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Tiago TEIXEIRA da SILVA SIQUEIRADoctorant en sciences économiques au LEREPSUniversité Toulouse – Jean Jaurès et INRAtiago.teixeira [at] toulouse.inra.fr&#160;Domaines de recherche : Économie rurale, Économie écologique et de l’environnement, Économie du développement ; Économie institutionnelle ; Coexistence et durabilité de systèmes de production agricole ; Filière lait, Brésil et FranceSujet de thèse : Déterminants de la durabilité environnemental des systèmes de productions agricoles familiales et entrepreneuriales au Brésil et en FranceLa thèse en deux mots : Cette thèse cherche à comprendre les facteurs internes et externes à l’exploitation agricole qui vont influencer le choix de modes de production avec des performances environnementales différentes.Résumé du papier : Concerns about the sustainability of beef production are increasing around the world, mainly in the Amazonian region. We intend to improve understanding of economic and environmental issues of the typical Amazonian beef farms by considering the characteristics of these systems. In this study we analyze how the farm’s internal structures and use of its resources impact economic performances and greenhouse gas (GHG) emissions. We use production cost and profitability analysis to assess farm economic issues. We propose an original methodological approach to address environmental issues. We assess farm GHG emissions using a Life Cycle Assessment model integrating regional characteristics of land-use change and forest and grassland soil carbon storage (SCS). We relate economic and environmental results with farmland use and farm management to identify economic and environmental hotspots. Economic results show that the beef farm is profitable in the short term but not in the middle/long term, because farm revenue covers cash costs but not total costs. The main hotspots for farm profitability are land opportunity cost and livestock costs. The largest source of GHG emissions (15 kg CO2equivalents per kg of live weight produced) comes from enteric fermentation (83%). Conversion of primary forest to grassland caused substantial GHG emissions and a loss of soil carbon. Therefore, forestland preserved on the farm is an important site of SCS that can compensate all farm GHG emissions. Based on the literature, we conclude that economic failure and the substantial GHG emissions are related to the low productivity of animals and land. These are consequences of farm technical and managerial inefficiencies, which are a common characteristic of extensive Brazilian livestock farms. Improvements in grassland and animal management can be promising initial insights to address economic and GHG issues.Statut du papier : soumis