Evaluation of structure and natural regeneration status of woody plant species in sudanian domain : Case of eastern part of National Park of Sena Oura, Chad

Many scientific studies confirmed that plants have an important ecological role maintaining the productivity of the environment and regulating the global climate. In order to valorize the wild phytogenetic resources for the efficient in situconservation and sustainable use in Sudano-zambezian region, a study was carried out in Sudanian domainprovidingquantitative informations on the community structure and natural regeneration status of woody plant species.The study site is the eastern part of National Park of Sena Oura in Chad. Adults plants (trees and shrubs) were systématically collected in 10 linear transects (20 m x 1000 m). Juvenile plants (saplings and seedlings) weresystematically collected within 40 plots (20 m × 20 m). These plots were randomly stablished in the transects, at a rate of four plots per transect.In total, 84 adults plants species grouped in 58 genera and 29 families and 66 juvenile plants species grouped in 45 genera and 27 families were inventoried. Bell andreverse J-shaped patterns of selected woody species were identified.The stand regeneration status wasgood.The stand regeneration rate were SRR = 52.29% and Hymenocardia acida (SIR = 17.95%), Combretum collinum (SIR = 14.12%), Annona Senegalensis (SIR = 6.67%) and Isoberlinia doka (SIR = 6.22%) had the most important specific index of regeneration. The specific structures showed that the structure of the total stand is the result of the dynamics of all species and their interactions.The global stand regeneration status was good.The obtained results provided quantitative informations on the community structure and natural regeneration status of woody plant species for the efficient conservation and sustainable use

Comparaison des diversités génétiques de Dacryodes edulis (G.Don) H.J. Lam et de Dacryodes buettneri (Engel.) H.J. Lam (Burséracées), deux espèces forestières utiles en Afrique centrale

Dacryodes buettneri et Dacryodes edulis sont des espèces à usages multiples en Afrique centrale. Elles servent principalement de bois d’oeuvre et de fruitier. Des échantillons de leurs folioles ont été récoltés sur 694 arbres répartis dans 29 populations au Cameroun et au Gabon, afin d’extraire l’ADNn et amplifier cinq marqueurs microsatellites. Les paramètres génétiques des populations ont été calculés pour évaluer et comparer leur diversité génétique. Les moyennes des nombres d’allèles sont respectivement 4,43 ± 1,37 et 5,36 ± 1,13. Il n’existe pas de différence significative dans la répartition des nombres d’allèles par locus entre les espèces. Les paramètres de la diversité intra-population de D. buettneri (P = 0,76 ± 0,15; Hatt = 0,35 ± 0,06 et Hobs = 0,26 ± 0,04) sont significativement inférieurs à ceux de D. edulis (P = 0,9 ± 0,12; Hatt = 0,47 ± 0,05 et Hobs = 0,41 ± 0,07), alors que le coefficient de consanguinité de D. buettneri (F = 0,25 ± 0,08) est deux fois supérieur à celui de la deuxième espèce (F = 0,12 ± 0,03). Un important flux de gènes inter-espèce a été trouvé, Nm = 0,44. Les analyses ont ressorti trois groupes de populations, séparés par la distance géographique et l’isolement taxonomique. D. edulis se croise parfaitement si les individus sont géographiquement proches, même avec les individus spontanés forestiers. Aucune séparation variétale au sein de D. edulis n’a été détectée. Cette étude est une contribution à la valorisation de la diversité génétique des espèces forestières africaines pour une conservation durable.Mots clés : Espèces à usages multiples, marqueurs microsatellites, génétique de populations, conservation durable

Dinosterol deltaD values in stratified tropical lakes (Cameroon) are affected by eutrophication

In freshwater settings, dinosterol (4a,23,24-trimethyl-5a-cholest-22E-en-3b-ol) is produced primarily by dinoflagellates, which encompass various species including autotrophs, mixotrophs and heterotrophs. Due to its source specificity and occurrence in lake and marine sediments, its presence and hydrogen isotopic composition (dD) should be valuable proxies for paleohydrological reconstruction. However, because the purity required for hydrogen isotope measurements is difficult to achieve using standard wet chemical purification methods, their potential as a paleohydrological proxy is rarely exploited. In this study, we tested dD values of dinosterol in both particulate organic matter (POM) and sediments of stratified tropical freshwater lakes (from Cameroon) as a paleohydrological proxy, the lakes being characterized by variable degrees of eutrophication. In POM and sediment samples, the dD values of dinosterol correlated with lake water dD values, confirming a first order influence of source water dD values. However, we observed that sedimentary dinosterol was D enriched from ca. 19 to 54‰ compared with POM dinosterol. The enrichment correlated with lake water column conditions, mainly the redox potential at the oxic–anoxic interface (Eh OAI). The observations suggest that paleohydrologic reconstruction from dD values of dinosterol in the sediments of stratified tropical lakes ought to be sensitive to the depositional environment, in addition to lake water dD values, with more positive dinosterol dD values potentially reflecting increasing lake eutrophication. Furthermore, in lake sediments, the concentration of partially reduced vs. non-reduced C34 botryococcenes, stanols vs. stenols, and bacterial (diploptene, diplopterol and bb-bishomohopanol) vs. planktonic/terrestrial lipids (cholesterol, campesterol and dinosterol) correlated with Eh OAI. We suggest using such molecular proxies for lake redox conditions in combination with dinosterol dD values to evaluate the effect of lake trophic status on sedimentary dinosterol dD values, as a basis for accurately reconstructing tropical lake water dD values

Diversity of used plant species for producing charcoal and its trade-off in Far-North Region, Cameroon

 The Northern Regions of Cameroon belong to sudano-zambesian region. In these regions, woody species are scarce compared to Guinean-Congolese Region and they undergo the human pressure like abusive exploitation of plants. In order to contribute to valorization of phytogenetic resources and contribute to struggle desert progression in sahelian region, a study on plants diversity which are used to produce charcoal and its trade-off was carried out in Far-North Region of Cameroon. Census of plants species was made on the basis of semi-structured surveys through the producers of charcoal and identification of tree trunks on the sites of charcoal production. Data of trade of charcoal was collected by direct observation and a semi-structured survey questionnaire in Maroua. In total, 25 species grouped in 17 genera and 8 families have been recorded. Acacia and Combretum were the richest genera with four species each. They were quoted as multipurpose species which can be used elsewhere as fruits, timbers, medicinal plants or essential oils and exudates. In Maroua almost, 98 % of households use charcoal for heating. In the absence of the charcoal, up to 60 % of those use firewood, 18.46 % use domestic gas and 18.46% use kerosene. Because of poverty and unemployment, people of primary education are mostly charcoal sellers.  INTERNATIONAL JOURNAL OF ENVIRONMENTVolume-6, Issue-2, Mar-May 2017, Page: 19-29</p

Effect of aridity on delta ¹³C and delta D values of C₃ plant- and C₄ graminoid-derived leaf wax lipids from soils along an environmental gradient in Cameroon (Western Central Africa)

The observation that the hydrogen isotope composition (δD) of leaf wax lipids is determined mainly by precipitation δD values, has resulted in the application of these biomarkers to reconstruct paleoclimate from geological records. However, because the δD values of leaf wax lipids are additionally affected by vegetation type and ecosystem evapotranspiration, paleoclimatic reconstruction remains at best semi-quantitative. Here, we used published results for the carbon isotope composition (δ13C) of n-alkanes in common plants along a latitudinal gradient in C3/C4 vegetation and relative humidity in Cameroon and demonstrated that pentacyclic triterpene methyl ethers (PTMEs) and n-C29 and n-C31 in the same soil, derived mainly from C4 graminoids (e.g. grass) and C3 plants (e.g. trees and shrubs), respectively. We found that the δD values of soil n-C27, n-C29 and n-C31, and PTMEs correlated significantly with surface water δD values, supporting previous observations that leaf wax lipid δD values are an effective proxy for reconstructing precipitation δD values even if plant types changed significantly. The apparent fractionation (εapp) between leaf wax lipid and precipitation δD values remained relatively constant for C3-derived long chain n-alkanes, whereas εapp of C4-derived PTMEs decreased by 20‰ along the latitudinal gradient encompassing a relative humidity range from 80% to 45%. Our results indicate that PTME δD values derived from C4 graminoids may be a more reliable paleo-ecohydrological proxy for ecosystem evapotranspiration within tropical and sub-tropical Africa than n-alkane δD values, the latter being a better proxy for surface water δD values. We suggest that vegetation changes associated with different plant water sources and/or difference in timing of leaf wax synthesis between C3 trees of the transitional class and C3 shrubs of the savanna resulted in a D depletion in soil long chain n-alkanes, thereby counteracting the effect of evapotranspiration D enrichment along the gradient. In contrast, evaporative D enrichment of leaf and soil water was significant enough to be recorded in the δD values of PTMEs derived from C4 graminoids, likely because PTMEs recorded the hydrogen isotopic composition of the same vegetation type

Hydrogen isotope ratios of lacustrine sedimentary n-alkanes as proxies of tropical African hydrology: insights from a calibration transect across Cameroon

Hydrogen isotope values (δD) of sedimentary aquatic and terrestrial lipid biomarkers, originating from algae, bacteria, and leaf wax, have been used to record isotopic properties of ancient source water (i.e., precipitation and/or lake water) in several mid- and high-latitude lacustrine environments. In the tropics, however, where both processes associated with isotope fractionation in the hydrologic system and vegetation strongly differ from those at higher latitudes, calibration studies for this proxy are not yet available. To close this gap of knowledge, we sampled surface sediments from 11 lakes in Cameroon to identify those hydro-climatological processes and physiological factors that determine the hydrogen isotopic composition of aquatic and terrestrial lipid biomarkers. Here we present a robust framework for the application of compound-specific hydrogen isotopes in tropical Africa. Our results show that the δD values of the aquatic lipid biomarker n-C17 alkane were not correlated with the δD values of lake water. Carbon isotope measurements indicate that the n-C17 alkane was derived from multiple source organisms that used different hydrogen pools for biosynthesis. We demonstrate that the δD values of the n-C29 alkane were correlated with the δD values of surface water (i.e., river water and groundwater), which, on large spatial scales, reflect the isotopic composition of mean annual precipitation. Such a relationship has been observed at higher latitudes, supporting the robustness of the leaf-wax lipid δD proxy on a hemispheric spatial scale. In contrast, the δD values of n-C31 alkane did not show such a relationship but instead were correlated with the evaporative lake water δD values. This result suggests distinct water sources for both leaf-wax lipids, most likely originating from two different groups of plants. These new findings have important implications for the interpretation of long-chain n-alkane δD records from ancient lake sediments. In particular, a robust interpretation of palaeohydrological data requires knowledge of the vegetation in the catchment area as different plants may utilise different water sources. Our results also suggest that the combination of carbon and hydrogen isotopes does help to differentiate between the metabolic pathway and/or growth form of organisms and therefore, the source of hydrogen used during lipid biosynthesis