references/scheffer-2009.html

Scheffer, M. (2009). Critical Transitions in Nature and Society. Princeton, NJ, Princeton University Press.

Outline:

Critical Transitions

Definition:

Regime shift - movement to a new dynamic stable state, may be forced by external factors, does not necessarily imply that there were multiple stable states.

could be forced by external forces

Critical transition - system may gradually become increasingly fragile to the point that a minor perturbation can trigger a drastic change toward another state.

change is driven by internal relationships after a trigger

Linear, threshold, catastrosphe fold

figure 2.4

hysteresis happens when you go back on the catrostrophe fold

figure 2.5

 

example with turbidity and vegetaion, increasing of decreasing nutrients as the driving force

figure 2.9

 

similar diagram for climate moisture and microclimate moisture

figure 2.10

 

graphical model for poverty trap

figure 2.14

 

Example 1: shallow lakes

figure 7.2 Two states - emergent vegtation and turbid with algae

 

figure 7.3 - many feedbacks reinforce each state

 

figure 7.4 graphical models of how there are two stable states

 

 

Example 2: local climate, trees and precipitation

trees can bring deeper water up to the surface and through transpiration into the air

microclimate becomes more humid leading to localized humidity, soil moisture and even rain in the basin

trees absob heat from the sun and cause convection which can lead to rain

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figure 11.1 graphical model showing the two stable states and drier and wetter climate outcomes

 

figure 11.2 Expanding savanna in the Amazon basin (see

Restoration

Find out how to reduce the resilience of the bad state first, and then flip out of the bad state with less effort.

time your pulse of restoration work when the systems "bad" resilience is at its lowest

example: dry tropical forest

Trees are required to maintain soil moisture. If you plant trees get the browsers eat them. After a good rain year, many trees will automatically sprout and do well enough to protect the soil if you can keep them from getting eaten.

strategy - wait for a good rain year (such as during the El Nino rains), actively exlcude the browsers

picture of a savanna with scrub

 

figure 17.4 stability model on top of the rain vs. forest biomass catastrophe curve

 
 

Notes:

pg 2 - "Understanding such transitions can open up surprising new ways of managing change."

"Tipping point" book is about social traps and shifts

pg 6 - "Regime shifts seem often triggered by a major external impact. ...

such disturbances are not always the complete story. "

"A much trickier aspect is that systems may gradually become increasingly fragile to the point that even a mino perturbation will trigger a drastic change toward another state. I will call such changes critical transitions.

pg 7 - "underlying structures of the real world show up in the mirror world of math with a beautiful clarity that can never be seen in reality."

pg 13 - equilibrium in dynamical systems

steady state - also called an attractor

such as when birth rate = death rate

pg 16 - alternative equilibria such as the Allee effect, in which there is a population level below which the population can't have net growth

two states are carrying capacity and total disappearance of the population

pg 18 - catastrophic shifts - vs. the simpler threshold

catastrophic shifts lead to hysteresis

pg 22 - width of the basin of attraction is the Hollings resilience

"size of the valley of basin of attraction around a state that corresponds to the maximum perturbation that can be taken without causing a shift to an alternative stable state."

examples:

figure 2.5 shallow lake

figure 2.10 moisture in a forest

figure 2.14 poverty trap