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Past & Present Philosophies!?! Succession and Regression State and Transition Theories

Past & Present Philosophies!?! Succession and Regression State and Transition Theories Pat L. Shaver Rangeland Management Specialist West National Technology Support Center Portland, OR. EQUILIBRIUM SYSTEM DYNAMICS. CLEMENTS (1916) vegetation as a ‘superorganism’ determined by climate

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Past & Present Philosophies!?! Succession and Regression State and Transition Theories

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  1. Past & Present Philosophies!?! Succession and Regression State and Transition Theories Pat L. Shaver Rangeland Management Specialist West National Technology Support Center Portland, OR

  2. EQUILIBRIUM SYSTEM DYNAMICS CLEMENTS (1916) vegetation as a ‘superorganism’ determined by climate succession was predictable and had a predetermined outcome vegetation change was an autogenic process DYKESTERHIUS (1949, 1958) concept of functional edaphic units plant community/soil combination resulted in a unique (range) site established concept of ‘dynamic equilibrium’ described in terms of species dominance ( from Brown and Tugel 2001)

  3. RANGE SUCCESSION MODEL Above-average rainfall Drought VEGETATION Successional tendency Grazing Pressure 0 25 50 75 100 Early successional Climax Condition scale Poor Condition Excellent Condition Range Trend (adapted from Westoby, Walker, Noy-Meir 1989)

  4. Range Succession Model Potential to work well in many systems • Great Plains • Mountain Grasslands • Some dynamics in arid and semi-arid systems Many instances where this model does not adequately describe vegetation change

  5. ECOLOGICAL SYSTEM DYNAMICS competing paradigms CLEMENTS (1916) DYKSTERHIUS (1949, 1958) climatic climax endpoint change linear deterministic disturbance unimportant competition important VON BERTALANFFY 1968 HOLLING 1973 MAY 1977 WESTOBY et al 1989 STRINGHAM et al 2003 multiple steady states change nonlinear disturbance important competition-less important thresholds

  6. NONEQUILIBRIUM SYSTEM DYNAMICS HOLLING 1973: RESILIENCE AND STABILITY MAY 1977: THRESHOLDS AND BREAKPOINTS WESTOBY et al 1989: STATE AND TRANSITION STRINGHAM et al 2003 multiple steady states-structural dominance, function may change thresholds-point of entry into new domain (state) hysteresis-lag times, failure to return to original system feedbacks-positive feedback accelerates change negative feedback suppresses change ( from Brown and Tugel 2001)

  7. State and Transition Models • West (1999) - Successional change in sagebrush steppe • Laycock (1991) - S & T for sagebrush-grass vegetation • Olivia et al. (1998) - Patagonia • Many others • Stringham et al (2003)

  8. LINEAR CHANGE IN ECOLOGICAL SYSTEMS Climax vegetation fire grazing climate Vegetation attribute Succession Competition time

  9. STATES • STATE - a recognizable, resistant and resilient complex of two ecosystem components, the soil base and the vegetation structure • soil - developed through time from specific parent material, climate, landscape position and interaction with biota • - determine the site’s capability • - interaction between soil and vegetation determines functional status of site and inherent resistance to change Stringham, et al., 2003

  10. STATES Vegetation attribute(S) time

  11. TRANSITIONS • TRANSITION - the trajectory of a change • - change is precipitated by natural events, management actions, or both • - degrades the integrity of one or more of the state’s primary ecological processes beyond the point of self repair • THRESHOLD- boundary in space and time between two states • - irreversible for practical purposes Stringham, et al., 2003

  12. TRANSITIONS thresholds Vegetation attribute(S) transition time

  13. Graminoid-driven succession Shrub-driven succession Perennial grasses Short / low A = Tall / mid-grasses B = Mid / short grasses C = Short grass / annuals = Threshold D = Clusters and groves E = Woodland Herbaceous retrogression A B C Time or cultural energy increments required to drive system to new configuration CommunityComposition D E Woody plants Long / high Time high low low low low high Fire Frequency Modified from Archer, 1989 Grazing Pressure high Probability & rate of woody plant establishment

  14. Function, Resistance and Resilience • Resistance:the capacity of a process to continue to function through a disturbance (resist change) • Resilience:the capacity to recover functional and structural integrity following a disturbance (rate and level of recovery) (Seybold, et al, 1999)

  15. Function, Resistance and Resilience Disturbance High resistance Process function (% of capacity) Low resistance Low resistance and low resilience and high resilience Time (years) (Modified from Seybold, et al, 1999)

  16. BUILDING STATE AND TRANSITION MODELS

  17. PLANT COMMUNITY PHASES PLANT COMMUNITY PHASES -Different assemblages within a state that do not represent a state change since a threshold has not been crossed - Vegetation dynamics within a state (succession/regression and/or non-equilibrium) COMMUNITY PATHWAYS - Causes of change between plant communities

  18. Upland Loam Mountain Big Sagebrush-Bunchgrass

  19. Upland Loam Mountain Big Sagebrush

  20. Upland Loam Cool Season Bunchgrass

  21. Sagebrush\Bunchgrass - Juniper

  22. Upland Loam

  23. LINEAR CHANGE IN ECOLOGICAL SYSTEMS Climax vegetation fire grazing climate Vegetationattribute Succession time

  24. JUNIPER/GRASSLAND

  25. Upland Loam

  26. JUNIPER/CHEATGRASS COMPLEX

  27. Upland Loam

  28. STATES thresholds Vegetation attribute(S) transitions time

  29. Upland Loam State 1: Mtn. Big Sagebrush / Bunchgrass State 2: Juniper/Cheatgrass Complex 20 ft + Western juniper 20 + Year old stand 30% + Canopy T1a

  30. Upland Loam State 1 1.1a Mtn. Big Sagebrush / Bunchgrass State 2 1.1c ARTR/Bunchgrass <3 ft + juniper <5% Canopy Juniper/Cheatgrass Complex 20 ft + Western juniper 20 + Year old stand 30% + Canopy T1a Cool Season Bunchgrass 1.1b

  31. Upland Loam State 1 1.1a Mtn. Big Sagebrush / Bunchgrass State 2 1.1c ARTR/Bunchgrass <3 ft + juniper <5% Canopy Juniper/ Bunchgrass T1a Cool Season Bunchgrass 1.1b 2.1a Juniper/Cheatgrass Complex 20 ft + Western juniper 20 + Year old stand 30% + Canopy

  32. BUILDING STATE AND TRANSITION MODELS • States • Transitions • Thresholds • Plant Communities Phases • Community Pathways

  33. Upland Loam State 1 1.1a State 2 Mtn. Big Sagebrush / Bunchgrass Juniper/Bunchgrass 1.1c ARTR/Bunchgrass <3 ft + juniper <5% Canopy 2.1a T1a Cool Season Bunchgrass Juniper/Cheatgrass Complex 20 ft + Western juniper 20 + Year old stand 30% + Canopy 1.1b T1b R3a R2a State 3 Open Grassland (Crested Wheatgrass Seeding) T2a 3.1 3.2 Open Grassland/ Juniper invasion

  34. Threshold Upland Loam

  35. Pat’s Nightmare Questions?!?

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