---
title: "bounce back to what?"
canonical_url: https://ensurance.app/guide/bounce-back-to-what
markdown_url: https://ensurance.app/guide/bounce-back-to-what.md
subtitle: "a beam returns to its shape. a lake, a reef or a kelp forest pushed too far becomes something else"
category: natural-capital
---

# bounce back to what?

*a beam returns to its shape. a lake, a reef or a kelp forest pushed too far becomes something else*

**Ecological resilience** is how much disturbance a living system can absorb before it becomes a different system. Walker, Holling and colleagues put it this way in 2004, for social–ecological systems: "the capacity of a system to absorb disturbance and reorganize while undergoing change so as to still retain essentially the same function, structure, identity, and feedbacks."

Most people hear the word and picture a rebound: the beam springs back, the town reopens. Bounce back to what? A steel beam has one shape to return to. A shallow lake, a coral reef or a kelp forest may not. Push one far enough and it can settle into another state, and getting it back can take more than undoing what pushed it.

The marsh takes the edge off the surge and the floodplain spreads the flood. They do that work whether or not anyone pays for it. [**Ensurance**](/?from=guide) is how the people who depend on them can pay for their keeping. It is not the marsh, and it does not stop a storm.

:::johnson
**a beam has one shape to return to. a living system can have more than one.**

Pushed past a threshold, a lake, a reef or a kelp forest can settle into another state. The question for a place is how close its living systems are to that threshold.

[see a kelp forest that crossed one →](/guide/you-dont-have-an-empty-reef-you-have-a-missing-forest?from=guide)
:::

## two questions behind one word

The engineers who first measured resilience asked how much a material can take in and give back without permanent change; [resilience means to leap back](/guide/resilience-means-to-leap-back?from=guide) tells that history. Ecologists asked something else. In 1973 C. S. Holling pulled apart two ideas. The first he called stability: "the ability of a system to return to an equilibrium state after a temporary disturbance," an equilibrium being a steady state, and the faster the return, the more stable. The second he called resilience: the ability "to absorb change and disturbance and still maintain the same relationships between populations or state variables."

In a 1984 review, S. L. Pimm treated resilience as the rate of return to equilibrium, "often measured as its reciprocal, the return time," according to a 2016 summary by Donohue and colleagues, Pimm among them. In 1996 Holling named the two views. The speed-of-return view, whose aims he described as "efficiency, constancy, and predictability," he called **engineering resilience**: an ecologist's label for a view inside ecology, not the materials engineers' own measure.

| | engineering resilience (Holling 1996) | ecological resilience (Holling 1996) |
|---|---|---|
| The question | How fast does the system return to equilibrium after a disturbance? | How much disturbance can it absorb before it changes its structure? |
| How it is measured | By "resistance to disturbance and speed of return to the equilibrium" (citing Pimm 1984 and others) | By "the magnitude of disturbance that can be absorbed before the system changes its structure" |
| Our reading: where each fits | Where one state and a quick return are the goal: a pump station, a water main | Where a system has more than one state it can settle into: a lake, a reef, a kelp forest |

A place needs both. The trouble starts when a reef is treated like a beam, as if it had one shape to return to.

## when a living system flips

Scheffer and colleagues called these "catastrophic shifts" in 2001, reviewing studies on "lakes, coral reefs, oceans, forests and arid lands" that showed "smooth change can be interrupted by sudden drastic switches to a contrasting state." Three cases show the shape.

**A shallow lake.** Shallow lakes can hold two "alternative equilibria," Scheffer and colleagues wrote in 1993: "a clear state dominated by aquatic vegetation, and a turbid state characterized by high algal biomass," turbid meaning cloudy.

**Reefs in Jamaica.** Hughes reported in 1994 that coral abundance in Jamaica had fallen from more than 50 percent in the late 1970s to less than 5 percent "today," with fleshy seaweed (macroalgae) above 90 percent cover: "a dramatic phase shift." Hughes wrote that fish on the north coast were already scarce by the late 1970s. Hurricane Allen in 1980 initiated a rapid decline, as Hodgson summarized Hughes's data, and in 1983 disease killed about 100 million *Diadema*, a grazing sea urchin, over eight weeks, followed at once by an algal bloom. The cause was argued: Hodgson pointed to nutrient enrichment, Hughes to the loss of grazers.

**A kelp forest in northern California.** Rogers-Bennett and Catton reported in 2019 that a previously robust bull kelp forest shifted to urchin barrens in 2014, with canopy down more than 90 percent along more than 350 kilometers of coast. The sequence ran: sea stars dying from 2013, intense ocean warming from 2014 to 2017, urchin barrens from 2015. They wrote that the relative roles of warming and sea star disease in the surge of purple sea urchins remained open questions. [The missing-forest post](/guide/you-dont-have-an-empty-reef-you-have-a-missing-forest?from=guide) follows that coast with other surveys.

In each case the sources describe a change of state, not a slow rebound. A system that flips does not bounce back. It does not simply spring back the way a beam does, and for the lake, the next section shows what getting it back can take.

## the road back is not the road over

Add phosphorus to a clear lake a little at a time and the water can stay clear for a long while, then turn green. Take the phosphorus away and you might expect the lake to clear at the level where it turned. Often it does not.

Carpenter, Ludwig and Brock sorted lakes in 1999 into three kinds: "reversible (recovery is immediate and proportional to the reduction in P input), hysteretic (recovery requires extreme reductions in P input for a period of time), or irreversible (recovery cannot be accomplished by reducing P input alone)."

That middle word names the effect. **Hysteresis** means the way back is not the way over: cutting phosphorus back to the level at which a lake flipped is often not enough to flip it back. One likely reason, on our reading, sits on the lake bottom. The Stockholm Resilience Centre notes that phosphorus stored in the sediment "can increase over a long time without any impact on the water quality"; a store that large may also be slow to run down. The 1993 shallow-lake paper adds that "Nutrient reduction alone may have little impact on water clarity," while a food-web change can bring a lake back to a stable clear state.

## the slow thing often erodes first

The storm gets the blame, but it is often the last push. Scheffer and colleagues wrote that although diverse events can trigger a shift, "a loss of resilience usually paves the way."

What wears resilience down is often slow. Walker and colleagues described it in 2012: outside drivers change the slow, controlling variables, and "as slow variables approach threshold levels, the fast-moving variables in the system fluctuate more in response to environmental and other shocks." Not every push is slow, though. The northern California kelp went over after a sea star die-off and a run of hot water within a few years.

## bounce back, or bounce forward

According to David Alexander's history of the word, Manyena and colleagues argued in 2011 for resilience as a "bounce forward" notion. Folke and colleagues warned in 2010 that "confusion arises when resilience is interpreted as backward looking, assumed to prevent novelty, innovation and transitions to new development pathways."

Past the threshold, there may be no "back" waiting. The useful work happens before the flip, while the system is still itself.

## ask how close the edge is, not only how fast it rebounds

For a place, the question is how far its living systems sit from their thresholds.

| alongside asking | ask |
|---|---|
| How fast did the reef recover after the storm? | Is what holds it in its state still there: the grazers, the water, new coral settling? |
| Did the lake clear this summer? | How much phosphorus is in the sediment, and is it rising? |

Speed of recovery still has a job, as one warning light. In a 2012 experiment, Veraart and colleagues found that "recovery from small perturbations becomes slower as the system comes closer to the critical point," the point where it tips over. That was a lab result in one living system; whether it reads out the same way on a reef or a marsh is not shown here.

For a land steward, that means watching the slow variables on your own ground. For an underwriter, the question is whether a marsh or reef counted as a buffer is still the same system. For a city or county, it means asking about condition, not only acreage. When a living system fails, losses spread: [what systemic risk actually is](/guide/what-systemic-risk-actually-is?from=guide). For those who depend on that system, paying to keep it is [not a donation](/guide/resilience-is-not-a-donation?from=guide).

## what this cannot tell you

Not every system has a sharp edge. Carpenter's sorting includes reversible lakes, where recovery is "immediate and proportional" to cutting phosphorus. Where an edge exists, it is hard to see ahead of time. Scheffer and colleagues wrote in 2009 that "predicting such critical points before they are reached is extremely difficult," and Veraart and colleagues that randomness "prohibits prediction of the timing of critical transitions."

A system kept far from its edge still has limits: no reef or marsh stops every storm.

## where ensurance fits

An account does not move a lake back from its edge. What **ensurance** does is give a named living system an account, so the ones who depend on it can pay toward its keeping. [Risk Resilience](/risk-resilience.ensurance?from=guide) is one of the flows the protocol tracks. See which places already have accounts on [the map](/explore?from=guide), or, if you keep land, [how this applies to land stewards](/solutions/land-stewards?from=guide&topic=resilience).

Next: [what makes a living system resilient](/guide/what-makes-a-living-system-resilient?from=guide), the properties that keep a system far from its edge.

## frequently asked questions

### what is ecological resilience?

Ecological resilience is the amount of disturbance a living system can absorb before it changes into a different system. C. S. Holling set out the idea in 1973 and named it in 1996; the word itself is older.

### what is the difference between engineering and ecological resilience?

Engineering resilience, as Holling named it in 1996, asks how fast a system returns to its one equilibrium after a disturbance. Ecological resilience asks how much disturbance it can absorb before it changes its structure. Holling said the first maintains "efficiency of function" and the second "existence of function." Materials engineers measure something else again: how much energy a material can take in and give back.

### what is a regime shift in ecology?

A sudden switch of an ecosystem into a contrasting state: a kelp forest turning to urchin barren, a clear lake turning cloudy with algae, a coral reef overgrown by macroalgae. Scheffer and colleagues found in 2001 that a loss of resilience usually paves the way.

## sources

[Holling, C. S. (1973), "Resilience and stability of ecological systems," *Annual Review of Ecology and Systematics* 4: 1–23 (IIASA reprint)](https://pure.iiasa.ac.at/id/eprint/26/1/RP-73-003.pdf) — Stability and resilience defined as two different properties

[Holling, C. S. (1996), "Engineering Resilience versus Ecological Resilience," in *Engineering Within Ecological Constraints*, National Academy Press](https://www.nationalacademies.org/read/4919/chapter/4) — The two definitions named; "efficiency, constancy, and predictability"; efficiency and existence of function

[Donohue et al. (2016), "Navigating the complexity of ecological stability," *Ecology Letters*](https://dukespace.lib.duke.edu/server/api/core/bitstreams/fb9bab76-a744-42ad-9941-5cf713eb4302/content) — Pimm's 1984 review as summarized here: resilience as the rate of return, measured by return time

[Walker, B., C. S. Holling, S. R. Carpenter and A. Kinzig (2004), "Resilience, adaptability and transformability in social–ecological systems," *Ecology and Society* 9(2): 5](https://www.ecologyandsociety.org/vol9/iss2/art5/) — The definition of resilience quoted above

[Scheffer, Carpenter, Foley, Folke and Walker (2001), "Catastrophic shifts in ecosystems," *Nature* 413: 591–596](https://doi.org/10.1038/35098000) — Sudden switches in lakes, coral reefs, oceans, forests and arid lands; loss of resilience usually paves the way

[Hughes, T. P. (1994), "Catastrophes, Phase Shifts, and Large-Scale Degradation of a Caribbean Coral Reef," *Science* 265: 1547–1551](https://researchonline.jcu.edu.au/26506/) — Jamaican coral cover from more than 50% to less than 5%; macroalgae above 90%

[Hodgson, Ogden and Hughes, letters and response, *Science* 266: 1930–1933 (1994)](https://researchonline.jcu.edu.au/26513/1/26513_Hodgson_Ogden_Hughes_1994.pdf) — The 1980 hurricane; about 100 million *Diadema* lost in 1983; the argument over nutrients

[Woodley (1980), "Hurricane Allen destroys Jamaican coral reefs," *Nature* 287: 387](https://doi.org/10.1038/287387a0) — The name of the 1980 hurricane

[Scheffer, Hosper, Meijer, Moss and Jeppesen (1993), "Alternative equilibria in shallow lakes," *Trends in Ecology & Evolution* 8: 275–279](https://doi.org/10.1016/0169-5347%2893%2990254-M) — Clear and turbid states; nutrient reduction alone may do little; food-web change can restore clarity

[Carpenter, Ludwig and Brock (1999), "Management of eutrophication for lakes subject to potentially irreversible change," *Ecological Applications* 9: 751–771](https://doi.org/10.1890/1051-0761%281999%29009%5B0751%3AMOEFLS%5D2.0.CO%3B2) — Reversible, hysteretic and irreversible lakes

[Rogers-Bennett and Catton (2019), "Marine heat wave and multiple stressors tip bull kelp forest to sea urchin barrens," *Scientific Reports* 9: 15050](https://doi.org/10.1038/s41598-019-51114-y) — Canopy down more than 90% along more than 350 km; the sequence; open questions on the urchin surge

[Walker, Carpenter, Rockström, Crépin and Peterson (2012), "Drivers, 'slow' variables, 'fast' variables, shocks, and resilience," *Ecology and Society* 17(3): 30](https://www.ecologyandsociety.org/vol17/iss3/art30/) — Slow variables defined; fast variables fluctuate more as thresholds near

[Stockholm Resilience Centre, "Applying resilience thinking," February 19, 2015](https://www.stockholmresilience.org/research/research-news/2015-02-19-applying-resilience-thinking.html) — Phosphorus in lake sediment as a slow variable

[Scheffer et al. (2009), "Early-warning signals for critical transitions," *Nature* 461: 53–59](https://doi.org/10.1038/nature08227) — Predicting critical points before they are reached is extremely difficult

[Veraart et al. (2012), "Recovery rates reflect distance to a tipping point in a living system," *Nature* 481: 357–359](https://doi.org/10.1038/nature10723) — In a lab experiment, recovery slowed near the critical point; timing cannot be predicted

[Alexander, D. E. (2013), "Resilience and disaster risk reduction: an etymological journey," *Natural Hazards and Earth System Sciences* 13: 2707–2716](https://nhess.copernicus.org/articles/13/2707/2013/nhess-13-2707-2013.pdf) — His account of Manyena et al. on "bounce forward"

[Manyena, B., G. O'Brien, P. O'Keefe and J. Rose (2011), "Disaster resilience: a bounce back or bounce forward ability?" *Local Environment* 16(5): 417–424](https://researchportal.northumbria.ac.uk/en/publications/disaster-resilience-a-bounce-back-or-bounce-forward-ability/) — The paper Alexander describes; not quoted directly here

[Folke, C. et al. (2010), "Resilience thinking: integrating resilience, adaptability and transformability," *Ecology and Society* 15(4): 20](https://www.ecologyandsociety.org/vol15/iss4/art20/) — Confusion when resilience is read as backward looking and assumed to prevent novelty

## the series

1. [resilience means to leap back](/guide/resilience-means-to-leap-back?from=guide) — **Read first:** The word's root, its travels, and the question that changed in 1973
2. [bounce back to what?](/guide/bounce-back-to-what?from=guide) — A beam returns to its shape; a lake or a reef pushed too far becomes something else
3. [what makes a living system resilient](/guide/what-makes-a-living-system-resilient?from=guide) — Many kinds doing one job, spare capacity, connection and the slow things nobody watches
4. [the resilience a place already has is alive](/guide/the-resilience-a-place-already-has-is-alive?from=guide) — The floodplain, the marsh, the canopy and the soil as infrastructure
5. [how to build resilience for a place](/guide/how-to-build-resilience-for-a-place?from=guide) — Six steps, starting with the living systems a place already stands on
6. [no place is resilient alone](/guide/no-place-is-resilient-alone?from=guide) — Why the unit that works is the region, and every place in it