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Lowland rainforest response to hydrological changes during the last 1500 years in Gabon, Western Equatorial Africa

Published online by Cambridge University Press:  20 January 2017

Alfred Ngomanda ,
Dominique Jolly ,
Ilhem Bentaleb ,
Alex Chepstow-Lusty ,
M'voubou Makaya ,
Jean Maley ,
Michel Fontugne ,
Richard Oslisly  and
Nicaise Rabenkogo
Alfred Ngomanda*
Affiliation:
Institut des Sciences de l'Evolution de Montpellier, UMR 5554, Université de Montpellier II Place Eugène Bataillon, cc 61, 34095 Montpellier Cedex 5, France
Dominique Jolly
Affiliation:
Institut des Sciences de l'Evolution de Montpellier, UMR 5554, Université de Montpellier II Place Eugène Bataillon, cc 61, 34095 Montpellier Cedex 5, France
Ilhem Bentaleb
Affiliation:
Institut des Sciences de l'Evolution de Montpellier, UMR 5554, Université de Montpellier II Place Eugène Bataillon, cc 61, 34095 Montpellier Cedex 5, France
Alex Chepstow-Lusty
Affiliation:
Institut des Sciences de l'Evolution de Montpellier, UMR 5554, Université de Montpellier II Place Eugène Bataillon, cc 61, 34095 Montpellier Cedex 5, France Centre de Bio-Archéologie et d'Ecologie (UMR 5059-CNRS/UM2/EPHE), Institut de Botanique, 163 rue Broussonnet, F-34090, Montpellier, France
M'voubou Makaya
Affiliation:
Laboratoire d'Etude de Géo-Environnements Marins, Université de Perpignan 52, Avenue Paul Alduy, 66000 Perpignan, France
Jean Maley
Affiliation:
Institut des Sciences de l'Evolution de Montpellier, UMR 5554, Université de Montpellier II Place Eugène Bataillon, cc 61, 34095 Montpellier Cedex 5, France
Michel Fontugne
Affiliation:
Laboratoire des Sciences du Climat et de l'Environnement, UMR CEA/CNRS 1572, Domaine du CNRS, 91198 Gif sur Yvette cedex, France
Richard Oslisly
Affiliation:
Wildlife Conservation Society, BP 7847 Libreville, Gabon and IRD, 5 rue du Carbone, 45072 Orléans cedex 2, France
Nicaise Rabenkogo
Affiliation:
IRSH/GREH, Centre National de Recherche Scientifique et Technique (CENAREST), BP 846 Libreville, Gabon
*
*Corresponding author. E-mail addresses:[email protected], [email protected] (A. Ngomanda).
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Abstract

Pollen and δ13CTOM data obtained from two contrasting lake sequences (Lakes Kamalété and Nguène), located 200 km apart in the lowland rainforest of Gabon, provide complementary local and regional 1500-yr records of high resolution (15–30 yr) vegetation change. A combination of aquatic, semi-aquatic and terrestrial pollen showed in both records that the tropical rainforest increased during periods of high rainfall and decreased during drought intervals. The strong fluctuations of water balance at decadal scale during the “Medieval Warm Period” (∼ 1100–800 cal yr BP) coincided with a noticeable increase in shade-intolerant taxa, indicating recurring rainforest canopy disturbance. The δ13CTOM signal showed high-amplitude variations in both records, which positively correlates with the rainforest dynamics and local vegetation changes. The similar trends in both the pollen and the δ13CTOM signals between these sites demonstrate the regional broadly synchronous timing of shifting hydrological conditions. The largely positive co-variation between strong fluctuations of hydrological conditions and changes in rainforest structure and composition indicate that regional climatic change is probably the driving force for major rainforest dynamics in Gabon. Any significant anthropogenic impact on vegetation has not been clearly identified, and this issue still needs to be resolved independently by obtaining detailed archeological records across the interval 1400–800 BP, which currently seem to be extremely rare or not easily available.

Keywords

PollenCarbon isotopesLake-level changesRainforest responseCanopy disturbanceGabonLate Holocene
Type
Research Article
Information
Quaternary Research , Volume 67 , Issue 3 , May 2007 , pp. 411 - 425
Copyright
University of Washington

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