Self‐Organization of Vegetation in Arid Ecosystems

Abstract

Scientists are still searching for possible unifying mechanisms \nto explain this range of spatial patterns (Tongway \nand Ludwig 2001), and an important question of this research \nis whether this range is the result of preexisting \nenvironmental heterogeneity, the result of spatial selforganization, \nor both (Klausmeier 1999; Couteron and \nLejeune 2001; HilleRisLambers et al. 2001; Von Hardenberg \net al. 2001). Here, we contribute to the ongoing debate \nabout vegetation pattern formation in arid ecosystems \nby presenting novel, spatially explicit model analyses and \nresults, extending on the work of HilleRisLambers et al. \n(2001). Our results show that these different vegetation \npatterns observed in arid ecosystems might all be the result \nof spatial self-organization, caused by one single mechanism: \nwater infiltrates faster into vegetated ground than \ninto bare soil, leading to net displacement of surface water \nto vegetated patches. This model differs from earlier model \nresults (Klausmeier 1999; Couteron and Lejeune 2001; \nHilleRisLambers et al. 2001; Von Hardenberg et al. 2001) primarily in two ways: it is fully mechanistic, and it treats \nthe lateral flow of water above and below the soil as separate, \nnot independent, variables. Although the current \nmodel greatly simplifies the biophysics of arid systems, it \ncan reproduce the whole range of distinctive vegetation \npatterns as observed in arid ecosystems, indicating that \nthe proposed mechanism might be generally applicable. \nWe further show that self-organized vegetation patterns \ncan persist far into regions of high aridity, where plants \nwould become extinct if homogeneously distributed, \npointing to the importance of this mechanism for maintaining \nproductivity of arid ecosystems (Noy-Meir 1973). \nOur analyses are based on the model first developed in \nHilleRisLambers et al. (2001)