Introduction to Ecological Resilience Jan Sendzimir International Institute of Applied Systems Analysis Laxenburg, Austria sendzim@iiasa.ac.at

Surprise in Florida Bay Sea grass Clear Water Muddy Water Algae Blooms Florida Bay

Ecological Succession South-eastern North America Premise: system tends toward stable equilibrium Vegetation characteristic of different successional stages (After E.P. Odum 1971 Fundamentals of Ecology)

Adaptive Cycle Graphic Metaphor for Dynamism of Resilience Dynamic systems do not tend toward a stable equilibrium, but cycle through four phases (r  K   ) These definitions emerged from the need to characterize regimes common to resource management systems.

Resilience Theory Develop common tools to study the development, decline, and collapse or persistence of socio-ecological systems. You are resilient if your identity persists: In the face of shock or disturbance the same set of organizing processes remain to control the behavior and structure of a resilient system.

Ecological Resilience is related to the… Size of the Stability Domain Amount of change a system can undergo and still retain the same controls on function and structure Degree to which system can: Self-organize Learn and adapt  the amount of stress it can sustain and still retain the same configuration of interactions between ecological variables.

Resilience: Three Levels of Meaning Metaphor related to sustainability A property of dynamic models A quantity measurable in field studies

Lake Eutrophication The flip from clear to turbid water Some lakes remain clear for decades until one summer storm churns up the sediments, and it remains turbid for decades, despite all “cures.”

Percent Of Lake Covered By Macro- Phytes Phosphorus in Water Response of charophyte vegetation in the shallow Lake Veluwe to increase of the phosphorus concentration in the 1960s. Figure from Scheffer et al. 2001 Nature Vol. 413 pp. 591-596.

Hysteresis Percent Of Lake Covered By Macro- Phytes 28 1 2 27 3 26 5, 6…25 4 Response of charophyte vegetation in the shallow Lake Veluwe to increase and subsequent decrease of the phosphorus concentration. Red dots represent years of the forward switch in the late 1960s and early 1970s. Black dots show the effect of gradual reduction of the nutrient loading leading eventually to the backward switch in the 1990s.

If the equilibrium curve is folded backwards (c), three equilibria can exist for a given condition. Equilibria on the dashed middle section are unstable and represent the border between the basins of attraction of the two alternative stable states on the upper and lower branches. Figure from Scheffer et al. 2001 Nature Vol. 413 pp. 591-596.

Examples of Multiple Stable States Coral Reefs coral vs. algae Arid Landscapes shrubland vs. grassland Shallow Lakes eutrophic vs. clear North Florida Forest longleaf pine savanna & fire vs. hardwood forest without fire

Stability Landscape View of Multiple “Stable” States Potential Energy Ecosystem State An ecosystem may have multiple stability domains. Within each domain many configurations are possible with the same set of processes organizing structure and function

Stability Landscape View of Evolution Shift from one domain to the next as the rules change As it changes, a system modifies its own possible states. Here a smaller and smaller perturbation can shift the equilibrium from one stability domain to another. Finally the stability domain disappears and the system spontaneously changes state.

External conditions affect the resilience of multi-stable ecosystems to perturbation. The bottom plane shows the equilibrium curve. The stability landscapes depict the equilibria and their basins of attraction at five different conditions. Stable equilibria correspond to valleys; the unstable middle section of the folded equilibrium curve corresponds to a hill. If the size of the attraction basin is small, resilience is small and even a moderate perturbation may bring the system into the alternative basin of attraction.

Resilience as Metaphor Simple story to communicate complex ideas Explain consequences of equilibrium-based sciences and derivative policies Not as a testable hypothesis Theory itself is rarely tested directly As a generator of concepts useful in generating testable hypotheses

Resilience as Metaphor Guiding how we define its aspects To assess resilience in terms of a hierarchal context, measure the resilience of what to what. These aspects change depending on the temporal, social, and spatial scale at which one measures. Geomorphology Soil P Lake Sediment P A socioecological system can be resilient at one time scale because of the technology it has adopted. Iron axes, for example, probably helped emerging agricultural societies to persist over a particular span of time because they enabled their possessors to clear more forest and grow more food. But at a longer time scale, once some threshold of forest cover had been crossed, fallowing could no longer maintain soil fertility and the resilience of the system was compromised (Ruthenberg 1976). Water P Resilience at one scale can be subsidized by resilience at a broader scale in space and/or time. Panarchy -A Cross-scale Nested Set of Adaptive Cycles

Resilience: Three Levels of Meaning Metaphor related to sustainability A property of dynamic models A quantity measurable in field studies

In theory and in the model, resilience is tracked as the size of the attractor for the clear water condition. Plot of system equilibria on axes of fast (water P) and slow (sediment P) variables Slow Variable (Sediment Phosphorus) Fast Variable (Water Phos- phorus) Higher R Lower R Resilience of clear water state to large runoff events,.

Resilience As a property of dynamic models Resilience within & between scales1 Surface waters & non-point source pollution2. Rangeland management3 Fire-driven forest dynamics4 1 - Peterson G, Allen CIR, Holling CS. 1998. Ecological resilience, biodiversity, and scale. Ecosystems 1:6–18.   2 - Carpenter SR, Caraco NF, Correll DL, Howarth RW, Sharpley, AN, Smith VH. 1998. Nonpoint pollution of surface waters with phosphorus and nitrogen. Ecol Appl 8:559–68. 3 - Janssen MA, Walker BH, Langridge J, Abel N. 2000. An adaptive agent model for analysing co-evolution of management and policies in a complex rangeland system. Ecol Model 131:249–68. 4 - Peterson GD. 1999. Contagious disturbance and ecological resilience [dissertation]. Gainesville (FI): University of Florida.

Resilience Indicator Fish Population Dynamics Model Rates of Birth and Mortality (per year) birth birth Fish Population Density (number per ha.)

Resilience As a property of dynamic models Are system-specific. Not all are measurable in the field May be possible to calculate them in the model.

Resilience: Three Levels of Meaning Metaphor related to sustainability A property of dynamic models A quantity measurable in field studies

Status of 9 Indicator Variables during the Adaptive Cycle In practice, resilience could be tracked by monitoring the slowly changing variables that control the attractor for the clear water condition. Soil P affects the persistence of clear water in 2 ways: Resilience (shape of attractor) Probability distribution of disturbances (major runoff events)

Using Model Insights to identify R Indicators Ecological Soil P, Animal stocking densities, Built area Institutional Best practices Education, enforcement or innovation Economic Markets for water quality, soil runoff Social Networks to facilitate appropriate action Power asymmetries between interest groups

Resilience: Three Levels of Meaning Metaphor related to sustainability A property of dynamic models A quantity measurable in field studies