Pentadesma butyracea Sabine est l’une des quatre espèces du genre Pentadesma endémique de l’Afrique. Elle est distribuée de la Sierra Léone au Gabon dans deux grands types d’habitats :les forêts denses humides discontinues du domaine guinéo-congolais (Haute- et Basse-Guinée) et le domaine soudanien du couloir sec du Dahomey (assimilé à une barrière à l’échange de gènes et d’espèces entre les deux blocs guinéo-congolais). Dans ce dernier, l’espèce se retrouve dans des galeries forestières et occupe une place capitale dans le développement socio-économique des communautés locales en raison des multiples biens et services que procurent ses produits (alimentation, médecine et pharmacopée traditionnelle, etc.). Cependant, des pressions d’origines multiples, telles que le ramassage des graines pour fabriquer du beurre, la fragmentation de l’habitat et sa destruction en faveur du maraîchage, les pratiques culturales inadaptées, les incendies, font peser de lourdes menaces sur l’espèce.<p>Le but de ce travail est d’acquérir les connaissances requises pour la conservation et la gestion durable des ressources génétiques de l’espèce. Trois objectifs ont été définis :(i) étudier la phylogéographie de l’espèce, (ii) étudier sa variabilité morphologique et génétique au Bénin et (iii) caractériser sa biologie de reproduction. En amont de ces travaux, nous avons développé onze marqueurs microsatellites nucléaires chez P. butyracea (chapitre 2). Ils ont été utilisés pour l’étude de la phylogéographie et la diversité génétique de P. butyracea (chapitres 3 et 5), ainsi que pour étudier la dépression de consanguinité et les paramètres de son système de reproduction (chapitre 7).<p>La caractérisation de la répartition spatiale des lignées génétiques de régions intergéniques de l’ADN chloroplastique et de l’ADN ribosomal (ITS) a détecté deux lignées génétiques allopatriques entre le Haut et le Bas-Guinéen, indiquant une forte différenciation génétique et un signal phylogéographique. L’analyse des microsatellites détecte trois pools géniques correspondant aux trois régions étudiées (Haute Guinée, Dahomey Gap et Basse Guinée). La diversité génétique est faible dans le Dahomey Gap, modérée dans le Haut-Guinéen et élevée dans le Bas-Guinéen. Ces résultats indiquent une séparation très ancienne des populations d’Afrique centrale et d’Afrique de l’ouest, alors que celles du Dahomey Gap pourraient résulter des forêts denses humides de l’Afrique de l’ouest lors de la période Holocène humide africaine. Dans ce couloir sec, les populations ont subi une forte dérive génétique, potentiellement due à des évènements de fondation. Au Bénin, deux groupes éco-morphologiques ont été détectés suivant un gradient nord-sud, contrastant avec deux pools géniques présentant une distribution est-ouest. <p>P. butyracea est une espèce auto-compatible majoritairement allogame. La corrélation de paternité est plus élevée aux niveaux intra-fruit vs. inter-fruits, et au sein d’une population de petite taille vs. de grande taille. Les principaux pollinisateurs au Bénin sont deux oiseaux (Cyanomitra verticalis, Cinnyris coccinigastrus) et trois abeilles (Apis mellifera, Meliponula togoensis, Hypotrigona sp.). La productivité totale en fruits augmente en fonction de l’âge de l’arbre et varie en fonction de l’année, atteignant un pic pour les arbres ayant un diamètre de 60-80 cm. Les graines sont récalcitrantes et ont une teneur en eau de 42.5 ± 2.9 %. <p>L’analyse des paramètres de reproduction et de diversité génétique, associés aux facteurs écogéographiques, nous a permis de proposer un échantillon de neuf populations représentatives de la diversité à l’échelle du Bénin, dans la perspective d’une conservation in situ. Le succès de celle-ci dépendra des efforts conjugués des communautés locales, de la recherche forestière et de la définition d’un cadre législatif par le politique pour la protection des habitats. La conservation ex situ est envisagée sous forme d’un verger rassemblant diverses origines, présentant l’intérêt supplémentaire de permettre d’étudier les contributions de la diversité génétique et de la plasticité phénotypique à la variation phénotypique. / Pentadesma butyracea Sabine is one of the four species of the endemic genus Pentadesma in Africa. The species is distributed from Sierra Leone to Gabon in two major types of habitats: the discontinuous and dense Guineo-Congolian rainforests (Upper and Lower Guinea) and the Sudanian domain of the dry corridor of Dahomey (considered as a barrier to the exchange of genes and species between Upper and Lower Guinea). In the latter, the species is found in gallery forests and plays a vital role in the socio-economic livelihood of local communities due to the various resources and services that provide its products (food, medicine and traditional, etc.). However, pressure from many sources including the collection of seeds to make butter, habitat fragmentation and its destruction for market gardening, inadequate agricultural practices, fires, are serious threats to the species.<p>The aim of this work was to acquire appropriate knowledge for the conservation and sustainable management of genetic resources of the species. Three objectives were defined (i) study the phylogeography of the species; (ii) evaluate its morphological and genetic variability in Benin; and (iii) characterize its reproductive biology. In a preliminary work, eleven nuclear microsatellite markers of P. butyracea were developed (Chapter 2). They were used for the study of phylogeography and genetic diversity of P. butyracea (chapters 3 and 5), and to study the inbreeding depression and parameters of its breeding system (Chapter 7).<p>The characterization of the genetic lineages and their spatial distribution using intergenic regions from chloroplast DNA and ribosomal DNA (ITS) region detected two allopatric genetic lineages between Upper and Lower Guinea, indicating a high genetic differentiation and a phylogeographic signal. Microsatellite markers allowed us to detect three genepools matching with the three studied regions (Upper Guinea, Dahomey-Gap and Lower Guinea). Genetic diversity was low in the Dahomey Gap, moderate in Upper Guinea and high in Lower Guinea. These results indicate an ancient separation of populations from Central and West Africa, while those from Dahomey Gap could originate West African rainforests (Upper Guinea) during the African humid Holocene period. In this dry corridor, populations experienced high genetic drift, possibly due to founding events. In Benin, two eco-morphological groups were detected following a north-south gradient, contrasting with two gene pools presenting an east-west distribution.<p>Pentadesma butyracea is a self-compatible, mainly allogamous species. The correlation of paternity was higher within-fruit vs. among-fruits, and in population of small size vs. large size. The main pollinators in Benin are two birds (Cyanomitra verticalis, Cinnyris coccinigastrus) and three bees (Apis mellifera, Meliponula togoensis, Hypotrigona sp.). Total productivity in fruit increases with tree age and varies yearly, reaching a peak for trees of 60-80 cm of diameter class. Seeds are recalcitrant (i.e. they cannot be conserved at low temperature), having a water content of 42.5 ± 2.9% at maturity.<p>The analysis of reproduction and genetics parameters, associated with eco-geographic factors, enabled us to select nine populations representative of the diversity in Benin, from the perspective of in situ conservation. The success of the latter will depend on combined efforts of local communities, forest research and an adequate legislative framework for the protection of habitats. Ex situ conservation is envisaged as an orchard assembling various origins, and would have the additional advantage of allowing to study the contribution of genetic diversity and phenotypic plasticity to phenotypic variation. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

<p>Here, we seek to address the importance of biodiversity in plant ecosystems. We examined the productivity-diversity relationship through the lens of the modern coexistence theory, using a combination of both experimentation and mathematical simulation. We did this by tracking and comparing the productivity of mixed and monoculture plots, analyzing the growth responses of individual trees at forest plots (Chapter 1), confirming the productivity-diversity relationship in a greenhouse experiment using local herbaceous plants (Chapter 2), and finally simulating the productivity response of monoculture vs polyculture plantations to specialist enemy attack (Chapter 3).</p><p>It is no surprise that biodiversity has been decreasing at an exponential rate on the global scale because of effects such as habitat fragmentation, invasive species, spreading pathogens, and anthropogenic influences. Ecologists often found that plants in more species rich locations often exhibited higher productivity and stability in the face of stress. One such phenomenon is known as the productivity diversity relationship that implies biodiversity is key to sustaining ecosystems. Notably, while efforts are being put forth to address ecosystem destruction, much of the current tree planting strategy in the USA is based on timber profit rather than forest productivity and species coexistence with tree biology often being a secondary consideration. These thought processes are in opposition with historical experiments that indicate polyculture communities create more biomass making them significantly more productive than monocultures. However, we also acknowledge that it is not simply biodiversity that must be taken into consideration for a productive ecosystem but also species interaction through coexistence indicate whether or not a community will persevere. These interactions can be addressed using the modern coexistence theory which depends on these complementarity and fitness similarities for species to coexist through time. Here, we seek to address the importance of biodiversity in plant ecosystems. We examined the productivity-diversity relationship through the lens of the modern coexistence theory, using a combination of both experimentation and mathematical simulation. We did this by tracking and comparing the productivity of mixed and monoculture plots, analyzing the growth responses of individual trees at forest plots (Chapter 1), confirming the productivity-diversity relationship in a greenhouse experiment using local herbaceous plants (Chapter 2), and finally simulating the productivity response of monoculture vs polyculture plantations to specialist enemy attack (Chapter 3). Our research across the combination of approaches used found that species with overlapping niches and very different finesses will exclude one another due to high competition. Further, the productivity diversity correlation is necessary for ecosystem growth, but it is not sufficient for species coexistence. However, species can maintain this positive relationship despite a lack of coexistence if they maintain niche complementarity. Lastly, using a theoretic game model we were able to identify the impacts of a specialist pest on polyculture and monoculture forest. These results showed that a polyculture forest was more productive than that of a monoculture forest regardless of the presence of a specialist enemy. The results of the multiple threads of evidence found from these combined experiments indicate that while the productivity diversity correlation is important to ecosystems it is likely due to the impacts of niche complementarity that determine whether or not species will be productive within an ecosystem.</p>

<p dir="ltr">Non-native biological invasions are one of the leading concerns for global biodiversity. The establishment of invasive species reduces local biodiversity, shifts species composition, changes successional trajectories, and alters ecosystem functions. This thesis examines two aspects of invasive plants: (1) the distribution and the most important climatic and anthropogenic drivers of invasive trees across the eastern United States, and (2) an evaluation of invasive plant removal and herbaceous recovery from a government cost-share program that provides financial support for invasive plant management by private landowners.</p><p><br></p><p dir="ltr">Our first study focused on identifying the distribution of invasive trees, and the factors associated with their distribution. This is essential to predicting spread and planning subsequent management. Using USDA Forest Inventory Analysis (FIA) data and random forest modeling, we examined the distribution, and variables associated with the distribution, of invasive tree species. Invasive trees were found in 10,511 out of 299,387 FIA plots. Invasive species basal area and density (trees per ha; TPH) were highest within the central and southern Appalachian Mountains, Michigan, the Northeast, and the southern Coastal Plain of the United States. A random forest model of invasive species basal area (R²= 0.47, RMSE = 0.47) and density (R²=0.46, RMSE=0.50) vs. environmental variables found that both invasive basal area and density were most strongly associated with human footprint, followed by various climatic variables. An equivalent model of native tree basal (R²=0.53, RMSE=9.25) and TPH (R²=0.47, RMSE=8.64) found that native tree basal area and density were most strongly associated with aridity followed by various climatic variables. As human footprint increased, invasive tree basal area and density increased. These results suggest that the distribution of invasive trees is reliant on human alterations to forests.</p><p><br></p><p dir="ltr">Our second study focused on Environmental Quality Incentives Program (EQIP), a federal cost-share program that has provided $25 billion of financial assistance to farmers and non-industrial private forest owners. Few studies have examined whether this program facilitates the recovery of the herbaceous layer while decreasing the dominance of invasive plant species. We surveyed the herbaceous layer of EQIP-treated and untreated (reference) forests across three physiographic regions of Indiana. Using non-metric multidimensional scaling (NMDS) ordination and linear mixed effects models, we evaluated the species composition, richness, diversity, evenness, floristic quality index, and herbaceous-layer cover of EQIP and reference sites. We also used linear mixed models to evaluate how EQIP site treatment affected the diversity of native plant species. Sites treated with EQIP contracts typically had significantly higher native species richness, Shannon’s diversity, and floristic quality than reference sites. There were significant separations in species composition between EQIP treated and reference forests state-wide and in the southern non-glaciated region of Indiana, although composition overlapped between EQIP and reference forests. Our study suggests that EQIP-funded treatments promote increased species richness and diversity. However, the persistent overlap in species composition we observed may signify biotic homogenization due to a long-shared history of anthropogenic disturbances between EQIP and reference sites. Therefore, active restoration of the herbaceous layer might be needed to allow a full recovery after invasive removal.</p>

Floristic, Ecological and Phytosociological, Study of the Forests of the Mbiye Island at Kisangani, DR Congo The Mbiye Island is situated on the Congo River, in the Eastern part of Kisangani. It is located upstream of the Wagenia Falls, between latitude 0º31’ North and longitude 25º11’ East, with 376 m of altitude. It adjoins the town of Kisangani, and it is 14 km long and 4 km wide. All around Kisangani, the Mbiye Island is the only ecosystem which has a dense forest that is relatively well preserved. This Island has an area of 1,400 ha, and it comprises three types of forest: dry land forest, periodically flooded forest and swampy forest. The main purpose of this study has been to make a qualitative and quantitative analysis of the physiognomy and structure of these three types of forest. I relied on two methods in data collecting: the Phytosociological plotting method with a sampling equal to 100 individuals for the higher strata and 100 m² grass strata, associated with dbh measure for trees whose diameter is ≥ 10 cm. In total, out of the 80 plottings, 67 multi strata and structurals each of which has been decomposed in 4 sub-plottings fit together. Based on the presence-absence criterion, the other 13 multi strata and structurals have been made into Chablis, and all the data have been globally analyzed. An inventory of 33991 individuals has been made in this study. After their identification, it has been found out that there 470 species belonging to 297 types and 90 families. Rubiaceae, Caesalpiniaceae and euphorbiaceae families have been found out to be the most important in Genus and species. In the raw spectra of biological types, the phanerophyts (83.0%) are the most predominant, and within which the mesophanerophyts (trees 10 to 30 m tall in their old age) are the most predominant (39.0%). The Phytogeographical spectra have more omni-guineo-congolese (35%) elements; and amongst the diaspore types, the sarcochores (69%) are the most predominant. 58 endemic species (12.3%) of the central forest sector have been found out at the Mbiye Island. After the classification and ordination of the 80 plottings by Twinspan and DCA, three Phytosociological groupings have been found out in the dry land forest: (1) grouping of Funtumia elastica and Albizia ealaensis, (2) grouping of Nesogordonia leplaei and Antiaris toxicaria, (3) prouping of Olyra latifolia and Campylospermum elongatum; two others for floodable forests (1) grouping of Rinorea oblongifolia and Byrsocarpus coccineus, (2) grouping of Pachystela seretii, Dracaena kindtiana and Culcasia yangambiensis, and three others for swampy forests: (1) grouping of Strombosia grandifolia, Calamus deerratus, Culcasia angolensis and Elaeis guineensis, (2) grouping of Cleistopholis patens and Pterygota bequaertii, (3) grouping of Diospyros bipendensis, Strychnos icaja and Palisota barteri and then two groupings for the Chablis plottings (1) grouping of Palisota schweinfurthii, Eremospatha haullevilleana, Thomandersia hensii and Pycnocoma insularis and (2) grouping of Nephrolepis biserrata and Scaphopetalum thonneri. The coelocaryon botryoides has shown a uniform spatial distribution in the in the forest periodically flooded, whereas Gilbertiodendron dewevrei has shown an aggregated distribution. Comparison of richness in different taxa within the sampling has given high values as far as the numbers of species is concerned and genus of the same family in the phytosociological sampling. Out of all the species listed, 189 have been considered to be common species with regard to the three forest types, other 144 belonged to two types. 90 species have been listed only on solid land, 27 on periodically flooded forest 20 on swampy forest. Euphorbiaceae, Rubiaceae and Caesalpiniaceae families were the best represented in species and genus. With regard to richness in each forest type, the forest of solid soil was the only one to have high values both in species<p>and genus, and the swampy forest was less represented. With reference to richness according to strata, the herbaceous and under-shrub stratum (H) was the richest whereas the stratum of dominant trees (E+A1) was the poorest. Mbiye island forest is the nearest one of Kisangani for which it plays the most important role with regards to supplies in different forest products and non-ligneous forest products. In total, 12.3% endemic species of Central forest sector have been listed there, but due to frequent use by man this time, all these endemic species may disappear from this island. It is therefore urgent that particular attention be paid on it. Actions of conservation and lasting exploitation must be started in order to block their extinction. Key words: DRCongo, Flora, Ecology, Phytosociology, insularity, flooding, spatial distribution, biodiversity, synusie, Mbiye Island, Kisangani./Etude floristique, écologique et phytosociologique des forêts de l'île Mbiye, Kisangani, RDCongo. L'île Mbiye est une île du fleuve Congo située dans la partie Est de la ville de Kisangani, en amont des chutes Wagenia, entre 0° 31' de latitude Nord et 25° 11' de longitude Est, avec une altitude de 376 m. Elle jouxte la ville de Kisangani et sa longueur maximale est de 14 km sur 4 km de largeur. Elle est le seul écosystème à proximité de la ville, possédant encore une forêt dense relativement bien conservée et formant un îlot de 1400 ha comprenant trois types forestiers :la forêt de terre ferme, la forêt périodiquement inondée et la forêt marécageuse. L’objectif principal de cette étude a été de faire une analyse quantitative et qualitative de la physionomie et la structure de ces trois types forestiers. Deux méthodes ont permis la récolte de données ;la méthode de relevés phytosociologiques à effort d’échantillonnage égal à 100 individus pour les strates supérieures et 100 m² pour la strate herbacée, associée à celle de mesure de D130, pour les arbres à diamètre ≥ 10 cm. Au total, 80 relevés dont 67 multistrates et structurels, décomposés chacun en 4 sous-relevés emboîtés, ont été mis en place. 13 autres ont été faits dans les chablis avec l’appréciation basée sur le critère de présence-absence et toutes les données ont été analysées globalement. A l’issue de cette étude, 33991 individus ont été recensés. Après leur identification, au total 470 espèces appartenant à 297 genres et 90 familles ont été obtenues. Les familles des Rubiaceae, des Caesalpiniaceae et des Euphorbiaceae sont les plus importantes, tant en genres qu’en espèces. Dans les spectres bruts de types biologiques, les phanérophytes (83,0 %) sont les plus abondants et au sein desquels les mésophanérophytes (arbres de 10 à 30 m au stade adulte) sont les plus dominants (39,0 %). Les spectres phytogéographiques ont montré une prédominance d’éléments omni-guinéo-congolais (35 %) alors que parmi les types de diaspores, les sarcochores (69 %) sont les plus dominants. 58 espèces endémiques du Secteur forestier central (soit 12,3 %) ont été recensées à l’île Mbiye. Après classification et ordination de ces 80 relevés par Twinspan et DCA, trois groupements phytosociologiques ont été obtenus dans la forêt de terre ferme: (1) groupement à Funtumia elastica et Albizia ealaensis, (2) groupement à Nesogordonia leplaei et Antiaris toxicaria, (3) groupement à Olyra latifolia et Campylospermum elongatum ;deux autres pour les forêts inondables (1) groupement à Rinorea oblongifolia et Byrsocarpus coccineus, (2) groupement à Pachystela seretii, Dracaena kindtiana et Culcasia yangambiensis ;trois autres encore pour les forêts marécageuses :(1) groupement à Strombosia grandifolia, Calamus deerratus, Culcasia angolensis et Elaeis guineensis, (2) groupement à Cleistopholis patens et Pterygota bequaertii, (3) groupement à Diospyros bipendensis, Strychnos icaja et Palisota barteri, et enfin, deux groupements pour les relevés de chablis (1) groupement à Palisota schweinfurthii, Eremospatha haullevilleana, Thomandersia hensii et Pycnocoma insularum et (2) groupement à Nephrolepis biserrata et Scaphopetalum thonneri. L’espèce Coelocaryon botryoides a montré une répartition spatiale uniforme dans la forêt périodiquement inondée alors que Gilbertiodendron dewevrei y a montré une répartition agrégée. La comparaison de la richesse en différents taxa au sein de relevés et de placettes a donné de valeurs supérieures en nombre d’espèces, de genres et même de familles, dans les relevés phytociologiques. Sur le total des espèces recensées, 189 ont été considérées comme espèces communes aux trois types forestiers, 144 autres appartenaient aux deux types. 90 espèces<p>n’ont été recensées qu’en forêt de terre ferme, 27 en forêt périodiquement inondée et 20 dans la forêt marécageuse. Les familles des Euphorbiaceae, des Rubiaceae et celle des Caesalpiniaceae ont été les mieux représentées en espèces et en genres. En ce qui concerne la richesse dans chaque type forestier, la forêt de terre ferme était la seule à avoir des valeurs supérieures tant en espèces qu’en genres et la forêt marécageuse était la moins représentée. Quant à la richesse spécifique selon les strates, la strate herbacée et sous-arbustive (H) était la plus riche alors que la strate des arbres dominants (E+A1) était la plus pauvre. La forêt de l’île Mbiye est la seule forêt proche de la ville de Kisangani pour laquelle elle joue un rôle de premier plan en ce qui concerne le ravitaillement en différents produits forestiers et forestiers non ligneux. Au total, 12,3% d’espèces endémiques du Secteur forestier Central y ont été recensées, mais vue l’action anthropique qu’elle connaît ce dernier temps, toutes ces espèces endémiques risquent de disparaître de cette île. Il est alors urgent qu’une attention particulière, soit tournée vers elle. Des actions de conservation et d’exploitation durable doivent être amorcées en vue contrecarrer l’extinction des celles-ci. Mots clés :RDCongo, flore, écologie, phytosociologie, insularité, inondation, répartition spatiale, biodiversité, synusie, île Mbiye, Kisangani. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

<p dir="ltr">Global forest ecosystems provide essential ecosystem services that contribute to water and climate regulation, food production, recreation, and raw materials. They also serve as crucial habitats for numerous terrestrial species of amphibians, birds, and mammals worldwide. However, recent decades have witnessed unprecedented changes in forest ecosystems due to climate change, shifts in species distribution patterns, increased planted forest areas, and various disturbances such as forest fires, insect infestations, and urbanization. These changes can have far-reaching impacts on ecological networks, human well-being, and the well-being of global forest ecosystems. To address these challenges, I present four studies to quantify forest dynamics through mapping, classification, and projection, using artificial intelligence tools in combination with a vast amount of training data. (I) I present a spatially continuous map of planted forest distribution across East Asia, produced by integrating multiple sources of planted and natural forest data. I found that China contributed 87% of the total planted forest areas in East Asia, most of which are located in the lowland tropical/subtropical regions and Sichuan Basin. I also estimated the dominant genus in each planted forest location. (II) I used continent-wide forest inventory data to compare the range shifts of forest types and their constituent tree species in North America in the past 50 years. I found that forest types shifted more than three times as fast as the average of their constituent tree species. This marked difference was attributable to a predominant positive covariance between tree species ranges and the change of species relative abundance. (III) Based on individual-level field surveys of trees and breeding birds across North America, I characterized New World wood-warbler (<i>Parulidae</i>) species richness and its potential drivers. I identified forest type as the most powerful predictor of New World wood-warbler species richness, which adds valuable evidence to the ongoing physiognomy versus composition debate among ornithologists. (IV) In the appendix, I utilized continent-wide forest inventory data from North America and South America and the combination of supervised and unsupervised machine learning algorithms to produce the first data-driven map of forest types in the Americas. I revealed the distribution of forest types, which are useful for cost-effective forest and biodiversity management and planning. Taken together, these studies provide insight into the dynamics of forest ecosystems at a large geographic scale and have implications for effective decision-making in conservation, management, and global restoration programs in the midst of ongoing global change.</p>

L’origine de la structuration spatiale de la diversité inter spécifique (SSDS) des forêts d’Afrique centrale est l'objet de vigoureux débats quant à l’importance relative des facteurs historiques, stochastiques et déterministes. De plus, la SSDS est le plus souvent mal caractérisée, en particulier la variation spatiale de la composition des communautés (diversité beta).<p>L’hypothèse la plus souvent avancée pour expliquer l’origine des centres de diversité et d’endémisme est historique :ces centres constitueraient d’anciens refuges forestiers formés pendant les périodes sèches du Quaternaire. Cependant, la forte hétérogénéité environnementale de ces régions pourrait tout aussi bien expliquer la SSDS.<p>L'objectif principal de cette thèse est de tester l'importance de ces facteurs (historiques et/ou hétérogénéité environnementale) :si les facteurs historiques sont déterminants, on s’attend à observer une concordance spatiale entre la SSDS et la structure spatiale de la diversité génétique (SSDG). En effet, la variation neutre au sein des espèces est en grande partie soumise aux processus qui affectent également la SSDS (dérive génétique/écologique et dispersion des espèces/flux de gènes). L’approche utilisée dans cette thèse consiste donc à comparer et évaluer la concordance spatiale entre la SSDS et la SSDG.<p>Le modèle biologique et le cadre géographique de cette étude sont les communautés et les populations d’arbres des forêts humides d’Afrique centrale atlantique, avec une attention particulière pour les forêts gabonaises. La SSDS a été étudiée sur la base de relevés de communautés d’arbres (16308 individus) et la SSDG sur la base de séquences d’ADN chloroplastiques de six espèces d’arbres (Greenwayodendron suaveolens, Scorodophloeus zenkeri, Afrostyrax lepidophyllus, Afrostyrax kamerunensis, Santiria trimera et Erythrophleum suaveolens).<p>Quatre objectifs spécifiques ont été retenus :<p>(i)\ / Doctorat en Sciences / info:eu-repo/semantics/nonPublished