As a case study where management based on social-ecological principles should lead to sustainable supply of ecosystem services, the international project TERRECO (Complex Terrain and Ecological Heterogeneity) applies a transdisciplinary modelling approach to examine current and potential future natural resource use within the largest reservoir system of South Korea, Soyang Lake Watershed. Due to intensive fertilization, small catchments within the watershed export some of the world's highest levels for N and P, while steep terrain and monsoon rains result in extremely high material transport. To consider future management with climate change at regional scale, new integrated modelling approaches are being developed for land surface processes and production, for hydrology and transport, for economic evaluation of ecosystem services, and for associated management and decision-making. The models are supported by ground-based studies of ecosystem physiology and agricultural yield, of soil properties and erosion, of stream flows and transport, of groundwater exchange, of farm economic balances, of statistical data bases, and of individuals preferences in decision-making within particular regulatory and economic frameworks. Scenario evaluations are planned in partnership with provincial and national agencies that currently carry out land use planning and advise on policy making. A common interest among project participants and agency planners focuses on scenarios examining sustainability of ecosystem services. The required transdisciplinary integration for assess-ments of alternative futures, drives the development of modelling systems that apply at landscape to regional scales, couple to specific conceptual goals, and should provide for communication on uncertainties with managers and stakeholders.