1.4 Resilience to What? – Disturbances

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Managing resilience requires managing and working with disturbance regimes.

Example: Northwest New Orleans after Hurricane Katrina.Efforts to prevent or otherwise control disturbances can inadvertently weaken a system’s resilience. Disturbance regimes can also change over time requiring both an understanding of the historical pattern of disturbance and forward looking plans for adaptation.


Key Messages

• A disturbance can generally be thought of as anything that causes a disruption to a system. Disturbances in ecological systems can be such things as drought, fire, disease, or hurricanes. Disturbances in economic systems can come as recessions, innovations, or currency fluctuations, for example. Disturbances in social systems can include revolutions, new fashions, new values, or technological changes.

• Disturbances can be characterized in many ways—by their frequency, duration, severity, or predictability, to name just a few.

• Human intervention in an ecological system may also be considered a disturbance. Humans visit novel disturbances on ecological systems, such as the application of fertilizer, or the building of roads. As populations and consumption levels grow, human disturbances can intensify, with consequences for resilience.

• It is important to consider the suite of disturbances affecting a system. A previously benign disturbance might have much greater consequences if it follows another disturbance from which the system hasn’t had a chance to recover.

• Systems that have been ‘protected’ from disturbance may not have the capacity to cope in the absence of such protection.

• Management strategies that strive to overly control disturbances (e.g., by reducing variability) can erode the resilience of the managed system, making it susceptible to even small disturbance events.


Resilience Assessment

Consider the full suite of disturbances (from ecological, social, and economic domains) currently or historically affecting your focal system. Consider both ‘pulse’ and ‘press’ disturbances - pulse disturbances being events that occur and then cease before recurring (e.g. plowing, hurricanes, disease outbreaks) while press disturbances are unremitting (for instance, a grazing land that is stocked year round). Identify disturbances that have in the past fundamentally altered the nature of your system or its trajectory, such as those ‘triggering events’ you identified in the timeline activity. Enter them in the table below, and identify their attributes.

Consider known or potential disturbances that may affect your focal system in the future. Enter those in the table below, along with their attributes.

Which of these disturbances appear most threatening to the valued attributes of your focal system? In other words, which might have the capacity to introduce a severe ‘shock’ to the system? (This initial assessment will be a ‘best guess’ or ‘expert opinion’—we will revisit the role of disturbance in later chapters.) These are frequently disturbances that are changing in magnitude or intensity over time, indicating new challenges to the system.

Note that efforts to increase resilience of some system regime to a specified set of disturbances can unwittingly reduce the resilience of the system to other, non-specified (yet to be experienced) disturbances. This raises the issue of the need to maintain general resilience while engaged in necessary efforts to enhance specified resilience to known threats and disturbances.

Consider the disturbances identified above. Which of these are actively managed, or suppressed? Is there any reason to believe that there is too much suppression of any of the disturbances—in other words, that by overly protecting the system (be it ecological or human) you are making it less resilient and more vulnerable to unmanaged disturbances? Should any of these management strategies be reconsidered? Record any action items.

After completing this first part of the assessment, re-visit and consider whether you are still comfortable with the definition of earlier attributes (i.e. focal system boundaries, multiple scales, and historical timeline).


Table 1.4.1 Summary table of focal system disturbance

DISTURBANCE PULSE OR PRESS? FREQUENCIES OF OCCURRENCE (PULSE) DOES THE SYSTEM HAVE TIME TO RECOVER (PULSE) VARIABLE COMPONENT MOST AFFECTED (E.G. SOIL, MARKETS) MAGNITUDE OF IMPACT CHANGE OVER PAST FEW YEARS/DECADES (E.G. NONE, LESS FREQUENT, MORE INTENSE ETC.)
             
             
             
FUTURE
           
             
             

1.1 Bounding the System: Describing the Present

1.2 Expanding the System: Multiple Scales

1.3 Linking the Past to Present – Historical Timeline

1.4 Resilience to What? – Disturbances

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