Continued Development of Non-Equilibrium Ecology for Rangeland Applications

1. Northwest Watershed Research Center OREGON STATE UNIVERSITY Continued Development of Non-Equilibrium Ecology for Rangeland Applications Paul J. Meiman Dr. W.C. Krueger Dr. T.K. Stringham Department of Rangeland Resources

2. Review & Interpretation ofExisting Work Dept. of Rangeland Resources, Oregon State University

3. Models: Old & not as old! • Range Succession Model • Linear models (single or multiple) • Hysteresis ? • Works well in many applications • Great Plains • Mountain Grasslands • Some dynamics in arid and semi-arid systems • Many instances where this model does not adequately describe vegetation change Dept. of Rangeland Resources, Oregon State University

4. Models: Old & not as old! • Non-equilibrium Models (States, Transitions and Thresholds) • Encompass Range Succession Model where it fits • Accounts for thresholds, hysteresis and multiple steady states • Allows for more detail in triggers and pathways of vegetation change Dept. of Rangeland Resources, Oregon State University

5. Non-equilibrium Ecology:Theory in its infancy • Opportunities • Clear, accepted definitions needed for • States • Transitions • Thresholds • Clarification and incorporation of ‘Stability’ and ‘Resilience’ • Experiments to test hypotheses and further develop the theory Dept. of Rangeland Resources, Oregon State University

6. Definitions: State (Westoby et al. 1989) • …relatively stable, recognizable assemblages of species occupying a site. • Two types: transient and persisting • “…necessarily an abstraction encompassing a certain amount of variation…” Dept. of Rangeland Resources, Oregon State University

7. Definitions: State (Iglesias & Kothmann 1997) • physiognomically characterized ecological entities • usually described by botanical composition of dominant vegetation • one of only two types of objects in a state and transition model (thresholds not considered) Dept. of Rangeland Resources, Oregon State University

8. Application: States • The Westoby team’s “certain amount of variation” VARIES! • broad classifications • more specific classifications that sometimes approximate seral stages Dept. of Rangeland Resources, Oregon State University

9. States: Broad application • Westoby et al. (1989) • grass driven succession vs. shrub driven succession • Archer (1989) • assemblages within grassland domain & shrubland domain • Davenport et al. (1998) • low erosion state vs. high erosion state • Friedel (1991) • grass dominance vs. woody dominance Dept. of Rangeland Resources, Oregon State University

10. SCT States: Broad application • SRM Task Group, Unity in Concepts and Terminology Dept. of Rangeland Resources, Oregon State University

11. States: Specific application • West (1999) - Successional change in sagebrush steppe • Laycock (1991) - S & T for sagebrush-grass vegetation • Olivia et al. (1998) - Patagonia • Many others Dept. of Rangeland Resources, Oregon State University

12. States: Specific application (cont.) Examples: Late Seral Sagebrush, Dense Sagebrush, Native Perennial Grasses Dominate, etc. Threshold Dept. of Rangeland Resources, Oregon State University

13. Definitions: Transitions • “Transitions not always clearly defined” (Iglesias & Kothmann 1997) • Characteristics (Westoby et al. 1989) • triggered by natural events, management or both • may occur quickly or over a long period of time • once initiated, system does not come to rest 1/2 way through Dept. of Rangeland Resources, Oregon State University

14. Application: Transitions • Applied fairly universally • trajectory or pathway of change • among / between states • among / between assemblages within states Dept. of Rangeland Resources, Oregon State University

15. Definitions: Threshold • Westoby et al. (1989) didn’t define thresholds • transitions that do not occur • transitions that require management input • Friedel(1991) concentrated on thresholds • “…compatible with state and transition theory focusing on those transitions that are one-way.” • Archer (1989) identified a “transitional threshold” Dept. of Rangeland Resources, Oregon State University

16. Definitions: Thresholds (Friedel 1991) • Thresholds exist between alternative states & have 2 characteristics: • boundary in space and time between states • initial shift across the boundary is not reversible on a practical time scale without input Dept. of Rangeland Resources, Oregon State University

17. Applications: Thresholds • Most Common • thresholds between some, but not all states • if a threshold has not been crossed, has the state truly changed? Threshold Dept. of Rangeland Resources, Oregon State University

18. SCT Applications: Thresholds • An alternative • thresholds “define” the bounds of states • must cross a threshold to change states Dept. of Rangeland Resources, Oregon State University

19. Proposed Definitions and Model Dept. of Rangeland Resources, Oregon State University

20. Proposed Definitions (Draft) • State - A recognizable complex of two resilient and stable substates: the abiotic foundation and the biotic framework Dept. of Rangeland Resources, Oregon State University

21. Proposed Definitions (Draft) • State - A recognizable complex of two resilient and stable substates: the abiotic foundation and the biotic framework • Abiotic Foundation- A substate resulting from the interaction of climate, soils and topography that dictates the quantity and quality of water, air, nutrients and energy available for system function. Dept. of Rangeland Resources, Oregon State University

22. Proposed Definitions (Draft) • State - A recognizable complex of two resilient and stable substates: the abiotic foundation and the biotic framework • Abiotic Foundation- A substate resulting from the interaction of climate, soils and topography that dictates the quantity and quality of water, air, nutrients and energy available for system function. • Biotic Framework - A substate resulting from communities of living organisms, whose vital attributes competitively utilize the available air, water, nutrients, energy and space of an abiotic foundation. Dept. of Rangeland Resources, Oregon State University

23. Proposed Definitions (Draft) • Stability - An intra-state phenomenon that ensures the persistence of reversible relationships between the biotic framework and the abiotic foundation such that a given complex of natural and management stresses will yield the same ecological structure. Dept. of Rangeland Resources, Oregon State University

24. Proposed Definitions (Draft) • Stability - An intra-state phenomenon that ensures the persistence of reversible relationships between the biotic framework and the abiotic foundation such that a given complex of natural and management stresses will yield the same ecological structure. • Resilience - An intra-state phenomenon that indicates the potential of a state by encompassing the amount of variability necessary to ensure the persistence of reversible relationships within the system between complexes of natural/management stresses and ecological function. Dept. of Rangeland Resources, Oregon State University

25. Proposed Definitions (Draft) • Transition - Trajectory of system change, triggered by natural events, management, or both, that upon crossing a threshold, is irreversible and will not come to rest before the establishment of a new state. Dept. of Rangeland Resources, Oregon State University

26. Proposed Definitions (Draft) • Transition - Trajectory of system change, triggered by natural events, management, or both, that upon crossing a threshold, is irreversible and will not come to rest before the establishment of a new state. • Threshold - Boundary in space and time between any and all states, or along transitions, such that an abiotic or biotic process or resource has been irreversibly changed an must be actively restored before return to a previous state is possible. Dept. of Rangeland Resources, Oregon State University

27. Proposed Model Reversible Transition Irreversible Transition Threshold State Biotic Framework Abiotic Foundation Dept. of Rangeland Resources, Oregon State University