Exemples d'apports de la statistique dans l'etude et la validation de modeles dynamiques complexes

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Le logiciel FORSIM de resolution numerique des systemes d'equations differentielles ordinaires et/ou aux derivees partielles

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Perspectives de modélisation du réseau trophique en étang. Applications potentielles à l'optimisation et au contrôle de la production piscicole

The possibilities and prospects of creating a model of the trophic system in fish culture ponds are analysed on the basis of actual examples from Polish fish culture and ecosystem models developed for lacustrine media. The authors show which kind of information can be obtained from this model both for understanding the mechanisms involved in the dynamics of the aquasystem and for optimizing the bioconversion through the food chain. An attempt is made to investigate the kind of problems occurring most likely in pond fish culture and the trend of research to be developed

Analysis of prediction uncertainty : Monte-Carlo simulation and non-linear least-squares estimation on a vertical transport submodel for Lake Nantua.

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Modelisation dynamique de l'eutrophisation des lacs: comparaison et evaluation des diverses approches du probleme; application au cas du lac de Nantua, en vue de la prediction de son evolution et de la recherche de politique optimales de restauration. Suivi de 2 annexes

Comite: Milieux physiques - EauSIGLEAvailable from Centre de Documentation Scientifique et Technique, CNRS, 26 rue Boyer, 75971 Paris Cedex 20 (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Caracterisation et essais de restauration d'un ecosysteme degrade : le lac de Nantua

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Manuel Consistent System CS

*INRA, Biometrie, Mission Informatique, Centre de Jouy en Josas Diffusion du document : INRA, Biometrie, Mission Informatique, Centre de Jouy en JosasNational audienc

Land-atmosphere energy exchange in Arctic tundra and boreal forest: available data and feedbacks to climate

This paper summarizes and analyses available data on the surface energy balance of Arctic tundra and boreal forest. The complex interactions between ecosystems and their surface energy balance are also examined, including climatically induced shifts in ecosystem type that might amplify or reduce the effects of potential climatic change. High latitudes are characterized by large annual changes in solar input. Albedo decreases strongly from winter, when the surface is snow-covered, to summer, especially in nonforested regions such as Arctic tundra and boreal wetlands. Evapotranspiration (QE) of high-latitude ecosystems is less than from a freely evaporating surface and decreases late in the season, when soil moisture declines, indicating stomatal control over QE, particularly in evergreen forests. Evergreen conifer forests have a canopy conductance half that of deciduous forests and consequently lower QE and higher sensible heat flux (QH). There is a broad overlap in energy partitioning between Arctic and boreal ecosystems, although Arctic ecosystems and light taiga generally have higher ground heat flux because there is less leaf and stem area to shade the ground surface, and the thermal gradient from the surface to permafrost is steeper. Permafrost creates a strong heat sink in summer that reduces surface temperature and therefore heat flux to the atmosphere. Loss of permafrost would therefore amplify climatic warming. If warming caused an increase in productivity and leaf area, or fire caused a shift from evergreen to deciduous forest, this would increase QE and reduce QH. Potential future shifts in vegetation would have varying climate feedbacks, with largest effects caused by shifts from boreal conifer to shrubland or deciduous forest (or vice versa) and from Arctic coastal to wet tundra. An increase of logging activity in the boreal forests appears to reduce QE by roughly 50% with little change in QH, while the ground heat flux is strongly enhanced