While Ecosystem services have become the subject of wide attention at the academic and political level, knowledge gaps, complexity and uncertainty make them hard to manage in practice (Seppelt at al., 2011). This presentation proposes an innovative methodological tool to help stakeholders optimize the provision of ecosystem services at a landscape scale, a relevant scale to study both collective action and ecological processes (Prager et al., 2012). We present the results of an on-going case study carried out in a cereal plain in the West of France. It focuses on a pioneering initiative of a cooperative aiming to reconcile agricultural production with environmental protection. Our group of researchers in social and ecological sciences developed a method based on one of the most recent design theories, the Concept-Knowledge theory (Hatchuel & Weil, 2009) with local stakeholders, to involve them in the collective exploration of ecosystem services. Efforts were focused on the reintroduction of grasslands in the cereal crop rotations to improve ecological regulation services (Berthet et al., in press). "Grassland" is a subject of controversy, considered as a natural habitat by ecologists vs. a forage production area by farmers. The collective design method made it possible to identify a conceptual model of grassland and to explore its potential properties, some of which were not known by stakeholders initially. Innovative farming practices were developed, not focused on trade-offs between production and conservation, but rather on the identification of new values that could be created by farmers through a renewed management of ecosystem services. This collective exploration process revealed new interdependences between stakeholders. This paper brings together ecological and managerial knowledge to develop an innovative method aimed at fostering the collective design of ecosystem services at a landscape scale. It also gives useful insights to develop ad-hoc governance strategies.