Control theory and the management of ecosystems

Summary1 Control theory is a well‐developed branch of mathematics and engineering that identifies optimal control policies for dynamic systems. While it should be useful for managing ecosystems, it is currently used only in certain fields of ecology and resource management, and only certain aspects of the theory are applied. Where optimal control policies have been determined, such as oceanic fisheries, the control policy often fails. 2 The goals of this study were to determine why control theory has not been used very much and why it fails, and also to improve its applicability to natural resource management. Control theory methods and assumptions were reviewed, and applications to agriculture, forestry and fisheries summarized. A comparison was made between control theory assumptions and the real ecological systems to which the method was applied. A fisheries example was developed to illustrate some improvements to the application of this technique. 3 It was shown that the paradoxical aspects of control theory in resource management result from the points of divergence of real systems from the assumptions of control theory. Because of non‐linearities, noise, sampling difficulties, policy implementation error and other issues, ecosystems are neither readily observable nor easily controllable. This means that even theoretically correct control policies can lead to failure. 4 The fisheries example showed that measurement error and management lags can of themselves lead to the collapse of a fishery. It was shown that the costs of acquiring information and managing the system need to be incorporated explicitly into the control problem as decision variables. The solution to the fisheries control problem prevented extinction of the fishery by reducing sampling error and management lags to reasonable but non‐zero levels. 5 Other suggestions are made for applying control theory with more success. By taking into account the deviations between the idealized control model and real systems, better resource management can be achieved. Control theory could also profitably be applied to the design of monitoring programmes, to model parameter estimation, and to other aspects of ecology and resource management where it is currently not being utilized. 6 Synthesis and applications . Control theory needs to be re‐evaluated for its utility in natural resource management. It offers the potential for providing effective management policies. To achieve this potential, techniques borrowed from engineering must be expanded to incorporate the effects of state uncertainty (measurement error), environmental fluctuations (stochasticity), parameter uncertainty and policy implementation error.