Ecological resilience | blogmaths.info
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Do attempts to stabilize certain components of systems lead to a reduction in overall system resilience and greater potential for large changes Gunderson and Holling, ? Increasing resilience can reduce the risk that the system will cross critical thresholds and undergo a detrimental regime shift.
On the other hand, decreasing resilience can increase the probability of a beneficial regime shift. Understanding of how to increase or decrease system resilience places a premium on knowledge of system dynamics, including feedbacks among system components, as well as of uncertainty and variability in dynamic systems Walker and Salt, System resilience can play an important role in maintaining conditions that will sustain the provision of ecosystem services that contribute to human well-being.
However, a narrow focus on stabilizing complex systems to provide a constant flow of ecosystem services may reduce system resilience and increase vulnerability Gunderson et al. An event such as the DWH oil spill may disrupt service provision, but a resilient ecosystem will allow faster recovery so that services will return sooner rather than later or never.
Page 48 Share Cite Suggested Citation: The National Academies Press. Resilience provides a useful conceptual framework for managing complex systems. It focuses attention on system dynamics and how systems are affected by short-term disturbances and long-term stresses.
In the context of resilience of the Gulf of Mexico GoM ecosystem, the committee was charged with addressing the following questions from the Statement of Task see Chapter 1: In light of the multiple stresses on the Gulf of Mexico ecosystem, what practical approaches can managers take to restore and increase the resiliency of ecosystem services to future events such as the Deepwater Horizon Mississippi Canyon spill?
How can the increase in ecosystem resiliency be measured? As noted above, managing resilience requires understanding of the dynamics of complex and highly variable systems, which is often quite limited. Without such understanding, it can be difficult in practical contexts to know how management actions affect resilience. Limited data and understanding of complex system dynamics make it difficult to provide specific practical advice to managers on how to restore or increase the resilience of ecosystem services.
The next section explores definitions of resilience, its application in ecosystems and in integrated social-ecological systems, and the relationship between resilience and provision of ecosystem services. The final sections discuss options to manage systems to enhance resilience and approaches to measuring changes in resilience. The concept of resilience has been applied to ecological systems, social systems, and more recently to integrated social-ecological systems Berkes and Folke, ; Berkes et al.
With this expanded use of resilience has come multiple definitions of resilience. As long as each field of study used a definition that was well defined within the contexts of that field, few problems arose. However, in an interdisciplinary context such as the resilience of ecosys- Page 49 Share Cite Suggested Citation: For this report, resilience is defined as the ability of a system subject to disturbance to retain its essential structure, function, and feedbacks Walker and Salt, and return to its predisturbance state.
Two distinct notions of resilience fit within this general definition, depending on whether the system is characterized by a single equilibrium or multiple equilibria Holling, So, for example, a system may follow a regular cycle unless disturbed. The notion of resilience for a system with multiple equilibria focuses on the magnitude of disturbance the system can absorb without shifting to a new equilibrium Walker et al.
Engineering Resilience Engineering resilience refers to the speed with which a system returns to equilibrium after a disturbance. For example, how fast does a material return to its original form after a shock that deforms the material?
A related notion is resistance, which is the ability of a disturbed system to stay near equilibrium. A rubber band is easily stretched when force is applied low resistance but quickly returns to its original shape high resilience once the force is removed. A steel rod, on the other hand, is highly resistant to force, but it will bend once the force is sufficiently strong and remain bent even when the force is removed low resilience. Both the rubber band and the steel rod can retain their original forms after being subject to a disturbance, but only the rubber band returns to its original form after it is deformed by the force of the disturbance.
Ecological resilience - Wikipedia
A sufficiently strong disturbance will cause the rubber band to break or the steel rod to bend, which may lead to a new type of equilibrium discussed below under the heading of ecological resilience. Ecologists have a long history of studying disturbance and recovery. Clements held that the predictable succession of species followed trajectories toward a specific climax state after a disturbance. Considerable progress was made in the s to provide a solid theoretical basis and predictive capability for this view of resilience as recovery to a climax state.
This line of investigation led to seminal works on post-disturbance ecosystem recovery e. Ecologists have been especially interested in the relationship between species diversity and resilience.
Intuitively, it seems that high diversity should be related to greater resilience.
Similar to how an asset portfolio is diversified to reduce financial risks, highly diverse ecosystems are more likely to contain species that can respond well to particular kinds of disturbances, thereby allowing the system as a whole to better maintain functions in the face Page 50 Share Cite Suggested Citation: However, May showed mathematically that greater diversity could lead to lower system stability.
In principle, empirical evidence is largely supportive of the hypothesis that greater species diversity leads to greater system stability Tilman, ; Tilman and Downing, ; Tilman et al. However, some debate remains as to whether high species diversity contributes to system stability by increasing resilience Ives and Carpenter, ; McCann, ; Naeem, ; Rooney et al.
Ecological Resilience During the s ecologists questioned the view that ecological systems tended toward a unique climax state and instead raised the possibility that systems might have multiple potential equilibria Holling, ; Lewontin, Once disturbed, new conditions can foster a new set of feedbacks and prevent the system from returning to its pre-disturbance equilibrium. For example, plants absorb phosphorus and limit algal growth in shallow lakes with low levels of phosphorus.
An increase in phosphorus inputs, however, can lead to algal blooms that reduce light penetration and kill plants, releasing more phosphorus for algae. Algal domination can persist even when phosphorus inputs into the lake decline back to original levels Carpenter, With multiple equilibria, which equilibrium a system will tend to move toward depends upon the set of system conditions.
Multiple equilibria generate the potential for a system to cross critical thresholds and flip between equilibria see Figure 3.
In the context of multiple equilibria, resilience typically refers to the ability of a system to undergo disturbance without crossing a critical threshold and therefore return to the original equilibrium state Carpenter et al. Initially, the system is in equilibrium in regime 1. This elasticity means that ecosystem properties, such as changes in nutrient flow or the number of species, are more resilient due to changes in species composition.
For example, the disappearance of the American chestnut Castanea dentata in many forests in eastern North America due to chestnut blight has been largely compensated for by the expansion of oak Quercus and hickory Carya species, although there are certainly commercial consequences of this replacement. In Canadian ecologist C.
Holling recognized the importance of the qualities that allowed a forest to persist as a functioning forest rather than its ability to harbour particular species at fixed levels or to maintain an arbitrary level of primary production.
It has resonated in particular with the perspectives of individuals such as American biophysicist and geographer Jared Diamond, who is known for his examination of the conditions under which human societies developed, thrived, and collapsed. Resilience and the development of management tools Ecological resilience or robustness has also become central to conservation practices and ecosystem management, particularly as the latter has shifted its attention to the importance of ecosystem services.
Such services include the provision of food, fuel, and natural products e. Although many species retain importance within the framework of ecosystem services, much of the focus of conservation has moved from individual species to the maintenance of the ecosystem as a whole, especially its ability to retain its structure and rate of productivity.
Many lakes, for example, are managed to remain oligotrophic relatively nutrient poorwith ample oxygen to support species such as lake troutrather than managed to retain excess nutrients and algae. The OILPOL Convention recognized that most oil pollution resulted from routine shipboard operations such as the cleaning of cargo tanks. In the s, the normal practice was simply to wash the tanks out with water and then pump the resulting mixture of oil and water into the sea.
In the limits were extended by means of an amendment adopted at a conference organized by IMO. The marine ecosystem is highly complex and natural fluctuations in species composition, abundance and distribution are a basic feature of its normal function. The extent of damage can therefore be difficult to detect against this background variability.
Nevertheless, the key to understanding damage and its importance is whether spill effects result in a downturn in breeding success, productivity, diversity and the overall functioning of the system.
Spills are not the only pressure on marine habitats; chronic urban and industrial contamination or the exploitation of the resources they provide are also serious threats. The discharges of nitrogen, phosphorus, and other nutrients come from agriculture, waste disposal, coastal development, and fossil fuel use. Once nutrient pollution reaches the coastal zone, it stimulates harmful overgrowths of algae, which can have direct toxic effects and ultimately result in low-oxygen conditions.
Certain types of algae are toxic. Overgrowths of these algae result in harmful algal bloomswhich are more colloquially referred to as "red tides" or "brown tides". Zooplankton eat the toxic algae and begin passing the toxins up the food chain, affecting edibles like clams, and ultimately working their way up to seabirds, marine mammals, and humans.
The result can be illness and sometimes death. And, as more and more people move into densely populated cities, using massive amounts of water, energy, and other resources, the need to combine these disciplines to consider the resilience of urban ecosystems and cities is of paramount importance. This is a movement which causes wide concern in environmental and social forums and which Clive Hamilton describes as "the growth fetish".
Folke et al state that the likelihood of sustaining development is raised by "Managing for resilience"  whilst Perman et al.
Resilience questions the free market model within which global markets operate. Inherent to the successful operation of a free market is specialisation which is required to achieve efficiency and increase productivity. This very act of specialisation weakens resilience by permitting systems to become accustomed to and dependent upon their prevailing conditions.
In the event of unanticipated shocks; this dependency reduces the ability of the system to adapt to these changes. This occurs in a number of ways: Observed resilience within specific ecosystems drives management practice.