Tropical Grasslands (1994) Volume 28, 247255
State and transition models for rangelands
J. A. BELLAMY1 and J. R. BROWN2
1Division of Tropical Crops and Pastures, CSIRO, Brisbane, and
State and transition models have recently emerged as flexible conceptual frameworks for abstracting information concerning vegetation change in rangelands. They characterise the rangeland through both a partitioning of the system in terms of multiple steady states, and the identification of transitions between those states. This paper examines the steps and some of the issues involved in building such models for resource management and research purposes. The number and nature of states defined depends on: the specific objective of management: the way in which the rangeland functions; and the state of existing knowledge about its dynamics and structure. Each transition may be defined in terms of a suite of causes which explain the mechanisms of vegetation change involved. Each cause can then be defined in terms of a probability of occurrence, a time-frame for the cause to be maintained to effect a transition, and a confidence rating in the prediction. State and transition models should be applied at spatial and temporal scales that are relevant to the scale of disturbance as well as the context within which management decisions are made. Identifying the appropriate variables and processes that reflect these scales is critical. Developing these models should also be an iterative process involving progressive refinements to ensure validity, accuracy and usefulness.