Ministere des Eaux

Bangui, Central African Republic

Ministere des Eaux

Bangui, Central African Republic
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Mortier F.,CIRAD - Agricultural Research for Development | Ouedraogo D.-Y.,CIRAD - Agricultural Research for Development | Claeys F.,CIRAD - Agricultural Research for Development | Claeys F.,Agro ParisTech | And 8 more authors.
Environmetrics | Year: 2015

Understanding how environmental factors could impact population dynamics is of primary importance for species conservation. Matrix population models are widely used to predict population dynamics. However, in species-rich ecosystems with many rare species, the small population sizes hinder a good fit of species-specific models. In addition, classical matrix models do not take into account environmental variability. We propose a mixture of regression models with variable selection allowing the simultaneous clustering of species into groups according to vital rate information (recruitment, growth and mortality) and the identification of group-specific explicative environmental variables. We develop an inference method coupling the R packages flexmix and glmnet. We first highlight the effectiveness of the method on simulated datasets. Next, we apply it to data from a tropical rain forest in the Central African Republic. We demonstrate the accuracy of the inhomogeneous mixture matrix model in successfully reproducing stand dynamics and classifying tree species into well-differentiated groups with clear ecological interpretations. © 2014 John Wiley & Sons, Ltd.

Maisels F.,Wildlife Conservation Society | Maisels F.,University of Stirling | Strindberg S.,Wildlife Conservation Society | Blake S.,Wildlife Conservation Society | And 71 more authors.
PLoS ONE | Year: 2013

African forest elephants- taxonomically and functionally unique-are being poached at accelerating rates, but we lack range-wide information on the repercussions. Analysis of the largest survey dataset ever assembled for forest elephants (80 foot-surveys; covering 13,000 km; 91,600 person-days of fieldwork) revealed that population size declined by ca. 62% between 2002-2011, and the taxon lost 30% of its geographical range. The population is now less than 10% of its potential size, occupying less than 25% of its potential range. High human population density, hunting intensity, absence of law enforcement, poor governance, and proximity to expanding infrastructure are the strongest predictors of decline. To save the remaining African forest elephants, illegal poaching for ivory and encroachment into core elephant habitat must be stopped. In addition, the international demand for ivory, which fuels illegal trade, must be dramatically reduced. © 2013 Maisels et al.

PubMed | Max Planck Institute for Evolutionary Anthropology, University of Oxford, University of Bangui, University of Buea and 12 more.
Type: | Journal: Scientific reports | Year: 2015

Large tropical trees and a few dominant species were recently identified as the main structuring elements of tropical forests. However, such result did not translate yet into quantitative approaches which are essential to understand, predict and monitor forest functions and composition over large, often poorly accessible territories. Here we show that the above-ground biomass (AGB) of the whole forest can be predicted from a few large trees and that the relationship is proved strikingly stable in 175 1-ha plots investigated across 8 sites spanning Central Africa. We designed a generic model predicting AGB with an error of 14% when based on only 5% of the stems, which points to universality in forest structural properties. For the first time in Africa, we identified some dominant species that disproportionally contribute to forest AGB with 1.5% of recorded species accounting for over 50% of the stock of AGB. Consequently, focusing on large trees and dominant species provides precise information on the whole forest stand. This offers new perspectives for understanding the functioning of tropical forests and opens new doors for the development of innovative monitoring strategies.

Gourlet-Fleury S.,CIRAD - Agricultural Research for Development | Beina D.,University of Bangui | Beina D.,University of Picardie Jules Verne | Fayolle A.,Ministere des Eaux | And 6 more authors.
Forest Ecology and Management | Year: 2013

Timber production is an important economic sector in most forested countries of Central Africa, where about 14 million hectares of lowland moist forests are now planned for management. This production is expected to be sustainable, but the actual impact of logging on biodiversity is still questioned.To answer this question, we used a unique long-term controlled experiment implemented more than 20. years ago in an old-growth semi-deciduous moist forest of the Central African Republic (CAR). We tested whether (i) anthropogenic disturbances associated with silvicultural operations had an effect on the composition and diversity of tree communities, and (ii) there is a relationship between diversity and disturbance intensity in those forests.For this, we botanically identified all trees. ≥. 10. cm DBH in 28 1-ha plots where no treatment (controls), logging and logging. +. thinning operations were implemented 24. years ago and created a strong gradient of disturbance. We investigated the relationships between five diversity indices and a disturbance index calculated for each 1-ha plot, for all species and separately for three regeneration guilds.We found a strong positive monotonic relationship between the intensity of disturbance and the percentage of pioneer species in the tree communities, which proved to be equally detrimental, in terms of relative abundance, to the non-pioneer light-demanding and the shade-bearing species.Overall, disturbance appeared to have a weak monotonous negative effect on diversity, irrespective to the index considered. The diversity of shade-bearers slightly decreased along the disturbance gradient without significant decrease in species density; disturbance had no effect on non-pioneer light demanders, but a clear significant negative effect on the diversity of pioneers, with a significant decrease in species density. This negative effect was associated with the massive recruitment of the early-successional, fast-growing Musanga cecropioides R. Br. (Urticaceae), which rapidly preempted space and resources in the most disturbed plots. Despite this effect, disturbance did not significantly affect the local heterogeneity in species distribution.These results suggest that the semi-deciduous moist forests of CAR are locally resilient to small-scale disturbances associated with silvicultural operations. This may be a consequence of the past anthropogenic and/or climatic disturbances, which have been stronger and more long-lasting than elsewhere within the tropical forest biome, and would have removed the most vulnerable species. Because logging intensity in these forests is usually low, we do not expect any direct major impact on tree species diversity, at least after the first felling cycle. © 2013 Elsevier B.V.

Freycon V.,CIRAD - Agricultural Research for Development | Wonkam C.,CIRAD - Agricultural Research for Development | Wonkam C.,University of Yaounde I | Fayolle A.,Ministere des Eaux | And 6 more authors.
Journal of Tropical Ecology | Year: 2015

Despite the important functional role of deep roots in withdrawing water during drought, direct measurements of root distribution are very rare in tropical rain forests. The aim of this study was to investigate the root distribution of Entandrophragma cylindricum, a common tree species in the Central African semi-deciduous rain forest, in Ferralsols and Arenosols. We dug two pits to a depth of 6 m in Ferralsols and two pits to a depth of 3 m in Arenosols, close to E. cylindricum trees. The vertical soil profiles were divided into 10 × 10-cm grid cells and the roots counted were distributed in three diameter classes. We fitted a root distribution model to our dataset. We found that vertical root distribution was shallower in Arenosols than in Ferralsols. Root penetration was not stopped even by a Ferralsol with high gravel content in its subsoil. Overall, our measurements showed that 95% of all roots were distributed to depths of between 258 and 564 cm from the soil surface, which is much deeper than the 95 cm depth previously reported in the literature for tropical rain forests. As sampling depth could explain this discrepancy, we recommend a sampling depth of at least 3-5 m to accurately estimate root distribution. The drier the dry season, the deeper the sampling depth should be. Our results are consistent with global models of root distribution in forest ecosystems, which are driven by climate variables. We thus suggest that deep rooting could be common in rain forests with a marked dry season. Copyright © 2014 Cambridge University Press.

Gourlet-Fleury S.,CIRAD - Agricultural Research for Development | Mortier F.,CIRAD - Agricultural Research for Development | Fayolle A.,University of Liège | Baya F.,Ministere des Eaux | And 3 more authors.
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2013

Large areas of African moist forests are being logged in the context of supposedly sustainable management plans. It remains however controversial whether harvesting a few trees per hectare can be maintained in the long term while preserving other forest services as well. We used a unique 24 year silvicultural experiment, encompassing 10 4 ha plots established in the Central African Republic, to assess the effect of disturbance linked to logging (two to nine trees ha-1 greater than or equal to 80 cm DBH) and thinning (11-41 trees ha-1 greater than or equal to 50 cm DBH) on the structure and dynamics of the forest. Before silvicultural treatments, above-ground biomass (AGB) and timber stock (i.e. the volume of commercial trees greater than or equal to 80 cm DBH) in the plots amounted 374.5+58.2 Mg ha-1 and 79.7+45.9 m3 ha-1, respectively. We found that (i) natural control forest was increasing in AGB (2.58+1.73 Mg dry mass ha-1 yr-1) and decreasing in timber stock (20.33+1.57 m3 ha-1 yr-1); (ii) the AGB recovered very quickly after logging and thinning, at a rate proportional to the disturbance intensity (mean recovery after 24 years: 144%). Compared with controls, the gain almost doubled in the logged plots (4.82+1.22 Mg ha-1 yr-1) and tripled in the logged {thorn} thinned plots (8.03+1.41 Mg ha-1 yr-1); (iii) the timber stock recovered slowly (mean recovery after 24 years: 41%), at a rate of 0.75+0.51 m3 ha-1 yr-1 in the logged plots, and 0.81+0.74 m3 ha-1 yr-1 in the logged {thorn} thinned plots. Although thinning significantly increased the gain in biomass, it had no effect on the gain in timber stock. However, thinning did foster the growth and survival of small- and medium-sized timber trees and should have a positive effect over the next felling cycle. © 2013 The Authors.

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