"Given the vulnerability of mountain ecosystems and their importance as carbon storage systems, there is a pressing need to understand how mountain grassland ecosystems function –with the aim to asses the impact of global change and to determine the management mechanisms that can ameliorate its effects.This proposal focuses on the study of the annual C dynamics of semi-natural grazed grasslands in the Pyrenees. The central question will be to resolve how management and climate combine to regulate their productivity and carbon storage capacity. This will be pursued with multi-site analysis of ecosystem dynamics from eddy correlation towers data (description of annual cycles and main biotic and abiotic controlling factors, annual carbon balance, partition of ecosystem fluxes), process understanding (compartment functioning through stable isotope analyses and gas-exchange chambers), and exploration of process-based relationships to evaluate C balance in mountain pastures. Emphasis on the potential role of plant guild distribution as ecosystem regulators will be transversal to all activities.Dr Altimir will be hosted for a 24-month visit at the Technological Forestry Centre of Catalonia (Spain), where she will join the research at the Laboratory of Functional Ecology and Global Change. This group offers experience in grassland ecology as well as cooperation with isotope researchers. The groups coordinates the transnational and interdisciplinary project FLUXPYR and its unprecedented multi-site network for the integrated study of the carbon, energy and water cycles in the Pyrenean agro-ecosystems.Dr Altimir will receive training for an advance career level, emphasizing on project management and supervision skills. She will be also specifically trained for the use isotopic techniques, and guided in the characterization of plant guilds. Secondarily, she will be instructed in the application of remote sensing techniques as validation tools for ecosystem models"