Imagine an ecosystem such as a fresh-water lake that provides you with readily accessible drinking water. The quality of this water is linked to slowly changing variables such as the phosphorus concentra-tion in the sediment, which is in turn linked to fertiliser runoff into the lake. In the social domain, legal systems, values and traditions can also be important slow variables. They can affect existing ecosystem services, for instance, through agricultural practices, such as when and how much fertiliser is used in the fields surrounding a lake. Feedbacks are the two-way ‘connectors’ between variables that can either reinforce (positive feedback) or dampen (negative feedback) change. An example of reinforcing feedback is introduced grasses in Hawaii that cause fires, which promote further growth of the grasses and curb the growth of native shrub species. More grass leads to more fire which, in turn, leads to more grass. This becomes a loop and self-reinforcing feedback. An example of a dampening feedback is formal or informal sanctioning or punishment that occurs when someone breaks a rule. The appropriate punishment can prevent further misbehaviour and dis-courage others from misbehaving in future.
How can slow variables and feedbacks enhance resilience?
Social-ecological systems are complex adaptive systems, or self-organising systems that can adjust and reorganise in response to disturbance and change, such as floods or the migration of people into urban areas. In most cases, dampening feedback helps to counteract disturbance and change so that the system recovers and keeps working in the same way, producing the same set of ecosystem services. An example of this is the shift from clear to algae-dominated water in shallow lakes. Clear water shallow lakes usually have many rooted plants growing on the lake floor. These plants absorb phosphorous and nitrogen runoff from agricultural and urban development in the surrounding catchment and help to keep the water clear. In other words, they provide a damping feedback that counteracts the effects of nutrient pollution. However, there is a limit to how much disturbance or change a system can be exposed to before the dampening feedbacks are overwhelmed. If this happens, some feedbacks in the system may be broken, and other, new feedback connections may form. The system may then become configured in a different way, and produce a different set of ecosystem services. In the case of the lake, increasing agriculture in the surrounding area might result in phosphorous and nitrogen levels in the water (slow variable) that eventually exceed the absorptive capacity of the plants. Once this threshold is crossed, excess nutrients in the water lead to growth of free-floating algae. The algae in turn reduce light penetration, gradually leading to the death of the rooted vegetation and the loss of the dampening feedback they provided. Restoring a clear water regime usually requires repeated manual removal of algae, and the reduction of nutrient runoff to a level far lower than what it was before the regime shift occurred. Only then may the rooted plants re-establish themselves and help recreate a clear water regime.
How can we manage slow variables and feedbacks?
The key challenge in managing slow variables and feedback is identifying the key slow variables and feedbacks that maintain the social-ecological regimes which produce desired ecosystem services, and identifying where the critical thresholds lie that can lead to a reconfiguration of the system. Once this is known, even tentatively, the following guidelines can be applied:
Strengthen feedbacks that maintain desirable regimes. For example, hard coral reefs provide ecosystem services such as fisheries and ecotourism, but stresses such as climate change and fishing can cause the system to shift to a regime dominated by seaweed. The resilience of the hard coral regime can be enhanced by promoting the abundance of herbivores, such as parrot fish, that graze on seaweed and thereby provide a dampening feedback. Governance structures that prevent overfishing and protect reef users can also create dampening feedbacks that helps maintain the hard coral regime.
Avoid actions that obscure feedbacks. Certain activities and subsidies can mask or distort dampening feedbacks. Within the fishing industry, most organisations are legally restricted to a defined geographic location. This means that they have an incentive not to overfish, as it would undermine their longer term livelihood options. However, marine ‘roving bandits’, illegal and unregistered fishing vessels that move around the world and deplete local fisheries, undermine local institutions as they have no incentive to ensure the sustainability of fisheries in particular places. In other words, they sidestep the feedback between fish stocks and fish harvest by continuously moving around the world.
Monitor important slow variables. This is crucial in order to detect slow changes that may cause the system to cross a threshold and reorganise into a different regime. However, financial constraints are causing monitoring programmes all over the world to be cut. Understanding the role of slow variables and feedbacks can help managers recognise that investing in monitoring programmes that focus on the variables that underlie system functioning can be very cost-effective.
Establish governance structures that can respond to monitoring information. Knowledge and monitoring information is not enough to avoid regime shifts that can threaten ecosystem services. Establishing governance structures that can effectively respond to monitoring information is equally critical. One innovative example is the approach applied in the Kruger National Park in South Africa. Their system called “thresholds of potential concern” is based on constantly updated knowledge about key environmental indicators. If monitoring indicates that a critical threshold has been reached or is about to be reached, it triggers a formal meeting where it is required that a decision is taken on whether to take remedial action or adjust the suspected threshold to a new level.