A quiet revolution – the science of complex systems
Box 1 | Complex systems, resilience and ecological sustainability
Ecosystems are complex systems. They are made from many parts that are strongly connected, they behave in non-linear ways, are largely unpredictable, and can exist in alternate stable states in which their function, structure and feedbacks are different.
Complex systems can exist in alternative states
An example of an ecosystem of alternate stable states is a lake with clear water that receives too much phosphorus over time. Up to a certain point the lake can store phosphorus in the sediment and the water will remain clear. Beyond a certain level or threshold, phosphorus is released into the water, algae multiply and the water becomes murky – and stays that way.
Redefining sustainability
If you accept that ecosystems are complex systems, then definitions of sustainability need rethinking. In its broadest sense, sustainability is all about maximising the use of our resources today so that we don’t limit the options of future generations. It usually translates to being more efficient with our resources.
But many scientists are now worried that by focussing only on efficiency we are more likely to allow ecosystems to cross thresholds into undesirable stable states, such as murky lakes, salinised catchments and depleted fisheries. These scientists believe that resilience is the cornerstone of sustainability, not efficiency.
Resilience of ecosystems
Resilience is the capacity of a thing to absorb disturbance without shifting to a new stable state. A resilient ecosystem has a greater capacity to avoid unwelcome surprises that occur when you shift to a new stable state, and so has a greater capacity to continue to provide us with the goods and services that support our quality of life.
Efficiency, if applied to a complex system without consideration of how it functions over several scales, can result in the removal of redundancy, resulting in a reduction in resilience and the capacity to remain sustainable.
As is often the case when dealing with complex systems, sometimes the obvious approach to a problem ends up creating unwanted outcomes.
Boxes
Box 2. Building reliable networks
Box 3. It's a small world after all
Related sites
New insight into ecosystem management (News in Science, 19 October 2001)
Resilience and sustainability (Ohio State University, USA)
Resilience and sustainable development (Swedish
Environmental Advisory Council)
Defining thresholds (Nova: Science in the news, Australian Academy of Science)
Posted October 2006.