HOW OLD ARE TROPICAL TREES? THE PERSISTENCE OF A MYTH - Brill
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IAWA Journal, Val. 20 (3), 1999: 255-260
HOW OLD ARE TROPICAL TREES?
THE PERSISTENCE OF A MYTH
by
Martin Worbes 1 & Wolfgang Johannes Junk 2
SUMMARY
The recent report of ancient trees in the Amazon region (Chambers
et al. 1998) with a maximum radiocarbon dated age of about 1400
years for the long-living pioneer species Cariniana micrantha is dis-
cussed in the light of dendrochronological age determinations from
Africa and South America together with the results of indirect age
estimations from other sources. There is a tendency in the literature
to considerably overestimate the maximum ages of tropical trees.
Age determination by the direct counting of annual rings and mak-
ing estimations for hollow trees by measuring growth rates and diam-
eters result in ages between 400 and 500 years for the largest trunk
dimensions, e.g. in Cariniana legalis.
Key words: Age determination, dendrochronology, radiocarbon dat-
ing, tropical trees.
INTRODUCTION
Early scientists, such as Alexander von Humboldt (1815-1832) who visited tropical
forests, brought controversial impressions horne to Europe. On the one hand they
reported the inexhaustible richness of plants and animals and the rapid growth of
vegetation. On the other hand they found impressive tree giants which seemed to be
thousands of years old.
In the 1960s and early 70s the findings of the large productivity of some tropical
herbaceous plant communities were supported by reports of high net primary produc-
tion (NPP). Measurements of photosynthethic rates and climate modeling were ex-
trapolated to tropical forests (Lieth 1975) and strengthened the myth of highly pro-
ductive tropical forests. This raised the hopes of foresters, the logging industry, and
politieians that wood production eould be used as a persistent, quiekly renewable
resouree in tropical eountries. Deductions from NPP to wood production resuIted in
values of up to 18 t ha y-I (Bruenig 1996) whieh are three times higher than the pro-
duetion in temperate zones (Ellenberg et al. 1986). Only a few ealculations from
repeated diameter measurements (Jordan 1983) and from tree-ring analyses (Worbes
1997) indicated that the total wood produetion at only the most produetive sites in the
natural tropical forests equals the produetion of 6-7 t ha y -I in the temperate zones.
1) Forstbotanisches Institut, Büsgenweg 2, D-37077 Göttingen, Germany.
2) AG Tropenökologie, Max-Planck-Institut für Limnologie, D-24302 Plön, Germany.
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via free access256 IAWA Journal, Vol. 20 (3),1999
More recent research has focussed on the search for the oldest tropical forest tree,
stimulated by discussions on sustainable forest management, palaeoclimate, and car-
bon fluxes. The recent tendency is that the maximum age of tropical trees increases
rapidly from report to report, while the assumed growth rates decrease in the same
order (Clark & Clark 1992; Camargo et al. 1994; Koming & Balslev 1994; Condit
et al. 1995). The youngest report of a 1400-year-old Amazonian Cariniana micrantha
'tree in a terra firme forest (Chambers et al. 1998) follows this tendency. We feel that
the whole issue requires a critical discussion of different methods used and of the
results obtained in age determination of tropical trees.
METHODS TO ESTIMATE THE AGE OF TROPICAL TREES
There are four methods of age determination of living trees, one direct and three
indirect ones: age estimation by repeated diameter measurements (Lieberman et al.
1985), radiocarbon dating (e. g. Camargo et al. 1994), a mathematical approach based
on the estimation of mortality rates (e. g. Condit et al. 1995), and direct annual tree-
ring counting (e.g. Mariaux 1969).
• Repeated diameter measurements give information about the growth during the
measured period. Upscaling the data to the whole life span of the tree allows only
estimations because tree growth changes considerably depending on age and envi-
ronmental conditions (Worbes 1989).
• The interpretation of radiocarbon datings can be problematic. Ages of wood sam-
pIes oider than 50 years and younger than 350 years cannot be dated. The high
variation of atmospheric radiocarbon due to the Suess Effect results in up to five
possible ages for one radiocarbon age (Stuiver & Becker 1986). Five trees from
theAmazonian terra firme dated with the 14C method by Chambers et al. (1998) to
be between 200 and 300 years old could be much younger. Moreover, the variation
of the radiocarbon age cannot be added to the mean as it was done for the giant
Bertholletia excelsa tree from Para. This tree was originally reported by Camargo
et al. (1994) to be 440 ± 60 years old and not 500 years as was reported by Cham-
bers et al. (1998). Moreover, exceptional findings like the age of 1400 years for the
broadleaf Cariniana micrantha needs a confirmation of at least a repeated radio-
carbon measurement from the same tree sampie which apparently was not done.
• The estimation of a hypothetical age of 2000 years on the basis of mortality rates
in a tropical tree population (Swartzia simplex in Panama) is a mathematical exer-
cise which has never been confirmed by direct measurements (Condit et al. 1995).
• Growth rates and ages of tropical trees often give occasion to controversial dis-
cussions due to the assumed absence of annual tree rings. This is another of the
many myths about tropical forests, because in fact the existence of annual rings
in tropical trees under seasonal precipitation conditions has been proven since the
beginning of this century (Geiger 1915) and has meanwhile been confirmed in
numerous publications (Worbes & Junk 1989; overviews by Worbes 1992, 1995).
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A seasonal climate with one distinct dry season is widely distributed in the humid
tropics (Worbes 1995), e.g. in Central Amazonia. Tree-ring analyses give informa-
tion on individual growth rates and growth conditions during the whole life period
of the individiual tree. Therefore we are in a position to compare results from
direct tree-ring analyses with those from indirect methods.
RESULTS AND DISCUSSION
Estimations in Costa Rican (Lieberman et al. 1985) and Ecuadorian rain forests (Kor-
ning & Balslev 1994) derived from repeated diameter measurements used the slowest
observed growth trajectory to calculate a 'simulated life span' from dbh = 10 cm to
the largest observed diameter within one species. The hypothetical maximum age for
a small-stemmed mid-canopy species in Ecuador was 529 years (Koming & Balslev
1994). In reality, however, the cited investigations and our own findings (Klinge et al.
1996) point out that the largest diameters and highest growth rates were observed in
individuals of the upper storey, and that these trees must therefore be hundreds of
years younger than the artificiallifetime calculation suggests.
We directly counted on intact stern discs a maximum of 260 years for Guibourtia
tessmanii in Gabon (dbh = 84 cm) and 204 years for a Piranhea trifoliata (dbh = 60
cm) in the Central Amazonian floodplains. The trunks of the thickest (dbh > 1.2 m)
and probably oldest trees were generally hollow, even in trees with high wood density
and a high amount of heartwood substances (e.g., Piranhea trifoliata in Amazonian
floodplain forest, Manilkara sp. in the Venezuelan Gran Sabana). From some twenty
thousand cored trees in different forests between 34 and 62% showed damage in the
heartwood or were hollow due to attacks by aggressive fungi and high decomposition
rates in tropical environments (Lamprecht 1986). Therefore it is necessary to use
mean growth rates for a rough age estimation of hollow trees. Also the fact that the
trees investigated by us were comparably 'thin' needs an extrapolation to the observ-
ed diameters in the Amazonian terra firme.
On extremely nutrient-poor sites in the Rio Negro floodplains and in Venezuelan
highland forests we found a mean diameter increment of about 0.4 cm y-l in trees of
the upper crown layers. The growth rates of Cariniana micrantha, Dipteryx odorata
and Lecythis poiteaui (Chambers et al. 1998) in the Amazonian terra firme are in the
range (0.1 cm y-l ) ofthe slowest growing understorey shrubs (Psidium acutangulum)
in the Amazon floodplains which are exposed to a mean flood period of eight months
per year without any wood formation. Cariniana micrantha in the terra firme how-
ever is an emergent species and probably belongs to the group of long-living pio-
neers, such as Bombacopsis quinata, Swietenia macrophylla, Terminalia amazonica
in the Neotropics, Triplochiton scleroxylon in Africa or its South Brazilian counter-
part Cariniana legalis. One characteristic of this group is the moderate wood density
of up to 0.7 g cm- 3 as in C. micrantha (Loureiro & Silva 1968) which is usually as-
sociated with relatively high growth rates (Worbes 1989). For C. legalis we measured
0.5 cm diameter growth per year in a natural stand in the state of Säo Paulo, much
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via free access258 IAWA Journal, Vol. 20 (3),1999
higher than the C micrantha tree in the Amazonian terra firme. The oldest tree we
found was 2.75 m in diameter and hollow. We calculated from the growth rates of the
surrounding trees of this species a maximum age of between 400 and 500 years. It
seems to be impossible that an emergent long-living pioneer as Cariniana micrantha
grows much slower than all other species of this group and persists 2-3 times longer
than any other broadleaf tree species in the world.
These species never regenerate in the shade. From the time this Cariniana micrantha
was a seedling until an extremely old age, the tree must have been exposed to full
sunlight. Extremely low growth rates as estimated for this tree (Chambers et al. 1998)
are bound to a high mortality (Swaine et al. 1987) especially of light demanding
species and therefore do not lead to exceptional old ages. Considering the community
development it is evident that old individuals of large, long-living pioneer species
increase the survival chance of the population. Seedling establishment depends on
events of large-scale forest disturbance which occur at intervals of hundreds of years.
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This strategy requires fast growth in the youth in order to outcompete other pioneer
species until becoming established in the canopy. Many adult trees must survive for a
long time to produce a huge number of seeds for the reproduction in unpredictably
formed gaps in time. The combination of fast growth and longevity leads to enormous
trunk diameters of almost 2 m, as shown for the examples above, but not to excep-
tionally high ages. This is shown in Figure 1, where we plotted the diameter against
the age ofbig trees from our estimations, from Camargo et al. (1994) and from Cham-
bers et al. (1998). Our trees together with Bertholletia excelsa (Camargo et al. 1994)
form a relative small cluster with a regression coefficient of 0.73. The Carinana
micrantha tree however lies far outside of this regression due to its calculated excep-
tionallow growth rate. Assuming a realistic growth rate for the given species the tree
would not be older than 400-600 years. We cannot explain the difference between
our findings and the findings of Chambers et al. (1998) but propose arepetition of the
analysis or a dendrochronological confirmation.
In general the ages of individual Methuselahs provide little evidence for the inter-
pretation of the dynamics of any population. In the oldest growing broadleaf tree
species in North America (Quercus alba) and Central Europe (Quercus robur) trees
with an age of 600 years were found only exceptionally. The typical age in both cases
is only 300 years (Loehle 1988; Becker 1983). The rotation period of more or less
natural stands of Fagus sylvatica is about 200 years whereas the oldest individuals
have ages of about 400 years (Koop 1989).
The examples show that investigations on the growth of individual trees in the tropics
require direct age determinations by tree-ring analysis to confirm age estimations
achieved by indirect methods, and that a discussion of forest dynamics requires a
large number of growth data about the whole population.
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