This article presents a case study analysis that will interest researchers in three fields. In environmental governance, it demonstrates how mediated negotiations can produce agreements on ecosystem service valuation and payment mechanisms against a backdrop of paralyzing conflicts. In environmental economics, it demonstrates how deliberative valuation of ecosystem services and joint fact finding can overcome debilitating transaction costs and produce policy agreements. In urban and regional planning, it demonstrates how a participant-observer—acting as a participatory action researcher—can facilitate multi-stakeholder negotiations to design and institutionalize a landscape-level conservation initiative involving interdependent and, at times, conflicting local, regional, and national authorities. A detailed, practice-centered review of a conservation intervention in Oaxaca, Mexico highlights the value of combining multi-disciplinary theories and practical techniques to advance socioecological coherence. © 2023, The Author(s), under exclusive licence to Springer Nature Singapore Pte Ltd.