4.5.1 COMPONENTS AND INTERACTIONS

Man and arid ecosystems can be combined as a simple four-component system; man, and society, herbivores, herbage and soils, and climate (Fig. 4.5). In this system there are 10 interactive links between components that vary in strength. Each of these links may involve one or more ecological processes, e.g. herbivory or predation, and depending upon context the paired links operate as either positive or negative feedback loops.

   The proposition is that, within this simple system model, desertification results from changes in the strength and sign of the interactive links. No new patterns of linkage are established. The transformation is effected by a change in the nature of two feedbacks, from weak to strong and from negative to positive. That is, the beginning process of desertification will, by positive feedback, increase the probability that further desertification will occur.

   This is not a new proposition. It is a restating of commonly expressed conclusions that in desertification cause and effect are difficult to separate (Reining,1978), or that 'desertification feeds on itself' (UNCOD,1977; Warren and Maizels,1977). This proposition will be supported by examining each of the interactions involved.