Regular and irregular patterns in semiarid vegetation

Vegetation in many semiarid regions is strikingly patterned, forming regula r stripes on hillsides and irregular mosaics on fiat ground. A simple model of plant and water dynamics based on ecologically realistic assumptions an d with reasonable parameter values captures both of these types of patterns . The regular patterns result from a Turing-like instability; the irregular patterns arise when the ecological dynamics amplify slight small-scale top ographic variability. Because of the close agreement between observations a nd these theoretical results, this system provides a clear example of how n onlinear mechanisms can be important in determining the spatial structure o f plant communities.