Resilience in landscape exploitation systems

A generic model is developed that describes the broad properties of land-exploitation systems from hunting-gathering societies to modern, intensive agriculture. The framework includes social, economic and ecological drivers of change, going beyond the concept of sustainability to establish a paradigm of resilient exploitation that calculates the capacity of landscape exploitation systems to survive in uncertain and variable human and natural environments. The model is highly aggregated, consisting of two state variables: (1) human-made capital and labour (H) and (2) natural capital (N). Depending on the parameters, the model displays a single non-trivial equilibrium, two equilibria, or stable limit cycles. Our analysis focuses on the strategies that exploiters employ, through varying their investment in H, and how this affects resilience of the system. We measure resilience as the size of the basin of attraction near a desirable equilibrium and the return time following small perturbations. Four general strategies are analysed and discussed using grazing systems as a particular example: (1) constant stocking rate, (2) maintaining grass stock, (3) constant utilization rate, and (4) a non-linear, compound strategy. Like previous models of renewable resources, maximum sustainable yield and profit are determined by properties of the renewable resource, so all management strategies yield identical long-term sustainable production and identical equilibria. However, different management strategies drastically change the system's resilience. We assess the opportunity cost of the disparate objectives of resilience and profitability using multi-objective optimization and demonstrate that resilience decreases rapidly as maximum profit is approached. Thus, the same stable and sustainable equilibrium point in an exploitation system will be more or less resilient depending on the exploiter's strategy. Traditional economic analysis does not consider the impact of the management strategy employed to drive the system towards these long-term equilibria, and therefore misses large differences in dynamical behaviour away from equilibrium. The possibility of multiple steady states in these non-linear systems results in the potential for a discontinuous threshold in resilience, to one side of which resilience is maintained, while on the other resilience and production are greatly degraded. We further discuss how subsidies might increase or decrease resilience of exploitation systems by affecting an exploiter's strategy. (c) 2006 Elsevier B.V. All rights reserved.