Application of state and transition models to discussing the thicketization of steppe in Xilin River Basin,Inner Mongolia

The state and transition models is applied to discuss the threshold in vegetation composition from steppe to thicketization-steppe,Xilin River Basin,Inner Mongolia.From the increase of soil patchiness scale in the thicketization of steppe,it is suggested that the transition from steppe to thicketization-steppe dominated by Caragana microphylla patches could be irreversible once this threshold is passed.The thicketization of steppe is an important stage of grazing succession,which may be considered as a self-rehabilitation of a degraded ecosystem.The model on the steppe grazing succession is developed, and it is the important framework for the research into the thicketization of steppe in Xilin River Basin,Inner Mongolia.