Structure, long-term dynamics, and demography of the tree community

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Kalideos OSR MiPy : un observatoire pour la recherche et la démonstration des applications de la télédétection à la gestion des territoires

International audienceCes dernières années, le CESBIO a mis en place un Observatoire Spatial Régional 'OSR' : un dispositif d'observation couplant mesures de terrain et télédétection dans le sud-ouest de la France. L'OSR se base sur des acquisitions mensuelles de données satellitaires à résolution décamétrique depuis 2002 et sur des sites expérimentaux lourdement instrumentés (mesures en continu de flux d'eau et de carbone) à partir de 2004. Ce dispositif a été reconnu service d'observation par l'INSU/CNRS en 2007 et site KALIDEOS par le CNES fin 2009 : 'KALIDEOS OSR MiPy'. Le site atelier correspond à une emprise d'image SPOT, soit environ 50x50 km et couvre une grande diversité de milieux (pédologie, topographie), d'occupation et d'utilisation des sols, de pratiques et de modalités de gestion (agricole, forestière...) et de conditions climatiques (fort gradient de déficits hydriques estivaux). Pour la télédétection, ce site a servi la préparation de SMOS, et il soutient maintenant en priorité à la préparation des missions VENμS et Sentinel-2. Les aspects radar, imagerie thermique et les approches multi-capteurs se développent depuis peu. Le traitement du signal, la physique de la mesure et l'amélioration de la qualité des données constituent le premier axe de recherche. Au niveau thématique, le CESBIO a pour priorité les suivis et les modélisations des agrosystèmes de grandes cultures. L'implication récente d'autres partenaires scientifiques ou gestionnaires a permis d'initier des travaux sur d'autres aspects, comme la biodiversité, l'aménagement du territoire, le suivi de l'extension urbaine, les risques environnementaux, la santé des forêts, l'enfrichement, la diversité et la productivité des prairies. La valorisation des 10 années d'archives 2002-2011 débute et semble très pertinente pour la caractérisation en haute et en basse résolution des conséquences d'années climatiques atypiques (2003, 2011) sur les éco-agro-systèmes. L'extrapolation des résultats obtenus sur ce site atelier à toute la région Midi-Pyrénées ou à la chaine des Pyrénées est aussi initiée

Entretien avec Jean-Claude Menaut

Menaut Jean-Claude, Kintz Danièle. Entretien avec Jean-Claude Menaut. In: Journal des anthropologues, n°40-41, Septembre 1990. A propos de l'écologie : pistes croisées, sous la direction de Danièle Kintz, Marc Henri Piault et Rita Cordonnier. pp. 93-98

Alternative fire resistance strategies in savanna trees

International audienc

Seed shadows, survival and recruitment: how simple mechanisms lead to the dynamics of population recruitment curves

International audienc

Tree Community Dynamics in a Humid Savanna of the Cote-d’Ivoire: Modelling the Effects of Fire and Competition with Grass and Neighbours

International audienc

Neighbourhood analysis in the savanna palm Borassus aethiopum: interplay of intraspecific competition and soil patchiness

International audienceA previous study of the spatial patterns of Borassus aethiopum (a humid savanna palm tree) led to the following predictions: H I. Trees and termite mounds positively influence all developmental stages; H2. There is intense competition between B. aethiopum juveniles; H3. Juvenile and seedling survival and growth rates are higher away from mother plants; H4. Mound positive effect overwhelms the effect of intraspecific competition for very young B. aethiopum individuals, the reverse applies to older, non-reproductive individuals. To test for these hypotheses the potential positive and negative neighbourhood effects were analysed. Progression of seedlings into the juvenile stage and juvenile growth were analysed through logistic regression models including the effects of four neighbourhood indices designed to model the respective influence of B. aethiopum juveniles and adults, trees and termite mounds. Statistical results explain the observed spatial pattern and reveal two main neighbourhood effects that influence both B. aethiopum juveniles and seedlings: a positive effect of mounds due to the fact that they constitute nutrient-rich soil patches, and a negative effect of juveniles due to intraspecific competition. Seedlings would be mostly affected by the mound positive effect, whereas juveniles would be mostly affected by competition

Télédétection de la phénologie dans les régions boréales

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

The influences of tree biology and fire in the spatial structure of the West African savanna

International audienceUsing a spatially explicit cellular automaton model we explore the effects of tree demography, fire-induced mortality, and seed dispersal on the spatial spread of a single tree species in a humid savanna at Lamto in West Africa. The model system is described by six parameters and consists of a grass-surrounded square grid of connecting cells, each being either inhabited by grass alone or by grass and an individual tree. In the baseline numerical simulations the tree can only recroit seedlings in immediately adjacent cells. These seedlings may perish from annual grass fires in their first year of life if they are not protected from the advancement of the fire by neighbouring reproductively mature trees. Based on preliminary parameter estimates from data collected at field sites at Lamto, we predict that fire slows, but does not stop, the spread of the tree. In the absence of fire the doubling rate of the tree population is about 6 years, whereas we predict that yearly fires prolong this to at least 30 years. The temporal dynamics of the tree population are fairly smooth and predictable as long as there are more than c. 100 cells in the system. As the number of cells is decreased below c. 100 the trajectories become increasingly variable from year to year. Mortalities from fire act in an inverse spatially density-dependent fashion, enhanc­ing tree aggregation. The role of fire in enhancing tree aggregation is supported by additional simulations in which dispersal of seeds to non-adjacent cells can occur. When a small amount of dispersal is possible the rate of tree population growth is greatly accelerated as compared to when no such dispersal occurs. We present several hypotheses to explain why the savanna at Lamto is not tree­dominated as would be predicted by the model, discuss how seed dispersal and fire influence tree dynamics; and make predictions for future testing