In Argentina, livestock systems are faced with great uncertainty due to the financial crisis and to recent severe climatic events (e.g. drought in 2008-2009). In such context, what are the different production strategies and adaptations which livestock systems develop in front of climatic uncertainties and variability of meat prices and in particular, what is the role of resources (food and capital or labour) used by farming systems to adapt ? Our study aims at investigating how agroecological production systems grounded on natural pastures adapt themselves to multiple uncertainties. Choosing this focus, our central hypothesis is that these pastures may play an important role in the flexibility and sustainability of these production systems faced with severe climatic changes. Our objective is then to investigate how the use and the management of pastures contribute through time to endow production systems with adaptive capacities to face climatic crisis. Within a joint Argentinian-French cooperation program, our study was undertaken in Magdalena district (south-east of La Plata, province of Buenos Aires), which is part of the humid Pampa and where various types of agriculture (financial as well as family ones) coexist. As a conceptual basis, we chose a functional viewpoint on farming systems acknowledging the complex nature of these socio-technical systems. Data were collected within family farms with a comprehensive procedure (semi-directive interviews with farmers) allowing us to characterize in deep farm trajectory, feeding system and reactions to severe climatic crisis. We illustrate the preliminary results of this on-going study with illustrative case studies of family farms in Magdalena district.