Sheet n°273 - August 2007
ecosystems. Only 95 000
km² of this natural habitat now survives, just 8%
of the maximum surface
area reached during the
last Ice Age. Changes
that have occurred in
this tropical rainforest
for more than 100 000
years were studied by
a team of IRD researchers working jointly
with University of São
Paulo (1). Focus was placed on conifer species of
the genus Podocarpus,
endemic to the Brazilian
Atlantic forest. Aiming to
trace the forest’s history
during the Quaternary
era (2), the team combined data from three
disciplines: botany, palynology and genetics.
Results indicated that
this tropical rainforest
underwent successive
phases of regression
and expansion during
the course of the last
Ice Age. These fluctuations involved centres of
tree population that still
survive and appear to
be strongly linked to climate variations. Such a
finding should be useful
for identification of such
blocks of original forest,
refugia that could be the
basis for the forest’s
conservation in the face
of climate change.
Refugia of the Brazilian
Atlantic rainforest could be the
basis for its regeneration
© IRD/Marie-Pierre LEDRU
he Atlantic rainforest
T
in Brazil is one of the
Earth’s most threatened
In Brazil, the Atlantic forest is a large biodiversity reservoir, second in size only to the Amazonian forest
During the last glaciation, which ended
about 10 000 years Before Present (BP),
the Brazilian Atlantic forest extended over all
the eastern side of the country, covering more
than 1 200 000 km², 15% of Brazil’s territory.
Now only 95 000 km² of this natural habitat
survives, just 8% of its initial extent. It is still a
large biodiversity reservoir in Brazil, second
only to the Amazonian forest. On one hectare
of Atlantic forest the biologists recorded over
450 different tree species. But deforestation
and intensive farming methods make this
tropical forest one of Earth’s most seriously
threatened ecosystems. In the states of São
Paulo and Minas Gerais, regions where
agriculture has developed strongly in recent
years, the forest is largely fragmented, represented only as small blocks situated on the
abrupt slopes which plunge down towards
the Atlantic.
With the objective of analysing the changes
that have taken place in this ecosystem
over the Quaternary era, IRD researchers
and counterparts from the University of São
Paulo put together the results from three
scientific disciplines (botany, palynology,
genetics) applied to three species of the
tree genus Podocarpus: P. sellowii, P. lambertii and P. brasiliensis. These tropical trees
belong to the conifer family. They are good
indicators of geographical evolution of the
Atlantic forest with time, seeing that the
Brazilian species are endemic to this natural
habitat. Moreover, pollen grains from the
genus Podocarpus have a typical small bladder-like morphology and stay intact for a long
time in sediments. These two characteristics
make them good candidates for palynological studies.
The team recorded and then collected available plant material from different sites where
Atlantic forest stands are still present. This
involved 26 sampling points spread over a
rectangle 4000 km long by 500 km wide corresponding to the whole of the area of distribution of this ecosystem. They corresponded
to 26 different populations of Podocarpus.
This first investigation stage allowed subse-
>>
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CONTACTS :
MARIE-PIERRE LEDRU
Institut de recherche pour
le développement (IRD)
MONTPELLIER. DÉPARTEMENT
milieux et environnement
(DME), secteur - Glaciers et
ressources en eau d'altitude
- Indicateurs climatiques et environnementaux (GREATICE)
+33 (0)4 67 14 90 32
ledru@msem.univ-montp2.fr
PRESS OFFICE
+33 (0)1 48 03 75 19
presse@ird.fr
INDIGO, IRD PHOTO LIBRARY
+33 (0)1 48 03 78 99
indigo@ird.fr
www.ird.fr/indigo
IRD AUDIOVISUEL
+33 (0)1 48 02 56 24 ;
audiovisuel@bondy.ird.fr
www.audiovisuel.ird.fr/
REFERENCES :
MARIE-PIERRE LEDRU, MARIA LUISA
FERRAZ SALATINO, GREGORIO
CECCANTINI ET AL “Regional
assessement of impact climatic
change on the distribution of
tropical conifer in the lowlands
of South America”, Diversity and
Distributions, 2007
DOI: 10.1111/J.1472-4642.2007.00389.X
KEY-WORDS :
BOTANY, PALYNOLOGY,
GENETICS, PODOCARPUS,
ATLANTIC FOREST,
CLIMATE
sion, over an area twice the size of France,
was made possible only by the presence of
a mosaic of a multitude of patches of forest,
now dispersed sparsely over this arid terrain.
Predictions for climate changes for the next
few decades envisage an increase in the
duration and intensity of periods of drought in
the intertropical regions, as in Nordeste. If this
trend persists, the protection of such surviving
areas of Brazil’s Atlantic forest, these refugia,
will become essential for the conservation of
this ecosystem
Grégory Fléchet - IRD
Translation : Nicholas Flay
(1) This research work was financed by the Fondation
Amparo Pesquisa of the state of São Paulo
(2) The Quaternary era denotes a recent geological
period, which continues today. It is marked by alternating glacial and interglacial cycles and its lower boundary is set between 1.5 and 2.4 million years BP.
3) A group of living organisms descended from the
same ancestor which have certain characteristics in
common. The branches, classes, orders, families and
species are taxa. Here the term embraces all the species belonging to the genus Podocarpus.
© Sos Mata Atlantica
Sheet n°273 - August 2007
For further information
quent accurate genetic characterization of
each population. In parallel, six sedimentary
cores were taken at different latitudes where
Atlantic forest still grows so that analysis
could be made of the frequency of pollen
grains belonging to the Podocarpus genus
contained in the various samples collected.
The borehole sunk at Colônia (see Map)
in the state of São Paulo yielded a core
showing that the frequency of these pollen grains fluctuated with time; the phases
of expansion and regression of this taxon
(3) succeeded one another for periods of
varying length. Evidence for a rise in frequency of Podocarpus pollen grains was found for
periods of between 60 000 and 45 000 years
BP, then between 29 000 and 21 000 years
BP in the south of Brazil and between 16 000
and 15 000 years BP in the Nordeste region.
These fluctuating rises which occurred during
times of glaciation would correspond to phases of expansion of the Atlantic forest in these
regions.
In order to test this hypothesis, the
Franco-Brazilian team used techniques
from molecular biology. For each of the
26 pre-selected populations, the researchers
collected leaves of five individual trees of the
Podocarpus genus from which they extracted DNA. Nucleotide sequence amplification
was performed, then phylogenetic analysis.
Comparison was made between that analysis and the level of genetic differentiation
between each population of Podocarpus. The
scientists thus succeeded in delimiting three
large centres of original colonization distributed according to latitude.
The multidisciplinary approach also
showed that the expansion of tropical
conifer populations never occurred during
interglacial periods, in contrast to what usually
happened in our temperate latitudes. In the
tropics, the populations of Podocarpus that
make up the Atlantic forest in fact gained
ground in glacial periods owing to an increase
in humidity and a cooling of temperatures. At
present, in the Nordeste region where a more
arid climate prevails, this humid tropical forest
occurs in the form of small isolated populations. Nevertheless, it has not always been
like that. In that part of the country, the study
confirmed the notion that a dense rainforest
developed at 15 000 years BP. In the space
of about 10 years, its extremely rapid expan-
Location of the 6 core-sample boreholes and present
distribution of the Brazilian Atlantic rainforest (in grey).
Grégory Fléchet, coordinator
Délégation à l’information et à la communication
Tél. : +33(0)1 48 03 76 07 - fax : +33(0)1 40 36 24 55 - fichesactu@ird.fr