In less-favoured rural areas in Europe, the implementation of agri- environmental policies has encouraged land managers to reconcile pastoral stakes (producing feeding resources for livestock) and environmental ones (preserving biodiversity) in "concerted approaches". Previous works have shown that the effectiveness of such concerted approaches depends on cognitive synchronisation processes between the various stakeholders involved, and thus their collective ability to share knowledge. We present here an interdisciplinary research project (combining cognitive management science and ecology) to investigate the combination of heterogeneous knowledge from two different fields (agriculture and environment, respectively), By observing and participating in various land use management projects, especially in the Pyrenean pastoral areas, we will analyze how shared knowledge (especially to produce operational indicators on vegetation) is issued from formalising and combining different knowledge sources (know-how and knowing, formal and informal, empirical and scientific, etc.). As a first step, we built a typology to specify different knowledge-sharing situations.