Self-Organization of Vegetation in Arid Ecosystems

Vegetation in arid regions of Africa, America, Australia,and Asia reveals remarkable patterns, such as spotted vegetation,labyrinths, gap patterns, and regular bands (Bromley et al. 1997; Aguiar and Sala 1999; Klausmeier 1999;Leprun 1999; Couteron and Lejeune 2001; Von Hardenberget al. 2001). Here, the term "arid" refers to environmentscharacterized by an extended dry season, whereyearly potential evaporation exceeds yearly rainfall, andwhere plant growth is limited by water availability. Thetwo-phase mosaics of vegetation alternating with bare soilas observed in arid ecosystems differ in scale and shape,depending on slope gradient and rainfall. When slope gradientis <0.2% and mean annual rainfall ranges from 200to 550 mm yr⁻¹, observed vegetation patterns include spotswith a diameter of 5–20 m, labyrinths with a vegetatedband width of 10–50 m (fig. 1a), and gap patterns withbare spots in the vegetation with a diameter of 5–20 m(fig. 1b; Bromley et al. 1997; Aguiar and Sala 1999; Ludwiget al. 1999b; Valentin et al. 1999; Couteron and Lejeune2001). On slopes steeper than 0.2% in arid regions, typicalregular-banded vegetation patterns with a band width inthe range of a few tens of meters are observed (Klausmeier1999; Leprun 1999; Valentin et al. 1999; d'Herbes et al.2001).