January 31, 2003 Colloquium

A mathematical model for vegetation dynamics will be presented. The model reproduces a wide range of patterns observed in water limited regions, including drifting bands, spots and labyrinths, and transient forms such as rings. The model predicts transitions from bare soil at low precipitation to homogeneous vegetation at high precipitation, through intermediate states of spot, stripe and hole patterns. It also predicts wide precipitation ranges where different stable states coexist. These predictions shed new light on desertification phenomena and on the concept of aridity.