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Deblauwe V, Droissart V, Bose R, Sonké B, Blach-Overgaard A, Svenning J et al. (2016)
Remotely sensed temperature and precipitation data improve species distribution modelling in the tropics
Global Ecology and Biogeography.
Aim Species distribution modelling typically relies completely or partially on climatic variables as predictors, overlooking the fact that these are themselves predictions with associated uncertainties. This is particularly critical when such predictors are interpolated between sparse station data, such as in the tropics. The goal of this study is to provide a new set of satellite-based climatic predictor data and to evaluate its potential to improve modelled species–climate associations and transferability to novel geographical regions. Location Rain forests areas of Central Africa, the Western Ghats of India and South America. Methods We compared models calibrated on the widely used WorldClim station-interpolated climatic data with models where either temperature or precipitation data from WorldClim were replaced by data from CRU, MODIS, TRMM and CHIRPS. Each predictor set was used to model 451 plant species distributions. To test for chance associations, we devised a null model with which to compare the accuracy metric obtained for every species. Results Fewer than half of the studied rain forest species distributions matched the climatic pattern better than did random distributions. The inclusion of MODIS temperature and CHIRPS precipitation estimates derived from remote sensing each allowed for a better than random fit for respectively 40% and 22% more species than models calibrated on WorldClim. Furthermore, their inclusion was positively related to a better transferability of models to novel regions. Main conclusions We provide a newly assembled dataset of ecologically meaningful variables derived from MODIS and CHIRPS for download, and provide a basis for choosing among the plethora of available climate datasets. We emphasize the need to consider the method used in the production of climate data when working on a region with sparse meteorological station data. In this context, remote sensing data should be the preferred choice, particularly when model transferability to novel climates or inferences on causality are invoked.
Keywords: Association test, CHIRPS, GLM, MODIS, MaxEnt, TRMM, WorldClim, ecological niche model, habitat suitability, null model
Wansi J, Wandji J, Sewald N, Nahar L, Martin C, Sarker S (2016)
Journal of Ethnopharmacology.
AIMS Traditional medicinal use of species of the genus Drypetes is widespread in the tropical regions. The aim of this review is to systematically appraise the literature available to date on phytochemistry, ethnopharmacology, toxicology and bioactivity (in vitro and in vivo) of crude extracts and purified compounds. ETHNOPHARMACOLOGICAL RELEVANCE Plants of the genus Drypetes (Putranjivaceae) are used in the Subsaharan African and Asian traditional medicines to treat a multitude of disorders, like dysentery, gonorrhoea, malaria, rheumatism, sinusitis, tumours, as well as for the treatment of wounds, headache, urethral problems, fever in young children, typhoid and several other ailments. Some Drypetes species are used to protect food against pests, as an aphrodisiac, a stimulant/depressant, a rodenticide and a fish poison, against insect bites, to induce conception and for general healing. This review deals with updated information on the ethnobotany, phytochemistry, and biological activities of ethnomedicinally important Drypetes species, in order to provide an input for the future research opportunities. METHODS An extensive review of the literature available in various recognized databases e.g., Google Scholar, PubMed, Science Direct, SciFinder, Web of Science, www.theplantlist.org and www.gbif.org, as well as the Herbier National du Cameroun (Yaoundé) and Botanic Gardens of Limbe databases on the uses and bioactivity of various species of the Drypetes was undertaken. RESULTS The literature provided information on ethnopharmacological uses of the Subsaharan African and Asian species of the genus Drypetes, e.g., Drypetes aubrévillii, D. capillipes, D. chevalieri, D. gerrardii, D. gossweileri, D. ivorensis, D. klainei, D. natalensis, D. pellegrini (all endemic to Africa) and D. roxburghii (Asian species), for the treatment of multiple disorders. From a total of 19 species, more than 140 compounds including diterpenes, sesquiterpenes, triterpenes (friedelane, oleanane, lupane and hopane-type), flavonoids, lignans, phenylpropanoids and steroids, as well as some thiocyanates, were isolated. Several crude extracts of these plants, and isolated compounds displayed significant analgesic, anthelmintic, antidiabetic, anti-emetic anti-inflammatory, antioxidant, antiparasitic, central nervous system depressant, cytotoxic, and insecticidal activities both in vitro and in vivo. Some toxicities associated with the stem, bark, seed and leaf extracts of D. roxburghii, and the flavonoid, amentoflavone, isolated from the stem extract of D. littoralis as well as D. gerrardii, were confirmed in the animal models and in the rat skeletal myoblast cells assays. As a consequence, traditional medicine from this genus should in future be applied with care. CONCLUSIONS Plants of this genus have offered bioactive samples, both from crude extracts and pure compounds, partly validating their effectivity in traditional medicine. However, most of the available scientific litteratures lacks information on relevant doses, duration of the treatment, storage conditions and positive controls for examining bioefficacy of extract and its active compounds. Additional toxicological studies on the species used in local pharmacopeia are urgently needed to guarantee safe application due to higth toxicity of some crude extracts. Interestingly, this review also reports 10 pimarane dinorditerpenoids structures with the aromatic ring C, isolated from the species collected in Asia Drypetes littoralis (Taiwan), D. perreticulata (China), and in Africa D. gerrardii (Kenya), D. gossweileri (Cameroon). These compounds might turn out to be good candidates for chemotaxonomic markers of the genus.
Keywords: Bioactivities, Chemical constituents, Drypetes, Ethnopharmacology
Magwé-Tindo J, Zapfack L, Sonké B (2015)
Biodiversity and Conservation.
Plant genetic resources, especially crop wild relatives like wild yams, are under high risks of extinction due to habitat loss, climate change, unacceptable collection practices, shifting cultivation practice and over-exploitation. To contribute to their conservation, the diversity of wild yams (Dioscorea spp.) collected in continental Africa was analyzed. Specimens from Herbaria (B, BR, K, P, WAG and YA), databases, literature and actual collection from Cameroon were considered. The collection localities were georeferenced and projected to Lambert azimuthal equal-area projection. Spatial analyses of sampling and diversity were conducted at three different resolutions: 50 × 50-, 100 × 100- and 150 × 150-km sized grid cells. Four thousand and eighty-seven specimens, collected in 2895 localities, were inventoried and grouped into 55 taxa including 43 species, five subspecies, four varieties and seven morpho-species. The genus Dioscorea occurred in fifteen out of the eighteen phytochoria recognized on African mainland. The Guineo–Congolian regional centre of endemism was the most sampled and the richest phytochorion with 28 taxa. In terms of floristic composition, the Sudanian regional centre of endemism and the Guinea–Congolia/Sudania regional transition zone were the most similar (similarity coefficient SCi = 0.84). Globally, the most diversified grid cells were located in Sierra Leone, Liberia, Ivory Coast, Ghana, Togo, Benin, Nigeria, Cameroon, Gabon, Equatorial Guinea, CAR, Congo, DRC, Tanzania and Malawi. In terms of phytogeography, they were found in two regional centres of endemism (Guineo–Congolian and Zambezian), two regional transition zones (Guinea–Congolia/Zambezia and Guinea–Congolia/Sudania) and one regional mosaic (Zanzibar–Inhambane). These areas could therefore be considered as potential sites for in situ conservation of wild yams in continental Africa.
Keywords: Conservation, Diversity indices, Floristic similarity, Georeferencing, Herbarium specimens
Todou G, Onana J, Akoa A, Eeckenbrugge G, Joly H (2014)
Journal ofTropical Forest Science 26(3) 420-427.
Dacryodes buettneri is an important timber tree in Central Africa. Its wood, commercially called ozigo, is sold in domestic and international markets. The species is only occasionally planted, mostly in home gardens. It is locally threatened. To assist in management planning and sustainable in-situ conservation, a study of the geographic distribution and ecological niche of D. buettneri was conducted. Data from 218 georeferenced collections were used to describe the geographic distribution. Assimilations based on 19 climatic parameters were used in order to describe the areas where it grew and to determine optimal values of climatic factors. The results showed that there were more collections of D. buettneri from Gabon than from neighbouring countries, with only a few collections in southern Cameroon and southern Congo. The modelled optimal rainfall was between 1600 and 2000 mm year-1 and the modelled optimal mean annual temperature, 23.8–25.8 °C. Dacryodes buettneri grows at low altitudes, from 0 to 750 m above sea level. The results of this study will be used to optimise strategies for in-situ conservation of populations of D. buettneri.
Keywords: in-situ conservation, natural ecological niche, ozigo, potential geographic distribution
Todou G, D’Eeckenbrugge G, Joly H, Akoa A, Onana J, Achoundong G (2013)
Climatic niche of Dacryodes edulis (G. Don) H. J. Lam (Burseraceae), a semi-domesticated fruit tree native to Central Africa
Journal of Ecology and the Natural Environment 5(9) 231-240.
Dacryodes edulis is a fruit tree growing naturally in the rainforests of Central Africa. To provide data to scientists and forest managers for the habitat of D. edulis in the wild, the study of ecological niche and environmental adaptation was carried out. The geographical coordinates of 168 collections of wild individuals and 19 climatic parameters were treated under Geographical Information System. Potential spatial richness, favourable climatic parameters and elevation of the species were described. The favourable climatic conditions for natural growth of D. edulis were mainly revealed in the forests of Gabon and Equatorial Guinea. In Cameroon, these conditions were well marked in the regions of Kribi and Bipindi (South), in the forest of Yingui and Yabassi (Littoral), in the Dja Forest (East) and South- West towards the border with Nigeria. The mean of favourable annual precipitation is 2205.26 ± 505.5 mm per year. The optimal annual mean temperatures stretch from 23.5 to 25.5°C. The favourable elevations stretch from 0 to 800 m. These values are smaller than ones for domesticated individuals which represent fundamental climatic niche. Prospect in forest areas with the best favourable climatic conditions and elevation for natural growth of D. edulis should be encouraged to ensure in situ conservation of wild populations for maintaining genetic diversity.
Keywords: dacryodes edulis, ecological niche, environmental adaptation, in situ conservation
Peh K, Sonké B, Taedoung H, Séné O, Lloyd J, Lewis S (2011)
Investigating diversity dependence of tropical forest litter decomposition: experiments and observations from Central Africa
Journal of Vegetation Science online n/a-n/a.
Questions: Mixed litter may decompose at different rates to single-species litter, leading to differences in ecosystem functioning and decomposition. Studies of the effects of different litter species and combinations are rare in tropical forests and absent from African forests. Therefore we investigated: (1) Are there differences in litter decomposition in two forest types differing in tree diversity; and (2) is litter decomposition diversity-dependent? Location: Old-growth moist evergreen tropical forest Dja Faunal Reserve, southeast Cameroon. Methods We calculate decomposition rates (leaf litter fall/leaf litter standing crop) along a tree diversity gradient in two forest types (naturally occurring low-diversity monodominant and adjacent higher-diversity mixed forest). Both forests experience the same climate on the same soil type; the former is dominated by a single species, Gilbertiodendron dewevrei (De Wild.) J. Léonard, probably due to lack of a long-term disturbance and has similar edaphic factors. Decomposition experiments were conducted in both forest types using single and mixed species litter bags of standard high-quality (bay leaves; Laurus nobilis L.) and low-quality (G. dewevrei) litter over 9 months. Results The estimated decomposition rate in mixed forest was four times faster than in monodominant forest, and not significantly correlated with local quadrat-scale tree species diversity. The litter bag experiment showed that decomposition of high-quality leaves was faster than low-quality leaves (k values: 2.0 yr−1 vs 0.6 yr−1). Decay rates for each single species litter type were not significantly different in both forest types. However, G. dewevrei litter in mixed bags decomposed faster than in single-species bags in mixed forest, suggesting an impact of litter mixing on decomposition. In addition, bay litter in mixed bags decomposed faster in mixed than in monodominant forests across the three study sites. Conclusion The observed difference in litter decomposition rate between low-diversity monodominant and adjacent high-diversity forest is more likely due to dominance of low-quality G. dewevrei litter, rather than low-diversity of the litter itself.
Keywords: experiment, forests, functional diversity, leaf litter fall, litter bag, mixed forests, monodominant, standing litter crop, tree diversity
Waltert M, Bobo K, Kaupa S, Montoya M, Nsanyi M, Fermon H (2011)
PLoS ONE 6(1) e16238.
Despite an increasing amount of data on the effects of tropical land use on continental forest fauna and flora, it is debatable whether the choice of the indicator variables allows for a proper evaluation of the role of modified habitats in mitigating the global biodiversity crisis. While many single-taxon studies have highlighted that species with narrow geographic ranges especially suffer from habitat modification, there is no multi-taxa study available which consistently focuses on geographic range composition of the studied indicator groups. We compiled geographic range data for 180 bird, 119 butterfly, 204 tree and 219 understorey plant species sampled along a gradient of habitat modification ranging from near-primary forest through young secondary forest and agroforestry systems to annual crops in the southwestern lowlands of Cameroon. We found very similar patterns of declining species richness with increasing habitat modification between taxon-specific groups of similar geographic range categories. At the 8 km(2) spatial level, estimated richness of endemic species declined in all groups by 21% (birds) to 91% (trees) from forests to annual crops, while estimated richness of widespread species increased by +101% (trees) to +275% (understorey plants), or remained stable (-2%, butterflies). Even traditional agroforestry systems lost estimated endemic species richness by -18% (birds) to -90% (understorey plants). Endemic species richness of one taxon explained between 37% and 57% of others (positive correlations) and taxon-specific richness in widespread species explained up to 76% of variation in richness of endemic species (negative correlations). The key implication of this study is that the range size aspect is fundamental in assessments of conservation value via species inventory data from modified habitats. The study also suggests that even ecologically friendly agricultural matrices may be of much lower value for tropical conservation than indicated by mere biodiversity value.
Keywords: experiment, forests, functional diversity, leaf litter fall, litter bag, mixed forests, monodominant, standing litter crop, tree diversity