Assessment of fine scale population genetic diversity and regeneration in Congo basin logged forests

In the Congo Basin most of the light-demanding timber tree species display a deficit of natural regeneration which is a major handicap for sustainable production and certification. Whilst the majority of scientists investigate abiotic and biotic factors explaining that pattern, we hypothesize that tree population density or individual spatial isolation may also affect the tree fitness through inbreeding. In this study, we integrate ecological and genetic approaches to characterize the regeneration potential of a set of priority timber species by (i) estimating pollen dispersal distances at various tree population densities, and (ii) evaluating the impact of increasing spatial isolation on mating characteristics and tree fitness. The ultimate goal is the proposal of minimum population density that prevents inbreeding consequences. Method This ongoing study focuses on 10 timber species (Pericopsis elata, Milicia excelsa, Baillonella toxisperma, Entandrophragma cylindricum, E. utile, E. angolense, E. candollei, Afzelia bipindensis, Erythrophleum suaveloens, Terminalia superba). The data collection was carried out in the logging concession granted to Pallisco in Cameroon. We established two 400-ha plots, where all individuals (DBH > 10 cm) of the target species were inventoried and mapped. A sample of leave or cambium was collected for each of these individuals, as well as for seedlings to characterize patterns of gene flow using genetic tools (nuclear microsatellites). Dispersal agents were identified by direct observations and camera traps. Germination success was characterized in nursery for seeds collected on trees under an increasing isolation gradient. Results Main dispersal agents (wind, bat, rodent) and predators (rodent) were identified for all the species. The gene flow and germination data is still being analyzed and the main results will be presented in the poster. Conclusion Our data will allow characterizing the reproductive biology of a set of important timber species from the Congo basin. These information will strengthen sustainable forest management and the application of certification by adjusting harvesting norms through the use of scientifically-relevant data. In particular, we will tentatively define a maximum distance to be maintained between two adults to allow a qualitative reproduction

Globally, functional traits are weak predictors of juvenile tree growth, and we do not know why

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

Etude des relations entre ignames sauvages et ignames cultivees (dioscorea sp.) Dans deux sous-prefectures du Benin a l’aide de marqueurs aflp

Les relations entre des ignames sauvages,principalement Dioscorea abyssinica, et des cultivars du complexe D. cayenensis -D. rotundata ont été étudiées dans deux sous-préfectures du Bénin : Sinendé au Nord et Banté au Centre. Une comparaison de 71 accessions, dont 20 sauvages prélevées en bordure des champs de 23 paysans, a été faite par l’analyse multivariée de 66 niveaux de bandes AFLP polymorphes(«amplified fragments length polymorphism») de deux combinaisons d’amorces. Les cultivars forment deux groupes (1 et 2) dans les deux sous-préfectures, qu’ils soient tardifs ou précoces. Les cultivars de Sinendé présentent la plus grande diversité. Dans tous les cas, les ignames sauvages sont éloignées génétiquement des cultivars. Les cultivars étudiés ne sont peut être pas d’origine locale. C’est à Sinendéque les ignames cultivées et sauvages sont les plus éloignées. A Banté, les ignames cultivées du groupe 1B sont proches des ignames sauvages en bordure de champs. Les quinze ignames sauvages en cours de domestication sont d’une grande diversité :elles se répartissent dans les groupes de cultivars et dans celui des sauvages en bordure de champs ou sont intermédiaires entre ces deux groupes. Celles trouvées au sein des ignames cultivées peuvent provenir de descendances de cultivars, d’« échappés de culture » ou d’erreurs de manipulation pendant les nombreuses années de domestication. Les AFLP se révèlent d’efficaces marqueurs moléculaires pour caractériser les variétés (locales ou introduites) et les ignames sauvages ainsi que pour étudier les relations entre ignames cultivées et ignames sauvages. Relations between wild yams, mainly Dioscorea abyssinica, and cultivars from complex D. cayenensis - D. rotundata have been studied within two sub-prefectures of Benin (West Africa) : Sinendé in the North and Banté in the Centre. A comparison of 71 accessions, including 20 wild sampled in border of 23 farmers' fields, was made by the multivariance analysis of 66 polymorph AFLP («amplified fragments length polymorphism») markers from the combination of two primers. The early cultivars and the late cultivars form two groups (1 and 2) in the both subprefectures,those from Sinendé presenting a higher diversity than those from Banté.The most important gap between cultivated and wild yams is observed in Sinendé. In Banté, wild yams near fields are close from the group 1B.Domesticated wild yams form a group with high diversity: they are shared out among the groups of cultivars and of wild yams in the neighbourhood of fields or are intermediate between these two groups. Those found within the cultivated yams can come from cultivars offsprings or from «escaped from old cultures». These results prove that AFLP are good markers to characterise varieties (locals or introduced ones) or wild yams and to study the relationships between wild and cultivated yams

Evaluation de la diversité génétique par RAPD d'un échantillon de Discorea alata d'un region du Bénin, la Sous-préfecture de Savè

No Abstract Available j. Rech. Sci. Univ. Lomé (Togo) 2002, 6(1) : 167-17

La domestication de ignames sauvages Dioscorea abyssinica chez l\'ethni bariba du Benin

No Abstract. J. Rech. Sci. Univ. Lomé (Togo) Vol. 7(1) (Serie A) 2005: pp. 61-6