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In mobile pastoral systems, the spatial movement of herders is tied to requirements such as water, markets and medical services, resulting in the concentration of livestock in particular areas and subsequent desertification in those areas. The spatial and temporal distributions of these requirements are subject to changes in external forces, such as political regimes and economic systems. To assess and counteract desertification requires an understanding of, and ability to predict, the spatial and temporal arrangements of such concentration points and how these arrangements cause or inhibit desertification. To this end we developed a model that explicitly simulates how animals and vegetation interact. The model has spatial settings for extensive pasture to represent the points at which animals concentrate. We found that the spatial dynamics of the interaction between animal behavior and vegetation were nonlinear and markedly affected the size of the area desertified, and that the distribution of grazing pressure was more important than total grazing pressure, which had only a limited influence on desertification. These findings indicate that application of the carrying capacity concept is not capable of preventing desertification in extensive pasture, even under equilibrium conditions. Therefore, explicit management of the spatial distribution of animals is essential to prevent desertification in extensively grazed rangelands. Copyright (C) 2010 John Wiley & Sons, Ltd.