ON THE ORIGIN OF TIGER BUSH

We propose a model which describes the dynamics of vast classes of ter restrial plant communities growing in arid or semi-arid regions throug hout the world. On the basis of this model, we show that the vegetatio n stripes (tiger bush) formed by these communities result from an inte rplay between short-range cooperative interactions controlling plant r eproduction and long-range self-inhibitory interactions originating fr om plant competition for environmental resources. Isotropic as well as anisotropic environmental conditions are discussed. We find that vege tation stripes tend to orient themselves in the direction parallel or perpendicular with respect to a direction of anisotropy depending on w hether this anisotropy influences the interactions favouring or inhibi ting plant reproduction; furthermore, we show that ground curvature is not a necessary condition for the appearance of arcuate vegetation pa tterns. In agreement with in situ observations, we find that the width of vegetated bands increases when environmental conditions get more a rid and that patterns formed of stripes oriented parallel to the direc tion of a slope are static, while patterns which are perpendicular to this direction exhibit an upslope motion. (C) 1997 Society for Mathema tical Biology.