References of "Doucet, Jean-Louis"
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See detailThe need for site-specific height-diameter allometry of Central African moist forests
Loubota Panzou, Grâce Jopaul ULg; Doucet, Jean-Louis ULg; Fayolle, Adeline ULg

Conference (2015, March 21)

L’utilisation de l’allométrie hauteur-diamètre globale ou régionale en milieu tropical pourrait avoir des conséquences importantes dans les estimations de biomasse et des stocks de carbone. L’objectif de ... [more ▼]

L’utilisation de l’allométrie hauteur-diamètre globale ou régionale en milieu tropical pourrait avoir des conséquences importantes dans les estimations de biomasse et des stocks de carbone. L’objectif de ce travail est d’identifier les variations de l’allométrie hauteur-diamètre au sein de deux types de forêts (forêt sempervirente et forêt semi-décidue) au sud du Cameroun et d’examiner leurs conséquences sur les estimations de biomasse. Le diamètre et la hauteur ont été mesurés sur un total de 521 arbres appartenant à 15 espèces et couvrant une gamme de diamètre de 10 à 240 cm. Une calibration des mesures non destructives et destructives de la hauteur a été réalisée sur 60 arbres. Dix modèles allométriques ont été ajustés sur ces données. Le meilleur modèle a été sélectionné avec Akaike Information Criterion (AIC). L’allométrie hauteur-diamètre au niveau des sites et entre les espèces a montré une tendance asymptotique (Modèle de Michaelis-Menten). Pour un même diamètre, les arbres étaient plus hauts dans les forêts semi-décidues que dans les forêts sempervirentes. Les différences de biomasse entre les deux types de forêts sont dues par les variations de l’allométrie hauteur-diamètre. Les variations de l’allométrie hauteur-diamètre sont donc d’une extrême importance dans les estimations de biomasse et des stocks de carbone des forêts denses humides tropicales d’Afrique centrale. [less ▲]

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See detailDifferences in dung beetle activity at western gorilla defecation sites in south-east Cameroon: implications for establishment of Uapaca spp. seedlings
Petre, Charles-Albert ULg; Zinque, Marie-Hélène; Tagg, Nikki et al

in Journal of Tropical Ecology (2015), 31(02), 161-174

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See detailApproche agroforestière. Synthèse des travaux menés par le projet DACEFI2 en agroforesterie. Document de capitalisation.
Boldrini, Sylvie; Meunier, Quentin; Boukouendji, Basile et al

E-print/Working paper (2015)

Le projet DACEFI-2 a eu pour mission première la promotion de la foresterie communautaire comme outil de développement des communautés rurales. L’approche au Gabon en matière de gestion des terroirs ... [more ▼]

Le projet DACEFI-2 a eu pour mission première la promotion de la foresterie communautaire comme outil de développement des communautés rurales. L’approche au Gabon en matière de gestion des terroirs villageois s’est voulue plus embrassante, promouvant en sus de l’exploitation forestière des activités comme l’agriculture, le maraîchage, la collecte des produits forestiers non ligneux ou encore l’agroforesterie. L’agroforesterie est une thématique qui converge parfaitement avec la gestion raisonnée de la forêt, et idéalement avec les modes d’interaction préexistants des villageois avec celle-ci. Concilier dans un même espace la culture de plantes vivrières et l’accès à des arbres à fort intérêt socio-économique apporte une plus-value notoire aux parcelles cultivées. L’optimisation des techniques culturales permet une meilleure productivité et une incitation à la sédentarisation des cultures, élément important à considérer compte tenu des difficultés d’entretien des parcelles éloignées du village (notamment liées aux dégâts causés par les animaux). Ce recueil compile les travaux réalisés en agroforesterie par les équipes du projet DACEFI-2. Il rappelle la stratégie d’intervention et les différentes activités menées, de la sensibilisation auprès des plus jeunes à la promotion de certains produits forestiers non ligneux à potentiel économique avéré. La promotion de l’arbre, de la récolte de la graine jusqu’à sa plantation en passant par sa mise en pépinière aura également animé toute l’équipe durant ces années d’exercice, afin de faire un peu plus valoir ses multiples intérêts et susciter les efforts de gestion, de conservation et de reboisement. [less ▲]

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See detailSite-specific height-diameter allometry of Central African moist forests
Loubota Panzou, Grâce Jopaul ULg; Doucet, Jean-Louis ULg; Fayolle, Adeline ULg

Poster (2015, February 04)

In this study we aimed to identify the variation in height-diameter allometry between forest types and among species in Central African moist forests. We also examined the consequences on biomass ... [more ▼]

In this study we aimed to identify the variation in height-diameter allometry between forest types and among species in Central African moist forests. We also examined the consequences on biomass estimation. Two forest sites in southern Cameroon with contrasting levels of deciduousness. Height and diameter were measured for a total of 521 trees belonging to 12 timber species over a large range of diameter, 10-240 cm for the Ma’an site and 11-182 cm for the Mindourou site. Non-destructive height measurements were calibrated with destructive measurements for a total of 60 trees, 30 in each site. Commercial forest inventory data (n=7253 0.5ha plots) were gathered for the Ma’an (n=34 samples and 2101 plots) and Mindourou (n=117 samples and 5152 plots) sites. A total of ten allometric models (including asymptotic and non-asymptotic models) were fitted to the height-diameter data at species (n=12) and site (n=2) level. Biomass estimates were computed based on forest inventory data and general allometric models using both site-specific and published height-diameter equations. Given the strong correlation between the non-destructive and destructive height measurements we had confidence in using the non-destructive height measurements to establish site- and species-specific height-diameter allometric equations. The height measurements performed over a wide range of diameters, 10-240 cm, tended to support an asymptotic shape (and most often the Michaelis Menten model) for the height-diameter allometry either at species and site level. We identified a significant difference in height-diameter allometry between the two study sites. For a given diameter, trees tended to be taller in the more semi-deciduous Mindourou site than in the more evergreen Ma’an site, with a maximum height of 39.5 and 46.5 m, respectively. The two sites significantly differed in stand structure and biomass. This difference is due to the variation in height-diameter allometry. Height-diameter allometry strongly varies between sites and site-specific height-diameter allometric equations should be developed to further improve the estimation of biomass and carbon stock contained in tropical forests. [less ▲]

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See detailDifferential Performance between Two Timber Species in Forest Logging Gaps and in Plantations in Central Africa
Fayolle, Adeline ULg; Ouedraogo, Dakis-Yaoba ULg; Ligot, Gauthier ULg et al

in Forests (2015), 6(2), 380-394

To develop silvicultural guidelines for high-value timber species of Central African moist forests, we assessed the performance of the pioneer Milicia excelsa (iroko, Moraceae), and of the non-pioneer ... [more ▼]

To develop silvicultural guidelines for high-value timber species of Central African moist forests, we assessed the performance of the pioneer Milicia excelsa (iroko, Moraceae), and of the non-pioneer light demander Pericopsis elata (assamela, Fabaceae) in logging gaps and in plantations in highly degraded areas in south-eastern Cameroon. The survival and size of each seedling was regularly monitored in the silvicultural experiments. Differences in performance and allometry were tested between species in logging gaps and in plantations. The two species performance in logging gaps was significantly different from plantations and concurred with the expectations of the performance trade-off hypothesis but not with the expectations of species light requirements. The pioneer M. excelsa survived significantly better in logging gaps while the non-pioneer P. elata grew significantly faster in plantations. The high mortality and slow growth of M. excelsa in plantations is surprising for a pioneer species but could be explained by herbivory (attacks from a gall-making psyllid). Identifying high-value native timber species (i) with good performance in plantations such as P. elata is of importance to restore degraded areas; and (ii) with good performance in logging gaps such as M. excelsa is of importance to maintain timber resources and biodiversity in production forests. [less ▲]

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See detailIdentification of charred botanical remains provides more accurate information on past history in Central Africa
Morin, Julie ULg; Biwolé, Achille; Bourland, Nils et al

Poster (2015, January 30)

In palaeoenvironmental studies, charred botanical remains have rarely been identified to the species level before being sent to radiocarbon dating. Moreover, the age of most tropical spp. and thereby the ... [more ▼]

In palaeoenvironmental studies, charred botanical remains have rarely been identified to the species level before being sent to radiocarbon dating. Moreover, the age of most tropical spp. and thereby the age of the carbon sequestered during plant growth is not known. Dating unidentified charred wood in the tropics should be thus treated with caution because the accuracy of the dates is not guaranteed. Here we present 71 dates obtained on charred endocarps and wood charcoals sampled in soil pits in Cameroon and in the Rep. of the Congo. We taxonomically identified 43 samples then selected both identified and unidentified individual fragments for radiocarbon dating. We performed summed probability distributions of the dates calibrated in BP for the 43 identified and the 28 unidentified samples separately then for the whole dates. Results showed that the dates obtained on unidentified samples better fit the established chronology for Central Africa but that they also presented less precise standard deviations than the dates obtained on identified short-lived material, and that the dates on identified samples provide more detailed trends about the phases of human occupation in Central Africa after 2,500 BP. We can assume that dating unidentified material may introduce some blur into chronologies and that the selection of identified charred botanical remains should be systematically applied for palaeoenvironmental reconstructions in tropical contexts to refine the chronologies. [less ▲]

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See detailHow Tightly Linked Are Pericopsis elata (Fabaceae) Patches to Anthropogenic Disturbances in Southeastern Cameroon?
Bourland, Nils; Cerisier, François; Daïnou, Kasso ULg et al

in Forests (2015), 6(2), 293-310

While most past studies have emphasized the relationships between specific forest stands and edaphic factors, recent observations in Central African moist forests suggested that an increase of slash-and ... [more ▼]

While most past studies have emphasized the relationships between specific forest stands and edaphic factors, recent observations in Central African moist forests suggested that an increase of slash-and-burn agriculture since 3000–2000 BP (Before Present) could be the main driver of the persistence of light-demanding tree species. In order to examine anthropogenic factors in the persistence of such populations, our study focused on Pericopsis elata, an endangered clustered timber species. We used a multidisciplinary approach comprised of botanical, anthracological and archaeobotanical investigations to compare P. elata patches with surrounding stands of mixed forest vegetation (“out-zones”). Charcoal samples were found in both zones, but were significantly more abundant in the soils of patches. Eleven groups of taxa were identified from the charcoals, most of them also present in the current vegetation. Potsherds were detected only inside P. elata patches and at different soil depths, suggesting a long human presence from at least 2150 to 195 BP, as revealed by our charcoal radiocarbon dating. We conclude that current P. elata patches most likely result from shifting cultivation that occurred ca. two centuries ago. The implications of our findings for the dynamics and management of light-demanding tree species are discussed. [less ▲]

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See detailMicrosatellite Development and Flow Cytometry in the African Tree Genus Afzelia (Fabaceae, Caesalpinioideae) Reveal a Polyploid Complex
Donkpegan, Segbedji ULg; Doucet, Jean-Louis ULg; Daïnou, Kasso ULg et al

in Applications in Plant Sciences (2015), 3(1)

Premise of the study: Microsatellites were developed in the vulnerable African rainforest tree Afzelia bipindensis to investigate gene flow patterns. Methods and Results: Using 454 GS-FLX technique, 16 ... [more ▼]

Premise of the study: Microsatellites were developed in the vulnerable African rainforest tree Afzelia bipindensis to investigate gene flow patterns. Methods and Results: Using 454 GS-FLX technique, 16 primer sets were identified and optimized, leading to 11 polymorphic and readable markers displaying each six to 25 alleles in a population. Up to four alleles per individual were found in each of the loci, without evidence of fixed heterozygosity, suggesting an autotetraploid genome. Cross-amplification succeeded for all loci in the African rainforest species A. pachyloba and A. bella, which appeared tetraploid, and for most loci in the African woodland species A. africana and A. quanzensis, which appeared diploid, but failed in the Asian species A. xylocarpa. Flow cytometry confirmed the suspected differences in ploidy. Conclusions: African Afzelia species are diploid or tetraploid, a situation rarely documented in tropical trees. These newly developed microsatellites will help in the study of their mating system and gene flow patterns. [less ▲]

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See detailWestern lowland gorilla seed dispersal: Are seeds adapted to long gut retention times?
Petre, Charles-Albert ULg; Tagg, Nikki; Beudels-Jamar, Roseline et al

in Acta Oecologica: International Journal of Ecology (2015), 67

The degree of seed scarification in the frugivore gut, partly dependent on gut retention time, is a key component in determining the extent to which gut passage alters germination performances. Another ... [more ▼]

The degree of seed scarification in the frugivore gut, partly dependent on gut retention time, is a key component in determining the extent to which gut passage alters germination performances. Another potential benefit of gut passage arises as a result of the removal of fruit pulp which otherwise may act as a germination inhibitor. Using experiments designed to disentangle the respective effects of pulp removal (germination deinhibition) and seed scarification, and gut retention time as an explanatory variable, we investigated the effect of gut passage on germination performances (percentage and latency) of five tropical tree species dispersed by the western lowland gorilla (Gorilla g. gorilla). The percentage of seeds germinating after gut passage increased for three species, respectively, through the effects of scarification only, deinhibition only, and scarification and deinhibition combined. A negative scarification effect was observed for one species, and no effect of gut passage for another. Passage through the gut led to a decrease in germination latency of three species, as a result of the depulping of seeds. However, seed scarification resulted in germination delays for another species. The gut retention time of the five species averaged 39e56 h and had no effect on intra-specific germination performances except for one species whose germination probability increased as gut retention time increased. As gut retention time often correlates with dispersal distance, the fact that gut retention time per se does not reduce seed viability of these tropical tree species may have positive implications for their population dynamics and maintenance of genetic diversity. If no detrimental effect of gut retention time on germination performance is a general trait among tropical species, the extirpation of large frugivores with long gut retention time, such as the western lowland gorilla, would likely have negative long-term implications for tropical forests. [less ▲]

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See detailIs the western lowland gorilla a good gardener ? Evidence for directed dispersal in Southeast Gabon
Haurez, Barbara ULg; Brostaux, Yves ULg; Petre, Charles-Albert ULg et al

in Bois et Forêts des Tropiques (2015), 324(2), 39-50

In Central African tropical forests, the western lowland gorilla deposits most of the seeds it disperses in well-lit nesting sites that can favour seedling growth. The faecal matrix surrounding the seeds ... [more ▼]

In Central African tropical forests, the western lowland gorilla deposits most of the seeds it disperses in well-lit nesting sites that can favour seedling growth. The faecal matrix surrounding the seeds can act as a fertiliser and further enhance seedling development. This fertilisation effect had never been tested. Our research therefore aimed to determine whether seed deposition by gorillas (i) in faecal matter and (ii) in nest sites is advantageous for seedling development (growth rate and foliation rate) and survival (% of surviving seedlings). To assess the effect of the faecal matrix, seeds of Santiria trimera (Burseraceae), Chrysophyllum lacourtianum (Sapotaceae) and Plagiostyles africana (Euphorbiaceae) collected from gorilla faeces were sown in a nursery with and without a faecal matrix. Seedlings of Santiria trimera and Dacryodes normandii (Burseraceae) were established in nest sites and in closed canopy terra firme forest sites to assess the impact of seed deposition on seedling development and survival. The faecal matrix was observed to positively influence seedling development in the species studied, but showed no effect on survival. Regarding seed deposition sites, the development rates observed were two to ten times higher in the nest sites than in closed-canopy forest. This enhanced seedling development was positively correlated with canopy openness. In situ studies of seed germination, seedling growth and survival are needed to characterise the fate of gorilla-dispersed seeds more precisely. However, our results offer evidence that gorillas provide important directed dispersal services by depositing seeds most frequently in open canopy sites. [less ▲]

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See detailNew data on the recent history of the littoral forests of southern Cameroon: an insight into the role of historical human disturbances on the current forest composition
Biwolé, Achille ULg; Morin-Rivat, Julie ULg; Fayolle, Adeline ULg et al

in Plant Ecology and Evolution (2015), 148(1), 19-28

Background and aims – Prior to European colonisation of Central Africa, human populations were dispersed through the forests, where they practiced slash-and-burn cultivation. From the 19th century they ... [more ▼]

Background and aims – Prior to European colonisation of Central Africa, human populations were dispersed through the forests, where they practiced slash-and-burn cultivation. From the 19th century they were progressively concentrated in villages along roads, leaving large areas of forest derelict. In south-western Cameroon, and elsewhere in Central Africa, forest canopy is dominated by long-lived lightdemanding tree species, suggesting a possible role of human disturbance. The aim of this study was to bring new insights into the possible effect of historical human disturbances in terms of timing and spatial extent on the current forest composition. Location – Wet evergreen littoral forest in south-western Cameroon. Methods and key results – A combined vegetation sampling and archaeobotanical survey were conducted. Potsherds, oil-palm endocarps, and charcoal were found throughout the study area, suggesting generalised human occupation and anthropogenic fire. Human occupancy occurred in two periods: between 2200 and 1500 BP, and, more recently, beginning three centuries ago. High frequency of fire and the presence of Elaeis guineensis both dated recently (between 260 and 145 BP) suggest slash-and-burn shifting cultivation practices. These human-induced disturbances may coincide with the age of the current emergent lightdemanding species, the age of which can be estimated around 200 years, or with the phases of drying climate recorded in the Central African forest in the early 18th century. Conclusions – These results support the idea that historical human disturbances are one of the major factors that shaped the current forest composition in Central Africa. [less ▲]

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See detailLight Response of Seedlings of a Central African Timber Tree Species, Lophira alata (Ochnaceae), and the Definition of Light Requirements
Biwolé, Achille Bernard; Daïnou, Kasso ULg; Fayolle, Adeline ULg et al

in Biotropica (2015), 47(6), 681-688

Light is of primary importance in structuring tropical tree communities. Light exposure at seedling and adult stages has been used to characterize the ecological profile of tropical trees, with many ... [more ▼]

Light is of primary importance in structuring tropical tree communities. Light exposure at seedling and adult stages has been used to characterize the ecological profile of tropical trees, with many implications in forest management and restoration ecology. Most shadetolerance classification systems have been proposed based on empirical observations in a specific area and thus result in contradictions among categories assigned to a given species. In this study, we aimed to quantify the light requirements for seedling growth of a Central African timber tree, Lophira alata (Ochnaceae), taking into account effects of population origin. In two controlled experiments: a light response experiment and a comparative population experiment, conducted in southwestern Cameroon, using seeds collected from four populations (three from Cameroon and one from Gabon), we examined the quantitative responses to irradiance of seedlings. After 2 years, mortality was very low (<3%), even in extremely low irradiance. Growth and biomass allocation patterns varied in response to light, with intermediate irradiance (24–43%) providing optimal conditions. Light response differed between populations. The Boumba population in the northeastern edge of the species’ distribution exhibited the highest light requirements, suggesting a local adaptation. As a result of positive growth at low irradiance and maximum growth at intermediate irradiance, we concluded that L. alata exhibits characteristics of both non-pioneer and pioneer species. Implications of our results to propose an objective way to assign the light requirement for tropical tree species are discussed. [less ▲]

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See detailGlobally, functional traits are weak predictors of juvenile tree growth, and we do not know why
Paine, C.E. Thimothy; Amissah, Lucy; Auge, Harald et al

in Journal of Ecology (2015), 103(4), 978-989

1. Plant functional traits, in particular specific leaf area (SLA), wood density and seed mass, are often good predictors of individual tree growth rates within communities. Individuals and species with ... [more ▼]

1. Plant functional traits, in particular specific leaf area (SLA), wood density and seed mass, are often good predictors of individual tree growth rates within communities. Individuals and species with high SLA, low wood density and small seeds tend to have faster growth rates. 2. If community-level relationships between traits and growth have general predictive value, then similar relationships should also be observed in analyses that integrate across taxa, biogeographic regions and environments. Such global consistency would imply that traits could serve as valuable proxies for the complex suite of factors that determine growth rate, and, therefore, could underpin a new generation of robust dynamic vegetation models. Alternatively, growth rates may depend more strongly on the local environment or growth–trait relationships may vary along environmental gradients. 3. We tested these alternative hypotheses using data on 27 352 juvenile trees, representing 278 species from 27 sites on all forested continents, and extensive functional trait data, 38% of which were obtained at the same sites at which growth was assessed. Data on potential evapotranspiration (PET), which summarizes the joint ecological effects of temperature and precipitation, were obtained from a global data base. 4. We estimated size-standardized relative height growth rates (SGR) for all species, then related them to functional traits and PET using mixed-effect models for the fastest growing species and for all species together. 5. Both the mean and 95th percentile SGR were more strongly associated with functional traits than with PET. PET was unrelated to SGR at the global scale. SGR increased with increasing SLA and decreased with increasing wood density and seed mass, but these traits explained only 3.1% of the variation in SGR. SGR–trait relationships were consistently weak across families and biogeographic zones, and over a range of tree statures. Thus, the most widely studied functional traits in plant ecology were poor predictors of tree growth over large scales. 6. Synthesis. We conclude that these functional traits alone may be unsuitable for predicting growth of trees over broad scales. Determining the functional traits that predict vital rates under specific environmental conditions may generate more insight than a monolithic global relationship can offer. [less ▲]

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See detailThe role of great apes in seed dispersal of the tropical forest tree species Dacryodes normandii (Burseraceae) in Gabon
Haurez, Barbara ULg; Daïnou, Kasso ULg; Tagg, Nikki et al

in Journal of Tropical Ecology (2015), 31(05), 395-402

The identification of seed dispersers and predators is essential to understand the effect of anthropogenic disturbances, and the associated defaunation process, on tropical forest dynamics in Central ... [more ▼]

The identification of seed dispersers and predators is essential to understand the effect of anthropogenic disturbances, and the associated defaunation process, on tropical forest dynamics in Central Africa. In this study, the animals involved in seed predation and dispersal of Dacryodes normandii (Burseraceae), an endozoochorously dispersed tree species endemic to Gabonese forests, were identified in a site in south-east Gabon using two complementary methods: direct observation and camera-trap monitoring of fruit piles. The combined sampling effort (172 h of direct observations and 796 d of camera trapping) led to the identification of six disperser and eight predator species of D. normandii seeds. With high frequency of consumption (88% and 57% of their visits, respectively) and long visit duration (83 and 23 min, respectively), the western lowland gorilla and central chimpanzee were identified as the main dispersers of this species. Seeds passed through the gorilla gut exhibited high germination success (68%). Rodents were identified as predators of D. normandii seeds, potentially displaying rare secondary dispersal through scatter-hoarding. The results of this study highlight the importance of great apes in the seed dispersal of this tree species. [less ▲]

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See detailLe genre Guibourtia Benn., un taxon à haute valeur commerciale et sociétale (synthèse bibliographique)
Tosso, Dji-ndé Félicien ULg; Daïnou, Kasso ULg; Hardy, J. Olivier et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2015), 19(1),

Known as a genus of great socio-cultural and economical importance, Guibourtia Benn. includes morphologically very similar multipurpose sister species, found in various habitats with different climate and ... [more ▼]

Known as a genus of great socio-cultural and economical importance, Guibourtia Benn. includes morphologically very similar multipurpose sister species, found in various habitats with different climate and soil conditions. In many places, Guibourtia is subject to local overexploitation by forest companies and local communities. As the population density of Guibourtia species is generally very low, it may be necessary to conduct scientific investigations that will provide valuable information for the management of the populations concerned. This paper is based on an extensive literature review and summarizes the available information on the genus Guibourtia, in terms of botany, ecology, genetics, forestry and ethnobotany. Our review provided evidence that, to date, ecological and silvicultural knowledge regarding Guibourtia species is lacking and that it is very difficult to morphologically differentiate very similar sister species. In addition, we provide a new determination key for the genus Guibourtia. Based on the available information, it is difficult to assess the conservation status of these taxa. Further investigations are needed to suggest appropriate management strategies for Guibourtia. Moreover, species diversity within this genus and its distribution in various tropical biomes make it an excellent biological model for understanding the historical, biological and environmental mechanisms that explain the diversity of tropical moist forests. [less ▲]

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See detailWood anatomical characteristics of 600 African tropical species in relationship with their ecology
Morin, Julie ULg; Fayolle, Adeline ULg; Doucet, Jean-Louis ULg et al

Poster (2014, December 16)

The tropical moist forest is a biome with a high number of species that are functionally different. The question arises whether there are patterns in the spectra of wood anatomical features according to ... [more ▼]

The tropical moist forest is a biome with a high number of species that are functionally different. The question arises whether there are patterns in the spectra of wood anatomical features according to functional types. Here we propose to present the main anatomical characteristics of 600 tropical species from the Guineo-Congolian domain in relationship with their ecology. We cross-checked two databases: the anatomical database InsideWood and the CoForTraits database of functional traits produced during the CoForChange project. After characterizing the main trends of the dataset, we performed multivariate analyses between the wood traits (i.e. the anatomical features) and six groups of functional traits: leaf phenology, regeneration guild, dispersal syndrome, life form, plant maximum height, and wood specific gravity. Results showed (i) that several wood features were specific to the tropics, to Africa or only to the Guineo-Congolian region, and (ii) that phylogeny explained the main part of the variation among the traits, whereas (iii) wood structure provided nonetheless interesting functional information related to gradients in plant growth, survival, and dispersal, and (iv) that there was a functional convergence in the study species in response to similar environmental constraints. These observations suggest that certain anatomical features can be used as indicators of functional traits in species-rich biomes. Further research will enable us to increase the input of wood anatomy in explaining the functional trade-offs in African tropical species. [less ▲]

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See detailLe genre Erythrophleum (Fabaceae) en Afrique, un modèle pour l’étude des mécanismes de différenciation de niches climatiques
Gorel, Anaïs ULg; Duminil, Jérôme; Doucet, Jean-Louis ULg et al

Conference (2014, December 16)

Comprendre l’origine des patrons de diversité est un défi en écologie des communautés et en écologie évolutive, notamment dans le contexte du futur changement climatique. Ce poster aura deux objectifs : i ... [more ▼]

Comprendre l’origine des patrons de diversité est un défi en écologie des communautés et en écologie évolutive, notamment dans le contexte du futur changement climatique. Ce poster aura deux objectifs : i) présenter pourquoi le genre Erythrophleum en Afrique est un modèle d’étude idéal à la compréhension des mécanismes de différenciation de niche et de spéciation au sein d’une lignée d’arbre en région tropicale; ii) mettre en lumière les démarches statistiques et expérimentales permettant de valider et de comprendre ces mécanismes. Le genre Erythrophleum, largement distribué en Afrique, est représenté par quatre espèces d’arbre : E. ivorense, E. suaveolens, E. africanum et E. lasianthum. Ces espèces morphologiquement très proches, présentent des aires de distribution géographiques et climatiques adjacentes. Elles sont distribuées de façon parapatrique sur un gradient pluviométrique, du plus humide pour E. ivorense ou plus sec pour E. lasianthum. Ce mode de distribution apparent, combiné à des données issues d’études phylogénétiques, suggère un rôle majeur des gradients climatiques comme pilotes des différenciations spécifiques du genre et pourrait donc confirmer l’hypothèse du gradient écologique (« The ecological gradient hypothesis » suppose que des gradients environnementaux peuvent induire des spéciations parapatriques sans que les populations ne soient isolées géographiquement. Néanmoins, des études sur les niches climatiques et leurs degrés de conservatisme sont indispensables pour valider cette hypothèse. Aujourd’hui, ces études sont rendues plus aisées grâce au développement de nouvelles techniques de modélisation des niches environnementales (Species Distribution Model ou SDM) et de tests statistiques de quantification du conservatisme/divergence de niche (voire Warren et al., 2008). En complément de la modélisation des niches observées (c.à.d. niches réalisées selon la définition de Hutchison (1957)), il est intéressant de comprendre les stratégies fonctionnelles sous-jacentes aux différenciations de niche. Les différenciations de niche au sein des espèces du genre sont probablement issues d’une distinction de leurs stratégies d’utilisation des ressources (lumière/eau) et de leurs différents positionnements au sein du slow-fast continuum (sensu Reich, 2014). Cette hypothèse peut être testée par la mise en place d’expériences en milieu contrôlé mesurant les réponses des individus à des stress environnementaux. [less ▲]

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See detailLes progrès de la foresterie sociale en Afrique centrale
Vermeulen, Cédric ULg; Doucet, Jean-Louis ULg

Conference given outside the academic context (2014)

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See detailIntegrating phylogenetic and environmental niche models to explore speciation mechanisms in the Erythrophleum genus in tropical Africa
Gorel, Anaïs ULg; Fayolle, Adeline ULg; Doucet, Jean-Louis ULg et al

Conference (2014, December 10)

In the context of global climate change, it is of primary importance to understand the species response to climate (habitat tracking or adaptation). In this study we investigated the evolutionary history ... [more ▼]

In the context of global climate change, it is of primary importance to understand the species response to climate (habitat tracking or adaptation). In this study we investigated the evolutionary history of the climatic niche between and within closely related tropical tree species of the Erythrophleum genus (Fabaceae, Caesalpinioideae): E. ivorense, E. suaveolens and E. africanum. Two major hypotheses, the refuge theory and the ecological gradient hypothesis, have been developed to explain the current distribution of tree clades across tropical Africa. To identify the speciation mechanisms, we used a combination of geographic data and environmental factors to quantify the degree of niche conservatism (or divergence). We used two sets of distribution data for the purpose of this study. Species distribution data for the whole of tropical Africa were gathered from herbarium records. Distribution data of the two sister species E. ivorense and E. suaveolens assigned to genetic cluster were available for the lowland tropical forests of western and central Africa. Using a Species Distribution Model (SDM) approach based on MaxEnt algorithm, we tested for the environmental differences (BIOCLIM data) between species and genetic clusters within species. We developed SDMs for each of the three Erythrophleum species (over the whole range) and for each of the five genetic clusters. We quantified the niche overlap using new niche similarity metrics. At species level, the climatic niches differed significantly and overlapped only sligthly, suggesting a parapatric speciation along a climatic gradient. Within the two sister species, the niche of the parapatric central African clusters strongly overlapped, suggesting a secondary contact following the recolonization from different forest refugia. The west African cluster however showed contrasted climatic niches possibly due to either recent (< 100 yrs) climate change in west Africa, or ongoing differentiation on the dry part of the climatic gradient. [less ▲]

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