Productions scientifiques

Articles

Les premiers résultats de la recherche archéologique dans le sanctuaire de Banyang Mbo (Sud-Ouest du Cameroun)

Richard Oslisly, Christophe Mbida et Lee White (2000)

Résumé :

Le Sud-Ouest du Cameroun est une région qui est restée jusque-là inexplorée sur le plan archéologique. Cet article donne les résultats préliminaires d'une campagne de prospections et de sondages effectués au mois d'avril 1998, Au total, dix-neuf sites archéologiques ont été découverts et neuf ont fait]' objet de datations radiométriques et d'une étude détai11ée du matériel archéologique. L'ensemble des dates obtenues se situe entre le IXe et le XVlIT' siècle de notre ère, se rattachant à ce qu'on désigne communément l'Âge du fcr récent.

L'Anthropologie 104 : 341-354

L'Okoumé (Aucoumea klaineana) expansion et déclin d'un arbre pionnier en Afrique centrale atlantique au cours de I'Holocène

Lee White, Richard Oslisly, Kate Abernethy et Jean Maley (2000)

Résumé :

Les changements de végétation intervenus au cours des dix derniers millénaires dans la réserve de la Lope, au centre du Gabon, ont résulté essentiellement des déplacements de la limite forêt/savane. Ils ont pu être reconstitués grâce a une combinaison de cartes montrant la dynamique actuelle de la végétation, de spectres polliniques et de la datation des variations des valeurs du Sl3C de la matière organique dans des profils de sol. Les savanes ont perduré au cours de cette période mais leur superficie a varié à cause des changements des conditions climatiques et des feux de savanes allumés par l'homme.

Notre étude permet de démontrer qu'en l'absence du feu, trois espèces d'arbres, Aucoumea klaineana, Lophira alata et Sacoglottis gabonensis, sont capables de s'établir puis de se développer en savane. De plus les graines de ces arbres colonisateurs sont incapables de s'établir ultérieurement à l'ombre d'une canopée fermée et il en résulte que ces trois espèces deviennent rares ou absentes dans la succession des différentes phases forestières.

L'okoumé (Aucoumea klaineana) est une espèce endémique dont la distribution est restreinte aux deux tiers de la partie sud du Gabon. Nos résultats montrent que cette espèce a une stratégie de reproduction très efficace en phase d'expansion forestière, mais étant donné que sa reproduction ne peut intervenir qu'a l'interface foret/savane, l'okoumé est actuellement en déclin dans les forêts matures. En fait cet arbre est victime de son propre succés.

Dynamique à long terme des écosystèmes forestiers intertropicaux. Editeurs scientifiques : Michel Servant, Simone Servant-Vildary. Mémoire UNESCO, chap. 48.

Les paléoenvironnements de la fin du Pléistocène et de l’Holocène dans la réserve de la Lopé: approche par les indicateurs géomorphologiques, sédimentologiques, phytologiques, géochimiques et anthropogènes des milieux enregistreurs de la dépression

Bernard Peyrot, Richard Oslisly, Salah Abdessadok, Michel Fontugne, Christine Hatte, Lee White (2003)

Résumé :

Au Gabon, dans la moyenne vallée de l’Ogooué, la dépression de la Lopé constitue un milieu original dans une aire géographique dominée par la forêt. Elle se caractérise par des paysages de savane, une anomalie climatique à déficit hydrique sensible et une morphogenèse marquée par une vigoureuse érosion. Des analyses sédimentologiques soutenues par des dates radiocarbones C14 sur des niveaux archéologiques, des données isotopiques d13C semblent indiquer une certaine pérennité de conditions défavorables à la forestation de ce milieu, où l’homme, d’une manière nette, ca.9000 BP, mais déjà auparavant, a largement contribué à une anthropisation du paysage.

L’anthropologie 107 : 291–307

Vegetation changes during the past 1300 years in western equatorial Africa: a highresolution pollen record from Lake Kamalété, Lopé Reserve, Central Gabon

Alfred Ngomanda, Alex Chepstow-Lusty, Mvoubou Makaya, Patrick Schevin, Jean Maley, Michel Fontugne, Richard Oslisly, Nicaise Rabenkogo and Dominique Jolly1 (2005)

Résumé :

Vegetation changes during the past 1300 years are reconstructed in western equatorial Africa using a high-resolution pollen record from Lake Kamalété. This small marshy basin (c. 5-7 ha) is located in forest_/savanna mosaic in Lopé Reserve (0°43’S, 11°46’E), central Gabon. The Kamalété pollen data show the persistence over the past 1300 years of a relatively stable forest _/savanna mosaic, associated with significant changes of the forest component. Three successive stages of forest dynamics occurred. First, at 1325 cal. BP, moist semi-evergreen rainforest existed around the catchment of Lake Kamalété. However, it appears from the consistent presence of >/70% Gramineae pollen that the site was always primarily in savanna. Secondly, from c. 1240 to 550 cal BP, a noticeable increase in shade-intolerant plant species indicate openings in the rainforest canopy. The persistence of gap-colonizer species, such as Macaranga, Tetrorchidium and Musanga for several centuries in the rainforest, is explained by recurring canopy disturbance associated with shifts in available moisture. These hydrological changes may be related to a succession of longer and more severe dry seasons than observed today. Thirdly, at 550 cal BP, mature forest was re-established, corresponding to progressive savanna colonization by forest pioneer species such as Aucoumea klaineana, Lophira alata and Fagara macrophylla. This new phase of forest expansion coincided with a marked lithological change, indicating an increase in lake-level. It is concluded that the major vegetation changes observed are due to climatic variability, and anthropogenic action had limited influence.

The Holocene 15,7 pp. 1-/11

Tracking land-cover changes with sedimentary charcoal in the Afrotropics

 Julie C Aleman, Olivier Blarquez, Ilham Bentaleb, Philippe Bonté, Benoit Brossier, Christopher Carcaillet, Valéry Gond, Sylvie Gourlet-Fleury, Arnaud Kpolita, Irène Lefèvre, Richard Oslisly, Mitchell J Power, Olga Yongo, Laurent Bremond and Charly Favier (2013)

Résumé :

Fires have played an important role in creating and maintaining savannas over the centuries and are also one of the main natural disturbances in forests. The functional role of fires in savannas and forests can be investigated through examining sedimentary charcoal in order to reconstruct long-term fire history. However, the relationship between charcoal and vegetation structure in tropical grassy ecosystems remains to be elucidated. Here, we compared recent charcoal records from lake sediments in three tropical ecosystems (forest, savanna, and forest–savanna mosaic) with land cover inferred from remote-sensing images. Charcoal width-to-length (W/L) ratio is a good proxy for changes in fuel type. At one of the lakes, a significant W/L modification from values >0.5 (mainly wood) to <0.5 (˜grass) was recorded simultaneously with changes in land cover. Indeed, a significant deforestation was recorded around this lake in the remote-sensing imagery between 1984 and 1994. The results also indicate that a riparian forest around a lake could act as a physical filter for charcoal accumulation; we used the mean charcoal size as a proxy to evaluate this process. Charcoal Accumulation Rates (CHAR), a burned biomass proxy, were combined with W/L ratio and the mean charcoal size to investigate the land-use history of the landscapes surrounding the study sites. This combined approach allowed us to distinguish between episodic slash-and-burn practices in the forest and managed fields or pastures burning frequently.

The Holocene 23(12) 1853 –1862

West Central African peoples: survey of radiocarbon dates over the past 5000 years

Richard Oslisly, Ilham Bentaleb, Charly Favier, Michel Fontugne, Jean François Gillet, Julie Morin-Rivat (2013)

Résumé :

Tracing human history in west central Africa suffers from a scarcity of historical data and archaeological remains. In order to provide new insight into this problem, we reviewed 733 radiocarbon dates of archaeological sites from the end of the Late Stone Age, Neolithic Stage, and Early and Late Iron Age in Cameroon, Gabon, Central African Republic, Equatorial Guinea, Republic of Congo, and the western Democratic Republic of Congo. This review provides a spatiotemporal framework of human settlement in the forest biome. Beyond the well-known initial spread of Iron Age populations through central African forests from 2500 cal BP, it depicts the geographical patterns and links with the cultural evolution of the successive phases of human expansion from 5000 to 3000 cal BP and then from 3000 to 1600 cal BP, of the hinterland depopulation from 1350 to 860 cal BP, and of recolonization up to 500 cal BP.

Proceedings of the 21st International Radiocarbon Conference edited by A J T Jull & C Hatté RADIOCARBON, Vol 55, Nr 2–3, 2013, p 1377–1382

Climatic and cultural changes in the west Congo Basin forests over the past 5000 years

Richard Oslisly, Lee White, Ilham Bentaleb, Charly Favier, Michel Fontugne, Jean-François Gillet and David Sebag (2013)

Résumé :

Central Africa includes the world’s second largest rainforest block. The ecology of the region remains poorly understood, as does its vegetation and archaeological history. However, over the past 20 years, multidisciplinary scientific programmes have enhanced knowledge of old human presence and palaeoenvironments in the forestry block of Central Africa. This first regional synthesis documents significant cultural changes over the past five millennia and describes how they are linked to climate. It is now well documented that climatic conditions in the African tropics underwent significant changes throughout this period and here we demonstrate that corresponding shifts in human demography have had a strong influence on the forests. The most influential event was the decline of the strong African monsoon in the Late Holocene, resulting in serious disturbance of the forest block around 3500 BP. During the same period, populations from the north settled in the forest zone; they mastered new technologies such as pottery and fabrication of polished stone tools, and seem to have practiced agriculture. The opening up of forests from 2500 BP favoured the arrival of metallurgist populations that impacted the forest. During this long period (2500–1400 BP), a remarkable increase of archaeological sites is an indication of a demographic explosion of metallurgist populations. Paradoxically, we have found evidence of pearl millet (Pennisetum glaucum) cultivation in the forest around 2200 BP, implying a more arid context. While Early Iron Age sites (prior to 1400 BP) and recent pre-colonial sites (two to eight centuries BP) are abundant, the period between 1600 and 1000 BP is characterized by a sharp decrease in human settlements, with a population crash between 1300 and 1000 BP over a large part of Central Africa. It is only in the eleventh century that new populations of metallurgists settled into the forest block. In this paper, we analyse the spatial and temporal distribution of 328 archaeological sites that have been reliably radiocarbon dated. The results allow us to piece together changes in the relationships between human populations and the environments in which they lived. On this basis, we discuss interactions between humans, climate and vegetation during the past five millennia and the implications of the absence of people from the landscape over three centuries. We go on to discuss modern vegetation patterns and African forest conservation in the light of these events.

Phil Trans R Soc B 368: 20120304.

Hydrology of a rainforest headwater swamp from natural tracer analysis (Nsimi, Cameroon)

Maréchal J. C., Braun J. J., Riotte J., Bedimo Bedimo J. P., Boeglin J. L. (2011)

Hydrological Processes DOI: 10.1002/hyp.7989

Subsam­pling herbarium collections to assess geographic diversity gradients: a case study with endemic Orchidaceae and Rubiaceae in Cameroon

Droissart, V., Hardy, O., Sonke, B., Dahdouh-Guebas, F., Stévart, T. ( 2012)

Biotropica, 44 (1) : 44–52

Do plant families with contrasting functional traits show similar patterns of ende­mism? A case study with Central African Orchidaceae and Rubiaceae

Droissart, V., Sonke, B., Hardy, O., Simo, M., Taedoumg, H., Nguembou, C., Stévart, T. (2011)

Biodiversity and Conservation, 20 (7) : 1507-1531

Insecticide susceptibility of Aedes aegypti and Aedes albopictus in Central Africa

Kamgang B, Marcombe S, Chandre F, Ntchoutpouen E, Nwane P, Etang J, Corbel V, Paupy C. (2011)

Parasit Vectors. 4 (1): 79

Genetic Structure of the Tiger Mosquito, Aedes albopictus, in Cameroon (Central Africa)

Kamgang B, Brengues C, Fontenille D, Njiokou F, Simard F, Paupy C. (2011)

PLoS One. 6 (5): e20257

Rapports

Contribution of Augosoma centaurus beetle to rural livelihoods in the East region of Cameroon

Muafor F.J., Levang P., And Le Gall P. (2012)

ACBIODEV/IRD/CIFOR, 32 p

Etude sur l’exploitation de la viande de brousse dans le bloc forestier de Ngoyla-Mintom

M li M.V., Fotso E.E., Guetsa Takougan E., Beukam P. (2012)

BECOF/WWF/IRD/CIFOR, 86 p

Monographie et espaces ressources des Baka du secteur Alat Makay- Djoamedjoh dans le massif forestier de Ngoyla-Mintom

Ziwe C. (2012)

WWF/IRD/CIFOR, 54 p

Environnement et mutations socio-économiques dans le massif forestier de Ngoyla-Mintom. Etat des lieux et regard prospectif

Defo L. et Fongang G. (2012)

État des lieux et mutations du système de production agricole dans le massif forestier de Ngoyla-Mintom (secteur Lélé-Mbalam)

Ndoum A.N.L., Fotso Nghenzeko E.E., Guetsa T.E., Meli Meli V., et Witrant M. (2012)

BECOF/WWF/CIFOR/IRD, 73 p

Soutenances

Bio-écologie et génétique des populations d’Aedes aegypti et d’Aedes albopictus, vecteurs potentiels d’arboviroses au Cameroun

 Basile Kamgang

Thèse de doctorat, Université de Yaoundé I, sous la direction de Paupy Christophe (CR/IRD) et la supervision de Njiokou Flobert (MC Yaoundé I)

Mémoires de Mastère

Influence des différentes formes d’utilisation des terres sur l’abondance et la distribution des petits mammifères dans le massif forestier de Ngoyla- Mintom

Kuete P.L. (2012)

Université de Dschang/WWF/IRD, 38 p

Diversité des PFNL et impact des techniques d’exploitation sur le peuplement: cas d’Irvingia gabonensis Bail, de Baillonella toxisperma Pierre et de Ricinodendron heudelotii dans le secteur Mintom-Bi du massif forestier de Ngoyla- Mintom, Cameroun

Jiofack M. (2012)

Université de Dschang/WWF/IRD, 51 p

Pages