Fig. 2. Example of a state and transition diagram for a Simona soil in the northern Chihuahuan Desert. The structure of the model is based on Stringham et al. (2001). Arrows within boxes (states) represent easily reversible plant community composition and associated soil changes. Unidirectional arrows between states reflect that the transitions are nonreversible without external inputs. Text between states describes some of the processes associated with each transition. The diagram has been simplified and does not include all possible plant communities in States 3 and 4.