Projets tutorés

Modeling the carbone balance of logging in french Guiana

Camille Piponiot-Laroche et Antoine Cabon under the supervision of Bruno Hérault.

Selective logging is a dominant practice in tropical forests and has been designated by recent studies to have an important role in carbon emissions. In this study we seek to quantify the carbon fluxes between the atmosphere and the logged forest in French Guiana by modelling the biomass dynamic induced by logging. Our model takes into account the decay of the biomass loss caused by selective logging as well as the carbon storage from tree growth in logged parcels and is based data on harvested surfaces and extracted wood volumes inputs. We thus calculated that, during the considered period of 1974 – 2012, logging in French Guiana resulted in an average net emission of 1.7 Gg of carbon. The tendency of net carbon emission seemed to be mainly driven by the decay of biomass damaged by logging practices and left in the forest. However, on account of the high uncertainty over our results, we could not conclude on the significance of this net emission of carbon to the atmosphere. By analysing the large confidence interval of our results we concluded that our main source of error was the lack of data on the quantification of logging damages.

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Foliar traits variations in Cercopia obtusa : traits correlations and variations within the tree crown and during the ontogeny

Ariane Mirabel, Coffi Belmys Cakpo et Laurent Risser under the supervision of Patrick Heuret and Sabrina Coste.

Correlation and variation of leaf traits is a key issue to understand growth dynamics and its determinants. Those are known to depend on the species and the environmental context where they grew. However little is known about variations among individuals from the same species and even less about the intra-crown variations. We assumed that within the tree crown leaf traits and physiological characteristics depend on the age and local situation of the leaf. First due to natural senescence of the leaf and then because of variation in the micro-environment of the leaf (shading, height) leaf traits are assumed to depend on the rank, i.e. its age and situation within the tree crown. Moreover, trees follow steps during their development, from juvenile to mature and then senescent phase. This suggests an ontogenetic gradients of the traits depending on the development stage. Those hypothesis were tested using Cercopia obtusa datasets collected in French Guyana. First looking at traits correlations we then estimated their variation according to the leaf location in the tree crown, which depends on its age and changes its nearby environment. After explicating those variations we demonstrated a significant variation of traits following the development stage of the tree, partly due to the height of individuals.

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Studying a fire experiment for conservation management of savannas at Pripris de Yiyi

Elodie Guihlot et Cindyrella Silvani Kasanwapiro.

Tropical savannas, which have a bigger chance to transform into forests, are important to conserve, because of their high biodiversity. The use of fire has been considered a well-known method for the conservation of savannas. To know whether this method is suitable for the savannas in French-Guyana, this article will focus on a fire experiment in order to explore the effects on the evolution of the savanna within time. The study area is the savanna of the Pripris de Yiyi in French-Guyana. This area was divided into three large parcels, where an inventory on species was executed before and after the fire experiment, using the method of Braun-Blanquet. The results show that there are dissimilarities between the parcels before and after the fire experiment. It can be concluded that the fire does have an impact on the evolution of savannas.

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