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A conceptual model is proposed for the activity of sand dune systems on the northern Great Plains that incorporates vegetation growth theory and geomorphic system theory. Dunefield activity is modeled as a cyclic phenomenon, alternating between active and stable states, with the latter as the system state attractor. The model is divided into two constituent parts: an activation model and a stabilization model. The activation model is qualitative and describes the transition from stable to active dunes as the result of a climatic perturbation such as drought that decreases vegetation cover. The intensity and duration of the climatic perturbation determines the rate of decline of vegetation cover. The stabilization model is quantitative and describes the transition from active to stable dunes using a logistic model of vegetation growth. Small perturbations during stabilization can prolong the duration of recovery, enabling dunes to remain active well after the initial perturbation. Despite the geographic focus of this study, the model appears applicable to a variety of environments where dune activity is limited, in part, by vegetation cover. (c) 2005 Elsevier B.V All rights reserved.