To study disturbance in a system where minimal structure is not known, an initial, or the best available approximation to minimal structure should be used. Pickett et. al proposed an operational program that can be followed by first constructing a hierarchical model containing the focal system, or level. The levels included are determined by the processes of interest at the focal level. The last step is to examine the effect of disturbance at a particular level on adjacent levels. Without such a hierarchical model, however, statements about the nature of disturbance, its role and sources, and predictions about its consequences are not well founded. The application of the concept of disturbance that uses as a reference this hierarchical structure of ecological systems is a first step toward greater generalization in the study of disturbance.
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