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Sharp prediction of extinction times is needed in biodiversity monitoring and conservation management.The Galton-Watson process is a classical stochastic model for describing population dynamics. Its evolution is like the matrix population model where offspring numbers are random. Extinction probability, extinction time, abundance are well known and given by explicit formulas. In contrast with the deterministic model, it can be applied to small populations.Parameters of this model can be estimated through the Bayesian inference framework. This enables to consider nonarbitrary scenarios.We show how coupling Bayesian inference with the Galton-Watson model provides several features: i) a flexible modelling approach with easily understandable parameters ii) compatibility with the classical matrix population model (Leslie type model) iii) A non-computational approach which then leads to more information with less computing iv) a non-arbitrary choice for scenarios, parameters… It can be seen to go one step further than the classical matrix population model for the viability problem.To illustrate these features, we provide analysis details for two examples whose one of which is a real life example.

Vol. 2: Coviability Questioned by a Diversity of Situations Chapitre 40 La version en français sera publiée ultérieurement aux éditions Matériologiques en co-édition avec les éditions IRD; International audience; The babassu palm tree (Attalea speciosa Mart. ex Spreng.) is a species native to the Amazonian rainforest. The invasive nature of this palm tree results in a high density of babassu palm trees with a subsequent decrease in forage crop production. This is a serious problem for local farmers who have tried to resolve it by removing mature palms, seedlings and young individuals. Within these conditions, is coviability between the babassu palm tree and society possible? Our work consisted in developing tools and methods with the aim of producing knowledge and providing answers to this issue within a given territory. To understand the eco-socio-system, we have explored the available knowledge in the literature, produced specific field data, tools and methods such as mathematical modeling (dynamics of the palm tree population) and remote sensing (land use analysis thanks to Landsat high-resolution images and automatic detection of mature palm trees using Pleiades and GeoEye very high-resolution images). This multidisciplinary research in progress has already given us a good overview of the current situation of this eco-socio-system, enabling us to consider the best way to ensure its sustainability.

The babassu palm tree (Attalea speciosa Mart. ex Spreng.) is an endemic species of Amazon forests, and has social and economical impact/utility. Deforestation highlights this palm tree in anthropogenic open areas (pastures and cultivated fields). Simultaneously, knowledge concerning the sustainable functioning of the species within these manmade environments is sorely lacking: its life cycle is not well known, and its population dynamics remains unstudied. In this study, our objective was to generate a model of the population dynamics of the babassu palm tree, validated by in situ analysis, to understand how babassu, a forest species, adapts to pastureland and, under certain conditions, becomes invasive. We propose a random matrix model with aggregated variables based on the biological stages of the species as the input. The probabilities of the between-stage transition matrix were modelled using a Dirichlet-multinomial model with a hierarchy taking geographical organization, i.e. transect level, into account. The integration of prior information was formulated through a Bayesian approach. This Bayesian hierarchical matrix model enabled us to demonstrate a bottleneck in the population dynamics and a high year-dependent mortality rate at an early stage.

Resume Nous proposons un test d'adequation pour des modeles de regression non-lineaire monotone. Ce test s'appuie sur le paradigme des tests lisses de Neyman (1937) pour tester l'adequation des densites. Il s'applique tout particulierement aux fonctions de croissance. Nous completons cette approche en incorporant une methode de selection automatique des parametres du test par les donnees. Pour citer cet article : B. Fontez, G.R. Ducharme, C. R. Acad. Sci. Paris, Ser. I 338 (2004).

Le mécanisme financier de la Réduction des émissions dues à la déforestation et à la dégradation des forêts (Redd) intéresse les pays du bassin du Congo, qui disposent de peu de données précises sur les stocks de carbone en forêt. Les principales équations allométriques pantropicales disponibles ont pour paramètres : le diamètre, la hauteur et la densité spécifique du bois ; mais aucun des arbres mesurés ne provient de forêts africaines. Les rares équations établies en Afrique s'avèrent insuffisantes, notamment par déficit d'échantillon en arbres de grande taille. Ainsi, pour pallier cette carence, 55 arbres de 10 à 120 cm de diamètre, appartenant à 23 espèces, ont été mesurés en forêt dense semidécidue du Sud-Est du Cameroun. Après abattage, les arbres tronçonnés ont été mesurés jusqu'à la découpe d'un centimètre de diamètre. Cet échantillon a permis de relier le diamètre et le volume total de bois des arbres via des modèles polynomiaux et non linéaires (additif et multiplicatif). La biomasse des arbres pourra être alors déduite par l'utilisation de la densité spécifique et un facteur correctif pour le feuillage. Dans la perspective de cette étude, afin d'affiner les mesures, l'échantillon sera augmenté lors d'une prochaine campagne de mesures, pour mieux estimer le volume total des gros arbres., The REDD mechanism (Reducing Emissions from Deforestation and forest Degradation) is of interest to the Congo Basin countries, but they have few precise data on their forest carbon stocks. The parameters for the main pan-tropical allometric equations are tree height and diameter and specific timber density, but none of the trees measured are from African forests. The few equations established for Africa turn out to be insufficient, in particular because large trees are not sufficiently represented in the samples measured. To address this data deficit, we measured 55 trees with a diameter of 10 to 120 cm, from 23 different species in a dense semi-deciduous forest in south-eastern Cameroon. After felling, the logs were cross-cut and measured until the one centimetre in diameter cutting. The sample was used to link the diameter and total timber volume of the trees via polynomial non-linear models (addition and multiplication). Then tree biomass should be deduced by applying the specific density and a correction factor for foliage. In order to refine these measurements, the sample will be enlarged during a further measurement campaign to produce a closer estimation of the total volume of huge trees., El impacto de una explotación forestal en términos de emisión de carbono ha sido raramente contemplado en trabajos de investigación reales en África Central. Sin embargo, en el marco de los mecanismos REDD (Reducción de Emisiones por la Defo- restación y la Degradación), este problema plantea importantes desafíos con el incre- mento del número de concesiones sujetas a ordenación y la creciente importancia de las técnicas de aprovechamiento de bajo impacto. Este estudio constituye un ensayo de metanálisis que incluye las distintas experiencias procedentes de la literatura existente. Los datos así obtenidos se apli- caron a una hipotética explotación para elaborar un balance teórico del impacto en las reservas de carbono. Los resultados ponen de manifiesto que, con las hipótesis adoptadas, la ordenación de un bosque permitiría una reducción de la décima parte de las pérdidas de carbono, para una extracción por hectárea de 10 a 20 m 3 de madera de construcción; todo ello compa- rado con una concesión forestal convencio- nal sin manejo planificado. La parte funda- mental en el ahorro del carbono procedería sobre todo del aumento de los diámetros mínimos de aprovechamiento. Por otra parte, los beneficios que podrían impulsar la práctica de un aprovechamiento de bajo impacto serían los derivados de la mejora del trazado de pistas y carreteras, esto es: del 5 al 8% de las pérdidas de carbono debidas al aprovechamiento convencional. Estos beneficios son superiores al error constatado en la medición de biomasa por tala total, la más cerca de la realidad, hecho en Guayana francesa. Sin embargo, dichos beneficios son muy inferiores a los errores calculados en la estimación de la biomasa en varios estudios disponibles en la literatura científica. En cualquier caso, la implementación de la ordenación en una concesión forestal y el uso de técnicas de aprovechamiento de bajo impacto son capaces de generar una diferencia favora- ble de las reservas de carbono en el bos- que denso.