Diversité Floristique Et Variation Altitudinale De La Structure Des Formations A Gnidia Glauca (Fresen) Gilg. Dans Les Forêts Communautaires De KilumIjim (Nord-Ouest Cameroun)

In order to find strategies for sustainable management of resources, a study was carried out on the analysis and management of stands of Gnidia glauca in the Kilum-Ijim region (North-West Cameroon). All individuals were identified and counted in 33 plots of 40mx40m established between 1963 and 2785 m altitude in these Gnidia glauca formations. The height and diameter of each individual were measured. A quadrat of 1m² was established around the mature trees to evaluate the regeneration. ANOVA was used to compare the average density of the species in various plots and the DUNCAN test at the 5% significance level (SPSS software version 17.0) was used to separate these means. It emerges from this study that the Thymelaeaceae (G. glauca) family is mainly represented. The Asteraceae, Rubiaceae, Poaceae and Fabaceae are the most diverse families in these formations. The distribution of individuals of G. glauca in diameter classes shows a decreasing pattern. The low density of G. glauca is observed at low altitudes (166.66 stems / hectare), and the high density is between 2350 and 2450 m (778.18 stems / ha). The average standing densities of G. glauca varies between 64.58 and 459.37 stems per hectare; these values indicate a good regeneration of this species in the site. G. glauca can therefore be rationally exploited in a sustainable way for the well-being of the surrounding human populations

The Lake CHAd Deep DRILLing project (CHADRILL) - targeting ~ 10 million years of environmental and climate change in Africa

At present, Lake Chad ( ~13°0 N, ~14° E) is a shallow freshwater lake located in the Sahel/Sahara region of central northern Africa. The lake is primarily fed by the Chari-Logone river system draining a ~600 000 km2 watershed in tropical Africa. Discharge is strongly controlled by the annual passage of the intertropical convergence zone (ITCZ) and monsoon circulation leading to a peak in rainfall during boreal summer. During recent decades, a large number of studies have been carried out in the Lake Chad Basin (LCB). They have mostly focused on a patchwork of exposed lake sediments and outcrops once inhabited by early hominids. A dataset generated from a 673m long geotechnical borehole drilled in 1973, along with outcrop and seismic reflection studies, reveal several hundred metres of Miocene-Pleistocene lacustrine deposits. CHADRILL aims to recover a sedimentary core spanning the Miocene-Pleistocene sediment succession of Lake Chad through deep drilling. This record will provide significant insights into the modulation of orbitally forced changes in northern African hydroclimate under different climate boundary conditions such as high CO2 and absence of Northern Hemisphere ice sheets. These investigations will also help unravel both the age and the origin of the lake and its current desert surrounding. The LCB is very rich in early hominid fossils (Australopithecus bahrelghazali; Sahelanthropus tchadensis) of Late Miocene age. Thus, retrieving a sediment core from this basin will provide the most continuous climatic and environmental record with which to compare hominid migrations across northern Africa and has major implications for understanding human evolution. Furthermore, due to its dramatic and episodically changing water levels and associated depositional modes, Lake Chad's sediments resemble maybe an analogue for lake systems that were once present on Mars. Consequently, the study of the subsurface biosphere contained in these sediments has the potential to shed light on microbial biodiversity present in this type of depositional environment. We propose to drill a total of ~1800m of poorly to semi-consolidated lacustrine, fluvial, and eolian sediments down to bedrock at a single on-shore site close to the shoreline of present-day Lake Chad. We propose to locate our drilling operations on-shore close to the site where the geotechnical Bol borehole (13°280 N, 14°440 E) was drilled in 1973. This is for two main reasons: (1) nowhere else in the Chad Basin do we have such detailed information about the lithologies to be drilled; and (2) the Bol site is close to the depocentre of the Chad Basin and therefore likely to provide the stratigraphically most continuous sequence

Long and short-time scale climatic variability in the last 5500 years in Africa according to modern and fossil diatoms from Lake Ossa (Western Cameroon)

The reconstruction of paleoenvironmental changes from diatoms in lake sediments is based on the usual assumption that, in each studied sample, the dominant species reflect the environment that prevailed during the time of deposition. If the environment changed significantly during the period of deposition (several years) one can expect a mixture of species having different or contradictory ecological affinities. In this paper we present analyses of diatoms in surface sediment samples collected in the Lake Ossa area (3 degrees 50'N, 9 degrees 36E) and fossil diatoms from a mid-late Holocene core retrieved in the deepest part of the lake. The Lake Ossa area alternates between a short dry season centered at around the northern winter and a long rainy season during the rest of the year entailing significant changes in water level and pH. Based on multivariate analyses, we will show here that mean annual water depth is the most significant variable explaining the distribution of diatoms in the entire Lake. However, seasonal changes of water level are poorly recorded by diatom assemblages, except in some flat areas on the borders of the lakes where a mixing between species with different affinities to water depth is likely due to seasonal changes in water level. Inferred water depth based on a quantitative transfer function reflected essentially secular to millennial changes in the studied core. The relationship between pH and diatoms is not statistically significant but seasonal to multi-annual pH variations mainly observed in the central parts of the lake are reflected by a mixing of acidophilous and alkaliphilous species. Hierarchical ascending cluster analysis (HAC) considered as the most efficient mean of describing diatom mixing shows that seasonal to multi-annual changes in pH are recorded both in the modern and fossil assemblages. According to the degree of mixing between diatoms with different pH affinities we conclude that short-term pH variability was weaker than today between 5200 and 2700 cal yr BP, stronger between 2700 and 2000 cal yr BP, weaker again between 2000 and 600 cal yr BP and similar to present from 400 cal yr BP onwards. Short-term changes were thus superimposed on secular to millennium trends recorded by modifications in the abundance of alkaliphilous diatoms. All these changes are interpreted as variations in precipitation according to a previous model showing that pH is strongly controlled by acidic meteoric water. Inferred water depth slightly changed over the last 5500 years showing weak variations of precipitation minus evaporation balance at secular to millennial time scales. These results will be used to refine previously published paleoclimatic interpretations, which explained changes in precipitation and P-E balance by modifications in the vertical structure of the atmosphere and subsequently by changes in cloud cover, convective or stratiform

Macrophyte diversity in polluted and non-polluted wetlands in Cameroon

Inventory of macrophyte species in four wetlands in the Olezoa drainage basin in Yaoundé, two wetlands in the Bamenda central town, and two wetlands in the rural areas in the Menoua Division, was carried out from October 2003 to June 2004. The belt transect method was used for sampling and collecting plant specimens. In the four polluted wetlands studied in Yaoundé, 13 species belonging to 13 genera and 12 families were recorded. The families Cyperaceae and Poaceae were the most abundant, with the later being the only family represented by more than one species. A total of 43 species in 40 genera and 20 families were recorded in Bamenda wetlands, which were also polluted, as evidenced by some physicochemical analysis of wastewater. The family Poaceae appeared the most represented, having a total of 12 species in these wetlands. In the wetlands of the rural areas, a total of 67 macrophyte species in 55 genera and 27 families were identified. The family Cyperaceae was the most represented, with 16 species, followed by the Poaceae with 9 species. The macrophyte species identified were both terrestrial, aquatic and wetland species, some of which have already been tested in other countries in constructed wetlands for wastewater treatment. The number of macrophyte species recorded in the polluted wetlands was low compared with that of the wetlands in the rural areas. The species that grow well in polluted wetlands represent potential candidates for tests in artificial wetlands for phytopurification of wastewater in the studied area. Keywords: Macrophytes, wetlands, diversity, phytopurification, wastewater, tropics. RESUME L'inventaire des macrophytes de quatre marécages dans le bassin versant Olezoa à Yaoundé, deux marécages dans la ville de Bamenda, et deux marécages des zones rurales dans les hautes terres de l'Ouest du Cameroun, a été conduite d'octobre 2003 à juin 2004. La méthode de transect a été utilisée pour recenser et récolter les espèces macrophytiques présentes dans chaque marécage. Dans les quatre marécages pollués de Yaoundé, 13 espèces appartenant à 13 genres distribués dans 12 familles ont été identifiées. Les familles des Cyperacées et des Poacées sont les plus abondantes, la dernière famille étant la seule représentée par plus d'une espèce. Un total de 43 espèces distribuées dans 40 genres et 20 familles a été enregistré dans les marécages de Bamenda dont le caractère pollué a été prouvé par des analyses physicochimiques. La famille des Poacées est la plus représentée avec un total de 12 espèces dans ces marécages. Dans les marécages des zones rurales, un total de 67 espèces appartenant à 55 genres et 27 familles ont été identifiées. La famille des Cyperacées était la plus représentée, avec 16 espèces, suivie par celle des Poacées avec 9 espèces. Les macrophytes identifiés dans ces milieux sont terrestres ou aquatiques et certaines ont été testées en marécages artificiels pour l'épuration des eaux usées. Le nombre d'espèces de macrophytes recensées dans les marécages recevant les eaux usées est faible comparée à celui des marécages des zones rurales. Les espèces qui prolifèrent dans les marécages pollués pourraient servir dans les essais de phytoépuration d'eaux usées par marécages artificiels dans la zone d'étude. Mots clés: macrophytes, marécages, diversité, phytoépuration, eaux usées, régions tropicales Cameroon Journal of Experimental Biology Vol. 1(1) 2005: 26-3