Understanding Ecosystem Stability and Adaptive Cycles

1. Ecosystem Stability, Adaptive Cycles and Panarchy

5. Temporal, spatial and structural features of complex system Amand et al. (2010)

6. Tweets (social interactions) in Japan in response to the 2011 Tsunami have a scale-free pattern

7. Ecosystem Stability Concepts • Ecosystem stability:as the ability of an ecosystem to maintain its structure and function over long periods of time and despite disturbances. • Resistance: ecosystem keeps its structure and continues normal functions even when environmental conditions change. • Resilience:ecosystem eventually regains its normal structure and function after a disturbance.

8. Ball-and-cup model of system stability Ball=Current state of system Cup = Current stability domain Stability, the speed at which the ball returns to homeostasis; correlated with productivity Resilience, the amount of energy that the system can absorb without leaving the cup for an alternative stability domain.

9. Tundra: low stability, low resilience ICH: high stability, high resilience CWH: high stability, low resilience IDF: low stability, high resilience

10. Managing ecosystems within the range of natural variability (RONV) • RONV= resilience=range of possible locations of the ball within the cup • Resilience: “the capacity of a system to absorb disturbance and reorganise while undergoing change so as to still retain essentially the same function, structure, identity, and feedbacks”. • Management goal: make sure you stay in the cup and that it remains as wide and deep as possible

11. Ecosystem stability or response to disturbance depends on: • Resistance: Ability of system to absorb small disturbances and prevent amplification • Resilience: Ability of system to return to its original state • Robustness: amount of disturbance system can absorb without flipping to alternative state • Response: Magnitude of change • Recovery: Extent of return to original state

12. Three types of change Non-reversible Tree cover % Tree cover % % Forest Cover Tree cover % Precipitation Precipitation Precipitation Dry Wet Dry Wet Dry Wet dry dry dry wet wet wet

13. Maintaining stability • Species diversity is often the key to both ecosystem resistance and resilience. • An ecosystem rich in biodiversity will likely be more stable than one whose biodiversity is low.

14. Alive then dead: shifting stability domains

15. Perry’s cup vs peak models of system stability • Destabilization of ball depends on force (cup) versus type or foreignness (peak) of disturbance. • Ecosystem has plenty of warning (cup) for threshold disturbances versus surprises (falls off peak) (tipping points) • Ball movement in cup reversible once disturbance removed, but not once knocked off peak (domino effects common) • Cup model suggests equilibrium, but ecosystems are always in disequilibrium

16. Adaptive cycle Potential: the number and kinds of future options available (e.g. high levels of biodiversity provide more future options than low levels) Connectedness: the degree to which a system can control its own destiny through internal controls, as distinct from being influenced by external variables Resilience: how vulnerable a system is to unexpected disturbances and surprises that can exceed or break that control. The adaptive cycle is the process that accounts for both the stability and change in complex systems.

17. Adaptive cycle of recovery (succession) after disturbance Complex system undergoes change through ‘adaptive cycle’ r α K Ω r=exploitation (disturbance, ruderale growth; stand initiation) K=conservation (carrying capacity, competition, niche specialization; stem exclusion) Ω=release (self-thinning or gap disturbance, new opportunity, understory re-initiation) α=re-organization (stratification of survivors, old-growth) Gunderson & Holling 2002

18. Four stages of adaptive cycle 1) Exploitation: rapid expansion, e.g., population grows. 2) Conservation: population reaches carrying capacity and stabilizes for a time. 3) Release: population declines due to a competitor, or changed conditions 4) Reorganization: certain members of the population are selected for their ability to survive despite the competitor or changed conditions that triggered the release.

19. Adaptive cycle: four stages r K Ω α Ω α r K

21. Global to arctic Mann et al. Polar amplification Chapman and Walsh

22. Permafrost is thawing in many places, not just southern margins

23. Mineral deposit, Siberia Cryoturbated soil, thin peat, Alaska Frozen peat, Canada, Siberia Schuur et al. 2008

24. Melting permafrost Hudson Bay, Canada Science Daily, Sept 2, 2008

25. What is panarchy? “The term [panarchy] was coined as an antithesis to the word hierarchy (literally, sacred rules). Our view is that panarchy is a framework of nature's rules, hinted at by the name of the Greek god of nature, Pan.” Lance Gunderson and C. S. Holling, Panarchy: Understanding Transformations in Systems of Humans and Nature, Island Press, p.21, 2001.

26. Panarchy: all-encompassing nested system of adaptive cycles (Gunderson and Holling 2001).

27. Panarchy in natural ecosystems Temporal scale Spatial scale

28. These cycles connect with cycles ‘above’ and ‘below’ them in the hierarchy: “Revolt" – this occurs when fast, small events overwhelm large, slow ones, as when a small fire in a forest spreads to the crowns of trees, then to another patch, and eventually the entire forest “Remember" – this occurs when the potential accumulated and stored in the larger, slow levels influences the reorganization. For example, after a forest fire the processes and resources accumulated at a larger level slow the leakage of nutrients, and options for renewal draw from the seed bank, physical structures and surrounding species that form a biotic legacy. 7/10

29. There are ‘discontinuities’ in variables of interest Discontinuities determine dominant scales

30. Panarchy predicts discontinuities in adaptive cycles across scales

31. Summary • Complex adaptive systems are inherently stable • Stable systems change but are homeostatic, like a dancer • Stables systems have resistance, where small disturbances are contained, and resilience, where the system returns to the same stability domain • Complex systems change through adaptive cycles • Adaptive cycles and panarchy are stabilizing characteristics • Positive feedbacks and crossing tipping points can lead to loss of stability • Climate change could cause instability • Maintaining complexity will be crucial

32. Melting permafrost Hudson Bay, Canada Science Daily, Sept 2, 2008