Meeting the diverse sustainability targets of modern society has led to the development of national-level management frameworks meant to guide resource management actions and conservation funding decisions. In U.S. rangelands, state-and-transition models have been developed within the Ecological Site Description (ESD) Database as an application of alternative state theory and to move the discipline toward a more dynamic platform for resource management. After 15 years of development, and with government-mandated collaboration among federal agencies, these models are set to become one of the world-s largest guiding frameworks for terrestrial ecosystem management. State-and-transition models originated from the rangeland discipline- s long-held debate on the appropriateness of equilibrium and non-equilibrium paradigms of vegetation dynamics and community reorganization. State and transition models within ESDs are meant to move past previous rangeland assessment models, which were applications of Clements- (1916) theory of succession and vegetation climax and its refinement by Dyksterhuis (1949), to suggest that succession and retrogression of vegetation are well-defined, predictable changes along a single reversible trajectory. Our research team is evaluating how alternative state theory is being applied within state and transition models in the ESD Database, with the intent of providing feedback that helps close the gap between theory and application in rangeland ecology and management.
Applications of theories in ecosystem ecology within rangeland management. Classical ecological theory of community climax (Clements 1916) served as the foundation for the classical range model. The classical range model (based on Dyksterhuis 1949) guided rangeland management actions from approximately 1950-1995 and proposed that vegetation composition could be maintained at a desired equilibrium solely by changing grazing pressure. Rejection of classical ecological theory, its displacement by alternative state theory, and the lack of empirical evidence to support the classical range model led to the emergence of state and transition models as the preferred framework for rangeland management since 1997. Alternative state theory is represented here using landscapes with transient equilibria that change with differing external conditions (modified from Scheffer et al. 2001 and Scheffer and Carpenter 2003); however, state shifts also result from changes in the parameters of ecosystem states (see overview by Beisner et al. 2003). The ball represents the ecosystem state and its position is contingent upon feedback mechanisms (shown as dashed loops) operating within the historical configuration and trajectory of the stability landscape (refer to Scheffer et al. 2001, Scheffer and Carpenter 2003 for further explanation). State changes can be gradual (linear), nonlinear and rapid (threshold), or exhibit multiple states over a range of conditions and follow alternate trajectories of collapse and recovery (hysteresis) (adapted from Scheffer and Carpenter 2003, Suding and Hobbs 2009). The state and transition model given here is a qualitative model based on expert opinion that characterizes alternative ecosystem states as boxes and the feedback mechanisms driving transitions between states as arrows (adapted from Westoby et al. 1989, Briske et al. 2008, ESD User-s Guide 2011).
Twidwell, D., B.W. Allred, S.D. Fuhlendorf. 2013. National-scale assessment of ecological content in the world-s largest land management framework. Ecosphere 4:art94.