stem II the major axis of the ellipse, from an external
point Z to the fusion point O. This is also the transverse
diameter from NW to SE, with a length ZO =6.44 m. The
present center of stem II can be approximated by the
midpoint of the axis ZO, marked as C
II
. The two major
semi-axes/major radii are ZC
II
=C
II
O=3.22 m.
The original center/pith of stem II, labeled C
II(o)
, can be
approximated by the midpoint of the transverse diameter at
the fusion moment. After fusion, stem II had no more room
for growing in direction SE. Consequently, the original
center C
II(o)
is shifted toward SE relative to the present
center C
II
. For calculating the increase in radius of stem II
over the past 450 years toward NW, we used the age of
sample 13x, which indicates a growth of 0.20 m over the
past 250 years. As stated, this low value indicates that the
growth of stem II slowed down considerably over this time
frame. If one considers that the mean radial increase was
around twice faster from the fusion moment up to 250 years
ago, the linear increase toward NW over the past 450 years
was of ca. 0.52 m. Thus, the corresponding axis/diameter of
stem II was of 6.44−0.52=5.92 m at the fusion time, with the
two semi-axis/radii, including C
II(o)
−O of 2.96 m. The
distance between the present center C
II
and the original
center C
II(o)
becomes C
II
−C
II(o)
=0.26 m. The segment 6x
was practically positioned on the axis ZO, at 2.02 m from
the fusion point O and at 0.94 m from the original center
C
II(o)
,i.e.,O−6x=2.02 m and 6x−C
II(o)
=0.94 m.
For determining the age of the stem II, one should add to
the age of the oldest segment 6x(940±25 years) the time
needed to stem II for growing from 0 to a radius of 0.94 m.
If we consider that the stem II of Platland tree has grown
much slower than stem I, its smaller dimensions, the older
sample ages and also our previous research, we can
estimate that the time needed to stem II for reaching a
radius of 0.94 m was of ca. 120 years. All approximations
are within the final error of ± 75 years. The calculated final
age of stem II becomes 1,060 ±75 years, indicating that it
started growing around AD 950.
4 Discussion
4.1 The size of Platland tree
The Platland tree is listed in the South African National
Register of Big Trees and is included in the South African
List of Champion Trees (Esterhuyse et al. 2001; Depart-
ment of Water Affairs and Forestry 2008). The only
accurate parameter of the true size of a tree is the wood
volume. The overall wood volume of Platland tree
(501.2 m
3
) is considerably larger than that of the Sagole
tree (414.1 m
3
), which is generally considered to be the
biggest baobab (Van Pelt, unpublished results). Therefore,
according to the volume values reported here, the Platland
tree becomes the largest known African baobab.
4.2 The relation size–age in the case of Platland tree's stems
Commonly, one considers that the life span/longevity of a
tree specimen, in our case of an African baobab, depends
on several factors: (1) its genetic potential; (2) the
environment (including mean annual rainfall, altitude, mean
annual temperature, number of rainy seasons per year,
number of frosty days per year, nature of the soil, slope of
the land, availability to underground water sources, etc.);
(3) the number and severity of dangerous events and
disease episodes during its life cycle (fire episodes, fungi
attack, insects, baobab disease, elephant damage, human
damage, drought periods, flood, frost episodes, etc.).
Theoretically, individuals having all these factors iden-
tical should grow over time at the same rate. Consequently,
under identical conditions, the biggest/largest trees may
also be the oldest. Such considerations justify the common
fallacy about trees that size is in direct proportion to their
age. Certain baobab researchers noted, however, consider-
able size differences between individuals of identical age,
which were attributed to site differences. Moreover,
important size differences between specimens growing on
the same site were reported; these dissimilarities were
considered to be mainly of genetic origin (Breitenbach
1985; Wickens and Lowe 2008).
Our study on the Platland tree demonstrates, once again,
how questionable the size–age relation is and the large
errors it can generate. According to complete measurements
and dating results, the very large stem I is considerably
younger than the smaller stem II (overall wood volume
364.5 vs. 136.7 m
3
; age 750 vs. 1,060 years). A preliminary
genetic research (Catana and Patrut, unpublished results)
suggested that the two stems of Platland tree possess
identical DNA and belong to a single individual. The two
stems have also grown on the same site. In this case, we
need an explanation for the unexpected finding that a stem
which is almost three times bigger is, however, over
300 years younger than the smaller stem of the same tree.
Researchers of tall and large tree species around the
world learned from their field experience that the largest
specimens are usually not also the oldest. Typically, the
largest specimens are those which had grown very fast
when they were young and, eventually, continued their
Age determination of large live trees 1001
rapid growth (Hartesveldt et al. 1975). The research
reported here demonstrates that such statements might be
also valid for the African baobab. Our research on
radiocarbon dating of baobabs (Patrut et al. 2010c), as well
dating results presented by other researchers (Swart 1963;
Woodborne et al. 2010) show that very large specimens are
not necessarily among the oldest trees and that medium-
sized individuals can also be very old. If one considers that
the largest baobabs are those which grew very fast over
their first ca. 100 years of life and maintained their rapid
growth, we may have an explanation for our results on the
two stems of Platland tree. In this case, stem I had probably
grown much faster and is also considerably bigger, as the
climate conditions in the area over its first century of life
(ca. AD 1260–1360) were probably much more favorable
for baobabs than over the first century of stem II (ca. AD
950–1050).
4.3 The Platland tree system
According to dating results, the present trunk of the
Platland tree comprises two stems of different ages.
Therefore, morphologically, it can be considered a double
tree. On the other hand, according to the preliminary
genetic analysis, the Platland tree is a single individual.
Both stems sprouted very probably from the same
rootstock at different times and, therefore, they have
identical DNA.
However, in the case of multi-stemmed and multi-
generation baobabs, such as the Platland tree, it is a difficult
to state whether they are single or multiple trees. They
should be rather considered “tree systems”, with a complex
development over a long life cycle. Over time, stems might
die and collapse, while new stems can sprout at any
moment from the roots or from the other broken or
unbroken stems.
Based on the dating results, stem II of Platland tree had
grown over 300 years without being disturbed by the
presence of another stem. Nevertheless, it has an important
lean toward NW (up to 40°) and the cross-sections show an
obvious miss in its ellipsoidal shape in the present fusion
area. These aspects suggest that stem II could have been
pushed constantly toward NW after it started growing,
possibly by a larger and older stem 0, located approximate-
ly on the site of stem I. In this hypothetical scenario, stem
0 died and collapsed at a certain moment and was
“replaced”by the present stem I, which might have
emerged from its remains. However, it is improbable that
stem I would still comprise somewhere old wood traces
originating from stem 0. If this scenario had happened,
then the multi-stemmed and multi-generation Platland tree
system should be much older than the age we derived from
radiocarbon dating.
Acknowledgements This work was fully funded by the Romanian
Authority CNCSIS-UEFISCDI under grant PN II-IDEI 2354, Nr.
1092. AMS radiocarbon dating at the NOSAMS Facility is supported
by the U.S. National Science Foundation under Cooperative Agree-
ment OCE-0753487. We would like to thank Heather and Doug van
Heerden, the owners of Sunland Nursery, for granting permission for
on-site investigation and also for sampling the Platland tree.
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