MAXIMUM SIMPLIFIED DYNAMIC-MODEL OF GRASS FIELD ECOSYSTEM WITH 2 VARIABLES

Based on general consideration and analysis, a maximum simplified dyna mic model of grass field ecosystem with a single species is developed. The model consists of two variables: grass biomass of grass field per unit area and soil wetness, and is suitable for describing their mutu al interaction. Other factors such as physical-chemical characteristic s of soil, precipitation, irrigation, sunlight, temperature and consum ers, are taken into account as parameters in the dynamical system. Qua litative analysis of the model shows that grass biomass of a possible ecological regime is determined by the stable equilibrium state of the dynamical system. For the grass species interacting weakly with soil wetness the grass biomass continuously depends on the precipitation. W hile, for a species interacting strongly with soil wetness, grass biom ass is abundant if precipitation is larger than some critical value; o therwise, it becomes a desertification regime with very little or even zero grass biomass. The model also shows that there exists a critical (maximum) consuming value, the grass field with abundant biomass can be restored if the consuming is less than the critical value; otherwis e, it becomes desertification.