Caractérisation de la Biomasse sèche des mosaïques forêt-savane des plateaux Okouma et Bagombé au sud-est du Gabon

Objectif : Quantifier la biomasse sèche de savanes et du sous-bois en forêts dans la mosaïques forêtsavane au Sud-est du Gabon (Okouma et Bagombé).Méthodologie et résultats : La méthode destructive a été utilisée pour l’acquisition des données. En effet, elle a consisté à identifier, mesurer l’aide d’un pied à coulisse et peser les différents arbustes dans une parcelle de 25m2.Pour les arbustes dont les diamètres sont compris entre 1 et 5cm, ont été sectionnés, mesurés et pesés .Les aliquotes prélevés sur chaque échantillon ont permis d’estimer la biomasse en laboratoire .Ainsi, l’analyse statistique réalisée sur ces données a montré que la productivité moyenne de biomasse sèche est beaucoup plus importante en savane (35466760kg/ha) qu’en sous-bois (3442996kg/ha). Par ailleurs, la comparaison statistique «ANNOVA» entre la biomasse sèche produite dans les différents biotopes anthropisés montre que la productivité moyenne de biomasse sèche n’est pas différente d’un biotope à un autre, et afin une estimation des gains perçus par la vente des stockes de carbone dans le cadre du programme REDD a été simulée sur une aire de 3700haConclusion and application : Ce travail a permis de quantifier les stocks de carbone en savane et dans les sous-bois des mosaïque-forêt-savane. Ces travaux sont également d’intérêt capital pour les gouvernants à la fois dans la mise en oeuvre des politiques de réductions des émissions des gaz à effet des serres et d’un impact économique notamment dans le cadre du programme REDD.Mots clés: Carbone, Biomasse sèche, Gabon, savanes, forêt, changement climatiqu

Central African biomes and forest succession stages derived from modern pollen data and plant functional types

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 taxa. Using the biomisation method, we reconstructed (1) modern potential biomes and (2) potential succession stages of forest regeneration, a new approach in Atlantic Central African vegetation dynamics and ecosystem functioning reconstruction. When compared to local vegetation, potential biomes are correctly reconstructed (97.5% of the sites) and tropical rain forest (TRFO biome) is well identified from tropical seasonal forest (TSFO biome). When the potential biomes are superimposed on the White's vegetation map, only 76.4% of the sites are correctly reconstructed. But using botanical data, correspondence and cluster analyses, the 43 sites from Congo (Mayombe) evidence more affinities with those of central Gabon and so they can also be considered as correctly reconstructed as TRFO biome and White's map should be revised. In terms of potential succession stages of forest regeneration, the mature forest (TMFO) is well differentiated from the secondary forest (TSFE), but inside this latter group, the young and the pioneer stages are not clearly identified due probably to their low sampling representation. Moreover, linked to their progressive and mosaic character, the boundaries between two forest biomes or two forest stages are not clearly detected and need also a more intensive sampling in such transitions

Etude De Quelques Caracteristiques Physicochimiques Et Biochimiques De Wavé-fortex Un Complement Alimentaire Naturel Du Gabon

Wavé-fortex is a dietary supplement designed to Gabon, to fight against the problems of malnutrition and undernourishment. It would also contain diuretic properties, purgative, antimicrobial, aphrodisiac, influenza, regulating blood pressure, reducing overweight and stimulating sperm production. This work was carried out to study the physicochemical and biochemical characteristics of this health food. The results revealed that Wavé-fortex was heavily dehydrated and contained 6.27% of crude ash and 11.32% of total gross fibers. The mineral level, Wavé-fortex contains 1.27% of calcium, 0.09% of iron, 0.37% of magnesium, 0.87% of potassium and 0.01% of zinc. Biochemical analyzes showed that this functional food contained 45.69% of carbohydrates, 26.01% of protein and 4.67% of fat. This gives it an energy value of 3.55 kcal / g of dry matter. Wavé-fortex is an acidic product (pH 4.02) with high levels of vitamin A (2.38%), vitamin C (1.93%) and phenolic compounds (11.83%). The different levels of these compounds are capable of validating the various nutritional properties attributed to this food powder

Unfolding long-term Late Pleistocene–Holocene disturbances of forest communities in the southwestern Amazonian lowlands

Linking the distribution of plant species to geology has generally been biased by the over-simplification of landscape evolution and the lack of understanding of complex geological processes. The Amazonian lowlands have forests in different successional stages, and a growing perception is that such heterogeneity results from long-term environmental changes. This hypothesis is investigated by designing an analytical model based on past and present-day vegetation and successions of the plant communities, combined with an advanced understanding of geological history. An area of southwestern Amazonia was selected for floristic inventories, and we interpreted the paleovegetation based on C/N and δ13C analyses of sedimentary organic matter. These data were examined in the context of the geological evolution on the basis of new sedimentological and chronological data. The topographically high Late Pleistocene deposits had continuous and highly diversified late-successional terra firme forests as well as local fluvial paleolandforms of younger ages with less diversified campinarana forests. Late Pleistocene–Holocene terrains in intermediate elevations had terra firme forests, but shorter trees with lower basal areas and ecotonal forests appeared near the confines of the forest–savanna, while Holocene deposits recorded only seasonally flooded varzea forests. Several deposits of Late Pleistocene and Late Pleistocene–Holocene age recorded an expansion of C4 terrestrial plants before the establishment of the forest from ~20,000 cal yr BP to 7578 cal yr BP, which is not related to past arid episodes. We recorded forests with onsets at 6130–3533 cal yr BP, 3402–2800 cal yr BP, and 1624–964 cal yr BP to terra firme, varzea, and ecotonal forests, respectively. However, not all forests have reached maturity stages due to their location on terrains with a diverse history of terrace downcutting and deposition, which had a direct impact on local hydrology with the interaction of topographic gradients. The hydrology of the study area was also controlled by the distance from the main river valley. Capturing long-term disturbances over this region of still pristine forests may help elucidate the potential mechanisms that also determine trends in tree growth and forest diversity in other Neotropical regions. © 2018 The Authors

Long-Term Vegetation Change in Central Africa: The Need for an Integrated Management Framework for Forests and Savannas

peer reviewedTropical forests and savannas are the main biomes in sub-Saharan Africa, covering most of the continent. Collectively they offer important habitat for biodiversity and provide multiple ecosystem services. Considering their global importance and the multiple sustainability challenges they face in the era of the Anthropocene, this chapter undertakes a comprehensive analysis of the past, present, and future vegetation patterns in central African forests and savannas. Past changes in climate, vegetation, land use, and human activity have affected the distribution of forests and savannas across central Africa. Currently, forests form a continuous block across the wet and moist areas of central Africa, and are characterized by high tree cover (>90% tree cover). Savannas and woodlands have lower tree cover (<40% tree cover), are found in drier sites in the north and south of the region, and are maintained by frequent fires. Recent tree cover loss (2000–2015) has been more important for forests than for savannas, which, however, reportedly experienced woody encroachment. Future cropland expansion is expected to have a strong impact on savannas, while the extent of climatic impacts depends on the actual scenario. We finally identify some of the policy implications for restoring ecosystems, expanding protected areas, and designing sustainable ecosystem management approaches in the region

Relation pollen-végétation-climat actuels en Afrique centrale (une approche numérique appliquée à la séquence quaternaire du lac barombi Mbo, Cameroun)

Ce travail présente l'analyse de 80 nouveaux échantillons polliniques actuels d'Afrique centrale atlantique, en particulier de milieu forestier. Les assemblages polliniques obtenus ont été complétés par des données déjà existantes dans cette région, soit un total de 199 assemblages. L'application d'analyses statistiques et de la méthode de biomisation a permis de tester la fiabilité du contenu pollinique de cette base de données par rapport aux données botaniques mettant en évidence que plus de 95% des sites étaient correctement reconstruits en termes de biomes (forêt tropicale humide, forêt tropicale saisonnière, savane) ou de stades de succession forestière (savane, forêt secondaire, forêt mature). Sur une base de données polliniques plus étendue à l'Afrique de l'ouest, la méthode de biomisation a été appliquée à la séquence pollinique du lac Barombi Mbo, Cameroun, afin de recontruire les différents biomes et stades forestiers qui se sont succédés au cours des derniers 33 000 ans cal BP. L'application de la technique des meilleurs analogues, parallèlement à celle des réseaux de neurones artificiels a permis de reconstruire sur cette séquence la pluviosité et l'évapotranspiration moyennes annuelles, ainsi qu'un indice bioclimatique représentatif de la physionomie de la végétationThis work presents the analysis of 80 new modern pollen samples from central Africa, mainly in forest environment. Complemented by pollen assemblages previously obtained in this region, i.e. a total of 199 assemblages, statistical analysis and the application of the biomisation method have allowed to test the reliability of the pollen content of this dataset compared to local botanical data, showing that potential biomes (tropical rain forest, tropical seasonal forest, savanna) and forest successional stages (savanna, secondary forest, mature forest) were reconstructed with more than 95% of confidence level. Based on a more extended pollen database toward drier vegetations from West Africa and using the biomisation method, the best analogues and the artificial neural networks techniques, we proposed new quantitative and more precise reconstructions of the vegetation and climate at Lake Barombi Mbo, in Cameroon, during the last 33,000 cal yrs BPMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Pollen, vegetation change and climate at Lake Barombi Mbo (Cameroon) during the last ca. 33 000 cal yr BP : a numerical approach

This paper presents quantitative reconstructions of vegetation and climate along the pollen sequence of Lake Barombi Mbo, southwestern Cameroon (4 degrees 39'45.75 ' N, 9 degrees 23'51.63 ' E, 303ma.s.l.) during the last 33 000 cal yr BP, improving previous empirical interpretations. The biomisation method was applied to reconstruct potential biomes and forest successional stages. Mean annual precipitation, mean annual potential evapotranspiration and an index of moisture availability were reconstructed using modern analogues and an artificial neural network technique. The results show a dense forested environment around Lake Barombi Mbo of mixed evergreen/semi-deciduous type during the most humid phases (highest precipitation and lowest evapotranspiration), but with a more pronounced semi-deciduous type from ca. 6500 cal yr BP to the present day, related to increased seasonality. This forest displays a mature character until ca. 2800 cal yr BP, then becomes of secondary type during the last millennium, probably due to increased human activity. Two episodes of forest fragmentation are shown, which are synchronous with the lowest reconstructed precipitation and highest potential evapotranspiration values. The first of these occurs during the LGM, and the second one from ca. 3000 to ca. 1200 cal yr BP, mainly linked to high precipitation seasonality. Savanna were, however, never extensive within the Barombi Mbo basin, existing instead inside the forest in form of savanna patches. The climate reconstructions at Lake Barombi Mbo suggest that the artificial neural networks technique would be more reliable in this region, although the annual precipitation values are likely under-estimated through the whole sequence

Forest-savannah dynamics on the Adamawa plateau (Central Cameroon) during the “African humid period” termination: A new high-resolution pollen record from Lake Tizong

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Modern pollen rain in savanna and forest ecosystems of Gabon and Cameroon, Central Atlantic Africa

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