Vegetation–soil water interaction within a dynamical ecosystem model of grassland in semi-arid areas

A dynamical ecosystem model with three variables, living biomass, wilted biomass and available soil wetness, isdeveloped to examine the vegetation—soil water interaction in semi-arid areas. The governing equations are based onthe mass conservation law. The physical and biophysical processes are formulated with the parameters estimated fromobservational data. Both numerical results and qualitative analysis of the model as well as observational data indicate thatthe maintenance of a grassland requires a minimum precipitation (or equivalently, a minimum moisture index), and thegrassland and desert ecosystem can coexist when precipitation is within a range above this threshold. Sensitivity studiesshow that these numerical results are robust with respect to model parameters and the transformation functions. It isalso found that the wilted vegetation plays a very important role in shaping the transition between grassland and desert.By using the theories of an attractor basin and multiple equilibrium states, the conditions for grassland maintenance andthe strategy of grazing are also analysed.