H. Elenga

H. Elenga
Marien Ngouabi University · Géologie

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68
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Publications

Publications (68)
Article
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Cet article traite d’un phénomène urbain encore méconnu en Afrique, mais qui est fréquent ailleurs, à savoir la décroissance des villes. En effet, ce phénomène s’est fortement développé depuis les années 1990 dans plusieurs régions du monde. Les villes en décroissance sont celles qui perdent leurs populations qui migrent en direction d’autres ville...
Article
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Tropical savannah and forest are thought to represent alternative stable states in ecosystem structure in some climates. The implication is that biomes are maintained by positive feedbacks, e.g. with fire, and that historical distributions could play a role in determining modern ones. In this context, climate alone does not govern transitions betwe...
Article
In order to predicttechnological properties of local clay based materials mixed to wood waste and to prevent human health andenvironment, experimental mineral structure and composition study were conducted. The influence of wood waste on the structural properties of clay samples were also investigated. Non and stabilized clay sample at 4% of cement...
Article
The survey of the road construction materials within the Brazzaville Area in the Congo was conducted on the geotechnical data of materials collected from different sites in order to establish a correlation with the norms of their use in Civil Engineering fields. These data include grading curves, consistency limits for the fine fraction, modified P...
Article
An experimental study was carried out on bricks using local materials in order to take into ac-count the waste wood management to protect the environment and to reduce the cost of the habi-tat. Chips and sawdust were built-in clay bricks in order to study their influence on the compres-sive strength, Young's modulus and the speed for soundproofing....
Article
Full-text available
New detailed vegetation reconstructions are proposed in Atlantic Central Africa from a modern pollen data set derived from 199 sites (Cameroon, Gabon and Congo) including 131 new sites. In this study, the concept of plant functional classification is improved with new and more detailed plant functional types (PFTs) and new aggregations of pollen ta...
Article
Full-text available
Abstract. New detailed vegetation reconstructions are proposed in Atlantic Central Africa from a modern pollen data set derived from 199 sites (Cameroon, Gabon and Congo) including 131 new sites. In this study, the concept of plant functional classification is improved with new and more detailed plant functional types (PFTs) and new aggregations of...
Article
New detailed vegetation reconstructions are proposed in Atlantic Central Africa from a modern pollen data set derived from 199 sites (Cameroon, Gabon and Congo) including 131 new sites. In this study, the concept of plant functional classification is improved with new and more detailed plant functional types (PFTs) and new aggregations of pollen ta...
Chapter
Full-text available
The pollen data available for the Atlantic equatorial African region indicate that during the Late Quaternary, major climate changes occurred and caused important modifications in tropical lowland rain-forest in terms of composition and distribution (Maley 1991; Elenga et al. 1991; 1994; Farrera et al. 1999; Vincens et al. 1999). Nevertheless, desp...
Article
Full-text available
African pollen data have been used in many empirical or quantitative palaeoenvironmental reconstructions. However, the pollen types used in these studies were not controlled and standardised, preventing the precise understanding of pollen–plant and pollen–climate relation that is necessary for the accurate quantification of continental scale climat...
Article
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BIOME 6000 is an international project to map vegetation globally at mid-Holocene (6000 14C yr bp) and last glacial maximum (LGM, 18,000 14C yr bp), with a view to evaluating coupled climate-biosphere model results. Primary palaeoecological data are assigned to biomes using an explicit algorithm based on plant functional types. This paper introduce...
Article
This paper presents the most recent and detailed Holocene palynological research carried out on the Congolese Atlantic littoral, in the region of Pointe-Noire, as part of the ECOFIT program (CNRS-IRD). The results are obtained on two continental sedimentary sequences (core S2 from Songolo site: 4 degrees 45'51"S, 11 degrees 51'55"E, alt. 5 m and co...
Article
This paper presents the most recent and detailed Holocene palynological research carried out on the Congolese Atlantic littoral, in the region of Pointe-Noire, as part of the ECOFIT program (CNRS-IRD). The results are obtained on two continental sedimentary sequences (core S2 from Songolo site : 4°45'51''S, 11°51'55''E, alt. 5 m and core 2 from Cor...
Article
Modern soil samples from South Congo were analyzed for pollen content and compared to forest inventories to define modern pollen-vegetation relationships. A correspondence analysis (CA) was applied independently to botanical and pollen data and a hierarchical cluster analysis to pollen data only. Subsequently, a CA using a presence-absence approach...
Article
Full-text available
Pollen data from 18,000 14C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present-...
Article
This review paper synthesizes the recent published palaeoecological results obtained in Atlantic Equatorial Africa (ECOFIT program) on the history of forest ecosystems and inferred climate changes during the past 4000 years. Evidence are mainly provided by pollen analysis carried out at nine sites from Congo, Cameroon and Ghana, locally supported b...
Article
Full-text available
Biome reconstruction from pollen and plant macrofossil data provides an objective method to reconstruct past vegetation. Biomes for Africa and the Arabian peninsula have been mapped for 6000 years bp and provide a new standard for the evaluation of simulated palaeovegetation distributions. A test using modern pollen data shows the robustness of the...
Article
We have made photoemission studies of La2-xSrxCuO4 (LSCO) and found the following: (1) suppression of the chemical potential (mu) shift fur small x indicates a breakdown of the Fermi-liquid picture in the underdoped regime and suggests the opening of a pseudogap: (2) valence band spectra have indeed shown a pseudogap whose magnitude increases with...
Article
Pollen analysis of two cores from the Lake Sinnda, located in one of the driest areas of the southern Congo, reveals a history of vegetation and climate in this region during the past 5000 yr. A major change centered around 3000–2500 yr B.P. is indicated by an abrupt decrease in forest pollen and by a corresponding increase in grassland pollen. Con...
Article
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Lake Tele has a nearly perfect ellipsoidal shape and is surrounded by swamps and barely penetrable flooded forests in the heart of the Congo-Zaire watershed basin, and has intrigued the international scientific community for decades. In June 1992, a first Franco-Congolese multidisciplinary scientific expedition was finally able to reach the lake wh...
Article
Lake Tele, a vast elliptic water body located in the equatorial Sorest of north Congo, shows hydrological exchanges almost exclusively vertical, which are the reason for the low mineralisation of its waters. However, these are very rich in organic materials and highly acid (pH < 4). Palynological observations indicate that a highly hydromorphic for...
Article
Le lac Télé, vaste lentille d'eau ellipsoïdale située au coeur de la forêt équatoriale du nord-Congo, présente des échanges hydriques essentiellement verticaux qui confèrent une très faible minéralisation à ses eaux, par ailleurs très riches en carbone organique et très acides (pH < 4). Les observations palynologiques anciennes et récentes indiquen...
Article
Lake Tele, a vast elliptic water body, located in the equatorial forest of north Congo, shows hydrological exchanges almost exclusively vertical, which are the reason for the low mineralisation of its waters. However, these are very rich in organic materials and highly acid (pH <4). Palynological observations indicate that a highly hydromorphic for...
Article
Full-text available
Les régions intertropicales ont longtemps été considérées comme peu sensibles aux variations paléoclimatiques (Richards, 1952 ; Ashton, 1969,...). Par suite,la grande biodiversité de ces régions a souvent été attribuée à cette relative stabilité. Cette thèse a été combattue dans les années 1965-1970 par différents c hercheurs, dont Haffer (1969) ou...
Article
Palynological data of a core from Lake Kitina, located beyond the western part of the Congolese Mayombe provide new information on the evolution of both climate and vegetation of the surroundings of the lake since 5,400 BP. A forest vegetation has always covered the area, but major modifications are recorded after a climatic drying of about 2,500 B...
Article
Full-text available
L'analyse palynologique d'une carotte prélevée dans le lac Kitina, sur la bordure occidentale du Mayombe congolais, apporte des informations nouvelles sur l'évolution, depuis 5 400 ans BP, des conditions paléoclimatiques et sur les associations végétales présentes autour du lac. Si une couverture arborée a toujours été présente, des modifications i...
Article
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Des carottes de sédiments lacustres ont été prélevées au Congo dans deux contextes différents (figure I): J Lac Kitina (carotte KT3), situé en bordure du Mayombe, en zone de forêt dense, J Lac Sinnda (carotte SN2). dans une zone de savane comprise entre les massifs fores-tiers du Mayombe et du Chaillu.
Article
A detailed palynological analysis of two cores recovered from a swamp in the Southern Batéké Plateaux (Congo), provides information on the botanical history of this region during the last 24,000 yr B.P. Rich and well-diversified pollen counts exhibit changes in the vegetational communities related to hydrological and climatic fluctuations. Around 2...
Article
Full-text available
GEOSCIENCES DE SURFACE/ SURFACE GEOSCIENCES (PALÉOÉCOLOGIE PALEOECOLOGY) C.R. Acad. Si. Paris, t. 318, série II, p. 1521 A 1526, 1994 Changement majeur de la végétation du lac Sinnda (vallée du Niari, Sud-Congo) consécutif à l’assèchement climatique holocène supérieur : apport de la palynologie. Annie Vincens, Guillaume Buchet, Hilaire Elenga, Ma...
Article
Fossil roots from different species of Monopetalanthus as well as from other trees such as Saccoglottis gabonensis have been recovered on the Congolese littoral, near Pointe Noire (11-degrees-E, 4-degrees-S, elevation 0m). Dated between 6 500 and 3 000 yr B.P., these macro remains indicate the occurrence of a dense broad leaved forest under a humid...
Article
Fossil roots from different species of Monopetalanthus as well as from other trees such as Saccoglottis gabonensis have been recovered on the Congolese littoral, near Pointe Noire (11°E, 4°S, elevation 0m). Dated between 6500 and 3000 yr BP, these macro remains indicate the occurrence of a dense broad leaved forest under a humid climate. After 3000...
Article
Pollen analysis carried out on a core taken from the "bois de Bilanko' depression (3°31′S, 15°21′E, 700 m) on the Plateau Bateke in Congo shows, ca. 10 850 yr BP, an increase in the relative percentages of Podocarpus latifolius, Olea hochstetteri and Ilex mitis. This indicates the migration of the afromontane vegetational association towards the lo...
Article
Full-text available
Holocene pollen data from Kitina lake (Congo): palaeoclimatic and palaeobotanical changes in the Mayombe forest area Palynological data of a core from Lake Kitina, located beyond the western part of the Congolese Mayombe provide new information on the evolution of both climate and vegetation of the sur- roundings of the lake since 5,400 BP. A fores...

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