The research for a maximum stand density that maintains sustainable development is necessary in arid and semiarid areas where the conflict between limited soil water storage and the need for more plants in improving environmental quality almost always exists. However, the quantification of the research is not easy since it requires insight interpretations of the effects of plant density on soil water storage and soil water stress on plant growth. Such quantification is incomplete with current empirical methods or physical models because the dynamics effects of soil water stress and its feedbacks are not included. This paper presents a physically-based model of soil water carrying capacity for vegetation (SWCCV). The model build on the concept of an equilibrium adjustment of vegetation growth to soil water dynamics, by iterative calculation between hydrologic and biogeochemical processes that account for the interactions between the limiting effects of soil moisture on photosynthesis and evaporative demand on soil water. It is capable to calculate the maximum plant density at any given initial conditions (site-specific data, vegetation, weather, and etc.) through hourly, daily and yearly cycles. Exploratory simulation to evaluate the model against results from previous studies for two sites indicated that the predictions by the model had good agreement with measured soil water contents in each layer, LAI and NPP for plants. Under the same initial conditions the predicted soil water carrying capacity captured well the soil water difference between two sites in terms of controlling vegetation density. Overall, the SWCCV model is capable in terms of predicting soil water carrying capacity, providing a new approach for understanding soil-vegetation interactions and making recommendations for better management of vegetation construction in arid and semiarid areas.

Keywords: Hydrologic cycle; Biogeochemical processes; Soil water carrying capacity; Arid and semiarid area; Vegetation density; Model