State and transition modeling: An ecological process approach

State-and-transition models hold great potential to aid in understanding rangeland ecosystems' response to natural and/or management-induced disturbances by providing a framework for organizing current understanding of potential ecosystem dynamics. Many conceptual state-and-transition models have been developed, however, the ecological interpretation of the model's primary components, states, transitions, and thresholds, has varied due to a lack of universally accepted definitions. The lack of consistency in definitions has led to confusion and criticism indicating the need for further development and refinement of the theory and associated models. We present an extensive review of current literature and conceptual models and point out the inconsistencies in the application of nonequilibrium ecology concepts. The importance of ecosystem stability as defined by the resistance and resilience of plant communities to disturbance is discussed as an important concept relative to state-and-transition modeling. Finally, we propose a set of concise definitions for state-and-transition model components and we present a conceptual model of state/transition/threshold relationships that are determined by the resilience and resistance of the ecosystems' primary ecological processes. This model provides a framework for development of process-based state-and-transition models for management and research.