Integrating research on ecohydrology and land use change with land use management Brad Bass, 1 * Ralph E. Byers 2 and Nina-Marie Lister 3 1 Great Lakes and Corporate Aairs, Environment Canada±Ontario Region, 4905 Duerin Street, Downsview, Ontario M3H 5T4, Canada 2 Orillia, Ontario, Canada 3 School of Urban and Regional Planning, University of Waterloo, Ontario, Canada Abstract: One objective of the International Geosphere±Biosphere Programme is to provide a scienti®c basis for sustainable development policies. Land use change and ecohydrology are important components of this scienti®c basis, but predicting change is dicult because of the scale and complexity of the interactions between non-linear ecohydrological and socio-economic processes at dierent spatial and temporal scales. A systems framework, the Ecosystem Approach, has been developed to conceptualize these interactions for the purpose of providing information for sustainable development policy. The Ecosystem Approach combines the dynamics of the Holling ®gure-eight model Ð a conceptual model of dynamics that stresses discontinuous change and destruction as an internal property of the system Ð and the properties of self-organizing systems with the socio political aspects of decision making. The Ecosystem Approach highlights the problems of managing change in complex systems when that change may involve unpredictable shifts to a dierent attractor. Although there are methods available to detect the occurrence of such shifts, both detection and modelling are complicated by the presence of semi-stable attractors. When a model oran ecosystem is on a semi-stable attractor, it may appear to remain stable for an extended period prior to changing as a consequence of inherent instabilities. When the shift to a new attractor occurs, it is quite sudden and unpredictable. A technical discussion on prediction under conditions of semi- stability and chaos is included because it enhances our understanding of the role of surprise in ecosystems, as well as the utility of simulation models. The principles of the Ecosystem Approach are derived from the theoretical discussion and an example of a land use policy in the Huron Natural Area in south-western Ontario. These principles provide a clear role for scienti®c research, and particularly simulation modelling, within the larger context of policy and land use management. # 1998 John Wiley & Sons, Ltd. KEY WORDS modelling; ecohydrology; land use; semi-stability; ecosystem approach INTRODUCTION Ecosystem models are always wrong, in the sense that reality conforms to their numerical projections only very rarely. Models are indispensable because without them human misunderstanding persists, unaware of its errors (Lee, 1993, p. 62). Lee (1993) summarized the basic conundrum that faces any scienti®c research programme, particularly one, such as the International Geosphere±Biosphere Programme (IGBP), that relies heavily on numerical simulation models in translating the science into eective decision making. What is clear is that the role of CCC 0885±6087/98/132217±17$1750 Revised 1 May 1998 # 1998 John Wiley & Sons, Ltd. Accepted 5 May 1998 HYDROLOGICAL PROCESSES Hydrol. Process. 12, 2217±2233 (1998) *Correspondence to: Brad Bass, Great Lakes and Corporate Aairs, Environment Canada±Ontario Region, 4905 Duerin Street, Downsview, Ontario M3H 5T4, Canada.