Towards an understanding of West African montane forest response to climate change
Corresponding Author
Anne-Marie Lézine
Laboratoire des Sciences du Climat et de l'Environnement, UMR 8212 CNRS-CEA-UVSQ, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
Correspondence and present address: Anne-Marie Lézine, Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques, UMR7159, Université Pierre et Maire Curie, case 100, 75252 Paris Cedex 05, France.
E-mail: [email protected]
Search for more papers by this authorChimène Assi-Kaudjhis
Laboratoire des Sciences du Climat et de l'Environnement, UMR 8212 CNRS-CEA-UVSQ, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
Département de Géologie, Laboratoire de Paléobotanique, Paléopalynologie et Micropaléontologie, Université de Liège, 4000 Liège 1, Belgium
Search for more papers by this authorEmile Roche
Département de Géologie, Laboratoire de Paléobotanique, Paléopalynologie et Micropaléontologie, Université de Liège, 4000 Liège 1, Belgium
Search for more papers by this authorAnnie Vincens
Centre Européen de Recherche et d'Enseignement de Géosciences de l'Environnement, UMR 7330 CNRS, Université Aix-Marseille-IRD-Collège de France, 13545 Aix-en-Provence Cedex 4, France
Search for more papers by this authorGaston Achoundong
Institut de Recherche Agricole pour le Développement, Yaoundé, Cameroon
Search for more papers by this authorCorresponding Author
Anne-Marie Lézine
Laboratoire des Sciences du Climat et de l'Environnement, UMR 8212 CNRS-CEA-UVSQ, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
Correspondence and present address: Anne-Marie Lézine, Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques, UMR7159, Université Pierre et Maire Curie, case 100, 75252 Paris Cedex 05, France.
E-mail: [email protected]
Search for more papers by this authorChimène Assi-Kaudjhis
Laboratoire des Sciences du Climat et de l'Environnement, UMR 8212 CNRS-CEA-UVSQ, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
Département de Géologie, Laboratoire de Paléobotanique, Paléopalynologie et Micropaléontologie, Université de Liège, 4000 Liège 1, Belgium
Search for more papers by this authorEmile Roche
Département de Géologie, Laboratoire de Paléobotanique, Paléopalynologie et Micropaléontologie, Université de Liège, 4000 Liège 1, Belgium
Search for more papers by this authorAnnie Vincens
Centre Européen de Recherche et d'Enseignement de Géosciences de l'Environnement, UMR 7330 CNRS, Université Aix-Marseille-IRD-Collège de France, 13545 Aix-en-Provence Cedex 4, France
Search for more papers by this authorGaston Achoundong
Institut de Recherche Agricole pour le Développement, Yaoundé, Cameroon
Search for more papers by this authorAbstract
Aim
Our aims were to provide a detailed chronology of past vegetation changes in the tropical mountains of west-central Africa since the Last Glacial Maximum and to discuss montane forest responses to climate change in terms of distribution and biodiversity.
Location
Lake Bambili, western Cameroon (05°56′ N, 10°14′ E, 2273 m a.s.l.).
Methods
Fossil pollen was extracted from a long, continuous and well-dated sedimentary sequence extending back 20,000 years. Pollen diversity and evenness estimates were based on rarefaction analysis and on Simpson's (1/D) index.
Results
Forest was nearly absent from high elevations during the last glacial period. It expanded gradually from 18.4 cal. kyr bp, interrupted only by reversals coincident with the Heinrich 1 (H1) and Younger Dryas (YD) climatic events, and then suddenly collapsed at 3.3 cal. kyr bp. This switch from forest to grassland communities occurred within a time span of three centuries. After 3.3 cal. kyr bp only short and taxon-poor forest phases are recorded, specifically between 2.7 and 1 cal. kyr bp and in recent centuries.
Main conclusions
Our data indicate that the mountain forests of Cameroon are recent, resulting from plant migrations from various sources from 18.4 cal. kyr bp onwards. Their progressive development closely followed intensification of the Atlantic monsoon, leading to the formation of a dense forest between 11.7 and 3.3 cal. kyr bp. The composition of this forest included the co-occurrence of species whose ranges do not overlap today, and indicates the potential for the development of unique iterations of climax forests through time. These forests appear to be very sensitive to Northern Hemisphere climate change, with phases of expansion/contraction coeval with the boreal deglacial signal, including widely recognized events such as H1, the YD and the 8.2 ka event. From 8.2 cal. kyr bp onwards, the progressive opening of the canopy is likely to reflect increased seasonality in rainfall related to more frequent El Niño/Southern Oscillation (ENSO) events. The final step of this history was the collapse of the montane forest at 3.3 cal. kyr bp. During the last millennium, very severe disruptions have meant that only the most rapidly dispersing species could spread, contributing to a drastic loss of forest biodiversity that has been accentuated by human impact in the last few centuries.
Supporting Information
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| Filename | Description |
|---|---|
| jbi2770-sup-0001-AppendixS1.docWord document, 168 KB | Appendix S1 Depth–age model of the Bambili sequence, western Cameroon. |
| jbi2770-sup-0002-AppendixS2.docWord document, 148.5 KB | Appendix S2 Pollen identification. |
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