Actualité scientifique
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N° 479
April 2015
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Amazonia: soil carbon stocks examined
The pasture land in the Amazon do not have the largest carbon storage potential they were supposed to deliver (© IRD / M. Grimaldi).
Along with the oceans and forests, soils are one of the planet’s main
carbon reservoirs. In the 20th century, carbon stocks fell dramatically due to
deforestation, intensive farming and the associated poor cultivation practices.
Consequently, large amounts of carbon have been emitted into the atmosphere
in the form of CO2 contributing to global warming…
IRD researchers and their partners have just published a summary in the Global
Change Biology journal on soil organic carbon stocks changes in Amazonia.
Useful facts
In Brazil, and to a lesser extent Colombia and Venezuela, a large part of the Amazonian rainforest has been cut
down to make way for extensive cattle farming from the 1960s, and more recently, annual crops such as soya and
maize. Although deforestation levels have fallen recently thanks to policies implemented in the Brazilian Amazon,
20,000 km² of forest disappeared each year between 1996 and 2005.
CONTACTS
Deforestation: a source of carbon emissions
Deforestation is a major contributor to
greenhouse gas emissions, particularly
carbon dioxide (CO2). It contributes in two
different ways: through the clearing and
burning of the trees, and through the soils
which are stripped and then cultivated.
Indeed, these soils then release, in the form
of CO2, the carbon they previously stored in
the form of organic matter.
This soil response after deforestation is
extremely diverse. In the current climate
change context, it is crucial that we
understand and characterise this response,
particularly in the Brazilian Amazon where,
up to now, the work carried out on this subject
had not been compiled.
A global view of the Brazilian Amazon
IRD researchers and their partners have
just published a summary in the Global
Change Biology journal, a meta-analysis
of carbon stock changes in the region’s
soils. To complete this analysis, they closely
examined around twenty studies conducted
from 1976 on cattle pasture land and soya
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They then compared the organic carbon
quantities measured in these deforested soils
with those recorded when they were initially
covered with forest.
Pasture land: a moderate restoration potential
However, researchers expected much higher
values in pasture land, which are thought
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potential. Furthermore, the increase in
carbon quantities from the grasses in pasture
land reaches a threshold after around twenty
years. Therefore, it certainly does not offset
global greenhouse gas emissions from
deforestation.
Lastly, this summary reveals that, contrary
to what is observed elsewhere in the world,
rainfall amounts have no impact on the
carbon storage capacity of Amazonian soils.
Coordination
Gaëlle COURCOUX
Information and Culture
Department
T. +33 (0)4 91 99 94 90
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www.ird.fr/la-mediatheque
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of different land management methods
such as overgrazing, labour and alternative
farming systems like agroforestry on carbon
sequestration in Brazilian Amazon soils.
Partners
Centre technique interprofessionnel des oléagineux
et du chanvre (CETIOM) en Guyane et Empresa
Brasileira de Pesquisa Agropecuária (EMBRAPA)
au Brésil.
Media Contact
Cristelle DUOS
T. +33 (0)4 91 99 94 87
References
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FUJISAKI KENJI, PERRIN A-S, DESJARDINS THIERRY,
BERNOUX MARTIAL, BALBINO LC, BROSSARD MICHEL.
From forest to cropland and pasture systems: a
critical review of soil organic carbon stocks changes
in Amazonia. Global Change Biology, 2015.
DOI:10.1111/gcb.12906
Contacts
Kenji Fujisaki, PhD student CIFRE/CETIOM
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Michel Brossard, researcher at IRD
T. +33(0)4 99 61 30 80
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Indigo, IRD Photo Library
Daina RECHNER
Tél. : +33 (0)4 91 99 94 81
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Luiz Carlos Balbino, researcher at EMPRAPA
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UMR Ecologie fonctionnelle et biogéochimie des
sols et des agro-écosystèmes - Eco&Sols (IRD /
Montpellier SupAgro / CIRAD / INRA)
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© IRD/DIC, Mars 2015 - Conception et réalisation graphique : L. CORSINI
Soil carbon stocks fall when land is cultivated
Unsurprisingly, the French-Brazilian research
team shows that replacing the forest with
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to an average 8.5% drop in the soil’s carbon
stocks. This phenomenon can be explained
by the low quantities of organic matter
returned to the soil without forest cover, as
well as cultivation practices which favour
carbon losses.
However, in pasture land, the quantity
of organic carbon in the soil has slightly
increased since the forest’s disappearance.
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grasses improves the soils’ carbon storage.
Pedologists thus observe an average 11%
increase in this element in meadows that are
not overgrazed.